Sorry, But Lasers Aren't Taking You To Mars Anytime Soon 193
An anonymous reader writes: It's long been a dream of humanity to travel interplanetary distances at great speeds, or to make it to another star system within a human lifetime. Until recently, technologies to get us there — antimatter propulsion, wormholes or warp drive — have all been composed of physically unrealistic solutions. But recent developments in laser technology make directed energy propulsion a feasible solution. By building a giant laser array in space and developing a new type of solar sail that reflects the laser light with incredible efficiency, a laser sail, this propulsion system is scalable to arbitrarily large powers. There are many technical obstacles to be overcome, and so it's unlikely we'll see the fruit of this anytime in the next few decades (despite the promises of some), but this may well be the technology that takes us to the stars in the coming centuries.
Forbes dot com (Score:5, Informative)
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Ethan Siegel -- WARNING Forbes link (Score:5, Informative)
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"Arbirarily Scalable" (Score:5, Insightful)
"Scalable to arbitrarily large powers" = "I haven't thought about this very hard"
Got the crew from Mote Prime to New Cal (Score:2)
I recall there was some trick at the turnover about charging the sails an using the lasers for deceleration too.
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Acceleration on the first half of the trip is done & then mandatory deceleration on the last half unless you don't care about stopping.
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well... if you aim it right you'll stop one way or the other.
it's really about who decides what the deceleration looks like... and over what time-frame. either you handle it yourself... or physics is certainly up to the task of decelerating your craft for you.
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then mandatory deceleration on the last half unless you don't care about stopping.
Stopping without catastrophic results. Stopping is easy.
Nuclear (Score:2)
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Re:Nuclear (Score:4, Informative)
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Rocheworld (Score:3, Interesting)
Thats Good (Score:2)
cool way or the easy way (Score:3)
when doing something new, should we begin with an untested unknown technology, or with existing technology modified to meet the need ?
imo the second method. and in this case, choosing that way would probably get us to mars in decade or three, but choosing first will only delay it ever further (though it would allow us to paint and write cool impotent pictures to pass the time).
and we are not doing a new potential technology a service by saddling it with solving complex task start with.
Succinctly Solar Sails Suck (Score:4, Interesting)
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FTFL, "But you really need lasers for this â" regular light spreads out too fast. Maybe a set of lasing cavities orbiting the sun â¦" Ah, but if you had some way to line up regular light, then you'd really have something. Maybe we'll come up with some kind of snazzy metamaterial to do that soon.
Anyway, the big argument for laser propulsion is not efficiency of the system. It's mass savings on the spacecraft. It doesn't work unless you have power to waste, so clearly we won't use it any time s
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Not sure where you got "not practical" out of that. It's a piece about an interesting paper to get more efficiency out of the setup. A plain old solar sail (even without the lasers) works pretty well if you're going far enough or you need a little bit of fuel-free thrust for things like station keeping or attitude control.
You know we've launched solar sails, right?
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LOL ... "This is awful. If we were lifting the squirrel with a motor, railgun, or electric catapult, with 1.21 gigawatts we could send it screaming upward at ridiculous speeds."
I live in a place with an overabundance of squirrels ... and I insist someone does the 1.21 gigawatt squirrel railgun thingy ... you know, purely in the name of science.
C'mon, PMA (Score:2)
Sorry, But Lasers Aren't Taking You To Mars Anytime Soon
a) I didn't think they were going to; this is the first I've heard of it at all
b) Well, not with that attitude.
C'mon, Slashdot, put a positive spin on it. Lasers might take you to Mars some day.
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"Lasers might take you to Mars some day."
Sure, they might take you there, but you'll only be passing by , because unless someone has built another laser array ON mars you won't be stopping until you hit something. Which could be the same day or a billion years later as the dried out dust that used to be your corpse slowly orbits the galaxy.
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because unless someone has built another laser array ON mars
Well there you go. Problem solved.
