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Sorry, But Lasers Aren't Taking You To Mars Anytime Soon
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.
Lasers would get me to Mars faster than I would click on a Forbes link.
Seven puppies were harmed during the making of this post.
Another Ethan Siegel blogspam that will take you to Forbes which HAS BEEN KNOWN TO deliver malware via their adserver. Do not follow the Forbes link!
...how would you slow down when you get there? Acceleration without deceleration won't work.
"Scalable to arbitrarily large powers" = "I haven't thought about this very hard"
I recall there was some trick at the turnover about charging the sails an using the lasers for deceleration too.
Screw that.
Also, as long as Elon Musk goes to Mars and shuts the hell up, I'll chip in a few bucks to make that happen.
Nuclear is still the best way to get to Mars. If it weren't for the fact that the words "nuclear rocket" in the same sentence is somehow horrifying, we would have been there a while ago. I mean, it isn't even going to be on Earth people. If you really want we can even have it dock with the ISS so we just have to carry it up.
If interested in this potential star-reaching tech, read Robert L. Forward's book Rocheworld.
Non-Linux Penguins ?
I was always worried about being kidnapped by lasers to another planet.
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.
What about, if we strap the lasers to sharks' heads?
or even better - killer whales!
XKCD covered this and came to the conclusion that laser propulsion just isn't practical, even by the lofty standards of theoretical intrastellar space travel.
I read the internet for the articles.
Crazy Eddie!
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.
systemd is Roko's Basilisk.
It took New Horizons about 10 years to travel 32AU from the Sun with the greatest radial velocity yet achieved by conventional rockets (Atlas V/Centaur). Alpha Centauri lies 250,000 AU distant. It would take a disheartening 78000+ years to get there. We need a factor of 1000 in speed which is about 5% the speed of light just to reach it in a human life time.Interstellar travel not only depends on new propulsion technology, but greatly by increasing the duration of human life. Both are possible. We won't get there with our current pathetic, uninspiring LEO-bound space program.
Why try to make all that laser energy on Earth. The Sun has all we need. Just setup a large magnetic field and channel it to a filter to take out the bad stuff and collumate the light into a beam to power your ships. The laser beam station can even be powered from the sun as well. Dispating exess heat might be a the big problem. Three or four of these Boost (just had to use that word) Satations would do for all directions out of the Solar system. Also will provide protection from hostile Aliens! Zap your dead MoFo! We can carry our War like nature into the new world(s) or err.. New Space!
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.
This posting is provided 'AS IS' without warranty of any kind, implied or otherwise.
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
8 of 13 people found this answer helpful. Did you?
How do you stop at the other end?
Just drop into Rekall for the trip of a lifetime!
Sailing into the wind relies on the keel to resist any sideways motion of the hull so that the only component of force remaining is one which points into the wind. You cannot do that in space. The only way I can think to do anything close to that in space is to use a gravitational field which will be very different to wind-based sailing.
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.
How do you stop at the other end?
Cross the streams.
>> ("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.
computers got better and 3D printers? I thought everything just keeps scaling at the same rate as computer memory?
Nobody reading this today is going to Mars.
It's time for you all to accept that and just move on.
You are welcome on my lawn.
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!)
getting home, that'sthe problem
Eric Laithwaite invented a space drive device that was shown on the 'Heretics' television series several decades ago. He reported how he gave a talk (I believe at the Royal Society, but correct me if I'm wrong), which was never published, for the first time in the history of the Royal Society, because it was 'heresy' - he showed how he could pick up a spinning 40lb gyroscope disc (or around that weight) on the end of a one metre long metal rod, and raise it above his head - only while it was spinning. Because they couldn't explain what they were seeing with their own eyes, they decided not to publish the contents of his talk. On the same programme he showed a model of a space drive he had invented, that would use a gyroscope to convert electrical energy to (I presume) 'gravitational' energy - or at least, it would drive a spaceship through space.
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?
excitingthingstodo.blogspot.com
...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?
No.
Not going to happen. Politics, Generals, Military-industrial complex.... won't allow it
Having propulsion-scale lasers anywhere would violate several armament treaties.
Having one in geo-synchronous orbit would start a war. And maybe end it...
As in : weapons.
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 can derive from thermodynamics. Or from the Liouville theorem, take your pick.). That's a little bit obscure, I'm afraid, but if you just think of it as the brightness theorem, you've got the important part of it.
http://eckop.com/illumination/...
http://www.geoffreylandis.com
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 fact it is exactly analogous to the lift and drag on a wing, in the Newtonian approximation.
http://www.geoffreylandis.com
pointed in one direction drive a ship in the other.
