11 ms·

So the whole thing should weigh in the order of several grams, yet it should be able to deflect 100GW of incoming radiation near perfectly (otherwise it will in

by yongjik 11y ago

So the whole thing should weigh in the order of several grams, yet it should be able to deflect 100GW of incoming radiation near perfectly (otherwise it will instantly vaporize) while maintaining structural integrity under the acceleration of 60,000g for two minutes? And whatever laser sources we're using must track this smartphone-sized object during these two minutes across several million kilometers. Perfectly. (It also means that whatever course deviation the object experiences must be anticipated seconds before it happens, because at the end of the two minutes the object will be ~10 light-seconds away.) If they could pull this off it will be the next Apollo, but I'm skeptical. Edit: Just realized we have even more problems, about the reflective coatings. If the laser is green, by the time it's flying away at 0.2c, the laser won't be green any more thanks to the Doppler effect! I'm too lazy to calculate, but it will definitely shift toward the red. So whatever reflective coating we use must be able to work near-perfectly over a wide range of spectrum.

AnthonyAguirre 11y ago
The plan calls for ultra-reflective coatings that are tuned to the wavelength of the laser. Apparently these exist, though I have not checked the numbers. In my class I abandoned laser propulsion quickly for just this reason (incinerated the target), but with these coatings it might work.
tachyonbeam 11y ago
Setting incredibly ambitious goals has definitely lead to impressive achievements in the past. I think it's definitely worth studying. Worst case, we'll learn something.
- a_imho 11y ago
  >Worst case, we'll learn something we might learn something, but we have to use resources for studying and there might just be better and/or more useful alternatives
  - bbcbasic 11y ago
    Side effects of these projects, even if they fail, may be massively valuable. Sometimes solving problem X that isn't a big concern for society will solve problem Y down the track. History of maths is littered with things that were useless when they where first invented, such as imaginary numbers.
    - a_imho 11y ago
      I'm still not arguing that and I'm as excited as everyone else when someone comes with a bold idea as this, still, you can't gouge how well the money will be spent and downplaying risks and alternatives of undertaking a multi decade project because we are in the heat of the moment is not wise. Science justice warriors should take a deep breath before pointing fingers imo. We are inherently in a box and I doubt anyone can imagine what technology will look like in 10 years, let alone 40.
0bfus 11y ago
One thing to note is the reported mindset of the program. It doesn't really talk about their expectations around plausability of this, but rather that they seem to be targeting success through large numbers even at low probabilities. They might not care to anticipate/correct anomalous "course deviations" but rather write those off as a loss completely, hoping that just a few of many initially accelerated succeed.
- paulmd 11y ago
  It would be impossible/unlikely to correct any course deviations anyway. First off, even if the beam is collimated to within a degree or something, a degree at even a million miles is a pretty big spot, and you'd probably not be able to hit any specific unit. Even if you collimated it more finely - good luck hitting the target. The other problem is that the beam would ideally go straight between earth and Alpha Centauri, and the sail just rides the beam. The Earth does rotate around the sun but the parallax this provides (over 3-6 months) is pretty low relative to the distance travelled by the probes over that time. If you try to do selective course corrections (i.e. bump one side harder than the other) then you're going to need a super fine beam that is going to miss frequently and probably hit the target when you hit. This is pretty much inherently a shotgun approach. You don't get a mid-course correction on the birdshot that misses its target. Or rather, it's like putting out balloons into the wind and letting them drift.
tambourine_man 11y ago
Solar sails seems more feasible to me.
iwwr 11y ago
A laser capable of propelling an interstellar probe is also a mighty space weapon. Some people proposed constructing that on the far side of the Moon so that it hass less of a chance of being used as against Earth targets (intentionally or by accident).
- joeyspn 11y ago
  > A laser capable of propelling an interstellar probe is also a mighty space weapon. Yes, but maybe it could also give us the technology to quickly deflect perilous asteroids... ?
  - HerpDerpLerp 11y ago
    or at least those that weigh about the same as a piece of paper...
- LyndsySimon 11y ago
  That sounds like a good idea... as long as no one develops mirrors :)
  - dragonbonheur 11y ago
    .
    - nolite 11y ago
      The laser is definitely a weapon at the powers they're talking about
      - deleted 11y ago
        [deleted]
jessriedel 11y ago