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"Lasers might take you to Mars some day."
Sure, they might take you there, but you'll only be passing by , because unless someone has built another laser array ON mars you won't be stopping until you hit something. Which could be the same day or a billion years later as the dried out dust that used to be your corpse slowly orbits the galaxy.
If you have a laser propulsion system on the moon, you accelerate the ship up to speed, then the ship separates a mirror to go ahead of the ship and the laser hits the forward mirror and is reflected back to the ship, slowing it down. The forward mirror will continue to accelerate on it's way out of the solar system like a Voyager, but so long as it's mass is less than what it would take for equivalent thrust from fuel, it's all good.
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Hmm, now why are lasers being suggested in the first place. Is it because the amount of fuel required to get to that speed (and hence the same amount required to slow down from it) is infeasible? Yeah. maybe thats it A/C. Course, you'd have known that if you had a single working braincell.
Monkeys in a can (Score:3)
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The biggest technical hurdle to human spaceflight is enabling them to survive the experience. Robots are far more likely, I think, for the next few centuries at least. Of course, some new disruptive technology could change that picture.
There is this website "Rocketpunk" retro future like steampunk (I'm too lazy to find the link) which stated back in 1940s and 1950s it was envisioned there will be lots of people in space to manage weather and communication stations in orbit along with orbiting telescopic platforms that look both at earth and into space. And not only that but all these people will be working on the McGuffinite (the Alfred Hitchcock term) But then along comes NASA that is able to replace all these people with just a few kg o
Giant laser array (Score:3)
By building a giant laser array in space BLAH BLAH BLAH unlikely we'll see the fruit of this anytime in the next few decades
You had me at giant laser array 3
One question about laser propulsion (Score:2)
How do you stop at the other end?
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You reverse the polarity of the neutron flow.
Shit. Are you sure it's not a tachyon pulse?
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You reverse the polarity of the neutron flow.
Well, if you're going to do that, might as well reverse the particle flux from the sun.
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You get there in the first place by using the light sail to speed up or slow down in your orbit around the sun, NOT by lifting straight out. You speed up by reflecting light at a vector that increases your speed, slow down by reflecting it in the other direction.
Nobody stops in space, unless they want to fall into the sun. You just match up orbital speeds and directions (sometimes for orbits around orbiting objects).
rgb
Shark Overlords (Score:2)
>> ("lay-zers") may well be the technology that takes us to the stars in the coming centuries
I, for one, welcome our new shark overlords.
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It's *space* shark overlord to you, chum.
That said, I'm pretty sure exploration isn't the first reason governments would want to put giant lasers in space. They might also want to cook some popcorn, if you get my drift.
Real Talk (Score:2)
Nobody reading this today is going to Mars.
It's time for you all to accept that and just move on.
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hey kid, we went to mars in the 60s and 70s but never left the farm
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I can't argue with success.
Diffraction (Score:2)
The limiter in space communications, and in the space-sail-propulsion application, is diffraction. Don't think additive diffraction, as in crystallography, but the basic mechanism.
Waves diffract (change path) when they pass near the edge of an aperture. This is how nature works.
You might tightly collimate your beam, but the more you do so, the greater the 'spread' of the beam over long distances. For reference, see The Opticks, by I. Newton. (I hope you can read Latin!)
You can sail faster than the wind. (Score:2)
I will ignore the obvious joke about going faster than the speed of light, but I wonder if we could do a similar effect using a solar sail? Anyone know if you can use a solar sail to get 'lift' as well as push?
What is lift? What is drag? (Score:2)
Anyone know if you can use a solar sail to get 'lift' as well as push?
"Lift" is defined relative to the direction of motion (it is the component of force on a wind perpendicular to the airflow). The force on a lightsail is defined relative to the incident direction of the beam.
If you were to define "drag" as force in the direction of the beam, and "lift" as force perpendicular to the beam, then, yes, you can have lift on the sail.
