MARIA PREFER as a sophisticated robot aircraft in its appearance penetrates several million light years from Earth using the relativita ability of the distance of light which is a reference to fly from the perspective of the earth and mars in this century AMNIMARJESLOW GOVERNMENT soft 17 +++ Hoshi akari no kyori no nōryoku Nikkō no kyori nōryoku rēzā-kō kyori kinō inazuma to denkyū no kyori no nōryoku ___ Thank you to Lord Jesus about soft : because believe: like having a mustard love we can move and translate a mountain of hard problems into a mountain of light problems: The Lord Jesus teaches that you can and must have loyal Love to be able to translate a heap of heavy mountains: Move from this place to there , then this mountain will move, and nothing will be impossible for you Father in heaven ___ Gen. Mac Tech Zone the ability of the distance of lightning and light bulbs transformation, translation and range that can penetrate space and time using the ability of the speed of light for transformation to the sophisticated spaceship ROBOT wanted by MARIA PREFER .

                                                           DECEMBER 2019


                                  



                                EINSTEIN = Energy Intern Saucer Tech Energy IN put

                    Space, Time, and an Obsession of Einstein 

1. Einstein, in his theory of special relativity, determined that the laws of physics are the same for all non-accelerating observers, and he showed that the speed of light within a vacuum is the same no matter the speed at which an observer travels. 

2. As for backwards time travel, it is possible to find solutions in general relativity that allow for it, but the solutions require conditions that may not be physically possible. 

3. A causal loop is a paradox of time travel that occurs when a future event is the cause of a past event, which in turn is the cause of the future event. Both events then exist in spacetime, but their origin cannot be determined. 

4.  speed of light. Sometimes c is used for the speed of waves in any material medium, and c₀ for the speed of light in vacuum. 

5. Space-time is a mathematical model that joins space and time into a single idea called a continuum. This four-dimensional continuum is known as Minkowski space. ... This is because the observed rate at which time passes depends on an object's velocity relative to the observer.

6. Time in physics is defined by its measurement: time is what a clock reads. In classical, non-relativistic physics it is a scalar quantity and, like length, mass, and charge, is usually described as a fundamental quantity. 

7. space time is any mathematical model that fuses the three dimensions of space and the one dimension of time into a single four-dimensional continuum. Spacetime diagrams can be used to visualize relativistic effects such as why different observers perceive where and when events occur differently. 

8. Time is a component quantity of various measurements used to sequence events, to compare the duration of events or the intervals between them, and to quantify rates of change of quantities in material reality or in the conscious experience. ... Time in physics is unambiguously operationally defined as "what a clock reads". 

9. Space is the boundless three-dimensional extent in which objects and events have relative position and direction. Physical space is often conceived in three linear dimensions, although modern physicists usually consider it, with time, to be part of a boundless four-dimensional continuum known as space time.

10.  A five-dimensional space is a space with five dimensions. If interpreted physically, that is one more than the usual three spatial dimensions and the fourth dimension of time used in relativistic physics. It is an abstraction which occurs frequently in mathematics, where it is a legitimate construct.

11.  Time dilation explains why two working clocks will report different times after different accelerations. For example, at the ISS time goes slower, lagging 0.007 seconds behind for every six months. For GPS satellites to work, they must adjust for similar bending of spacetime to coordinate with systems on Earth.

12. The Universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. 

13.Spatial dimensions

Classical physics theories describe three physical dimensions: from a particular point in space, the basic directions in which we can move are up/down, left/right, and forward/backward. Movement in any other direction can be expressed in terms of just these three.

 14. One notable feature of string theories is that these theories require extra dimensions of space time for their mathematical consistency. In bosonic string theory, spacetime is 26-dimensional, while in super string theory it is 10-dimensional, and in M-theory it is 11-dimensional.

 15. theory of special relativity. It introduced a new framework for all of physics and proposed new concepts of space and time.

 16. Einstein realized that massive objects caused a distortion in space-time. Imagine setting a large body in the center of a trampoline. The body would press down into the fabric, causing it to dimple. A marble rolled around the edge would spiral inward toward the body, pulled in much the same way that the gravity of a planet pulls at rocks in space.

 17.          relativity formula   e=mc2

18.           

19.         e- STAR C  ( in my Book Before ) 

20.          

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                     Starlight problem

The starlight problem states that if the universe was only 6,000 years old — as Biblical literalism and Young Earth Creationism (YEC) state — then there would not be sufficient time for distant starlight to reach Earth. We can see light from stars more (way more) than 6,000 light years away, therefore the universe cannot be a mere 6,000 years old.
The furthest objects visible, quasars, have been detected 13 billion light years away. After allowing for the metric expansion of space, this puts the lower limit of the age of the universe at near 13 billion years. The methods of measuring distances to the billions of light years are rather complicated, but there are direct measurements well beyond the limits of YEC, using only parallax. There are the measurements of the supernova SN1987A at about 168,000 light years, and the Gaia space mission should obtain many distances of objects up to about 30,000 light years.
Numerous attempts to solve this problem - including some hand-waving about whether such a problem even exists - have been attempted by creationists. Some are bizarre, some outright absurd, and none are taken seriously by the scientific community. However, they are all united by a desperate need to shoehorn an absurdly young age for the universe into a reality that says otherwise.

                                            

To solve the starlight problem, some creationists have proposed a change in the speed of light; this proposition became known as c-decay. The idea was first systematically advanced by creationist Barry Setterfield in his 1981 book The Velocity of Light and the Age of the Universe. Setterfield claimed that, at the date of creation, light traveled millions of times faster than it does today and has been decaying precipitously ever since (until it stopped at its present value coincidentally with the ability to detect small changes). This idea is fundamentally absurd and since its inception has been universally derided by scientists. The idea was supported into the late eighties by creationists whose claims became more and more bizarre in attempts to prop up their failing model, until it finally collapsed under the weight of the evidence against it. In 1988, the idea was given up by the major creationist organization Institute for Creation Research, which, in an attempt to distance themselves from the scientific debacle that c-decay had become, became vocal critics of it .

Galaxies over 12 billion light years away.

Typically for an ad-hoc explanation, c-decay conflicts with things we know about how the universe works. A change in the speed of light would quite literally end the world as we know it. The speed of light is not an arbitrary speed with no effect on outside systems, but is in fact a component in one of the most fundamental equations in the universe, the equation for matter: E = mc² where E is energy, m is mass, and c is the speed of light in a vacuum. This means that any increase of the speed of light would in turn increase the amount of energy released by the reactions of matter. Because the Sun, or indeed any star, relies on the reactions of matter, most notably nuclear fusion, a change in the speed of light would alter its energy output; if light were traveling as fast as some creationists demand, then the energy output of the Sun could be expected to increase over 800,000,000 times.
It is important to note that c-decay is in many ways, a class of "tired light" proposal such as those posited by Fritz Zwicky one of the most notable physicists of his era to explain redshift of galaxies.

White hole cosmology

White hole cosmology is a creationist cosmology invented by creationist Russell Humphreys and put forward in his 1994 book Starlight and Time. The main idea of white hole cosmology is that the world was created inside a black hole and that earth was subjected to intense time dilation so billions of years could have passed outside the field while only a few days would pass inside it.

Omphalos hypothesis

The Omphalos hypothesis or argument provides an unscientific and unfalsifiable explanation for the starlight problem. The argument relies on the logically weak argument goddidit by claiming that the starlight we see is not natural but was in fact created in transit by God.
Many creationists have rejected this explanation on theological grounds because it implies a deliberately deceitful God, much like the "dinosaur fossils are a test of my faith" arguments.
But if you accept the hypothesis, it opens a big can of worms. One could proceed to reject the 9,900 years of time given by dendrochronology by saying extra tree rings, over and above 4,004 BCE, were not natural but were in fact created in situ by God.
The most logical only possible explanation is as follows: Since God is a supernatural being, he could perfectly well have created photons with positions and velocities which are consistent with having been traveling from distant stars for many billions of years. This non-testable explanation could be used to escape any of the evidence against Young Earth Creationism, as there is no way to tell if the universe was brought into existence 6,000 years ago in a state consistent with a much older age or if the universe is in fact as old as the evidence shows it to be.
However, if this were the case, then scientists would still have to treat the universe as though it were ancient and so the actual date of creation is irrelevant. For some creationists, the possibility of God being deliberately deceptive is uncomfortable. (For example, did human-observed supernovae ever actually occur?) This solution also raises the problem of deciding when God created the apparently old universe — was it 6,000 years ago, or last Thursday? Moreover, many young-earth creationists also believe in the imminent destruction of the universe, which raises the question of whether stars farther away than 10,000 or so light-years ever actually existed to begin with.

Anisotropic synchrony convention

Jason Lisle's 2010 paper published in the Answers Research Journal (meaning, despite his apparent confidence in its explanatory power and his doctoral education in astrophysics, that he was unwilling to submit to peer review - any ideas as to why?) aims to solve the starlight problem by taking advantage of a quirk of physics--it isn't certain, after 70 years of discussion, whether a "one way" speed of light can be measured or is a convention. Lisle thus proposes that light traveling towards the Earth does so at an infinite speed while light traveling the other way goes at half the measured speed; which is not original to him. Thus it becomes possible for light to arrive from distant stars in line with the 6000-year chronology of young Earth creationism (and equally well, or perhaps even better, with Bertrand Russell's deliberately ridiculous five minutes ago hypothesis) even though we still measure the speed of light as a fairly lumbering 299,792,458 m/s.
The problem with Lisle's proposal is that it results in a geocentric universe and would create observational differences which have not been seen, in addition to violating the endlessly validated physical principle of isotropy; that is, that the laws of physics behave the same way in all directions.