Agreed on the extreme skepticism warranted. I am imagining these "solar sails" to be essentially spherical, both for structural reasons and so that their response to applied laser power does not depend on orientation. The electronics in precision guided mortars in the US army survive 50,000g. http://proceedings.ndia.org/C347/Davis.pdf http://proceedings.ndia.org/C347/Davis.pdf (This is only for the fraction of a second when they are fired, and I don't know how it generalizes for longer durations.) I conjecture that the laser profile will be "shaped", if at all possible, so the trajectory of the projectile is somewhat self-correcting: if the projectile starts to get ahead of the planned trajectory, the acceleration will decrease, while if it lags the acceleration will increase. This wouldn't require any realtime feedback by the laser emitter. With many projectiles and a massive investment in a laser array, there will be some ability to repeatedly attempt this and iterate. Still, this is extremely aggressive even many decades in the future. EDIT: Their proposal confirms that the beam will need to be shaped for feedback. ("By modulating the beam modes, get greater uniformity could be attained, and feedback between the nanocrafts and the beamer array would allow real-time adjustments.") No details though. http://breakthroughinitiatives.org/index.php?controller=Forum&action=viewforum&id=6&page=1 http://breakthroughinitiatives.org/index.php?controller=Foru... Rather than the spherical shape a supposed above, they propose a thin sail with some undefined graphene skeleton. No idea how that is supposed to survive 2-minute long explosive accelerations. http://breakthroughinitiatives.org/index.php?controller=Forum&action=viewforum&id=21&page=1 http://breakthroughinitiatives.org/index.php?controller=Foru...
- gene-h 11y ago
  F=ma In this case m ~ 1 gram and a = 0.2c / 120 seconds =499654.097 m/s^2 F = 499654.097 m/s^2 * 1 gram = 500 newtons However this force is distributed over the whole sail which has an area is 16 m^2, so pressure applied to the sail is 500 N/16 m^2 = 31.25 pascals. This is a fairly low pressure. The pressure change going up or down a couple meters is about equal to this. Your typical cheap garbage bags can withstand this pressure.
  - jessriedel 11y ago
    Yea, thanks. I think my mistake was in imagining that the sail would need to be pulling a localized payload, so that force would need to be transmitted from sail to payload using a cross-sectional area small compared to the sail. But it sounds more like the payload is integrated into the sail.
phkahler 11y ago
And where does the reflected laser light go? Back to earth if it's reflected 180 degree. And how does a device weighing a few grams emit a signal capable of detection back on earth? The Voyager probes are over half a light-day from earth but they have rather large antennas.
- jessriedel 11y ago
  Relevant comment below: https://news.ycombinator.com/item?id=11481689 https://news.ycombinator.com/item?id=11481689
- LeifCarrotson 11y ago
  It goes back in the general direction of Earth. The reflector needs to be highly efficient, but it doesn't need to be perfectly flat.
leblancfg 11y ago
I love these napkin calculations. The relativistic effect shifts the frequency by 22.47% for 0.2c. Given a 445nm laser (the powerful blue ones), that's 545nm when redshifted (green). It's a bit of a jump, but that wavelength is still smack in the "solar atmospheric absorbtion spectrum window" -- you won't lose much of the energy in the atmosphere. Reading this page diagonally [http://www.edmundoptics.com/resources/application-notes/optics/metallic-mirror-coatings/ http://www.edmundoptics.com/resources/application-notes/opti...], I don't think that the idea of getting a >99.5% reflectance value for that bandwidth is that far off.
- yongjik 11y ago
  Umm... 0.5% of 100GW is 500MW, or about the power of a nuclear reactor. The spaceship won't survive a millisecond. We need way better than 99.5%.
  - nerfhammer 11y ago
    Article says it needs to be better than 99.999%
    - dharma1 11y ago
      iphone innards - done 99.999% reflective mirror - done (iphone gorilla glass ;)
  - jessriedel 11y ago
    Yep. "Use a material with better than 99.999% reflectivity. Usually, highly reflective surfaces are dielectric mirrors, which are composed of ‘sandwiches’ of material, with each layer reflecting back a modest fraction of the total. Each layer needs to be at least a quarter of a wavelength thick. The weight can be reduced by using a monolayer with high reflectivity at the correct wavelength. Based on recent research, this could be achieved by a ‘hole-pocked’ layer, highly reflective for very specific angles where reflectivity caustics arise. (These caustics occur for wavelengths of light that are actually longer than the sheet thickness.)" http://breakthroughinitiatives.org/index.php?controller=Forum&action=viewforum&id=5&page=1 http://breakthroughinitiatives.org/index.php?controller=Foru...
grondilu 11y ago
Freeman's speech was interesting in that regard. He doesn't think Alpha Centauri is a reasonable target for this project and according to him it should not be advertised as such. But he does think that using this technology to send probes in very deep space could both tell us more about what there is over there and help us improve the technology to go beyond and thus to the actual stars.
