Aces High Bulletin Board
General Forums => The O' Club => Topic started by: Krusher on May 02, 2005, 09:15:06 AM
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This is very interesting work.
SANDUSKY, Ohio (AP) -- Scientists working with a synthetic material 100-times thinner than a piece of paper are testing their theory that the sun can power interplanetary spacecraft. They believe that streams of solar energy particles called photons can push a giant, reflecting sail through space the way wind pushes sailboats across water.
The National Aeronautics and Space Administration has invested about $30 million in space-sail technology, something that existed solely in science-fiction novels a decade ago. Yet the reflective solar sail could power missions to the sun and beyond within a decade.
"It's OK to breathe on it and touch it," said David Murphy, of ATK Space Systems, showing off the sail.
ATK Space Systems, based in California, is one division of a $2.4 billion company that makes rocket motors, advanced weapons systems and ammunition for the military and the Department of Homeland Security. It has about 14,000 employees at operations in 23 states.
Last year it delivered 1.2 billion rounds of small-caliber ammunition to the Army.
The Space Systems division developed the solar sail, which is being tested in the world's largest vacuum chamber at the Cleveland-based NASA Glenn Research Center's Plum Brook Station in Sandusky. It has a space environment simulation chamber 100 feet in diameter and 122 feet high.
In that chamber, Murphy displayed four silvery, triangular pieces of sail stretched over four long booms, which form a square about 70 feet on each side. Murphy and others want to study how the sails will deploy and operate in a vacuum under various temperatures.
"We're going to cool it down and shake it out," Murphy said.
Just in case, the fabric, which resembles Mylar, has rip-stop threads to keep it from pulling apart when the chamber is closed and the air is pumped out.
"To get a lower pressure you'd have to go to space," said Edward Montgomery, an engineer from NASA's Marshall Space Flight Center in Huntsville, Ala.
The chamber has been used to test rocket components, radiators for the International Space Station and the crash bags that protected twin rovers when they landed on Mars last year.
The plasticlike fabric used to make the sails is a spinoff from technology used to develop spacecraft paint.
First missions - scientific payloads of a few hundred pounds - are likely to be to the inner planets, Venus and Mercury, and to the sun. But NASA scientists think the technology is a good bet for eventually powering spacecraft into deep space.
Since its fuel is free and doesn't have to be stored, a craft with solar sails would not have to slingshot around the moon or other planets for a gravity boost to reach distant destinations, as other craft do.
Craft propelled by solar sails could be launched on conventional rockets or released from space stations. In space, the force of sunlight would push the reflective sails, causing the craft to move, said NASA Marshall physicist Les Johnson.
The first sail tested in space will be about 130 feet on each side. Those on an actual mission could be twice as large.
While its thrust is low, it would be continuous so that the craft accelerates steadily, eventually reaching speeds of tens of thousands of miles an hour. Changing the sail's angle to the sun would allow the craft to slow down or speed up.
"Just by morphing its shape we can get it to turn," Montgomery said.
With the science worked out, Murphy said, it is now a matter of building larger sails.
"We have everything we need to do this," he said.
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Larry Niven has been doing that for decades :)
shamus
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"Renner, I intend to cut that probe loose from it's sail..."
;)
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Originally posted by Shamus
Larry Niven has been doing that for decades :)
shamus
sci-fi goes live !
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It's an interesting idea.
Up until something the size of a pebble hits it and ruins millions of dollars.
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It's awful funny that a fellow named 'lasersailor' would lack such basic comprehension of how laser sails are supposed to work... basic predictive design theory established 20+ years ago suggested that the structure be designed for distributed stress management so that if a portion of it was holed, it wouldn't kill the whole structure.
Secondly, the thinness of the material lessens the amount of mass that would be converted to energy on impact, meaning that it would be more likely to punch a tiny hole through it then, say, to go off like a stick of dynamite.
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I wonder how you could slow it by turning the sail. It's not like the photons would be going in a different direction. It's also not like a ship with a rudder and a hull... there is nothing to push from to force a change of direction.
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"Last year it delivered 1.2 billion rounds of small-caliber ammunition to the Army."
hmmmmm, thats alot of dead Iraqis
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Originally posted by Mini D
I wonder how you could slow it by turning the sail. It's not like the photons would be going in a different direction. It's also not like a ship with a rudder and a hull... there is nothing to push from to force a change of direction.
