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Japanese Deploy Solar Sail 433
Chuck1318 writes "The Japanese ISAS (Institute of Space and Astronautical Science) announced the launch and deployment of the first ever large-scale solar sail. In the news release they state "Because it carries no fuel and keeps accelerating over almost unlimited distances, it is the only technology now in existence that can one day take us to the stars.""
Stellar Pong? (Score:4, Insightful)
Re:Stellar Pong? (Score:4, Interesting)
Re:Stellar Pong? (Score:5, Informative)
A perfectly non-reflective surface (i.e. a black surface) would experience half the force that a perfectly reflective surface would. In other words, a black sail will work, but only half as well as a mirrored sail would work.
This is due to conservation of momentum. If a photon is reflected, its momentum p is reversed to be -p. Thus the sail must acquire a momentum 2p to conserve momentum. Whereas if the photon is absorbed, its momentum changes from p to 0, thus the momentum of the sail must increase by p, again to preserve momentum.
The difference in kinetic energy is converted into heat. A black sail heats up. An ideal, perfectly reflective mirrored sail does not heat up at all.
Re:Stellar Pong? (Score:3, Insightful)
If you could somehow cause the energy absorbed by the leading black surface of the sail to be emitted out the rear surface as photons, then you would have something practical.
The parent's point was that as the sail gets farther away from Sol, the energy from other, nearer stars (the destination) would "push" on the leading surface and this force would eventua
Re:Stellar Pong? (Score:5, Informative)
You are asking a textbook question :-)
No, the radiometer works in a different way. Notice in the radiometer that the rotation is clockwise when the black "sail" is exposed on the LEFT. If this were due to light pressure, the pressure would be greater on the RIGHT (reflective) sail and the radiometer would be spinning in the opposite direction.
What happens in the radiometer is the black sail heats up because it absorbs radiant energy. The gas around the sail (the glass bulb is very low pressure but not a perfect vacuum) conducts heat away from the sail, heating and expanding in the process. The expanding gas reacts against the sail, pushing it away.
If the radiometer bulb was evacuated to a perfect vacuum, the radiometer would actually spin the opposite direction because the light pressure effect would dominate.
Here you go: (Score:2, Informative)
Rest Mass from Wikipedia [wikipedia.org]
Re: Stellar Tron (Score:3)
No, see, that's where Jeff Bridges comes in.
Re:Stellar Pong? (Score:5, Insightful)
And what's so difficult about retracting the sail? The force on the sail at any given time is so miniscule it's trivial to retract them (as opposed to, say, when you have intense winds blowing on your sailboat's sail).
Obvious Answer (Score:5, Funny)
Rus
Re:Stellar Pong? (Score:2, Insightful)
Re:Stellar Pong? (Score:3, Funny)
Why not? Return trip? On to next destination?
LK
Re:Stellar Pong? (Score:5, Informative)
Read "Flight of the Dragonfy"/"Rocheworld" (they are the same book) by Doctor Robert L. Forward for an informative and entertaining novel using (laser pumped) solar sails.
Re:Stellar Pong? (Score:5, Informative)
There is also a sequel but I will leave that up to you as a project to find out what it is.
Re:Stellar Pong? (Score:3, Informative)
It's would have, you blithering idiot.
Re:Stellar Pong? (Score:2)
That was new!
Now, I'll agree with informative -- but entertaining??
I usually describe Forward as the absolutely worst author whose books I buy in hardcover.
You must be a nerd and talking about the physics and engineering as "entertaining" -- and not any literary qualities!
(-: Reminds me of when I recommended a Farmer book to
Re:Stellar Pong? (Score:4, Insightful)
"Once there, you jettison the sale, or use it to fly around the star system."
;).
Perhaps you'd like to explain how jettisoning a solar sail has enough force to slow down the craft.
That sail would have to be pretty massive, like the mass of a planet, in order to counteract years of acceleration so you could push it away from yourself to slow down
That is the problem with getting somewhere in space. To get there the fastest you have to accelerate continually there till the 1/2 way point, turn the ship around around and use an equal force / fuel to decelerate. Reminds me of a scene in Battle Star Galatica Crew Member: "Sir we've ran out of fuel", Admiral "Come to a complete stop", The right reply: "But Sir, I said we ran out of fuel".