skykooler 11y ago
10 light-seconds is a massive underestimate. If we assume a constant acceleration from zero to 0.2c over two years, the average speed is 0.1c. Therefore by the end of two years it will be 0.1 lightyears away. Deviations will have to be anticipated over a month in advance!
- ChrisClark 11y ago
  Not 2 years, they want to fully accelerate to 0.2c in 2 minutes!
  - skykooler 11y ago
    o.O I misread that, that's incredible!
cbhl 11y ago
I'm more worried about where the reflected light is going to go once it bounces off the sails. Presumably it'll fall back on earth, where that amount of energy could cause a lot of damage.
tuyguntn 11y ago
Its not about result, its about intention. Intention leads to results (even small) Small results lead to bigger results (bigger resources, like more knowledge) Bigger resource leads to greater intentions And here is why humans are still better than DeepMind, while (true) { learn, invent }
Terr_ 11y ago
> Edit: Just realized [...] the laser won't be green any more thanks to the Doppler effect! If the laser is tune-able, you could slowly increase the output-frequency based on how fast you expect the target to be moving at the time the light hits. This would counteract the Doppler effect and supply a consistent frequency to the target.
TallGuyShort 11y ago
Nevermind the issue of how you either (a) transmit back over 4 light years or (b) pull off a return trajectory with just a few grams of equipment. It's easy to poke holes at ambitious projects, so I look forward to seeing what they can come up with, but man - this would be phenomenal compared to Apollo, even given how far we've come.
- brianwawok 11y ago
  Why return? I bet you can find a lot of volunteers for a one way mission, especially if you offer to follow them with supply trains every year or so.
  - TallGuyShort 11y ago
    Even if this is possible, it'll probably be prohibitively expensive to do constant resupplies when you won't know for years if previous trips have worked. A manned mission or a resupply mission would also be orders of magnitude beyond the masses they're talking about, which strains credibility even further.
    - brianwawok 11y ago
      I am pretty sure you just sent out a new boat of supplies every year make it or not. Worse case the mission fails and the next mission has 20 supply ships in orbit waiting for them. I have no idea on the minimum mass required to send supplies, i.e. if you can recycle 99% of the water you need, would only need a few drops per day. If you can only recycle 50%, you are going to need a bunch.
      - TallGuyShort 11y ago
        Nah - they're already pushing some theoretical limits by talking about planetary levels of energy. You're talking about just throwing money at doing that many times in a row with no proof of success.
grecy 11y ago
You're right to be skeptical, because this is going to be very difficult and has many challenges that need to be overcome. But that doesn't mean we should sit here and say "nope, can't be done". People were skeptical when planes first flew, when it was attempted to put people on the moon, and so on. Jeez, people were skeptical when SpaceX said they could land a first stage on a barge at sea, and posted endlessly about how it couldn't be done. Don't be one of those people. Even if they "fail" to make all of this work and get something to Alpha Centauri, they're still going to vastly expand mankind's knowledge of a lot of difficult space-related technologies, which is a huge win. This is hacker news, where people are trying to do difficult things to change the world. That's the whole point.
- xbmcuser 11y ago
  If nothing else they might work out how to send larger probes to far out parts of our solar system that reach in days instead of months and years.
  - maxaf 11y ago
    This is exactly the point of long shot R&D: lesser milestones are useful in their own right. Who knows what else might come of it?
- xbmcuser 11y ago
  If nothing else they might work out how to send larger probes to far out parts of our solar system that reach in days instead of months and years.
- JoeAltmaier 11y ago
  I also am skeptical. Why not instead try to send a probe into the interior of the sun? (because its cooler there than at the point of those lasers) Why not create a survey of the Oort cloud (because its an order of magnitude closer). This project seems cool; but maybe not well thought out.
  - ryao 11y ago
mirekrusin 11y ago
And what exactly happens with reflected laser?
dTal 11y ago
>If the laser is green, by the time it's flying away at 0.2c, the laser won't be green any more thanks to the Doppler effect! I'm too lazy to calculate, but it will definitely shift toward the red. Interestingly, you also have to deal with Lorenz contraction - at .2c the ship itself will shorten by about half a percent, compounding the apparent wavelength shift. Admittedly this is a much smaller effect.
mirekrusin 11y ago
Worst case, if it doesn't work, maybe we can at least use built infrastructure to send new iPhones to Mars expedition.