Anthropic principle

The anthropic principle is based on the observation that any small change in any of the basic constants of physics, which include the speed of light, would make human life impossible. However the fact that light travels at the speed of light is merely a side effect of something deeper at play. Light actually travels at the fastest speed possible, the speed of causality itself. This means that for a photon of light, all of eternity is a single instant. The moment it is created and the moment it is destroyed and all the intervening time is simply one clock tick for any massless particle including the photon. Therefore any "anthropic claims" are prima-facie invalid. The underpinnings of physics are derived from the quantized clock ticks and the rate at which the clock ticks for the universe of mass vs the universe of the massless has huge variability without upsetting the actual physics at play one iota. (Assumes Quantum Loop Gravity and Quantized Time)

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                The Power of the Sun

The sun is the closest star to Earth. Even at a distance of 150 million kilometers (93 million miles), its gravitational pull holds the planet in orbit. It radiates light and heat, or solar energy, which makes it possible for life to exist on Earth. 

Plants need sunlight to grow. Animals, including humans, need plants for food and the oxygen they produce. Without heat from the sun, Earth would freeze. There would be no winds, ocean currents, or clouds to transport water.

Solar energy has existed as long as the sun—about 5 billion years. While people have not been around that long, they have been using solar energy in a variety of ways for thousands of years.

Solar energy is essential to agriculture—cultivating land, producing crops, and raising livestock. Developed about 10,000 years ago, agriculture had a key role in the rise of civilization. Solar techniques, such as crop rotation, increased harvests. Drying food using sun and wind prevented crops from spoiling. This surplus of food allowed for denser populations and structured societies. 

Early civilizations around the world positioned buildings to face south to gather heat and light. They used windows and skylights for the same reason, as well as to allow for air circulation. These are elements of solar architecture. Other aspects include using selective shading and choosing building materials with thermal mass, meaning they store heat, such as stone and concrete. Today, computer programs make applications easier and more precise. 

Solar power—the conversion of sunlight into electricity—is yet another application of solar technology. This can be done in a number of ways. The two most common are photovoltaic (solar cells) and concentrating solar power.

Solar cells convert sunlight directly into electricity. The amount of power generated by each cell is very low. Therefore, large numbers of cells must be grouped together, like the panels mounted on the roof of a house, to generate enough power. 

The first solar cell was constructed in the 1880s. The earliest major application was on the American satellite Vanguard I, launched in 1958. A radio transmitter powered by solar cells operated for about seven years; one using conventional batteries lasted only 20 days. Since then, solar cells have become the established power source for satellites, including those used in the telecommunications industry.

On Earth, solar cells are used for everything from calculators and watches to homes, commercial buildings, and even stadiums. Kaohsiung World Stadium in Taiwan, completed in 2009 to host the World Games, has more than 8,800 solar panels on its roof. Charles Lin, director of Taiwan’s Bureau of Public Works, said, “The stadium's solar energy panels will make the venue self-sufficient in electricity needs.” When the stadium is not in use, it can power 80 percent of the surrounding neighborhood.

Unlike solar cells, which use sunlight to generate electricity, concentrating solar power technology uses the sun’s heat. Lenses or mirrors focus sunlight into a small beam that can be used to operate a boiler. That produces steam to run turbines to generate electricity.  

           How far away could we travel from the Sun and still be able to see it?

Actually, this answer is more of an approximation. The Sun is by far the sky's brightest night sky object because we are so close to it: between 91.5 - 94.5 million miles, depending on the time of year. All the other stars are much fainter because they are so far away. (Think about it this way: a light beam requires about 8.3 minutes to travel from the Sun to Earth. A light beam from Proxima Centauri, the closest star to the Sun, requires about 4.2 years to reach Earth. Proxima Centauri is about 262,000 times farther away from us than the Sun.)

If we were to travel away from the Sun, it would become fainter. At Pluto's distance, the Sun will still be many millions of times brighter than the night sky's brightest star, Sirius. At the distance of Proxima Centauri, the Sun would be about as bright as Procyon, the  brightest star in Canis Minor and the 8th brightest star in our sky. The faintest stars that most people can see are about 185 times dimmer than Procyon. For the Sun to appear this faint to us, we would have to be about 58 light years away from it. Some people have keener eyesight than most of us and they can see fainter stars. However, if we were all in a space vessel that was 58 light years from the solar system, we could still just barely see the Sun. We'd likely need a highly detailed star chart to locate it. 

 
             

Sunlight travels at the speed of light. Photons emitted from the surface of the Sun need to travel across the vacuum of space to reach our eyes. 

The short answer is that it takes sunlight an average of 8 minutes and 20 seconds to travel from the Sun to the Earth.

If the Sun suddenly disappeared from the Universe (not that this could actually happen, don't panic), it would take a little more than 8 minutes before you realized it was time to put on a sweater.

We orbit the Sun at a distance of about 150 million km. Light moves at 300,000 kilometers/second. Divide these and you get 500 seconds, or 8 minutes and 20 seconds.

This is an average number. Remember, the Earth follows an elliptical orbit around the Sun, ranging from 147 million to 152 million km. At its closest point, sunlight only takes 490 seconds to reach Earth. And then at the most distant point, it takes 507 seconds for sunlight to make the journey.
But the story of light gets even more interesting, when you think about the journey light needs to make inside the Sun.
                                                                
You probably know that photons are created by fusion reactions inside the Sun's core. They start off as gamma radiation and then are emitted and absorbed countless times in the Sun's radiative zone, wandering around inside the massive star before they finally reach the surface.
What you probably don't know, is that these photons striking your eyeballs were ACTUALLY created tens of thousands of years ago and it took that long for them to be emitted by the sun.
Once they escaped the surface, it was only a short 8 minutes for those photons to cross the vast distance from the Sun to the Earth
As you look outward into space, you're actually looking backwards in time.
The light you see from your computer is nanoseconds old. The light reflected from the surface of the Moon takes only a second to reach Earth. The Sun is more than 8 light-minutes away. And so, if the light from the nearest star (Alpha Centauri) takes more than 4 years to reach us, we're seeing that star 4 years in the past.
There are galaxies millions of light-years away, which means the light we're seeing left the surface of those stars millions of years ago. For example, the galaxy M109 is located about 83.5 million light-years away.
If aliens lived in those galaxies, and had strong enough telescopes, they would see the Earth as it looked in the past. They might even see dinosaurs walking on the surface.

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                    Laser rangefinder

A laser rangefinder is a rangefinder that uses a laser beam to determine the distance to an object. The most common form of laser rangefinder operates on the time of flight principle by sending a laser pulse in a narrow beam towards the object and measuring the time taken by the pulse to be reflected off the target and returned to the sender. Due to the high speed of light, this technique is not appropriate for high precision sub-millimeter measurements, where triangulation and other techniques are often used.

                    

       A long range laser rangefinder is capable of measuring distance up to 20 km; mounted on a tripod with an angular mount. The resulting system also provides azimuth and elevation measurements. 

Pulse

The pulse may be coded to reduce the chance that the rangefinder can be jammed. It is possible to use Doppler effect techniques to judge whether the object is moving towards or away from the rangefinder, and if so, how fast.

Precision

The precision of the instrument is determined by the rise or fall time of the laser pulse and the speed of the receiver. One that uses very sharp laser pulses and has a very fast detector can range an object to within a few millimeters.

Range and range error

Despite the beam being narrow, it will eventually spread over long distances due to the divergence of the laser beam, as well as due to scintillation and beam wander effects, caused by the presence of air bubbles in the air acting as lenses ranging in size from microscopic to roughly half the height of the laser beam's path above the earth.
These atmospheric distortions coupled with the divergence of the laser itself and with transverse winds that serve to push the atmospheric heat bubbles laterally may combine to make it difficult to get an accurate reading of the distance of an object, say, beneath some trees or behind bushes, or even over long distances of more than 1 km in open and unobscured desert terrain.
Some of the laser light might reflect off leaves or branches which are closer than the object, giving an early return and a reading which is too low. Alternatively, over distances longer than 1200 ft (365 m), the target, if in proximity to the earth, may simply vanish into a mirage, caused by temperature gradients in the air in proximity to the heated surface bending the laser light. All these effects have to be taken into account.

Calculation

The distance between point A and B is given by

${\displaystyle D={\frac {ct}{2}}}$

where c is the speed of light and t is the amount of time for the round-trip between A and B.

${\displaystyle t={\frac {\varphi }{\omega }}}$

where φ is the phase delay made by the light traveling and ω is the angular frequency of optical wave.
Then substituting the values in the equation,

${\displaystyle D={\frac {1}{2}}ct={\frac {1}{2}}{\frac {c\varphi }{\omega }}={\frac {c}{4\pi f}}(N\pi +\Delta \varphi )={\frac {\lambda }{4}}(N+\Delta N)}$

In this equation, λ is the wavelength c/f; Δφ is the part of the phase delay that does not fulfill π (that is, φ modulo π); N is the integer number of wave half-cycles of the round-trip and ΔN the remaining fractional part.

Technologies

An OLS-27 IRST with laser rangefinder on the Sukhoi Su-27

Time of flight - this measures the time taken for a light pulse to travel to the target and back. With the speed of light known, and an accurate measurement of the time taken, the distance can be calculated. Many pulses are fired sequentially and the average response is most commonly used. This technique requires very accurate sub-nanosecond timing circuitry.
Multiple frequency phase-shift - this measures the phase shift of multiple frequencies on reflection then solves some simultaneous equations to give a final measure.
Interferometry - the most accurate and most useful technique for measuring changes in distance rather than absolute distances.

Applications

Military

An American soldier with a GVS-5 laser rangefinder

Rangefinders provide an exact distance to targets located beyond the distance of point-blank shooting to snipers and artillery. They can also be used for military reconnaissance and engineering.
Handheld military rangefinders operate at ranges of 2 km up to 25 km and are combined with binoculars or monoculars. When the rangefinder is equipped with a digital magnetic compass (DMC) and inclinometer it is capable of providing magnetic azimuth, inclination, and height (length) of targets. Some rangefinders can also measure a target's speed in relation to the observer. Some rangefinders have cable or wireless interfaces to enable them to transfer their measurement(s) data to other equipment like fire control computers. Some models also offer the possibility to use add-on night vision modules. Most handheld rangefinders use standard or rechargeable batteries.