It's pushing off the photons of light, so getting it to turn is identical to getting it going forward - you cant have one working without the other working too.
Think of how a mirror works. If the mirror is perpendicular to a light source it will reflect a light back to the orgin. The sail is a mirror, it reflects the photons back towards the sun and the opposite reaction propells the spacecraft forward. Now to turn, think of what happends when you place a mirror at a 45 degree angle, it deflects the photons of light to the side and not directly back to the source. So in the case of this sail, the opposite reaction would push the spcecraft to one side - effectively turning it.
This would slow the spacecraft too, or at lease lower its acelleration, because less energy is going into pushing it forward. You could do several turns in opposite directionms to slow the craft and wear down its kinetic energy.
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Same as with flying. When you turn, it's the horizontal component of lift that's at work. Exactly the same with 'tacking' your solar sail. It seems counterintuitive, but take a hose and spray water at something with a flat surface, then turn that object to 45 degrees and do it again. As long as you track it accurately, you should see the object moving to one side.
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It is not the same as flying. There is no avialable source of friction for direction or acceleration.
The force of the photons is singularly directional. You can turn the sale, but you will need something acting as a rudder to actually change the direction. Also, a turn would begin with VERY slow acceleration just by changing the angle of incident and would do nothing to slow the craft.
It's just an odd concept without a source of friction to slow the vehicle. I don't know how you can convert the directional energy of a photon in such a manner as to reverse the direction of impact.
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For turning, I think the size of the sail is manipulated. One side gets smaller while the other size gets bigger or stays the same size. You have more energy accelerating it on one side than the other, this could turn it right?
-SW
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If you can turn it you can slow it down.
What happnds if you do 10 consecutive turns in opposite directions? You dont need friction to slow it, you just need to use up its energy in turns. There is still mass, even without gravity, and getting this mass to change direction will use up energy and slow forward progress.
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Originally posted by AKS\/\/ulfe
For turning, I think the size of the sail is manipulated. One side gets smaller while the other size gets bigger or stays the same size. You have more energy accelerating it on one side than the other, this could turn it right?
-SW
No, not in space. There is no friction to slow the side with less energy and more drag.
The photons will siply bounce off and deliver proportional force to the surface area.
So reducing the sail in this way would simply slow the whole thing down.
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I dunno grun. You'd have to do alot more than turn the sail, you'd have to completely alter the direction of the object. Given the low acceleration that is being done, I don't see this as an effective way to stop something given that it would be at full speed all the way through the turn untill you can get on a tangent with the path of the photons. Even then, you'd need to stop it in only one direction without accelerating it in another. Once again, there is no directional aspect to the body... using it as a sail will slow a sideways motion, but will push it away to do it. It will only transfer the direction.
Sail boats would not be able to sail into the wind if it were not for the rudder and hull. They'd just keep being pushed away no matter how you turned them.
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won't they just use thrusters for maneuvering, collaspe the sail and rear thrusters to slow down?
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PS...
Reducing the sail size on one side would not slow down the object. It would reduce the acceleration on that side causing a spinning of the object.
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Originally posted by Torque
won't they just use thrusters for maneuvering, collaspe the sail and rear thrusters to slow down?
If that's what they were saying, we wouldn't be discussing it. They say they can do it with a sail. I obviously know more than a room full of engineers when I say I don't see how that's possible.
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I guess I didn't read the argument too closely before I responded. I don't see how tacking the sail could be used to slow down, just for turning.
Lesse, methods that could be used to slow down... I wonder how feasible it would be to energize the structure of the sail to generate a magnetic field to increase the drag profile of the spacecraft? Eg, the kind of field a Bussard ramjet uses, except instead of being used as a funnel, it's more like a drogue chute.
If you're travelling to another star, you can just the star itself to slow you with its light, of course, but for insystem travel, it'd probably be all about clever orbits. I doubt solar sail travel will ever be terribly speedy in-system, but it might be cheap. Heck, Niven had banks of high powered lasers on Mercury (solar powered) that would be used to provide boost to sails. Those lasers proved useful when the Kzin dropped in too. You put the ship into a transfer orbit to your destination, then retract the sail and perform an aerobraking maneuver to slow down.