by yongjik 11y ago

AnthonyAguirre 11y ago

The plan calls for ultra-reflective coatings that are tuned to the wavelength of the laser. Apparently these exist, though I have not checked the numbers. In my class I abandoned laser propulsion quickly for just this reason (incinerated the target), but with these coatings it might work.

tachyonbeam 11y ago

Setting incredibly ambitious goals has definitely lead to impressive achievements in the past. I think it's definitely worth studying. Worst case, we'll learn something.

a_imho 11y ago
>Worst case, we'll learn something we might learn something, but we have to use resources for studying and there might just be better and/or more useful alternatives
- bbcbasic 11y ago
  Side effects of these projects, even if they fail, may be massively valuable. Sometimes solving problem X that isn't a big concern for society will solve problem Y down the track. History of maths is littered with things that were useless when they where first invented, such as imaginary numbers.
  - a_imho 11y ago
    I'm still not arguing that and I'm as excited as everyone else when someone comes with a bold idea as this, still, you can't gouge how well the money will be spent and downplaying risks and alternatives of undertaking a multi decade project because we are in the heat of the moment is not wise. Science justice warriors should take a deep breath before pointing fingers imo. We are inherently in a box and I doubt anyone can imagine what technology will look like in 10 years, let alone 40.

0bfus 11y ago

One thing to note is the reported mindset of the program. It doesn't really talk about their expectations around plausability of this, but rather that they seem to be targeting success through large numbers even at low probabilities. They might not care to anticipate/correct anomalous "course deviations" but rather write those off as a loss completely, hoping that just a few of many initially accelerated succeed.

paulmd 11y ago
It would be impossible/unlikely to correct any course deviations anyway. First off, even if the beam is collimated to within a degree or something, a degree at even a million miles is a pretty big spot, and you'd probably not be able to hit any specific unit. Even if you collimated it more finely - good luck hitting the target. The other problem is that the beam would ideally go straight between earth and Alpha Centauri, and the sail just rides the beam. The Earth does rotate around the sun but the parallax this provides (over 3-6 months) is pretty low relative to the distance travelled by the probes over that time. If you try to do selective course corrections (i.e. bump one side harder than the other) then you're going to need a super fine beam that is going to miss frequently and probably hit the target when you hit. This is pretty much inherently a shotgun approach. You don't get a mid-course correction on the birdshot that misses its target. Or rather, it's like putting out balloons into the wind and letting them drift.

tambourine_man 11y ago

Solar sails seems more feasible to me.

iwwr 11y ago

A laser capable of propelling an interstellar probe is also a mighty space weapon. Some people proposed constructing that on the far side of the Moon so that it hass less of a chance of being used as against Earth targets (intentionally or by accident).

joeyspn 11y ago
> A laser capable of propelling an interstellar probe is also a mighty space weapon. Yes, but maybe it could also give us the technology to quickly deflect perilous asteroids... ?
- HerpDerpLerp 11y ago
  or at least those that weigh about the same as a piece of paper...
LyndsySimon 11y ago
That sounds like a good idea... as long as no one develops mirrors :)
- dragonbonheur 11y ago
  .
  - nolite 11y ago
    The laser is definitely a weapon at the powers they're talking about
    - deleted 11y ago
      [deleted]