Nobody actually does define lift and drag on a lightsail that way, but if you think of the laser (or solar) beam as the "incident wind", then in fa
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This works because you travel faster by eliminating friction by minimizing the surface of the boat in the water.
Has no one thought about the... (Score:2)
...Inverse Square Law? Fer ******* sakes! Even a "focused" beam spreads out over distances. Those who dream of "laser propulsion" might think of a huge laser onboard, but the power source to drive it would be immense!
Is it April 1st, yet?
Once upon a time in fantasyland... (Score:2)
I came to Slashdot many years ago to read about new and exciting technology and when an announcement was made or a proposal was evaluated there was a lot of excitement by everyone, criticism was common, but it was constructive criticism, almost as if the readers were interested and excited.
Now days, not so much, most posts are either haters that hate everything, or people trying to out negative everyone else by pointing out how "it will never happen".
sigh...
Not lasers, the sun, silly... (Score:2)
Lasers aren't ever going to lift a ship up from the surface of the earth via a light sail. It is not entirely impossible that ground-bound lasers cannot be directed into an ablative material in the base of a ship that then vaporizes, superheats, and emerges as a plasma drive, but even that is highly speculative and requires extremely precise alignment of thrust vectors and the ship's vertical axis in the presence of both turbulence and coriolis effects during liftoff.
The place light sails become arguably u
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Slowing down isn't the problem. Slowing down and staying in one piece is the tricky bit. Just ask the Mars Climate Orbiter team.
Re:But... (Score:5, Funny)
"...how would you slow down when you get there? "
Radio ahead to make a deal with the locals to build a similar laser for when you arrive.
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Enter orbit, fly back towards the beam as you come around a few times. Or just take a chemical rocket, it's still a huge weight saving. There is atmospheric braking as well, it depends how fast you need to decelerate.
Re:But... (Score:4, Interesting)
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Or use an EM massless drive if it turns out to be real and not an experimental error.
It is absolutely not real.
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Or use an EM massless drive if it turns out to be real and not an experimental error.
it is absolutely not real.
So we have multiple experiments showing it is, but you're not linking to what debunks it. Why?
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So we have multiple experiments showing it is, but you're not linking to what debunks it.
No we don't, we have several experiments which show that there is no effect larger than the current experimental errors.
Why?
Seriously? Would you expect me to provide a link if I claimed timecube is bunk? Anyway, start here:
Noether's Theorem.
Re:But... (Score:4, Insightful)
Seriously? Would you expect me to provide a link if I claimed timecube is bunk?
Actually, yes.
Disclaimer: I'm not the OP or GP or OG or anything like that.
I would expect it because Slashdot is a mixed crowd and some people (GASP!) actually read comments to get a better understanding of what's at hand. You, as a random Slashdotter, have no real standing with me. Not that I dislike you but I don't know you from Adam. You could be making up whatever you talking about or, worse, repeating something from someone else who also is just as clueless but now you've got an idea in your head that you're passing on as facts to others.
Telling someone their wrong in what could be a forward thinking forum would also carry the obligation of explaining why they would be wrong. Any jerk can make flippant remarks and be smug about it but it takes real knowledge to put something out there that will point the way to a better understanding for all involved.
I don't know why people around here think it's such a burden to discuss ideas with one another but is somehow acceptable to bad mouth others on matters that have very defined truths about them.
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It is unlikely to be real but your claim that the error level is higher than the measured effect is AFAIK wrong.
Not really, the experiments all have major flaws.
But your post is strictly anti-scientific
Except no it isn't. Noether's theorem means that breaking conservation of momentum means that the physical "constants" vary over space. There have been many attempts to accurately measure physical constants and none have shown any variation.
It's not unscientific to trust many very very carefully done experim
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It does seem unlikely that EM drives work, especially as stated, but it doesn't matter what Noether's or anyone else's Theorem states. After all it might be wrong, just as the vast majority of theorems to date have been shown to be wrong, or at least incomplete.