A Dutch ISAF sniper team displaying their Accuracy International AWSM .338 Lapua Magnum rifle and VECTOR IV Leica/Vectronix laser rangefinder binoculars

The more powerful models of rangefinders measure distance up to 25 km and are normally installed either on a tripod or directly on a vehicle or gun platform. In the latter case the rangefinder module is integrated with on-board thermal, night vision and daytime observation equipment. The most advanced military rangefinders can be integrated with computers.
To make laser rangefinders and laser-guided weapons less useful against military targets, various military arms may have developed laser-absorbing paint for their vehicles. Regardless, some objects don't reflect laser light very well and using a laser rangefinder on them is difficult.

3-D modeling

This LIDAR scanner may be used to scan buildings, rock formations, etc., to produce a 3D model. The LIDAR can aim its laser beam in a wide range: its head rotates horizontally, a mirror flips vertically. The laser beam is used to measure the distance to the first object on its path.

Laser rangefinders are used extensively in 3-D object recognition, 3-D object modelling, and a wide variety of computer vision-related fields. This technology constitutes the heart of the so-called time-of-flight 3D scanners. In contrast to the military instruments described above, laser rangefinders offer high-precision scanning abilities, with either single-face or 360-degree scanning modes.
A number of algorithms have been developed to merge the range data retrieved from multiple angles of a single object to produce complete 3-D models with as little error as possible. One of the advantages that laser rangefinders offer over other methods of computer vision is that the computer does not need to correlate features from two images to determine depth information as in stereoscopic methods.
Laser rangefinders used in computer vision applications often have depth resolutions of tenths of millimeters or less. This can be achieved by using triangulation or refraction measurement techniques as opposed to the time of flight techniques used in LIDAR.

Forestry

Laser rangefinder TruPulse used for forest inventories (in combination with Field-Map technology)

Special laser rangefinders are used in forestry. These devices have anti-leaf filters and work with reflectors. Laser beam reflects only from this reflector and so exact distance measurement is guaranteed. Laser rangefinders with anti-leaf filter are used for example for forest inventories.

Sports

Laser rangefinders may be effectively used in various sports that require precision distance measurement, such as golf, hunting, and archery. Some of the more popular manufacturers are Caddytalk, Opti-logic Corporation, Bushnell, Leupold, LaserTechnology, Trimble, Leica, Newcon Optik, Op. Electronics, Nikon, Swarovski Optik and Zeiss. Many rangefinders from Bushnell come with advanced features, such as ARC (angle range compensation), multi-distance ability, slope, JOLT (Vibrate when the target is locked), and Pin-Seeking. ARC can be calculated by hand using the rifleman's rule, but it's usually much easier if you let a rangefinder do it when you are out hunting. In golfing where time is most important, a laser rangefinder comes useful in locating distance to the flag. Many hunters in the eastern U.S. don't need a rangefinder, although many western hunters need them, due to longer shooting distances and more open spaces.

Industrial production processes

An important application is the use of laser rangefinder technology during the automation of stock management systems and production processes in steel industry.

Laser measuring tools

Laser rangefinder: Bosch GLM 50 C

Laser rangefinders are also used in several industries like construction, renovation and real estate as an alternative to a tape measure, and was first introduced by Leica Geosystems in 1993 in France. To measure a large object like a room with a tape measure, one would need another person to hold the tape at the far wall and a clear line straight across the room to stretch the tape. With a laser measuring tool, the job can be completed by one operator with just a line of sight. Although the tape measure is typically more accurate, laser measuring tools can be calibrated to be generally reliable when taking several measurements. Laser measuring tools typically include the ability to produce some simple calculations, such as the area or volume of a room, as well as switch between imperial and metric units. These units can be found in a hardware stores and online marketplaces.

Price

Laser rangefinders can vary in price, depending on the quality and application of the product. Military grade rangefinders need to be as accurate as possible and must also reach great distances. This could be in excess of hundreds of thousands of dollars. In other civilian applications, such as hunting or golf, they are more affordable and much more readily accessible.

Safety

Laser rangefinders are divided into four classes and several subclasses. Laser rangefinders available to consumers are usually laser class 1 or class 2 devices and are considered relatively eye-safe. Regardless of the safety rating, direct eye contact should always be avoided. Most laser rangefinders for military use exceed the laser class 2 energy levels.

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A Laser Distance Meter sends a pulse of laser light to the target and measures the time it takes for the reflection to return. For distances up to 30m, the accuracy is É3mm. On-board processing allows the device to add, subtract, calculate areas and volumes and to triangulate. You can measure distances at a distance. 

So light from the laser is definitely scattered as the distance increases - but in clear air, there isn't much of an effect in terms of power reduction. However, if there is anything floating around in the air (water vapor, smoke, etc) -then the laser's power may be sharply reduced as a consequence. 

Just for reference, a 5 mW laser is an eye hazard up to about 50 feet from the laser. For a pilot who is 1320 feet in the air, the laser light would be far too weak to cause any eye injury.

Most laser distance meters will have either 1/8-inch or 1/16-inch accuracy at 30 feet. For basic estimating, the 1/8-inch accuracy works just fine. ... Make the Call: Most applications for a laser distance measure will be fine with 1/8-inch accuracy. But more accurate is still more accurate

Have you ever played with a pocket-sized laser, wondering how far its light would travel? Could you, a naughty student inside a classroom on Earth, annoy a poor substitute teacher on Mars by waggling your laser pointer at him?​  

By the time the light finally reached Mars, the glint would be a million times dimmer than the faintest light visible to the human eye.

But you don’t need to take our word for it. The math needed to calculate the answer is surprisingly simple.
Partly inspired by a talk at a recent astronomy meeting that explored whether we could detect photons from potential exoplanet-dwelling aliens, Inside Science performed some of our own calculations to see if a hypothetical alien Galileo could observe photons coming from Earth.
All we need is an equation for calculating how quickly a laser beam spreads out as it travels through space. From that we can use straightforward geometry to derive the diameter of the beam when it hits its target. Finally, we divide the power output of the laser by the area of the final lit spot and voila! -- that's how intense the laser is at the destination. While the way humans, or aliens, perceive the brightness of this light is much less straightforward, for the purpose of this exercise we treat brightness and light intensity as the same thing.

Your pocket laser pointer

The power for an average laser pointer is a measly 0.005 watts. However, because of the narrow path of the laser beam, if you pointed it directly at your eye from an arm's length away, the little illuminated dot on your eyeball would be 30 times brighter than the midday sun. So, don't do this at home, or anywhere.
Still, the narrow beam will spread out over long distances. Around 100 meters away from a red laser pointer, its beam is about 100 times wider and looks as bright as a 100-watt light bulb from 3 feet away. Viewed from an airplane 40,000 feet in the air -- assuming there’s no clouds or smog -- the pointer would be as bright as a quarter moon. From the International Space Station, it would fade to roughly as bright as the brightest star in the night sky -- Sirius.

                                   

For Starman, the dummy driving the Tesla car that Elon Musk's company Space X recently launched into space, your little red laser pointer would be too dim to notice. If you want to get his attention, you'll need something brighter.

The Navy's missile-killer

The U.S. Navy might have what we need. According to recent reports, their current goal is to develop a laser that is both logistically practical and powerful enough to destroy incoming cruise missiles. A laser like that would need to put out about 500,000 watts of power -- 100 million times more powerful than your pocket laser pointer. These lasers typically operate in the infrared spectrum, which is invisible to humans. But for the sake of this exercise we'll assume that both Starman and the Martians can see in the infrared.
Weapons-grade lasers also tend to have a much larger opening, or aperture, which counterintuitively causes the laser beam to spread out less, thus enhancing the beam’s ability to maintain its intensity over longer distances.
Because of the larger aperture, if the missile-killer laser beam is aimed at the moon, the infrared spot it would make on the surface would only be about 1.5 miles across. For comparison, the incredibly dim red dot from your pocket laser pointer would be 8 miles wide once it reached the moon.
If you could see in the infrared and stood on the moon underneath the military laser’s beam, it would appear roughly 30 times brighter than the full Earth. That’s quite bright, but not blindingly so. It’s still only one-thousandth the brightness of the midday sun on Earth.
By the time the beam reached the Martians -- if we assume the shortest possible distance between Earth and the red planet, which is about 34 million miles -- the spotlight would be about 200 miles across. Its light should still be noticeable -- about half as bright as the brightest star in the sky sans the sun -- but not exactly attention grabbing.

                                 

The most powerful laser ever built

Several scientific facilities around the world have huge lasers that operate at more than a thousand trillion watts. In other words, these lasers have as much power as a million trillion pocket laser pointers -- that’s almost a billion laser pointers for every person on the planet!
If run continuously, these lasers would use up the entire world's electricity supply in seconds. Luckily, the only reason these lasers can put out such intense power is that they concentrate the release over an extremely short period of time -- usually less than a trillionth of a second. The extremely short laser pulse is then focused down to a point a few thousandths of a millimeter across, and can be 10 trillion trillion times brighter than the surface of our sun. It's so powerful that scientists are using them to rip apart empty space itself in a quest to learn more about the fundamental laws of our universe.
What if we just want to use this for fun and shoot it at space invaders? One major drawback is that these lasers usually produce ultraviolet light, which is mostly absorbed by the Earth’s atmosphere. If we don’t want to turn our air into plasma, we’d have to construct our building-sized super laser cannon in space instead.

                                  


For the extremely brief time we could afford to fire the laser at Mars, it would cast UV light a thousand times more intense than the midday sun on Earth over an area 150 miles across. Let’s hope that the Martians have some SPF-1,000 sunblock handy.
Sadly, as we know by now, there are no little green men on Mars, or most likely anywhere else in our solar system. However, there are thousands of discovered exoplanets -- planets that orbit around stars outside our solar system -- many of which have the possibility to contain life. What if we try to get their attention?