jessriedel 11y ago

Agreed on the extreme skepticism warranted. I am imagining these "solar sails" to be essentially spherical, both for structural reasons and so that their response to applied laser power does not depend on orientation. The electronics in precision guided mortars in the US army survive 50,000g. http://proceedings.ndia.org/C347/Davis.pdf http://proceedings.ndia.org/C347/Davis.pdf (This is only for the fraction of a second when they are fired, and I don't know how it generalizes for longer durations.) I conjecture that the laser profile will be "shaped", if at all possible, so the trajectory of the projectile is somewhat self-correcting: if the projectile starts to get ahead of the planned trajectory, the acceleration will decrease, while if it lags the acceleration will increase. This wouldn't require any realtime feedback by the laser emitter. With many projectiles and a massive investment in a laser array, there will be some ability to repeatedly attempt this and iterate. Still, this is extremely aggressive even many decades in the future. EDIT: Their proposal confirms that the beam will need to be shaped for feedback. ("By modulating the beam modes, get greater uniformity could be attained, and feedback between the nanocrafts and the beamer array would allow real-time adjustments.") No details though. http://breakthroughinitiatives.org/index.php?controller=Forum&action=viewforum&id=6&page=1 http://breakthroughinitiatives.org/index.php?controller=Foru... Rather than the spherical shape a supposed above, they propose a thin sail with some undefined graphene skeleton. No idea how that is supposed to survive 2-minute long explosive accelerations. http://breakthroughinitiatives.org/index.php?controller=Forum&action=viewforum&id=21&page=1 http://breakthroughinitiatives.org/index.php?controller=Foru...

gene-h 11y ago
F=ma In this case m ~ 1 gram and a = 0.2c / 120 seconds =499654.097 m/s^2 F = 499654.097 m/s^2 * 1 gram = 500 newtons However this force is distributed over the whole sail which has an area is 16 m^2, so pressure applied to the sail is 500 N/16 m^2 = 31.25 pascals. This is a fairly low pressure. The pressure change going up or down a couple meters is about equal to this. Your typical cheap garbage bags can withstand this pressure.
- jessriedel 11y ago
  Yea, thanks. I think my mistake was in imagining that the sail would need to be pulling a localized payload, so that force would need to be transmitted from sail to payload using a cross-sectional area small compared to the sail. But it sounds more like the payload is integrated into the sail.

phkahler 11y ago

And where does the reflected laser light go? Back to earth if it's reflected 180 degree. And how does a device weighing a few grams emit a signal capable of detection back on earth? The Voyager probes are over half a light-day from earth but they have rather large antennas.

jessriedel 11y ago
Relevant comment below: https://news.ycombinator.com/item?id=11481689 https://news.ycombinator.com/item?id=11481689
LeifCarrotson 11y ago
It goes back in the general direction of Earth. The reflector needs to be highly efficient, but it doesn't need to be perfectly flat.

leblancfg 11y ago

I love these napkin calculations. The relativistic effect shifts the frequency by 22.47% for 0.2c. Given a 445nm laser (the powerful blue ones), that's 545nm when redshifted (green). It's a bit of a jump, but that wavelength is still smack in the "solar atmospheric absorbtion spectrum window" -- you won't lose much of the energy in the atmosphere. Reading this page diagonally [http://www.edmundoptics.com/resources/application-notes/optics/metallic-mirror-coatings/ http://www.edmundoptics.com/resources/application-notes/opti...], I don't think that the idea of getting a >99.5% reflectance value for that bandwidth is that far off.

yongjik 11y ago
Umm... 0.5% of 100GW is 500MW, or about the power of a nuclear reactor. The spaceship won't survive a millisecond. We need way better than 99.5%.
- nerfhammer 11y ago
  Article says it needs to be better than 99.999%
  - dharma1 11y ago
    iphone innards - done 99.999% reflective mirror - done (iphone gorilla glass ;)
- jessriedel 11y ago
  Yep. "Use a material with better than 99.999% reflectivity. Usually, highly reflective surfaces are dielectric mirrors, which are composed of ‘sandwiches’ of material, with each layer reflecting back a modest fraction of the total. Each layer needs to be at least a quarter of a wavelength thick. The weight can be reduced by using a monolayer with high reflectivity at the correct wavelength. Based on recent research, this could be achieved by a ‘hole-pocked’ layer, highly reflective for very specific angles where reflectivity caustics arise. (These caustics occur for wavelengths of light that are actually longer than the sheet thickness.)" http://breakthroughinitiatives.org/index.php?controller=Forum&action=viewforum&id=5&page=1 http://breakthroughinitiatives.org/index.php?controller=Foru...

grondilu 11y ago

Freeman's speech was interesting in that regard. He doesn't think Alpha Centauri is a reasonable target for this project and according to him it should not be advertised as such. But he does think that using this technology to send probes in very deep space could both tell us more about what there is over there and help us improve the technology to go beyond and thus to the actual stars.

skykooler 11y ago

10 light-seconds is a massive underestimate. If we assume a constant acceleration from zero to 0.2c over two years, the average speed is 0.1c. Therefore by the end of two years it will be 0.1 lightyears away. Deviations will have to be anticipated over a month in advance!