All that matters is whether or not an anomalous force is actually being produced in the experiment. If so, then the theorems will be updated or replaced as needed, or we will develop an alternate explanation for the effect that allows it to exist w
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You are mistaken about theorems. They're not scientific theories, they are mathematics. I the case of Noether's theorem it proves mathematically that for conservation on momentum to hold then certain symmetries must be present. That's maths and it's proven in an absolute sense.
Where it connects with science is if the physical world has those symmetries. If it does, then momentum is conserved. For momentum to not be conserved, then physics as we know it does change over time or space. That link is inescapabl
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anyway, the historical accuracy of mathematics is compelling to convincing, but there's always that niggling doubt, that horror at the back of my mind, that 2+2 doesn't equal 4.
You might want to look at Galois fields (finite fields). There, 1+1=0 in GF(2) and 2+2=1 in GF(3).
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The truth of mathematics is NOT the truth of reality, so don't try proving the contrary. Mathematics is extremely useful in modeling reality, and, significantly in this case, providing a handy way to come up with consequences of a theory. If we can't get consequences out of a theory, we can't do science, because we can't perform experiments and/or observations to distinguish one theory from another.
2+2 == 4 not because of some fundamental principle of the Universe, but because that's how we've defined
Not yet replicated [Re:But...] (Score:3)
It is unlikely to be real but your claim that the error level is higher than the measured effect is AFAIK wrong. We also have replication in 3 separate places with separate groups of people using different hardware which reduces some error sources.
No, sorry, but I will challenge that last statement. There are three separate groups which have produced different results which are inconsistent with each other.
Most recently, the NASA Johnson "Eagleworks" group has tried to replicate both the EM drive proposed by Shawer and a result on a similar concept in China claimed by Yang-- and falsified both of these results. The EM drive proposal stated that the purported drive worked because of a specific asymmetry, but the Eagleworks test showed that the resul
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I can't judge if laser propulsion will become workable but external propulsion (as opposed to onboard) certainly makes sense. That is, between two of 'our own' locations, with a 'cannon' on both ends.
So you would need a stage of slow ships taking ages to reach the target and brake. Then they build the 'braking laser' and then you can get much faster traffic.
Re:But... (Score:5, Insightful)
... Better to put a liquid salt thorium nuclear reactor ... The light weight thorium reactor...
There seems to have developed a nerd cult of the "liquid salt thorium nuclear reactor" which is apparently endowed now with quasi-magical powers, the answer to all possible questions about power sources. The proposed "liquid salt thorium nuclear reactor concept, none of which has every been built, is an idea for large scale fixed power plant designs, and is a very complex system as conceived (involving circulating molten salt fuel, on-line fission product removal systems from the fuel, etc.) that only makes sense - if it is practical at all - as part of a world-wide nuclear power industry. It has absolutely no features of value for a space travel power source.
The notion that such a system could ever be "light weight" is ridiculous - tacking those words on to "thorium reactor" does not make it any sense.
Any real space-flight ready reactor use ceramic highly enriched uranium fuel (negligible hazard until the reactor core turns on for the first time in space), fast neutron operation (moderator is heavy), and as few moving parts as possible. Something more like this [wikipedia.org].
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Any real space-flight ready reactor use ceramic highly enriched uranium fuel (negligible hazard until the reactor core turns on for the first time in space), fast neutron operation (moderator is heavy), and as few moving parts as possible. Something more like this [wikipedia.org].
Maybe it's not great for "launch failure" scenarios, but plutonium cores are nice and compact.
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Indeed. There are far better fission reactor designs for space, such as the Russian TOPAZ reactor.
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Better to put a liquid salt thorium nuclear reactor and ion drives onboard the space craft.
That's an insane idea. Even regular SEP has better T/W ratio than a nuclear heat engine, and a laser-boosted SEP would be even better (and is probably one of the better. laser-related ideas in the realm of space propulsion).