Re:Stellar Pong? (Score:5, Funny)
The right reply: "But Sir, I said we ran out of fuel"
"and besides, complete stop related to what, Sir?"
Re:Stellar Pong? (Score:5, Funny)
Although that'd be a great way to freak out an alien race... Kind of like pulling a Rama on 'em.
Re:Stellar Pong? (Score:3, Funny)
Re:Stellar Pong? (Score:3, Interesting)
Re:Stellar Pong? (Score:2, Informative)
You use on board rockets to help steer as you draw close to your destination.
Re:Stellar Pong? (Score:5, Informative)
This doesn't help you stop. To do that, you flip yourself around so that the sail is pointing towards the destination, and you use the radiation pressure from that star to kill your velocity. Can't do this if you're already jettisoned it.
And, no, chemical rockets won't work to shed that much velocity. If you get get that much delta-v from chemical rockets, you'd just use chemical rockets to get on your way as well. But that's precisely why you're using a solar sail instead: chemical rockets suck in terms of specific impulse.
Re:Stellar Pong? (Score:5, Insightful)
no.
try sailing upwind in a circular boat.
Regardless of how late it is, you should have caught this one before you hit 'post'... or am I about to Have A Nice Day?
Re:Stellar Pong? (Score:5, Informative)
http://en.wikipedia.org/wiki/Sailing#How_sailing_
Cheers!
Re:Stellar Pong? (Score:5, Informative)
I'm not so sure that's the case - when we sail in water, we can either be on a run (the wind directly behind us, as you would expect a solar sail to work) or on a reach (the wind to one side).
On a reach the sail acts more or less like an aeroplane wing because of it's curved surfaces and as well as generating a forward force it generates a lot of lateral force too. The closer to the wind you sail, the greater the proportion of lateral force.
The only reason that's not a big problem for us is that your craft has a centreboard which greatly reduces it's ability to slide sideways, especially at speed - when I'm windsurfing in a reasonable wind, I will be doing about 30-35 knots and can easilly sail upwind with about 300cm^2 of fin area, but I won't be able to go upwind if the wind drops off because my speed will have greatly dropped. In space there is no way to have a centreboard to prevent the lateral forces pushing you sideways since there is nothing for it to react against.
I'm also not sure about the "aerodynamics" of a solar sail - as I described above, a modern sail works very much like an aeroplane wing when reaching and relies on the air have a laminar flow over both sides of the sail. I very much doubt photons are going to have a laminar flow over your sail so the sail isn't going to be anywhere near as efficient for reaching as boat or windsurfing sail. In windsurfing the most efficient point of sailing is on a slightly broad reach - i.e. the wind is coming from one side and slightly behind you, I would expect the most efficient use of a solar sail would be on a run.
Re:Stellar Pong? (Score:5, Informative)
Regardless of space or the ocean, basic principles of physics apply. Action and reaction.
Uh, that's a resounding negative, Houston. In the ocean, we have this thing called *water* in which one sails. Action: wind pushes against sails from somewhere near the front. Reaction: sail pushes back agains wind and pushes into the water; water pushes back, and ship tends to go forward. In space, there is no dense medium through which one sails. Action: photons from a star push against sails from somewhere near the front. Reaction: ship pushes back and moves further away from the star. You can't "tack" in a vacuum.
Re:Stellar Pong? (Score:5, Informative)
Actually, I was reading up on this a while back.. They'd use the gravity of the star to tack. Well, kinda.
It seems like a good idea, if they want to send something away from Sol for a long duration in one direction. Not too much navigation necessary (or possible).
The one thing I don't see really mentioned is debris in space. You know, micrometeors, and the like. It should make for a nice shreaded solar sail by the time it gets to the edge of the solar system. Hopefully it didn't encounter enough debris hitting it to knock it off course, or stop it all together.
But hey, if they're just looking to find out how fast a solar sail will accelerate away from SOL at Earth's distance, cool. It'd probably make for a faster way to get from Earth to our neighboring (outward) planets, if they can point it in the right direction. 1 degree makes a big difference over a few million miles.