                                          

Proxima Centauri, located roughly four light-years away, is the closest star to us and is orbited by several exoplanets. If we aimed our most powerful laser there, by the time the light reached it, it would appear brighter than the brightest star looks to us in a clear night sky. So, four years after we’ve fired our laser, if there's any alien astronomer looking at the right spot in their night sky, they may notice a nanosecond flash of ultraviolet light and go, "What was that?"


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                               When lightning strikes are your LED designs safe?

The advent of light-emitting diode (LED) technology marked a significant revolution in the electrical lighting industry. Since 1990, when LED lamps were introduced, it is increasingly replacing legacy light sources such as, mercury vapour, metal halide, and sodium vapor in outdoor lighting applications. LED lighting technology is astonishing for its development in efficiency (higher lumens per watt), secondary optics (better lenses/reflectors), and greater thermal dissipation.
Growth in demand for LED lighting is accelerating as consumers and industrial users seek more energy-efficient illumination options. Expansion of LED lighting mechanism is also being driven by government actions designed to discourage continued usage of incandescent lamps. This system the high adoption rate of LED lighting is definitely a global phenomenon. Countries with the most advanced economies have well-established plans and programs to phase out legacy incandescent lighting. That shouldn’t be surprising because, the global lighting account is about 25% of the total energy consumption.
Though the initial cost of installing outdoor LED lighting can be substantial, this cost is justified and payback is established based on the lower wattage demand, lower maintenance cost, and longer lifetime it offers. In order to protect outdoor LED lighting from failing within an investment payback period of about five years, the lighting must offer high durability and reliability.
One significant threat to outdoor LED lighting is transient surge events in AC power lines that can damage lighting fixtures. An LED lamp contains power conversion electronics (AC/DC), driver IC for the LEDs, a heat sink for thermal management and optics to optimise light quality. An LED light directly connected to AC mains, for example, 120/220 V AC can be damaged by short circuit and overload conditions caused by component and/or circuit failures inside the bulb. In addition, lightning surges or load switching transients which originate outside the bulb can create voltage spikes or ring waves that can stress and ultimately damage components, and cause the bulb to collapse. Given that the value proposition for LED bulbs is not only lower energy usage, but longer lifetimes, it will be crucial that transient voltage protection is taken into account to eliminate field failures driven by the electrical environment.
Indirect lightning-induced surges
Over-voltage transient surges can occur in AC power lines as the result of a nearby electrical equipment being switched on/off. Nearby lightning strikes can also generate transient surges in AC power lines, especially in outdoor environments.

Fig. 1: Transient surge in AC power lines.

Lightning strikes are travelling-electrostatic-discharges usually coming from cloud to the ground in the magnitude of millions of volts. Current carrying copper wires (for example, underground power cable for streetlight) can be induced up to thousands of volts from lightning strikes occurring up to a few miles away. These indirect strikes can be characterised with specific waveforms that often contain large amounts of energy in the magnitude of over 1000 A²s.
Approximately 70% of lightning occurs on land located in the tropics where the majority of thunderstorms occur. The African countries have the heaviest and persistent lightning attack from the beginning of time. The place where lightning occurs most often is near the small village of Kifuka in the mountains of eastern Democratic Republic of the Congo, where the elevation is around 975 m. On an average, this region receives 158 lightning strikes per 1 km²  a year. A large area around this place also is badly affected by the induced surge strikes which raise a chance to damage the outdoor LED lighting installations.
According to National Aeronautics and Space Administration’s (NASA) research on worldwide lightning strike frequency, Central and South America, Africa, Southern and Southeastern Asia have similar lightning strike frequency to the US, and thus we suggest equivalent surge immunity level to the US at 5 KA to 10 KA. For other regions with fewer lightning strikes like Europe, Eastern Asia, and Australia, lower surge immunity level could be considered at 3 KA to 5 KA.
This type of indirect lightning energy from storms can adversely affect outdoor LED lighting installations. The luminaire is susceptible to damage both in the differential and common modes:

• Differential mode: High voltage/current transient between the L-N or L-L terminals of the luminaire could damage components in the power supply unit or LED module board.
• Common mode: High voltage/current transient between the L-G (earth) or N-G (earth) of the luminaire could break over safety insulation in the power supply unit or LED module board, including the LED to heat-sink insulation.

The test waveform is a combination of 1,2 x 50 μs open circuit voltage and 8 x 20 μs short circuit current waveform. To perform this test, the specified peak current is calibrated on the surge generator by shorting the output to ground prior to connection to the luminaire.

Fig. 2: Combination wave open-circuit voltage.

Fig. 3: Combination wave short-circuit voltage.

The map below shows the density of lightning in various regions across the globe according to the research done by NASA on worldwide lightning frequency.

Fig. 4: Worldwide lightning frequency (by NASA Global Hydrology Resource Centre).

Units: Flashes/km²/year
Technologies to handle induced surge events
The way to protect outdoor LED lighting from induced surge strike is to block high voltage/current transient interference from entering the lighting. Surge protective device (SPD) is therefore utilised in outdoor LED lighting to suppress surge energy and minimise surge impact to the lighting.
There are several overvoltage protection components available for SPD, including components like metal oxide varistor (MOV), gas discharge tube (GDT), and transient voltage suppression (TVS) diode which are placed between AC power lines with normally high impedance and become low impedance when high voltage is detected. They divert surge energy back to AC power lines by its low impedance and turn back to high impedance after surge event. Among available technologies, MOV is preferred and widely implemented in SPD in power distribution panel for its high surge energy handling capability and fast response to transient voltage. Therefore MOV is the best suitable for surge protection device in outdoor LED lighting application.
Incorporating a robust surge suppression circuit in an outdoor luminaire can eliminate damage caused by surge energy, thereby enhancing reliability, minimising maintenance and enhancing the useful life of the lighting installation. A surge protection subassembly that can suppress excessive surges to lower voltage levels is an optimal way to protect the LED luminaire investment.

Fig. 5: LED street light protection scheme.

Thermally protected MOV for SPD safety
MOV technology is not only inexpensive but also a highly effective technology for suppressing transients in power supplies. It is also effective in many other applications, such as SPD modules that are often placed in front of an LED driver.
MOVs tend to degrade gradually after a large surge or multiple small surges. This degradation leads to increasing MOV leakage current, which in turn raises the MOV’s temperature, even under normal conditions like 120 VAC/240 V AC operating voltage. A thermal disconnect adjacent to the MOV can be used to sense the increase in MOV temperature while it continues to degrade to its end-of-life condition; at this point, the thermal disconnect will open the circuit, removing the degraded MOV from the circuit and preventing its catastrophic failure.

Fig. 6: Thermal disconnect prevents the failure of a degraded MOV.

MOVs are designed to clamp fast over-voltage transients within microseconds. However, in addition to short duration transients, MOVs inside SPD modules can be subjected to temporary over-voltage conditions caused by loss of neutral or by incorrect wiring during installation. These conditions can severely stress an MOV, causing it to go into a thermal runaway condition; in turn, this will result in overheating, smoke, and the potential for fire. UL 1449 and IEC 61643-11, the safety standards for SPDs, define specific abnormal conditions under which devices must be tested to ensure SPD safety. Robust designs include thermal disconnects within the SPD to protect the MOVs from thermal runaway.

Fig. 7: AC over current event.

End-of-life/replacement indication for SPDs
When MOV gets overheated due to temporary over-voltage or degradation end-of-life, thermal disconnect helps to cut MOV from AC circuit. The SPD therefore stops providing surge suppression function. Proper indication should be considered so that maintenance personnel know the SPD is not working and needs a replacement.
Luminaire designers can choose from two main types of SPD module configurations based on their maintenance and warranty strategies. Those are parallel- and series-connected surge protection subassemblies.
Parallel connection: The SPD module is connected in parallel with the load. An SPD module that has reached end-of-life is disconnected from the power source while leaving the AC/DC power supply unit energised. The lighting still remains operational, but the protection against the next surge to which the power supply unit and LED module are exposed is lost. In a parallel-connected SPD module, replacement indication can be added through the use of a small LED that indicates the SPD module status to the maintenance technician. Options for a green LED indicating an online SPD module or a red LED indicating an offline SPD module are available. Rather than an LED indication at each lighting fixture, the need for SPD module replacement could be indicated remotely to a light management center with SPD module end-of-life indication wires connected to a networked smart lighting system.
Series connection: The SPD module is connected in series with the load, where the end-of-life SPD module is disconnected from the power source, which turns the light off. The loss of power to the luminaire serves as indication for a maintenance call. The disconnected SPD module not only turns the lighting off to indicate the need for replacement but also isolates the AC/DC power supply unit from future surge strikes. General preference for this configuration is growing rapidly because the luminaire investment remains protected while the SPD module is awaiting replacement. It is far less expensive to replace a series-connected SPD module than the whole luminaire as in the case of a parallel-connected SPD module.

Fig. 8: Parallel and series connections.

Summary
The high energy savings offered by LED technology enhances the value of outdoor lighting. In order to help LED lighting fixtures reach their expected lifetime, a surge protection module should be added to outdoor LED lighting to prevent premature failure due to lightning surge events and other power line surges.
A surge protection module, installed along with the LED power supply unit, provides effective protection for lighting systems. However, it may be subject to temporary overvoltage threats and fatigue due to multiple surge events. Thermal disconnects placed in surge protection modules enhance the overall safety of the modules and help them to achieve UL 1449 and IEC 61643-11 certification.
When surge protection modules reach their end-of-life, a mechanism is needed to indicate that the modules require replacement. The series-connected SPD module provides the simplest way of indicating the need for replacement by disconnecting the light fixture from the power source, resulting in the light turning off. Parallel-connected SPD modules provide the option to interface with LEDs to indicate whether the modules are online or offline.