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A regular Stanford Encyclopedia of Philosophy has better Tesla per Watt ratio than a nuclear heat engine?
Please, your extremely generic capital letters are hard to follow.
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Unfortunately you are traveling faster than escape velocity. Therefore you CANNOT "enter orbit".
Did you forget about aerocapture? https://en.wikipedia.org/wiki/... [wikipedia.org] It would probably be about as viable as building giant lasers to propel a spacecraft.
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all i know is i must try this in KSP now... thanks asshole.
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do you even Kerbal?
you know how much of a pita gradual atmospheric breaking would be on mars too? you don't have to worry about your components melting... but you've also barely got an atmosphere to work with.
don't think a parachute would do much unless it were impractically large either.
Re: But... (Score:2)
Though if it was sturdy enough the sail could conceivably double as a parachute/kite. Whether it can be that sturdy (even for mars) and still light enough to be practical as a light sail is left as an excercise for Werner Von Kerman.
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gotta sky crane it, apparently aerobraking, and parachute won't do too well... though airbags might work good.
but powered descent is probably still necessary with a sizable payload.
yay
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The laser sail is already impractically large (ever try to collimate a laser beam for delivery at 10+ miles?) why not an impractically large braking sail? Better still, make them the same sail, the laser sail may have a larger outer portion, but the structural braking sail could already be deployed as a central portion of it - you'll just need to execute a 180 degree rotation just in time for atmo-braking... Make sure you don't catch Phobos or Demios while you're at it.
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Re: But... (Score:2)
Entering orbit requires decelerating. Any speed which gets to a planet is way too high to orbit it. You want your periapse as close to the planet as possible and you burn at periapse so gravity helps you break but you still need to slow down or you will just escape again (ina different direction)
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Tacking works because of the reaction of the keel on the sea water. Unfortunately, there is no sea water in space.
No it doesn't (Score:4, Insightful)
For example no tacking is required: if you want to move closer to the sun use your solar sail to slow your orbital velocity and then just retract the sails and fall. However if you are powered by a laser bank then getting bank to Earth will be a lot trickier since there is no gravitational field to pull you in at inter-planetary distances. You will likely need good timing and rely heavily on complex orbital maneuvers in which case it is hard to see how it is better than a rocket.
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Returning to the Earth involves getting into an orbit of the sun that is close to that of the Earth, at the right time. Actually entering orbit around the Earth is a matter of slowing down or speeding up a bit, relative to the sun.
You can go pretty much anywhere in the solar system using a laser based wherever (or the sun itself), and the orbital mechanics are pretty basic. Probably the easiest place to go is back to your light source.
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What's the other component, apart from wind, that keeps a sailboat on course?
What's the other component, apart from its own thrust, that keeps a spacecraft on course? I'll give you a hint: Everything in the solar system moves in a great big ellipse around the biggest source of it in our system.
What are you going to push against? Physics fail.
You can "push" (or maybe in this c
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Gravity doesn't work that way.
Gravity has a time component because it's an acceleration. If you're moving close to the speed of light (I mean this was the point, right?), you are going to be very far away before gravity (even the sun's gravity) has any chance to act on you. The other problem with being further away - you're further out of the gravitational field. Divided by r SQUARED, remember? So exactly how were you going to use this "force"?
Not to mention the fact that you are allowed two and only tw
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Solar sails would work differently than wind sails, as has been pointed out vehemently by others, but while it certainly is impossible to use the sail to move towards a sun, it is an interesting question whether a solar sail can be made that can push you sideways when flying towards the sun. after all, a mirror can deflect light sideways.
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Science, bitch. Now spare use your hand waving.
Re:But... (Score:4, Insightful)
If we are talking about sending very small micro satellite or slightly larger sized probes, then who cares about slowing down? You can get good data without slowing down.