Re:Stellar Pong? (Score:3, Informative)
In a sailboat, I can go sideways relative to the wind. I can even tie off the sheet and keep going sideways using only the winds energy.
With a solar sail, you can accelerate away from the star at some speed (sail fully unfurled); you can let gravity accelerate you toward the star (sail furled), or somewhere in between (sail partially furled; accelerating toward or away from the star at any speed between the two limits). But you cannot go sideways.
It is NOT like sailing. It is like flying a blimp with n
Ironically (Score:3, Funny)
Re:Ironically (Score:3, Funny)
Re:Ironically (Score:2)
(Hint: think conservation of energy.)
Re:Ironically (Score:2, Interesting)
Re:Ironically (Score:4, Interesting)
Interesting idea... you wouldn't be able to carry the mirror with you once you turned around (since the mirror would be producing exactly the opposite force of your solar sail), but you could probably drop it in space pointing in the right direction - the mirror would accellerate backwards because of the light pressure but it would still reflect the light forwards which I guess you could use.
Going to Sol (Score:3, Informative)
You heard it hear first -- America's Cup 2200.
---anactofgod---
Re:Going to Sol (Score:2, Funny)
Re:Going to Sol (Score:2)
You probably think you're being funny, but this is in fact exactly right [caltech.edu].
Turning around... (Score:2)
So, unless one had other means of propulsion to facilitate a return to Sol, one would have to change one's mind a whole heck of a lot sooner than ~half-way to Alpha Proxima, oth
Re:Ironically (Score:2)
Use the lateral thrust to kill your orbital velocity.
Furl the sail.
This would work great for a trip to Mercury, actually. If you want to reverse course in between stars you need to use one of the ideas the late Bob Forward played with, e.g. a disposable mirror in front of you reflecting a launch laser to force you backwards.
Re:Ironically (Score:2)
So that was why he stopped writing. :-(
You miss important stuff when you're too busy.
Re:Ironically (Score:5, Informative)
The truth is that a solar sail doesn't get you away from the sun by just having the sail aimed straight at the sun. It does it much more trickily than that
What happens is that you orientate the sail at 45% (or something like that) to the sun. That way, a large amount of the force from the sun actually goes to changing your orbital speed, and not just pushing you away from the sun. By orienting the sail so that it increases your orbital speed, you end up making greater size orbits around the sun, until you are far enough away from the sun and you can do some other tricky stuff to leave the solar system.
But, it works the opposite way too. Orient your sail so that you are decreasing your orbital speed. You go slower, and therefore your orbit size decreases, and you start approaching the sun.
Of course another poster queried why you would want to travel to the sun. Good question. But how about Mercury or Venus ?
Re:Ironically (Score:5, Insightful)
And, why not?
Sailing ships have sailed "upwind" for many centuries.
In outer space, you are either in orbit, or falling directly towards the nearest large body. A solar sail can be used to slow down or accellerate lateral speed simply by rotating it 45 degrees.
A simple google search turned up this [nasa.gov] in case you are curious.
Although they are right, in that solar sails do accelerate the entire trip and carry no fuel, I don't think that sails are "the way to go" unless we're talking about a ten thousand year multi-generational ship.
I consider the Bussard RamJet the "only way to fly". It carries no fuel, but is powered by carving a planet-sized swath out of the ambient hydrogen atoms out of interstellar space and fusing them.
With interstellar distances, the real issue is: how quickly can you get to relativistic speeds? Because, at
You need power to get you there in less than hundreds of years - thus the RamJet.
Solar vs. wind sail (Score:2, Informative)
Re:Solar vs. wind sail (Score:5, Informative)
Re:Ironically (Score:5, Informative)
A beamrider of some kind (leave the engines at home and ship momentum up to the spacecraft in some convenient form) or an antimatter rocket are looking like the best ideas at present.
Steve
Quantum teleportation propulsion (Score:3, Interesting)
The idea is to entangle two cesium atoms, then send one up into space. Back on earth, excite the one that remains and the one in space will do the same. In theory that could be used as an ion drive while keeping the bulk of your engine back on the ground.
Re:Ironically (Score:4, Informative)
You're forgetting the biggest drawback of the Bussard Ramjet... That is the gas collection.