ChrisClark 11y ago
Not 2 years, they want to fully accelerate to 0.2c in 2 minutes!
- skykooler 11y ago
  o.O I misread that, that's incredible!

cbhl 11y ago

I'm more worried about where the reflected light is going to go once it bounces off the sails. Presumably it'll fall back on earth, where that amount of energy could cause a lot of damage.

tuyguntn 11y ago

Its not about result, its about intention. Intention leads to results (even small) Small results lead to bigger results (bigger resources, like more knowledge) Bigger resource leads to greater intentions And here is why humans are still better than DeepMind, while (true) { learn, invent }

Terr_ 11y ago

> Edit: Just realized [...] the laser won't be green any more thanks to the Doppler effect! If the laser is tune-able, you could slowly increase the output-frequency based on how fast you expect the target to be moving at the time the light hits. This would counteract the Doppler effect and supply a consistent frequency to the target.

TallGuyShort 11y ago

Nevermind the issue of how you either (a) transmit back over 4 light years or (b) pull off a return trajectory with just a few grams of equipment. It's easy to poke holes at ambitious projects, so I look forward to seeing what they can come up with, but man - this would be phenomenal compared to Apollo, even given how far we've come.

brianwawok 11y ago
Why return? I bet you can find a lot of volunteers for a one way mission, especially if you offer to follow them with supply trains every year or so.
- TallGuyShort 11y ago
  Even if this is possible, it'll probably be prohibitively expensive to do constant resupplies when you won't know for years if previous trips have worked. A manned mission or a resupply mission would also be orders of magnitude beyond the masses they're talking about, which strains credibility even further.
  - brianwawok 11y ago
    I am pretty sure you just sent out a new boat of supplies every year make it or not. Worse case the mission fails and the next mission has 20 supply ships in orbit waiting for them. I have no idea on the minimum mass required to send supplies, i.e. if you can recycle 99% of the water you need, would only need a few drops per day. If you can only recycle 50%, you are going to need a bunch.
    - TallGuyShort 11y ago
      Nah - they're already pushing some theoretical limits by talking about planetary levels of energy. You're talking about just throwing money at doing that many times in a row with no proof of success.

grecy 11y ago

You're right to be skeptical, because this is going to be very difficult and has many challenges that need to be overcome. But that doesn't mean we should sit here and say "nope, can't be done". People were skeptical when planes first flew, when it was attempted to put people on the moon, and so on. Jeez, people were skeptical when SpaceX said they could land a first stage on a barge at sea, and posted endlessly about how it couldn't be done. Don't be one of those people. Even if they "fail" to make all of this work and get something to Alpha Centauri, they're still going to vastly expand mankind's knowledge of a lot of difficult space-related technologies, which is a huge win. This is hacker news, where people are trying to do difficult things to change the world. That's the whole point.

xbmcuser 11y ago
If nothing else they might work out how to send larger probes to far out parts of our solar system that reach in days instead of months and years.
- maxaf 11y ago
  This is exactly the point of long shot R&D: lesser milestones are useful in their own right. Who knows what else might come of it?
xbmcuser 11y ago
If nothing else they might work out how to send larger probes to far out parts of our solar system that reach in days instead of months and years.
JoeAltmaier 11y ago
I also am skeptical. Why not instead try to send a probe into the interior of the sun? (because its cooler there than at the point of those lasers) Why not create a survey of the Oort cloud (because its an order of magnitude closer). This project seems cool; but maybe not well thought out.
- ryao 11y ago

mirekrusin 11y ago

And what exactly happens with reflected laser?

dTal 11y ago

>If the laser is green, by the time it's flying away at 0.2c, the laser won't be green any more thanks to the Doppler effect! I'm too lazy to calculate, but it will definitely shift toward the red. Interestingly, you also have to deal with Lorenz contraction - at .2c the ship itself will shorten by about half a percent, compounding the apparent wavelength shift. Admittedly this is a much smaller effect.

mirekrusin 11y ago

Worst case, if it doesn't work, maybe we can at least use built infrastructure to send new iPhones to Mars expedition.