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...
Cheaper too.
We make fusion reactors here on campus, it's not that hard, plus there are a few space companies nearby.
-- Tigger warning: This post may contain tiggers! --
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 useful is in orbit (however you get there). At that point, IF one can generate a light sail shroud on the order of 1 km^2, one can start to get some nontrivial acceleration for a not completely absurd payload not from lasers, but from the sun. At that point, one can get order of 10 N of thrust, which for 1000 kg of payload yields an acceleration of 0.01 m/sec. This doesn't sound like much, but every two to five minutes one can add a meter/second to a selected vector. Every day one can add hundreds of meters/second. Sunlight is free, and for certain payloads (not humans) you don't care how long it takes.
A light sail is perfectly capable of promoting metric ton scale payloads from Earth orbit to Mars orbit, even if it takes a year or more to get there. By filling a queue of such payloads -- firing one off per day, for example -- one could transport substantial physical resources from Earth orbit to Mars over the course of a year or two and use them to build an orbital platform and/or drop them down to a targeted site on Mars. The only cost is the standard 32 MJ/kg net energy required to get to near-Earth orbit.
So the real question is: Can we use lasers plus ablation (not light sails) to reach near Earth orbit with less than the 1000 or so to 1 energy/fuel penalty associated with rocket launches? And that is not at all clear. It will have to compete with alternative solutions, as well, such as fusion drives (assuming we get fusion at some point) or electromagnetic cannon mass launchers.
The problem with reaching Mars, or Jupiter, or the stars themselves, isn't getting there from Earth orbit. It is getting TO Earth orbit. That's half of escape energy right there, and once you are in orbit and away from atmospheric drag, even low thrust solutions become efficient provided one can maintain them for long periods of time, and light sails or (maybe) high efficiency ion drives are both candidates for moving non-living mass around on timescales uncomfortable for humans but just fine for human food, or water, or other resources required for the colonization of space or at least the nearer planets or their moons.
This is all very expensive, to be sure, but it isn't infeasible from the physics point of view and as always, economies of scale or technical improvements may lower the costs over time. Grabbing a nickle-iron asteroid as it passes near the Earth and attaching one of the in-system drives might let us use resources already at the top of the orbital gravity well and avoid the cost of lifting all of that mass up entirely.
rgb
Even when the experts all agree, they may well be mistaken. --- Bertrand Russell.
We can use beamed power to help get us to Mars. As long as the weight per MW of the beam power receiver on the space ships is less than onboard power generation then beam power makes sense. The beam power could be microwave or laser. I once thought of a beamed powered space tug that would be used to launch space craft at Mars. It would start at low earth orbit with the Mars craft, used beam power to heat hydrogen, push the Mars craft to escape velocity. Then quickly decelerate. and return to low earth orbit.
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.
rgb
Even when the experts all agree, they may well be mistaken. --- Bertrand Russell.
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 result was the same whether or not the asymmetry is present: the Shawer driver does not work as proposed. They also tested the Yang result, and got a result... but the result was orders of magnitude different than the claimed Yang result. The net answer is that neither result was replicated.
Also, the test that was reported at a conference was not done in vacuum (although they only mentioned this detail in the "further work" section of their paper.) There has been a post to an internet forum saying that they have now tested it in vacuum, and gotten yet different results-- but internet forums are not scientific publications.
I'm in favor of good experimental work testing these ideas... but so far, it's way premature to suggest that the results have been replicated. They're not. The results are very, very small, and no two experiments seem to show the same thing.
Here's a Wired article from last year (which was the last anybody heard anything new) with some more discussion. (Sorry it's in Wired, which apparently everybody hates now, but that's where it is.) http://www.wired.com/2015/05/n...
http://www.geoffreylandis.com
This concept is totally cool, and apparently at least possibly workable for microsats. - Make 100,000 or so microsats, with a quantum entangled thingamabob (however that is done, I have no idea, but someone is doing it somehow) - Send 1000 to each nearby star...yes, they will flyby the star - figure out how to tweak trajectory a bit - send pictures back of planets in those systems.
If it ever got to the point in which they tried to moved a vessel that contained people or a cargo shipment the amount of force leaving the lasers would be very great, especially when trying to accelerate the vessel at greater distances. So they would need to install the lasers on a very large mass or us some sort of engine to maintain the position of the lasers. At that point why not just put the engines on the vessel and skip the transformation of energy.
I'm happy as a clam right here on Terra Firma.... The place has O2, sunshine, H2O and plenty of weed and tequila....