The gas collection mechanism will create such resistance at high velocities that it would jam up and slow the device down a lot.
I believe that there has been some research done which suggest that it would never be able to obtain velocities exceeding 0.1c let alone 'relativistic velocities'.
I think we are more or less stuck on this island Earth, until we can think of something better than Newtonian physics to traverse the gap between the stars... Some revolution akin to Gene Roddenberry's Warp drive or Iain Banks's Exotic Matter drive - something which doesn't require a reaction mass.
OT: Early STTOS was fun - somehow the warp drive sound effects always sound like the London Underground trains...
Re:Ironically (Score:5, Funny)
Re:Ironically (Score:4, Funny)
Solar sail (Score:4, Interesting)
What I dont understand is how they intend to protect these massive sails from being shot full of holes by meteorites and space dust as it propels its way through space.
Also, seing as how it is powered by solar wind, what happens when the craft is between 2 or more stars which are all exerting equal force on the sails. With no fuel it is doomed to slow down and be 'blown' around in space.
Re:Solar sail (Score:2, Informative)
Re:Solar sail (Score:2)
Re:Solar sail (Score:2)
Maybe you don't. Just make the sail big enough that to generate adequate "thrust" with a few holes in it. Solar sails are very big and very thin. Any debries that hits is just going to create hole and keep on going.
Also, seing as how it is powered by solar wind, what happens when the craft is between 2 or more stars which are all exert
Re:Solar sail (Score:2)
They don't have to. The force imparted by the solar radiation is probably not strong enough to cause any holes to expand on their own. They could further prevent tearing using a cross-hatch "rip-stop" pattern of slightly greater thickness.
Re:Solar sail (Score:2)
It is directional. It can only be pushed by solar wind from one direction, so unless they turn-around, the star they are approaching will not affect the solar sail much at all.
Re:Solar sail (Score:2)
Re:Solar sail (Score:5, Informative)
To clear up one point, solar sails are not powered by the solar wind, which is a stream of particles. They are powered by light, which exerts several thousand times more force than the solar wind.
The sail is not direction. It is affected by light coming from all directions, but it "blows" in the direction of the prevailing light, which would come from the brightest/closest star. To change direction a solar sail ship must change the angle of the sail in relation to the nearest star.
At the start of a journey the sail would be ahead of the ship, towing the ship behind it. Sometime between stars the ship could use small maneuvering jets or something to flip itself around and put the sail behind it. The increasingly strong light from the destination star would gradually slow it down.
More likely though, the sail would be retracted or jettisoned in mid-journey, when the light from the destination star equalled the light from the original star. This is when the ship would be at its maximum velocity. It would then coast at that speed for the rest of the trip and use the gravity of the destination star or planets to decelerate much more quickly.
Re:Solar sail (Score:4, Informative)
The speeds involved in inter-stellar are so high that gravity assisted decelleration is probably out of the question. Aero-braking in an atmosphere is certainly not an option. There have been some proposals for braking on interstellar hydrogen I believe (ramjet concept).
Re:Solar sail (Score:5, Interesting)
Ever seen a radiometer? or hear about the radiation pressure equation?
This is a common misconception... one that even Maxwell mistakenly believed. Apparently along with the folks at Encyclopedia Britannica as well.
Pay attention to which way a radiometer turns. If it were turning due to radiation pressure, it should act as if a force were pushing on the white side of the plates. Since the white plates reflect the light, there should be twice as much pressure on them as there is on the black plates which absorb the light. (It takes a greater transfer of momentum for something to bounce off of you than for you to catch it... think of the conservation laws).
The problem with the radiometer is that it turns the wrong directions... it acts as if something is pushing on the black side of the plates. And there is... air pressure. The black side will reach a higher temperature than the white side, and then due to the thermal transpiration, the gas near the edges moves from the hot side to the cool side, and in doing so it pushes the blades along.
Radiometers are in a near vacuum, but there is enough air pressure inside to allow this effect to happen.