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I don't see how tacking the sail would even turn the craft... only start accelerating it in a different direction that could never actually aproach a tangent to the source. Basically, I could get it to accelerate to the left or right, but I'd never be able to stop it from accelerating forward much less reverse that acceleration.
The only thing I could think that would do it is if the sails were transparent from one direction and the photons were traveling in infinite directions. Hell... that may be it in a nutshell, but the article didn't really mention that.
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I think that if the craft is orbiting the Sun, then slowing down would just mean using the sail so as to decelerate the tangential component of the velocity thus killing off the crafts angular momentum.
In the case that the craft was moving away from the Sun in a straight line, then just furling the sail would do the trick... unless the craft was moving at the escape velocity, or faster.
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Originally posted by Mini D
PS...
Reducing the sail size on one side would not slow down the object. It would reduce the acceleration on that side causing a spinning of the object.
Yep, that last post of mine was wrong.
But in reference to "accelerating in a different direction" that pretty much defines a turn.
Doing that lowers forward acceleration - forward mening the orginal course.
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Originally posted by Chairboy
It's awful funny that a fellow named 'lasersailor' would lack such basic comprehension of how laser sails are supposed to work... basic predictive design theory established 20+ years ago suggested that the structure be designed for distributed stress management so that if a portion of it was holed, it wouldn't kill the whole structure.
Secondly, the thinness of the material lessens the amount of mass that would be converted to energy on impact, meaning that it would be more likely to punch a tiny hole through it then, say, to go off like a stick of dynamite.
NERD! :D
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You're not turning the craft grun, you're sliding it. It's like playing 1942 without using forward/back... you move from right to left but you're always going forward.
Sliding would be a more accurate term than "turning"
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Funny how a guy named Chairboy criticizes me when he forgets how much **** is just flowing around randomly in space.
Death by a million paper cuts.
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Its original forward moment will not stop fully, you will add a new force that will act sideways. These forces combined will alter the crafts course - effectively turning it.
Just draw a two vector diagram, one representing the stong original forward vector an a new weaker (shorther) sideways vector. Whats the new direction made by the two?
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Originally posted by lasersailor184
Funny how a guy named Chairboy criticizes me when he forgets how much **** is just flowing around randomly in space.
Well, I guess you must be right. Good thing you came along, imagine the egg on their faces when the scientists find out!
I'll call JPL immediately and tell them they're wasting their time. I think science owes a great debt of gratitude to you, Lasersailor! Millions, if not BILLIONS of dollars have been saved! All the PHDs on the project couldn't see the one basic flaw that you could. It just goes to show you that amateurs CAN still contribute.
Everyone else here, I guess the thread is over. Decades of solar sail research, punctured like that by a 20 year old. Wow.
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A physicist from Cornell University says the Solar Sail won't work.
http://www.newscientist.com/article.ns?id=dn3895
Say Thomas Gold is wrong and it actually does work. I don't see how you could turn it either.
Imagine a hovercraft that has only vertical thrust and no directinal thrust. Put up a sail in a light breeze. How are you going to make it change direction? All you could do is make it spin.
Since there is no friction in space (or not enough to speak about) you won't be able to slow it down either unless you are fighting a force of gravity. Will the solar sail be enough to overcome the force of said gravity?
Also, you could never travel to Venus or Murcury as you would always be traveling away from the sun and never be able to turn around.
If it works cool. But I think they better get the trigectory right from the get go becouse I think it will only travel in a straight line.
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I’ve seen a few things about this but the last I heard the actual size of the sail would need to be about the surface area of Texas in order to get enough acceleration and keep it once outside the solar system.
Most of the stories I’ve seen on it though are for manned missions, one direction. I’m sure the size of the space craft would have a lot to do with the sail size. However, something has to be wrong somewhere… I don’t think that 260 feet would be large enough. I also don’t think you could go towards the sun with it, thus Venus and Mercury would be out.
As for the post above where someone mentions a pebble puncturing the sail, no maybe not one pebble, but what about a comet trail, or a million pebbles broken up from an asteroid that’s not been charted, a multitude of objects that has the ability to destroy the surface over time. This of course has a lot to do with the sail size. If it truly has to be as big as I’ve heard, it isn’t really feasible, although a cool idea.