I think that disposable probes is where you start. Sending small probes (anywhere) for a few million each to get you to a proof of concept.
Just play with them in Earth orbit to start.
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You'd probably have a more conventional propulsion system for slowing down. So you'd carry fuel or perhaps deploy your giant blast shield and use nukes to slow down. You may not want to nuke the shit out of your own solar system, but no one cares about some backwater like Alpha Centauri.
Seriously, though. Even if you had to carry fuel to brake with a rocket propulsion system, you'd only have to carry half the amount, which would be a pretty big win.
And obviously, for two way travel, you can certainly bui
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If you're going to another star, you dive in towards the sun and use it as a light source for your sail. If you're going to Mars, because of the way solar sails and orbital mechanics works, you can use the Earth-based laser to "slow down" (actually, speed up) to enter Mars orbit as well.
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...how would you slow down when you get there? Acceleration without deceleration won't work.
Laser propulsion systems usually are intended to decelerate by breaking off a section of the solar sail and sends it forward. The laser now hits that section of sail and bounced back to hit the main body, causing it to decelerate. So, just like a rocket, accelerate halfway there, then decelerate the second half. For added efficiency, the laser can continue be be bounced between the two making them separate even faster. Of course they could use that method to accelerate faster in the first half too.
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What's all this 0.3c stuff about? Mars is between 3 and 22 light minutes from Earth. If you launched when it was farthest away you'd have only hours to accelerate up to any appreciable fraction of the speed of light before you had to slow down.
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Lubin supposes that the system could propel crafts to an "unheard of" 30 percent the speed of light.
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just put a big superconducting ring around the sun, that can twist up a big streamer of plasma and then make it lase in ultraviolet. "they had a weapon bigger than worlds. Hindmost, I think Im going to feint."
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or maybe faint eh?
Can't collimate incoherent light perfectly (Score:2)
Why try to make all that laser energy on Earth. The Sun has all we need. Just...
collumate the light into a beam to power your ships.
For quick reference, you can't collimate incoherent light into a beam that doesn't diverge-- the "collimated" beam of solar light will still fan out with a solid angle exactly equal to the solid angle of the incident solar light no matter what you do to it optically. If you get closer to the sun, the intensity is higher but the solid angle is higher; if you get farther from the sun the solid angle is narrower but the intensity is lower.
This is the "law of conservation of etendue" (which if you want to, you
Re: Sobering distance (Score:2)
Getting the speed solves the lifetime problem. By 5% of lightspeed time is moving a lot slower (at 100% it stops entirely). 80 years may pass on earth but your astronaught would experience only mabe 30. Trouble is when he gets home 160 years have passed on earth. Everyone he knows is dead. His country is now a province of the empire of the grand Pumba of Jakarta. Pizzabagels have become the worlds prinary food supply. Nobody remembers sending him and on the way he probably got passed by another mission lau
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I've thought about this a lot. Once a person/society goes 'relativistic' there's essentially no going back (at least to a recognizable land).
There could be other ships/societies that are also relativistic and you could potentially meet them somewhere in space-time. One ship goes 20% the speed of light and the other goes 15% to get to the same space at the same time.
How the relativistic societies would communicate is still somewhat of a pickle though, as there's be some pretty huge delays, even with the sign
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Time dilation is insignificant at 5% of light speed. It's about 1/10 of 1%.
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It does. But light pressure is the Poynting vector divided by c. What that means is the thrust in Newtons is basically the power of the laser divided by c. That means that a megawatt laser can produce less than 0.001 Newtons of thrust, which applied to a mere 1000 kg payload gives you less than a millionth of a meter per second squared acceleration. One can grow old and die before building up a reasonable delta V, at 30 million seconds per year, assuming your 1000 payload could sustain a MW output for a
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Sigh. Newton lived in vain, I see.
Pardon me, I have to grab myself by the scruff of my neck and lift myself up out of my chair and go teach physics.
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