What Solar Sails Are (Score:5, Interesting)
Re:What Solar Sails Are (Score:2, Interesting)
Kind of counterintuitive. I thought the unbelievably small mass of a proton would still outweigh the nearly infinitesimal mass of a photon. But I guess our star puts
Physics (Score:4, Interesting)
Anyway, we should get to Mars and back a few times before we try to get to the stars... baby steps.
Re:Physics (Score:5, Informative)
This isn't about travel.
Either way, the Japanese are trying to make this look cool by saying it's star-faring technology. Probably true, but only because we're not likely to put humans on this thing -- so it's possible we'll do this before we get to Mars, because the expense and risk could be vastly lower.
Re:Physics (Score:2)
For the foreseeable future the real applications would be inside the solar system.
Re:Physics (Score:2)
But when it comes to interplanetary distances, 25KMPH is ... barely pokey.
Closest star to us is Proxima Centaury -- about 4.2 light years, or 2.5 * 10^13 miles.
Well, this [nasa.gov] explains it much better than I can. Basically, the Japanese mission is using 7.5um film; the NASA document posits th
Re:Physics (Score:3, Insightful)
I'm no scientist, but wouldn't the thrust follow the same inverse-square law as radiant light?
To make best use of a solar sail, it would probably make sense to use a conventional rocket to establish a highly eccentric (parabolic) orbit around the sun and then pop the sail open after perihelion where the sail would contribute the most energy to the orbit.
I think aiming the spacecraft (on the outbound
Re:Physics (Score:2, Insightful)
Wrong (Score:5, Informative)
Orion [islandone.org] can take us to the stars, and it can be done with today's technology, not something that's just starting to enter the very earliest test phases. But it's nuk-yu-ler, so it doesn't count.
Re:Wrong (Score:5, Insightful)
Because Orion needs to carry its fuel, its period of acceleration is necessarily limited. If you count Orion as a star-faring technology, then you need to count chemical rockets, too... Just ask Pioneer 10.
Re:Wrong-A "glowing" recommendation. (Score:5, Informative)
Re:Wrong-A "glowing" recommendation. (Score:2)
I'm a big fan of the Orion project. (And that design would use megaton fusion bombs! Cool!)
But a laser pumped solar sail could be faster. Those big laser will be a big investment, though... and the "misuse" applications should be about the same as for lots megaton bombs! (It's mentioned e.g. here [nasa.gov].)
dumb shmuck... (Score:3, Insightful)
OF COURSE it's not shining laser light into the sails from the ship itself, like a sailboat with a fan on it, you unbelievable moron. And as for getting "worse and worse with aim", you DO NOT TRY AND POINT THE LASER AT THE FAST-MOVING AND LIGHT-YEARS-DISTANT SPACESHIP, AND DO COURSE COR
How romantic (Score:2)
Please. One poster has already pointed out that this only works within the limit of a star's solar wind. It's also a very slow mode of transport. If you want to send your decayed remanants (even the bones will have disintegrated) HALF way to the stars this is definitely the way to go!
For travel within the inner solar system however, as a secondary form of propulsion it may have its uses.
Re:How romantic (Score:2)
Don't lecture me on inertia let alone as an AC.
Not a working solar sail as such (Score:5, Informative)
The pictures in the article which show the test sail deployed immediately behind the launch vehicle imply the same thing. The following text says that the launch vehicle reentered and splashed down 400 seconds after liftoff. This can only mean that both the LV and the sail experiment were in ballistic flight when the latter was deployed. For a solar sail to work, it would need to be deployed after orbital insertion (or after escaping the magnetosphere.) The article does not mention orbital insertion, nor was there time for this to occur.
Exactly - robotics competition coming too (Score:2)
Good to see (Score:4, Interesting)
Let's all raise a glass of Sake to the engineers behind this project!
CG? (Score:2)
Interstellar travel it wasn't. (Score:5, Informative)
Total trip, liftoff to crash-down, less than 7 minutes.
-
Not wind! (Score:3, Informative)
Solar sailing (Score:4, Funny)
2 questions (Earth altitude, Sol heliosphere exit) (Score:4, Interesting)
2. What happens to such sails when they cross the heliosphere of a regionally prominent star such as Sol? Is it all chaotic photons and miscellanous radiation in the interstellar "void?" Or are conditions regulated by the nearest stellar bodies?