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Somthing to think about...multiple stars of differing vectors.
shamus
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Nice thought, but the light pressure from other stars is... not a factor.
BTW, here's a quote from a 1920 editorial about 'crackpot' Robert Goddard (http://en.wikipedia.org/wiki/Robert_Goddard_%28scientist%29) and his theories on rocket propulsion.
That Professor Goddard, with his "chair" in Clark College and the
countenancing of the Smithsonian Institution, does not know the
relation of action to reaction, and of the need to have something
better than a vacuum against which to react--to say that would be
absurd. Of course he only seems to lack the knowledge ladled out
daily in high schools.
I feel it's appropriate, considering the conversation.
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Originally posted by ChickenHawk
Also, you could never travel to Venus or Murcury as you would always be traveling away from the sun and never be able to turn around.
If it works cool. But I think they better get the trigectory right from the get go becouse I think it will only travel in a straight line.
The thing is that the matter in the solar system is orbiting the sun. Getting from place to place can be accomplished by adjusting this tangential velocity at the right times and by the right amounts, thus changing the orbit.
Getting closer to the sun would be accomplished by having the sail to such an angle towards the sun that this orbital velocity is reduced. There will always be a force component pointing outwards in a straight line from the sun, but it won't matter if it is small. If starting from a roughly circular orbit, this would lead to the orbit becoming more eccentric (thus making the craft pass closer to the sun at the perihelion point). Now one would furl the sail and open it again as the craft gets closer to the sun to kill off the accumulating velocity. If done right, it would result in a circular orbit around the sun, but this time with a smaller radius.
Obviously, because the sail is most probably difficult to handle, and because of the low thrust, it won't be so simple. Getting the desired orbit might require many complete revolutions or whatnot.
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Originally posted by Chairboy
Nice thought, but the light pressure from other stars is... not a factor.
Why not..energy is energy no?
shamus
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Right, but the amount of actual energy reaching from other stars is many orders of magnitude weaker then anything local. Inverse square law at work here. Whereas you might be able to get good propulsion out of a sail the size of texas for within our solar system, it might need to be many times the diameter of the solar system to show an effect from the light from other stars.
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How would it not be stopped half way to the next star by the light emmited from there? Or do you get it to max speed and then pull in the sails?
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Either pull in the sails or turn it onits side so that it's slicing towards the target.
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Originally posted by SageFIN
The thing is that the matter in the solar system is orbiting the sun. Getting from place to place can be accomplished by adjusting this tangential velocity at the right times and by the right amounts, thus changing the orbit.
Getting closer to the sun would be accomplished by having the sail to such an angle towards the sun that this orbital velocity is reduced. There will always be a force component pointing outwards in a straight line from the sun, but it won't matter if it is small. If starting from a roughly circular orbit, this would lead to the orbit becoming more eccentric (thus making the craft pass closer to the sun at the perihelion point). Now one would furl the sail and open it again as the craft gets closer to the sun to kill off the accumulating velocity. If done right, it would result in a circular orbit around the sun, but this time with a smaller radius.
Obviously, because the sail is most probably difficult to handle, and because of the low thrust, it won't be so simple. Getting the desired orbit might require many complete revolutions or whatnot.
Of course your right Sage. Given an orbit around the sun and using the suns gravity for travel toward it and the solar wind to travel away from it, the craft should be able to manouver about the solar system. As you mentiond, it could take quite a while to make course changes though.
It should be interesting to see if the mirror sail will work or if a darker material would be needed as suggested by Thomas Gold. Also should be interesting to see how big the sail will need to be.
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Originally posted by GRUNHERZ
Its original forward moment will not stop fully
Wrong. It will not slow at all. As a matter of fact, it will continue accelerating as long as the sail is facing towards the sun at any degree.you will add a new force that will act sideways. These forces combined will alter the crafts course - effectively turning it.
Just draw a two vector diagram, one representing the stong original forward vector an a new weaker (shorther) sideways vector. Whats the new direction made by the two?
The vectors will not dictate the direction of motion, but merely the acceleration. You know this... right?