Incandescent Lights:

What is an Incandescent Light:

The incandescent light is your classic light bulb. It produces light by heating a wire filament to a temperature that results in the generation of light. The metal wire is surrounded by a translucent glass bulb that is either filled with an inert gas or evacuated (a vacuum). 

What’s The Upside to Incandescent Lights:

They’re really cheap to manufacture and accordingly, they’re really cheap to purchase (typically a dollar or two). Incandescent bulbs are widely available and adaptable to a large range of voltages, light outputs, and current (working well with both AC and DC power). They are the cheapest light on the market.  
Additionally, incandescent lights have a notoriously good ability to render color. The color rendering index (CRI) for an incandescent bulb with a color temperature of 2700K is 100 (a perfect score). As color temperature rises the CRI ratings drop off only slightly but typically remain above 95 (considered an excellent rating).

What are the Major Deficiencies in Incandescent Lights:

Amongst the deficiencies in incandescent lighting are the following:

1. Incandescent lights have the worst energy efficiency on the market. incandescent lamps have efficiency ratings around 10 lumens/watt. Unfortunately most of the energy they consume (~90%) goes into generating heat.
2. Incandescent lights have the worst lifespan on the market. The average bulb lasts around 1,200 operating hours. This means that even though incandescent bulbs are cheap to purchase, you have to purchase a whole lot of them (50-100) to equal the lifespan of a single LED. Overall that means high maintenance costs.

What are the Minor Deficiencies in Incandescent Lights:

Among the minor deficiencies in incandescent lighting are the following:

1. Incandescent lights are omnidirectional. Omnidirectional lights produce light in 360 degrees. This is a large system inefficiency because at least half of the light needs to be reflected and redirected to the desired area being illuminated. The need for reflection and redirection of light means that the output is much less efficient for omnidirectional lights due to losses than it would be for the same light if it were directional by its nature.

Where Are Incandescent Lights Commonly Used:

Common applications for incandescent lighting includes residential and interior lighting. It is typically not used in outdoor environments or for large organizations because of its short lifespan and poor energy efficiency.

                                             LED:

What is a Light Emitting Diode (LED):

LED stands for Light Emitting Diode. A diode is an electrical device or component with two electrodes (an anode and a cathode) through which electricity flows - characteristically in only one direction (in through the anode and out through the cathode). Diodes are generally made from semiconductive materials such as silicon or selenium - solid state substances that conduct electricity in some circumstances and not in others (e.g. at certain voltages, current levels, or light intensities). When current passes through the semiconductor material the device emits visible light. It is very much the opposite of a photovoltaic cell (a device that converts visible light into electrical current).

What’s The Major Upside to LED Lights:

There are four major advantages to LED lighting:

1. LEDs have an extremely long lifespan relative to every other lighting technology (including LPS and fluorescent lights but especially compared to incandescent lights). New LEDs can last 50,000 to 100,000 hours or more. The typical lifespan for an incandescent bulb, by comparison, is 1-5% as long at best (roughly 1,200 hours).
2. LEDs are extremely energy efficient relative to every other commercially available lighting technology. There are several reasons for this to include the fact they waste very little energy in the form of infrared radiation (heat), and they emit light directionally (over 180 degrees versus 360 degrees which means there are far fewer losses from the need to redirect or reflect light).
3. Very high light quality.
4. Very low maintenance costs and hassle.

What Are Minor Upside to LED Lights:

In addition to the major advantages, LED lights also offer several smaller perks. These include the following:

1. Accessories: LEDs require far fewer accessory lamp parts.
2. Color: LEDs can be designed to generate the entire spectrum of visible light colors without having to use the traditional color filters required by traditional lighting solutions.
3. Directional: LEDs are naturally directional (they emit light for 180 degrees by default).
4. Size: LEDs can be much smaller than other lights (even incandescent).
5. Warm-Up: LEDs have faster switching (no warm-up or cool-down period).

What’s The Downside to LED Lights:

Considering the upside you might think that LED lights are a no-brainer. While this is increasingly becoming the case, there are still a few tradeoffs that need to be made when you choose LED:  
In particular, LED lights are relatively expensive. The up-front costs of an LED lighting project are typically greater than most of the alternatives. This is by far the biggest downside that needs to be considered. That said, the price of LEDs are rapidly decreasing and as they continue to be adopted en masse the price will continue to drop.

Where is LED Commonly Used:

The first practical use of LEDs was in circuit boards for computers. Since then they have gradually expanded their applications to include traffic lights, lighted signs, and more recently, indoor and outdoor lighting. LED lights are a wonderful solution for gymnasiums, warehouses, schools and commercial buildings. They are also adaptable for large public areas (which require powerful, efficient lights over a large area), road lighting (which offer significant color advantages over low and high pressure sodium lights), and parking lots.

Further Qualitative Comparison:

What’s The Difference Between Sodium Vapor and LED Lights:

The two different technologies are entirely different methods of producing light. Sodium vapor bulbs contain metals that are evaporated into inert gas within the glass casing while LEDs are a solid state technology. Both technologies are very efficient. The difference is that sodium vapor lights were the most efficient technology of the 1970s while LEDs are the modern day equivalent. Although sodium vapor lighting beats virtually every other technology in terms of energy efficiency (which is why it was chosen to illuminate the streets of so many cities), it loses out to LEDs. Both LEDs and sodium vapor lights emit electromagnetic radiation across a small portion of the visible light spectrum, however, LEDs waste much less energy producing waste heat and they also provide an incredibly better variety of high Color Rendering Index options to the user (thus eliminating the monochromatic black appearance of objects illuminated by LPS and HPS bulbs).

Why would LEDs put incandescent bulbs out of business:

Incandescent bulbs are very inefficient energy consumers. They convert less than 1/20th of the energy they consume into visible light. The vast majority (approximately 90%) is lost as heat.
This all translates to cost. Although the sticker price is low, incandescent bulbs will cost you money over time based on the inefficient way in which they operate and the frequency with which they must be replaced. In a large-scale building (like schools, hospitals, or commercial buildings), this inefficiency will really add up.

Incandescent Lighting vs Light Emitting Diode (LED) Comparison:

Topic	LED Notes	Incandescent Notes	Winner
Correlated Color Temperature (read more here)	LEDs are available in a wide range of color temperatures that generally span from 2200K-6000K (ranging from “warm” yellow to light or “cool” blue).	Incandescent bulbs are also available in a range of color temperatures. The three primary options for consumers include Soft White (roughly 2700K – 3000K), Cool White (3500K – 4100K), and Daylight (5000K – 6500K).	-
CRI (read more here)	CRI for LED is highly dependent on the particular light in question. That said, a very broad spectrum of CRI values is available ranging generally from 65-95.	Incandescent bulbs generally have outstanding CRI ratings. A “warm” incandescent light (one with a color temperature of around 2700K) has a perfect CRI of 100. Values trend down a little as color temperature goes up but they tend to stay above 95 (still outstanding).	Incandescent
Cycling (Turning On/Off)	LEDs are an ideal light for purposely turning on and off because they respond rather instantaneously (there is no warm up or cool down period). They produce steady light without flicker.	Incandescent lights (similar to LED) do not generally flicker and/or cycle on and off as the bulb reaches the end of its useful life. Rather, incandescent light (again, like LEDs) tends to emit less light prior to total failure at the end of its useful life. Incandescent lights also turn on rather instantaneously and produce steady light generally without flicker.	-
Dimming	LEDs are very easy to dim and options are available to use anywhere from 100% of the light to 0.5%. LED dimming functions by either lowering the forward current or modulating the pulse duration. LED lights are not compatible with traditional incandescent dimmers (which lower the voltage sent to the light) so you need to purchase LED dimmer switches as well if you want to dim.	Incandescent lights are also very easy to dim. Incandescent light is extremely sensitive to voltage inputs and dimming works by exponentially emitting less light as the voltage is reduced. For better or worse (and different than LEDs) incandescent dimming has a larger effect on other characteristics of the light such as power consumption, lifetime, and color temperature.	-
Directionality	LEDs emit light for 180 degrees. This is typically an advantage because light is usually desired over a target area (rather than all 360 degrees around the bulb). You can read more about the impact of directional lighting by learning about  a measurement called “useful lumens” or “system efficiency.”	All Incandescent lights emit light omnidirectionally. This means they emit light 360 degrees, requiring fixture housings or reflectors to direct a large portion of the emissions to the desired target area or otherwise wasting the energy required to produce the light.	LED
Efficiency	LEDs are very efficient relative to every lighting type on the market and extremely efficient relative to incandescent bulbs. Typical source efficiency ranges 37 and 120 lumens/watt. Where LEDs really shine, however, is in their system efficiency (the amount of light that actually reaches the target area after all losses are accounted for). Most values for LED system efficiency fall above 50 lumens/watt.	Incandescent lights are the worst of all the modern lights in terms of efficiency because so much of the energy (90%) goes towards generating heat instead of light. Their source efficiency (the amount of light emitted from the bulb  in general) is around 10 lumens/watt and their system efficiency (the amount of light that actually reaches the target area after all losses are accounted for) is even lower.	LED
Efficiency Droop	LED efficiency drops as current increases. Heat output also increases with additional current which decreases the lifetime of the device. The overall performance drop is relatively low over time with around 80% output being normal near the end of life. Recent advances by researchers who have identified the reasons for droop in LEDs look to reduce losses even further.	Although incandescent lifespan is extremely short (around 1,200 hours), the bulbs maintain their luminescence really well throughout.	Incandescent Note: recent advances in LEDs will likely improve their droop qualities.
Emissions (In the Visible Spectrum)	LEDs produce a very narrow spectrum of visible light without the losses to irrelevant radiation types (IR, UV) or heat associated with conventional lighting, meaning that most of the energy consumed by the light source is converted directly to visible light.	Incandescent lights emit a very small percentage of their emissions as visible light. A much larger portion is emitted as infrared (essentially heat). Unless you are trying to heat a room with your lightbulbs this is a generally negative feature of incandescent light.	LED
- Infrared	None	The majority of an incandescent bulb’s emissions are put out in the infrared spectrum (essentially representing losses as heat).	LED
- Ultraviolet	None	None	-
- Heat Emissions	LEDs emit very little forward heat. The only real potential downside to this is when LEDs are used for outdoor lighting in wintery conditions. Snow falling on traditional lights like HID will melt when it comes into contact with the light. This is usually overcome with LEDs by covering the light with a visor or facing the light downward towards the ground.	Incandescent lights emit roughly 90% of their emissions as heat. In some circumstances heat emissions could be beneficial, however, it is a generally a bad thing to emit heat as it represents an energy inefficiency. The ultimate purpose of the device is to emit light, not heat.	LED
Failure Characteristics	LEDs fail by dimming gradually over time. Because LED lights typically operate with multiple light emitters in a single luminaire the loss of one or two diodes does not mean failure of the entire luminaire..	Incandescent lights generally hard fail meaning they stop working completely and all at once. Incandescent lights burn well throughout their lifetime but the extremely limited time of life (approximately 1,200 hours versus 100,000+ with LEDs) makes them a real bear with maintenance and replacement costs.	LED
Foot Candles (read more here)	Foot candle is a measure that describes the amount of light reaching a specified surface area as opposed to the total amount of light coming from a source (luminous flux). LEDs are very efficient relative to every lighting type on the market. Typical source efficiency ranges 37 and 120 lumens/watt. Where LEDs really shine, however, is in their system efficiency (the amount of light that actually reaches the target area after all losses are accounted for). Most values for LED system efficiency fall above 50 lumens/watt.	Foot candle is a measure that describes the amount of light reaching a specified surface area as opposed to the total amount of light coming from a source (luminous flux). Incandescent light is generally very inefficient for two principal reasons: first, most of the electricity goes to generating heat. Second, the bulb is omnidirectional meaning a large portion of the emissions are lost to non-relevant areas other than the intended target.	LED Note: Foot Candle ratings are very application specific and vary case by case so relative performance is difficult to generally quantify.
Lifespan	LEDs last longer than any light source commercially available on the market. Lifespans are variable but typical values range from 25,000 hours to 200,000 hours or more before a lamp or fixture requires replacement.	Incandescent lights have the worst lifespan of any bulb on the market (roughly 1,200 hours). Typical lifespan values for an HID bulbs like HPS or CFL are around 10,000-24,000 hours (10-20 times as long). LEDs last 2-10 times as long as HID bulbs which means they last roughly 50-100 times as long as incandescent.	LED
Lifetime Costs	LED lighting has relatively high initial costs and low lifetime costs. The technology pays the investor back over time (the payback period). The major payback comes primarily from reduced maintenance costs over time (dependent on labor costs) and secondarily from energy efficiency improvements (dependent on electricity costs).	Incandescent lights are by far the cheapest light to purchase on the market but they are a bear to maintain over time because their lifespan is so short. Incandescent lights will likely need to be purchased 20-50 times and the associated labor costs will need to be paid in order to attain the equivalent lifespan of a single LED light. Additionally, incandescent lights have the highest energy costs on the market.	LED
- Maintenance Costs	As a result of the operational lifetimes of LEDs and the frequency with which bulbs have to be changed out, LEDs are by far the best on the market in regards to lifetime costs.	Incandescent lights will likely need to be purchased 20-50 times and the associated labor costs will need to be paid in order to attain the equivalent lifespan of a single LED light.	LED
- Upfront Costs	LED light costs are high but variable depending on the specifications. The typical 100W-equivalent LED light costs somewhere between $10 and $20.	Incandescent lights costs vary depending on the specific type of light. They are cheap compared to LEDs ($1-$7 for a 100W bulb).	Incandescent
Shock Resistance	LEDs are solid state lights (SSLs) that are difficult to damage with physical shocks.	Incandescent bulbs are fragile relative to LEDs as they operate by using a filament encased by a glass bulb.	LED
Size	LEDs can be extremely small (less than 2mm in some cases) and they can be scaled to a much larger size. All in all this makes the applications in which LEDs can be used extremely diverse.	Incandescent Lamps come in all shapes and sizes but are typically used for indoor and residential applications where size isn’t a major factor. They can be small but not as small as an LED and they do not compare to the small size and robust build of a solid state light like LED.	LED
Temperature Tolerance
- Cold Tolerance	Minus 40 Degrees Celsius (and they will turn on instantaneously).	Small delays at very low temperatures can exist as the bulb takes a little longer to warm up to a temperature where light is emitted.	LED
- Heat Tolerance	100 Degrees Celsius. LEDs are fine for all normal operating temperatures both indoors and outdoors. They do, however, show degraded performance at significantly high temperatures and they require significant heat sinking, especially when in proximity to other sensitive components.	We couldn’t find any objective data on incandescent bulb performance in high temperature situations.	-
Warm-Up Time	LEDs have virtually no warm-up time. They reach maximum brightness near instantaneously.	Incandescent lights don’t generally require a warm-up time but there can be a short delay as the filament heats up when operating at extremely cold temperatures.	LED
Warranty	Often 5 to 10 years.	Typically N/A due to the short lifespan and low purchase price of incandescent lighting.	LED

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                      ROBOTS SPACE SHIPS TOMORROW

robots are used in space?Remotely operated vehicles (ROV) and remote manipulator system (RMS) are the two major types of space robots. A typical ROV can be a rover moving over the terrain upon landing, a lander operated from a stationary point and is in contact with an extra-terrestrial plain or an unmanned spacecraft.

Types of robots The most conventional robot used in space missions is the rover. This vehicle can move around the surface of another planet transporting scientific instruments. Usually both the vehicle and the instruments are operated autonomously

Rovers usually arrive at the planetary surface on a lander-style spacecraft. Rovers are created to land on another planet, besides Earth, to find out information and to take samples. They can collect dust, rocks, and even take pictures. They are very useful for exploring the universe.

Robotics deals with the design, construction, operation, and use of robots, as well as computer systems for their control, sensory feedback, and information processing. These technologies are used to develop machines that can substitute for humans and replicate human actions.

NASA (National Aeronautics and Space Administration) robots are robotic devices used to aid, augment, or substitute for astronauts in order to do difficult or rote tasks such as repairs in dangerous environments (such as those with radiation or micrometeorite risks), routine procedures (video capture), etc.

  

                     Robotic spacecraft

                    

A robotic spacecraft is an uncrewed spacecraft, usually under telerobotic control. A robotic spacecraft designed to make scientific research measurements is often called a space probe. Many space missions are more suited to telerobotic rather than crewed operation, due to lower cost and lower risk factors. In addition, some planetary destinations such as Venus or the vicinity of Jupiter are too hostile for human survival, given current technology. Outer planets such as Saturn, Uranus, and Neptune are too distant to reach with current crewed spacecraft technology, so telerobotic probes are the only way to explore them.
Many artificial satellites are robotic spacecraft, as are many landers and rovers.

                

Design 

In spacecraft design, the United States Air Force considers a vehicle to consist of the mission payload and the bus (or platform). The bus provides physical structure, thermal control, electrical power, attitude control and telemetry, tracking and commanding.
JPL divides the "flight system" of a spacecraft into subsystems. These include:

Structure

An illustration's of NASA's planned Orion spacecraft approaching a robotic asteroid capture vehicle

This is the physical backbone structure. It:

• provides overall mechanical integrity of the spacecraft
• ensures spacecraft components are supported and can withstand launch loads

Data handling

This is sometimes referred to as the command and data subsystem. It is often responsible for:

• command sequence storage
• maintaining the spacecraft clock
• collecting and reporting spacecraft telemetry data (e.g. spacecraft health)
• collecting and reporting mission data (e.g. photographic images)

Attitude determination and control

This system is mainly responsible for the correct spacecraft's orientation in space (attitude) despite external disturbance-gravity gradient effects, magnetic-field torques, solar radiation and aerodynamic drag; in addition it may be required to reposition movable parts, such as antennas and solar arrays.

In planetary exploration missions involving robotic spacecraft, there are three key parts in the processes of landing on the surface of the planet to ensure a safe and successful landing. This process includes an entry into the planetary gravity field and atmosphere, a descent through that atmosphere towards an intended/targeted region of scientific value, and a safe landing that guarantees the integrity of the instrumentation on the craft is preserved. While the robotic spacecraft is going through those parts, it must also be capable of estimating its position compared to the surface in order to ensure reliable control of itself and its ability to maneuver well. The robotic spacecraft must also efficiently perform hazard assessment and trajectory adjustments in real time to avoid hazards. To achieve this, the robotic spacecraft requires accurate knowledge of where the spacecraft is located relative to the surface (localization), what may pose as hazards from the terrain (hazard assessment), and where the spacecraft should presently be headed (hazard avoidance). Without the capability for operations for localization, hazard assessment, and avoidance, the robotic spacecraft becomes unsafe and can easily enter dangerous situations such as surface collisions, undesirable fuel consumption levels, and/or unsafe maneuvers.

Integrated sensing incorporates an image transformation algorithm to interpret the immediate imagery land data, perform a real-time detection and avoidance of terrain hazards that may impede safe landing, and increase the accuracy of landing at a desired site of interest using landmark localization techniques. Integrated sensing completes these tasks by relying on pre-recorded information and cameras to understand its location and determine its position and whether it is correct or needs to make any corrections (localization). The cameras are also used to detect any possible hazards whether it is increased fuel consumption or it is a physical hazard such as a poor landing spot in a crater or cliff side that would make landing very not ideal (hazard assessment).

Telecommunications

Components in the telecommunications subsystem include radio antennas, transmitters and receivers. These may be used to communicate with ground stations on Earth, or with other spacecraft.

Electrical power

The supply of electric power on spacecraft generally come from photovoltaic (solar) cells or from a radioisotope thermoelectric generator. Other components of the subsystem include batteries for storing power and distribution circuitry that connects components to the power sources.