-- In other words, how would one navigate effectively once the prominent wind from Sol fades and is replaced by other forces? Are you doomed to follow your trajectory mainly established by Sol once you leave its heliosphere, possibly modifed by various minor (uncontrollable) forces from other winds in the void? Can you take advantage of such extra-Solar winds to go where you want?
We already have sol here!! (Score:2)
Hit WINDOWS KEY + R type in SOL ENTER
Sol is right here, no need for travel!
Just a question... (Score:3, Interesting)
Anyone got any pointers?
Limitations of Solar Sails (Score:2, Informative)
Re:Limitations of Solar Sails (Score:3, Informative)
If you accelerate, you move into a higher orbit (and move away from the star). If you decelerate you move into a lower orbit (towards the star). Sideways vectors are used to change the plane of your orbit.
All
Ortw (Score:3, Informative)
Obligatory Star Wars reference (Score:2)
calculations from NASA (Score:5, Interesting)
Re:calculations from NASA (Score:3, Informative)
And a few millimeters per second per second is useless, why?
3 millimeters per second squared, and after a week you're moving at 1.8 kilometers per second. After a month, 7.2 kilometers per second. After 2 months, you've already exceeded Earth's escape velocity from the surface, let alone from or
Re:calculations from NASA (Score:4, Informative)
Except you're losing thrust faster than the escape velocity decreases. Escape velocity goes as 1/sqrt(r), whereas the light intensity (hence thrust) goes as 1/r^2. Solar sails probably aren't the best way to go interstellar. But then, neither is anything else we can imagine at the moment. sigh
And now, safely buried in the comments because I have limited bandwidth...
Photos of the Uchinoura Space Center [kevland.com], from back when they called it Kagoshima Space Center. (Kagoshima is the prefecture, Uchinoura is the town. Nobody in Japan has heard of Uchinoura, so they called it Kagoshima Space Center until with the increased level of joint projects with a certain American space agency they decided 'KSC' was too easy to confuse with Kennedy Space Center.)
Bullshit! (Score:3, Interesting)
Personally, I tend to believe things like ion drive are actually much more efficent and likely to work well with stare exploration (ion drive is just a fancy way of saying you shoot very small amounts of mass out the back going very fast. This is important because it means you can get more thrust from the same amount of fuel weight if you have something like a nuclear power source to accelerate the ions).
Yikes! (Score:3, Funny)
Featured in a BBC documentary (Score:5, Informative)
http://www.imdb.com/title/tt0273608/
http://www.bbcshop.com/invt/bbcdvd1090&bklist=i
One of the chapters discusses how travel to other stars would be possible. As far as I remember there is another technical solution in discussion which would involve nuclear detonations as part of a propulsion system. (I might have confused something there, though)
solar wind (Score:5, Interesting)
It's also not correct that solarsails can't be used to reach other suns, because the sun there gives an oposite force. It's quite trivial, when using adaptive (rotating) solarsails, which have only one higly reflective side, to slow down or accelerate when nearing a solarsystem. And even withing a solarsystem; for an interesting project in that regard, see the planetary society [planetary.org] where they plan to launch the first non-gov solarsail-powered probe.
The Wind from the Sun (Score:3, Interesting)
A beautiful story with an excellent description of some problems which may exist.Read the story,i will spare the spoilers.
Other Existing Technology (Score:3, Informative)
Of course what we really should be working on is actual nuclear rockets - controlled nuclear burn instead of explosives. Nuclear gas core rockets [nuclearspace.com] are really not beyond present technology, their exhaust is cleaner than the space shuttle's, and they're so powerful you can build big, heavy, safe vehicles.
Limited directions? (Score:3, Interesting)
Since a solar sail needs light pressure to accelerate, can it only accelerate in a direct line away from a star?
also
Isn't there a problem, once the sail gets far enough from its original star, that pressure from other stars will interfere w/ the path?
Re:Not so fast... (Score:5, Informative)
Um, no. As you approach the destination star, its light pressure will start to counteract your velocity and slow you down. The "brakes" are built in.
Re:Not so fast... (Score:2)
Re:Not the only way t o the stars. (Score:3, Insightful)