This device, once going forward, will always maintain forward momentum. You can accelerate/decelerate the right/left sliding, but you can never eliminate the forward acceleration. Please note I'm not saying speed... if you cannot eliminate acceleration, you can never maintain or reduce speed in a frictionless environment (it will continue increasing in speed).
SageFIN... the article specifically mentions not having to use gravity to slow the device. That's what got me wondering how the hell they'd stop it.
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Chairboy do you know what is that ?
(http://anh.free.fr/images/imagederiveur/laser.JPG)
It's a laser ;)
I am wrong on the origin of your handle lasersailor184 ?
I remember those boat were though b*tch now that I'm old ,ugly and lazy I prefer drinking booze on the beach :D
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Gsholz: Whenever I see the word 'only', I take it as a challenge.
1. Interstellar drag (both unassisted, and might be increased through use of magnetic fields)
2. Aerobraking
3. Tether
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Why not fit it out with an ion engine for maneuvering and breaking? How far has that technology come?
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Well, the main attraction of solar sailing has been:
1. No power source required for propulsion.
2. No reaction mass needs to be expended.
The weigh penalties for these is suddenly reinstated when you add an ion drive, which requires both power and reaction mass.
Maybe there's still a net gain since you only need to carry a fraction of the reaction mass to get to a certain speed, but the math gets pretty wonky. I can't really see the large scale usefulness of laser sails myself, but maybe I think small.
Personally, here's my thought on where this technology will go. Instead of propelling spacecraft around the system, perhaps the reflective and lightweight sail material will be fashioned into large solar reflectors/focusers that can be used to melt asteroids to enable easy processing. They could also be used in earth orbit to reflect extra sunlight into areas for the purpose of increasing crop yields/environmental sculpting. Want a longer spring? No problem, SolarCo can, for a modest fee, increase the sunshine in your country by 20%.
Heck, you could use the same sort of large scale solar reflectors to generate massive amounts of power too. Build passenger liner sized closed cycle liquid sodium reactors in orbit. Instead of using nuclear fission to heat the mix, use sunlight reflected from a 1,000 acre reflector that's affixed a mile or two away that will focus the sun on the heat exchangers.
Imagine huge farms of these balanced at L5 for constant sunshine, all microwaving their power to collection stations that hook into the grid.
Back to asteroids, there's also a proposal to use reflected sunlight to melt an asteroid, then release carefully sized packages of water that would flash to steam and carefully 'blow up' the asteroid like a balloon. When cooled, the resulting structure could be pressurized and converted into a colony.
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How about for freight missions to Mars or an outer planet?
The ship unfurls its sail and slowly but surely gets out there. Its large cargo is unloaded, then the sail is furled up and the lightweight craft is shot back towards our planet by rocket boosters.
This method is slow but cheap. Might be useful when bulky items are needed with low time priorities (i.e. construction).
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Originally posted by lasersailor184
Funny how a guy named Chairboy criticizes me when he forgets how much **** is just flowing around randomly in space.
Death by a million paper cuts.
you gotta admit this IS funny and ironic
It's awful funny that a fellow named 'lasersailor' would lack such basic comprehension of how laser sails are supposed to work...
BUT,
unless your in earth orbit the odds of you actually hitting somthing while traveling outside of orbit are slim to none.
Space is vast and empty the ods of two objects traveling on the same trajectory at the same time are astronomical (pun intended)
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Originally posted by GScholz
Sure, there are other ways, but I was only considering non-assisted acceleration in vacuum. Of course, ramming a planet would stop the ship quite effectively. ;)
man they let you back in? ;)
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Originally posted by Chairboy
Imagine huge farms of these balanced at L5 for constant sunshine, all microwaving their power to collection stations that hook into the grid.
A few problems to be overcome: Huge reflectors would reflect the solar wind and therefore have to withstand the thrust reaction. A solar flare could knock the reflector out of the L5 gravitational balance. An assymetrical reaction could spin the reflector. Reaction thruster would need to be constantly correcting the reflector.
A possible good outcome: hunters near the microwave beam collectors could hunt pre-cooked duck.
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Originally posted by Mini D
I obviously know more than a room full of engineers when I say I don't see how that's possible.
My new sig material:D
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The Answer Is: (http://www.landoverbaptist.org/audio/scientists.wav)