Temperature control and protection from the environment

Spacecraft are often protected from temperature fluctuations with insulation. Some spacecraft use mirrors and sunshades for additional protection from solar heating. They also often need shielding from micrometeoroids and orbital debris

Spacecraft propulsion is a method that allows a spacecraft to travel through space by generating thrust to push it forward. However, there is not one universally used propulsion system: monopropellant, bipropellant, ion propulsion, etc. Each propulsion system generates thrust in slightly different ways with each system having its own advantages and disadvantages. But, most spacecraft propulsion today is based on rocket engines. The general idea behind rocket engines is that when an oxidizer meets the fuel source, there is explosive release of energy and heat at high speeds, which propels the spacecraft forward. This happens due to one basic principle known as Newton's Third Law. According to Newton, "to every action there is an equal and opposite reaction." As the energy and heat is being released from the back of the spacecraft, gas particles are being pushed around to allow the spacecraft to propel forward. The main reason behind the usage of rocket engine today is because rockets are the most powerful form of propulsion there is.

Monopropellant

For a propulsion system to work, there is usually an oxidizer line and a fuel line. This way, the spacecraft propulsion is controlled. But in a monopropellant propulsion, there is no need for an oxidizer line and only requires the fuel line. This works due to the oxidizer being chemically bonded into the fuel molecule itself. But for the propulsion system to be controlled, the combustion of the fuel can only occur due to a presence of a catalyst. This is quite advantageous due to making the rocket engine lighter and cheaper, easy to control, and more reliable. But, the downfall is that the chemical is very dangerous to manufacture, store, and transport.

Bipropellant

A bipropellant propulsion system is a rocket engine that uses a liquid propellent. This means both the oxidizer and fuel line are in liquid states. This system is unique because it requires no ignition system, the two liquids would spontaneously combust as soon as they come into contact with each other and produces the propulsion to push the ship forward. The main benefit for having this technology is because that these kinds of liquids have relatively high density, which allows the volume of the propellent tank to be small, therefore increasing space efficacy. The downside is the same as that of monopropellant propulsion system: very dangerous to manufacture, store, and transport.

Ion

An ion propulsion system is a type of engine that generates thrust by the means of electron bombardment or the acceleration of ions. By shooting high-energy electrons to a propellant atom (neutrally charge), it removes electrons from the propellant atom and this results the propellant atom becoming a positively charged atom. The positively charged ions are guided to pass through positively charged grids that contains thousands of precise aligned holes are running at high voltages. Then, the aligned positively charged ions accelerates through a negative charged accelerator grid that further increases the speed of the ions up to 90,000 mph. The momentum of these positively charged ions provides the thrust to propel the spacecraft forward. The advantage of having this kind of propulsion is that it is incredibly efficient in maintaining constant velocity, which is needed for deep-space travel. However, the amount of thrust produced is extremely low and that it needs a lot of electrical power to operate.

Mechanical devices

Mechanical components often need to be moved for deployment after launch or prior to landing. In addition to the use of motors, many one-time movements are controlled by pyrotechnic devices.

Robotic vs. uncrewed spacecraft

Robotic spacecraft are specifically designed system for a specific hostile environment. Due to their specification for a particular environment, it varies greatly in complexity and capabilities. While an uncrewed spacecraft is a spacecraft without personnel or crew and is operated by automatic (proceeds with an action without human intervention) or remote control (with human intervention). The term 'uncrewed spacecraft' does not imply that the spacecraft is robotic.

Control

Robotic spacecraft use telemetry to radio back to Earth acquired data and vehicle status information. Although generally referred to as "remotely controlled" or "telerobotic", the earliest orbital spacecraft – such as Sputnik 1 and Explorer 1 – did not receive control signals from Earth. Soon after these first spacecraft, command systems were developed to allow remote control from the ground. Increased autonomy is important for distant probes where the light travel time prevents rapid decision and control from Earth. Newer probes such as Cassini–Huygens and the Mars Exploration Rovers are highly autonomous and use on-board computers to operate independently for extended periods of time.

Space probes

A space probe is a robotic spacecraft that does not orbit Earth, but instead, explores further into outer space. A space probe may approach the Moon; travel through interplanetary space; flyby, orbit, or land on other planetary bodies; or enter interstellar space.

SpaceX’s Dragon

An example of a fully robotic spacecraft in the modern world would be SpaceX's Dragon.The SpaceX Dragon is a robotic spacecraft designed to send not only cargo to low Earth orbit, but also humans as well. The SpaceX Dragon's total height is 7.2 m (23.6 ft) with a diameter of 3.7 m (12 ft). The maximum launch payload mass is 6,000 kg (13,228 lbs) with a maximum return mass of 3,000 kg (6,614 lbs), along with a maximum launch payload volume of 25m^3 (883 ft^3) and a maximum return payload volume of 11m^3 (388 ft^3). The maximum endurance of the Dragon in space is two years.
In 2012 the SpaceX Dragon made history by becoming the first commercial robotic spacecraft to deliver cargo to the International Space Station and to safely return cargo to Earth in the same trip, something previously achieved only by governments. Currently the Dragon is meant to transfer cargo because of its capability of returning significant amounts of cargo to Earth despite it originally being designed to carry humans.

Departure shot of Pluto by New Horizons, showing Pluto's atmosphere backlit by the Sun.

Robotic spacecraft service vehicles

AERCam Sprint released from the Space Shuttle Columbia payload bay

• MDA Space Infrastructure Servicing vehicle — an in-space refueling depot and service spacecraft for communication satellites in geosynchronous orbit. Launch planned for 2015.

• Mission Extension Vehicle is an alternative approach that does not utilize in-space RCS fuel transfer. Rather, it would connect to the target satellite in the same way as MDA SIS, and then use "its own thrusters to supply attitude control for the target."

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                      Interstellar travel

Interstellar travel is crewed or uncrewed travel between stars or planetary systems. Interstellar travel will be much more difficult than interplanetary spaceflight; the distances between the planets in the Solar System are less than 30 astronomical units (AU)—whereas the distances between stars are typically hundreds of thousands of AU, and usually expressed in light-years. Because of the vastness of those distances, interstellar travel would require a high percentage of the speed of light; huge travel time, lasting from decades to millennia or longer.
The speeds required for interstellar travel in a human lifetime far exceed what current methods of spacecraft propulsion can provide. Even with a hypothetically perfectly efficient propulsion system, the kinetic energy corresponding to those speeds is enormous by today's standards of energy development. Moreover, collisions by the spacecraft with cosmic dust and gas can produce very dangerous effects both to passengers and the spacecraft itself.
A number of strategies have been proposed to deal with these problems, ranging from giant arks that would carry entire societies and ecosystems, to microscopic space probes. Many different spacecraft propulsion systems have been proposed to give spacecraft the required speeds, including nuclear propulsion, beam-powered propulsion, and methods based on speculative physics.
For both crewed and uncrewed interstellar travel, considerable technological and economic challenges need to be met. Even the most optimistic views about interstellar travel see it as only being feasible decades from now. However, in spite of the challenges, if or when interstellar travel is realised, a wide range of scientific benefits is expected.
Most interstellar travel concepts require a developed space logistics system capable of moving millions of tons to a construction / operating location, and most would require gigawatt-scale power for construction or power (such as Star Wisp or Light Sail type concepts). Such a system could grow organically if space-based solar power became a significant component of Earth's energy mix. Consumer demand for a multi-terawatt system would automatically create the necessary multi-million ton/year logistical system

                       

Challenges

Interstellar distances

Distances between the planets in the Solar System are often measured in astronomical units (AU), defined as the average distance between the Sun and Earth, some 1.5×10⁸ kilometers (93 million miles). Venus, the closest other planet to Earth is (at closest approach) 0.28 AU away. Neptune, the farthest planet from the Sun, is 29.8 AU away. As of October 30, 2019, Voyager 1, the farthest human-made object from Earth, is 147.9 AU away.
The closest known star, Proxima Centauri, is approximately 268,332 AU away, or over 9,000 times farther away than Neptune.

Object	A.U.	light time
Moon	0.0026	1.3 seconds
Sun	1	8 minutes
Venus (nearest planet)	0.28	2.41 minutes
Neptune (farthest planet)	29.8	4.1 hours
Voyager 1	147.9	20:30 hours
Proxima Centauri (nearest star and exoplanet)	268,332	4.24 years

Because of this, distances between stars are usually expressed in light-years (defined as the distance that light travels in vacuum in one Julian year) or in parsecs (one parsec is 3.26 ly, the distance at which stellar parallax is exactly one arcsecond, hence the name). Light in a vacuum travels around 300,000 kilometres (186,000 mi) per second, so 1 light-year is about 9.461×10¹² kilometers (5.879 trillion miles) or 63,241 AU. Proxima Centauri, the nearest (albeit not naked-eye visible) star, is 4.243 light-years away.
Another way of understanding the vastness of interstellar distances is by scaling: One of the closest stars to the Sun, Alpha Centauri A (a Sun-like star), can be pictured by scaling down the Earth–Sun distance to one meter (3.28 ft). On this scale, the distance to Alpha Centauri A would be 276 kilometers (171 miles).
The fastest outward-bound spacecraft yet sent, Voyager 1, has covered 1/600 of a light-year in 30 years and is currently moving at 1/18,000 the speed of light. At this rate, a journey to Proxima Centauri would take 80,000 years.

Required energy

A significant factor contributing to the difficulty is the energy that must be supplied to obtain a reasonable travel time. A lower bound for the required energy is the kinetic energy ${\displaystyle K={\tfrac {1}{2}}mv^{2}}$ where ${\displaystyle m}$ is the final mass. If deceleration on arrival is desired and cannot be achieved by any means other than the engines of the ship, then the lower bound for the required energy is doubled to ${\displaystyle mv^{2}}$.
The velocity for a manned round trip of a few decades to even the nearest star is several thousand times greater than those of present space vehicles. This means that due to the ${\displaystyle v^{2}}$ term in the kinetic energy formula, millions of times as much energy is required. Accelerating one ton to one-tenth of the speed of light requires at least 450 petajoules or 4.50×10¹⁷ joules or 125 terawatt-hours (world energy consumption 2008 was 143,851 terawatt-hours), without factoring in efficiency of the propulsion mechanism. This energy has to be generated onboard from stored fuel, harvested from the interstellar medium, or projected over immense distances.

Interstellar medium

A knowledge of the properties of the interstellar gas and dust through which the vehicle must pass is essential for the design of any interstellar space mission. A major issue with traveling at extremely high speeds is that interstellar dust may cause considerable damage to the craft, due to the high relative speeds and large kinetic energies involved. Various shielding methods to mitigate this problem have been proposed. Larger objects (such as macroscopic dust grains) are far less common, but would be much more destructive. The risks of impacting such objects, and methods of mitigating these risks, have been discussed in literature, but many unknowns remain and, owing to the inhomogeneous distribution of interstellar matter around the Sun, will depend on direction travelled. Although a high density interstellar medium may cause difficulties for many interstellar travel concepts, interstellar ramjets, and some proposed concepts for decelerating interstellar spacecraft, would actually benefit from a denser interstellar medium.

Hazards

The crew of an interstellar ship would face several significant hazards, including the psychological effects of long-term isolation, the effects of exposure to ionizing radiation, and the physiological effects of weightlessness to the muscles, joints, bones, immune system, and eyes. There also exists the risk of impact by micrometeoroids and other space debris. These risks represent challenges that have yet to be overcome.

Wait calculation

It has been argued that an interstellar mission that cannot be completed within 50 years should not be started at all. Instead, assuming that a civilization is still on an increasing curve of propulsion system velocity and not yet having reached the limit, the resources should be invested in designing a better propulsion system. This is because a slow spacecraft would probably be passed by another mission sent later with more advanced propulsion (the incessant obsolescence postulate)
On the other hand, Andrew Kennedy has shown that if one calculates the journey time to a given destination as the rate of travel speed derived from growth (even exponential growth) increases, there is a clear minimum in the total time to that destination from now. Voyages undertaken before the minimum will be overtaken by those that leave at the minimum, whereas voyages that leave after the minimum will never overtake those that left at the minimum.

Prime targets for interstellar travel

There are 59 known stellar systems within 40 light years of the Sun, containing 81 visible stars. The following could be considered prime targets for interstellar missions:

System	Distance (ly)	Remarks
Alpha Centauri	4.3	Closest system. Three stars (G2, K1, M5). Component A is similar to the Sun (a G2 star). On August 24, 2016, the discovery of an Earth-size exoplanet (Proxima Centauri b) orbiting in the habitable zone of Proxima Centauri was announced.
Barnard's Star	6	Small, low-luminosity M5 red dwarf. Second closest to Solar System.
Sirius	8.7	Large, very bright A1 star with a white dwarf companion.
Epsilon Eridani	10.8	Single K2 star slightly smaller and colder than the Sun. It has two asteroid belts, might have a giant and one much smaller planet, and may possess a Solar-System-type planetary system.
Tau Ceti	11.8	Single G8 star similar to the Sun. High probability of possessing a Solar-System-type planetary system: current evidence shows 5 planets with potentially two in the habitable zone.
Wolf 1061	~14	Wolf 1061 c is 4.3 times the size of Earth; it may have rocky terrain. It also sits within the ‘Goldilocks’ zone where it might be possible for liquid water to exist.
Gliese 581 planetary system	20.3	Multiple planet system. The unconfirmed exoplanet Gliese 581g and the confirmed exoplanet Gliese 581d are in the star's habitable zone.
Gliese 667C	22	A system with at least six planets. A record-breaking three of these planets are super-Earths lying in the zone around the star where liquid water could exist, making them possible candidates for the presence of life.
Vega	25	A very young system possibly in the process of planetary formation.
TRAPPIST-1	39	A recently discovered system which boasts 7 Earth-like planets, some of which may have liquid water. The discovery is a major advancement in finding a habitable planet and in finding a planet that could support life.

Existing and near-term astronomical technology is capable of finding planetary systems around these objects, increasing their potential for exploration

Proposed methods

Slow, uncrewed probes

Slow interstellar missions based on current and near-future propulsion technologies are associated with trip times starting from about one hundred years to thousands of years. These missions consist of sending a robotic probe to a nearby star for exploration, similar to interplanetary probes such as used in the Voyager program. By taking along no crew, the cost and complexity of the mission is significantly reduced although technology lifetime is still a significant issue next to obtaining a reasonable speed of travel. Proposed concepts include Project Daedalus, Project Icarus, Project Dragonfly, Project Longshot, and more recently Breakthrough Starshot.

Fast, uncrewed probes

Nanoprobes

Near-lightspeed nano spacecraft might be possible within the near future built on existing microchip technology with a newly developed nanoscale thruster. Researchers at the University of Michigan are developing thrusters that use nanoparticles as propellant. Their technology is called "nanoparticle field extraction thruster", or nanoFET. These devices act like small particle accelerators shooting conductive nanoparticles out into space.
Michio Kaku, a theoretical physicist, has suggested that clouds of "smart dust" be sent to the stars, which may become possible with advances in nanotechnology. Kaku also notes that a large number of nanoprobes would need to be sent due to the vulnerability of very small probes to be easily deflected by magnetic fields, micrometeorites and other dangers to ensure the chances that at least one nanoprobe will survive the journey and reach the destination.
Given the light weight of these probes, it would take much less energy to accelerate them. With onboard solar cells, they could continually accelerate using solar power. One can envision a day when a fleet of millions or even billions of these particles swarm to distant stars at nearly the speed of light and relay signals back to Earth through a vast interstellar communication network.
As a near-term solution, small, laser-propelled interstellar probes, based on current CubeSat technology were proposed in the context of Project Dragonfly.

Slow, crewed missions

In crewed missions, the duration of a slow interstellar journey presents a major obstacle and existing concepts deal with this problem in different ways. They can be distinguished by the "state" in which humans are transported on-board of the spacecraft.

Generation ships

A generation ship (or world ship) is a type of interstellar ark in which the crew that arrives at the destination is descended from those who started the journey. Generation ships are not currently feasible because of the difficulty of constructing a ship of the enormous required scale and the great biological and sociological problems that life aboard such a ship raises ^.

Suspended animation

Scientists and writers have postulated various techniques for suspended animation. These include human hibernation and cryonic preservation. Although neither is currently practical, they offer the possibility of sleeper ships in which the passengers lie inert for the long duration of the voyage.

Frozen embryos

A robotic interstellar mission carrying some number of frozen early stage human embryos is another theoretical possibility. This method of space colonization requires, among other things, the development of an artificial uterus, the prior detection of a habitable terrestrial planet, and advances in the field of fully autonomous mobile robots and educational robots that would replace human parents.

Island hopping through interstellar space

Interstellar space is not completely empty; it contains trillions of icy bodies ranging from small asteroids (Oort cloud) to possible rogue planets. There may be ways to take advantage of these resources for a good part of an interstellar trip, slowly hopping from body to body or setting up waystations along the way.

Fast missions

If a spaceship could average 10 percent of light speed (and decelerate at the destination, for manned missions), this would be enough to reach Proxima Centauri in forty years. Several propulsion concepts have been proposed  that might be eventually developed to accomplish this , but none of them are ready for near-term (few decades) developments at acceptable cost.

Time dilation

Physicists generally believe faster-than-light travel is impossible. Relativistic time dilation allows a traveler to experience time more slowly, the closer their speed is to the speed of light. This apparent slowing becomes noticeable when velocities above 80% of the speed of light are attained. Clocks aboard an interstellar ship would run slower than Earth clocks, so if a ship's engines were capable of continuously generating around 1 g of acceleration (which is comfortable for humans), the ship could reach almost anywhere in the galaxy and return to Earth within 40 years ship-time (see diagram). Upon return, there would be a difference between the time elapsed on the astronaut's ship and the time elapsed on Earth.
For example, a spaceship could travel to a star 32 light-years away, initially accelerating at a constant 1.03g (i.e. 10.1 m/s²) for 1.32 years (ship time), then stopping its engines and coasting for the next 17.3 years (ship time) at a constant speed, then decelerating again for 1.32 ship-years, and coming to a stop at the destination. After a short visit, the astronaut could return to Earth the same way. After the full round-trip, the clocks on board the ship show that 40 years have passed, but according to those on Earth, the ship comes back 76 years after launch.
From the viewpoint of the astronaut, onboard clocks seem to be running normally. The star ahead seems to be approaching at a speed of 0.87 light years per ship-year. The universe would appear contracted along the direction of travel to half the size it had when the ship was at rest; the distance between that star and the Sun would seem to be 16 light years as measured by the astronaut.
At higher speeds, the time on board will run even slower, so the astronaut could travel to the center of the Milky Way (30,000 light years from Earth) and back in 40 years ship-time. But the speed according to Earth clocks will always be less than 1 light year per Earth year, so, when back home, the astronaut will find that more than 60 thousand years will have passed on Earth.

Constant acceleration

This plot shows a ship capable of 1-g (10 m/s² or about 1.0 ly/y²) "felt" or proper-acceleration can go far, except for the problem of accelerating on-board propellant.

Regardless of how it is achieved, a propulsion system that could produce acceleration continuously from departure to arrival would be the fastest method of travel. A constant acceleration journey is one where the propulsion system accelerates the ship at a constant rate for the first half of the journey, and then decelerates for the second half, so that it arrives at the destination stationary relative to where it began. If this were performed with an acceleration similar to that experienced at the Earth's surface, it would have the added advantage of producing artificial "gravity" for the crew. Supplying the energy required, however, would be prohibitively expensive with current technology.

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