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LCD 'Engine' For Spacecraft Attitude Control

kdawson posted more than 4 years ago | from the little-more-to-the-left dept.

Space 95

Bruce Perens writes "Japan's IKAROS satellite, which earlier performed the first successful demonstration of a solar sail, has broken more new ground. Liquid-crystal displays — yes, like in your video monitor — were fabricated into strips on the edges of the solar sail. By energizing some of the LCDs and changing the reflective characteristics of parts of the sail from specular to diffuse, JAXA scientists successfully generated attitude control torque in the sail, changing the spacecraft's orientation."

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I have a CRT (1, Insightful)

Anonymous Coward | more than 4 years ago | (#33072128)

"yes, like in your video monitor"
No, I have an old fashioned Sony CRT monitor.

Re:I have a CRT (3, Informative)

butterflysrage (1066514) | more than 4 years ago | (#33072194)

so.... ion propulsion then?

Re:I have a CRT (1)

lawnboy5-O (772026) | more than 4 years ago | (#33072252)

Number One, Make it so.

Re:I have a CRT (2, Insightful)

Culture20 (968837) | more than 4 years ago | (#33073222)

Number One, Make it so.

Riker had to be the worst first officer in Star Fleet; Picard had to keep telling him when to go pee.

Re:I have a CRT (4, Funny)

Chris Burke (6130) | more than 4 years ago | (#33073688)

Hello, this is Captain Jean Luc Picard.

On the bridge of the Enterprise, I have no problems with Number One. Number two is a different matter. That's why I use Star Fleet brand enemas. With a Star Fleet Enema, I can boldy go like no one has gone before!

Re:I have a CRT (1)

ooshna (1654125) | more than 4 years ago | (#33074050)

The new stool transporter technology is still finicky during the last test we didn't just transport the test subject's crap into space but part of his colon and a little of his spleen. But we will keep trying damn it! What kind of superior civilization are we if we still need to squat to void our waste?

Re:I have a CRT (1)

Muad'Dave (255648) | more than 4 years ago | (#33074022)

I hate all those contests telling me to do my business in public. You know the ones - they say "void where prohibited".

Re:I have a CRT (1)

elocinanna (1640479) | more than 4 years ago | (#33081462)

Riker had to be the worst first officer in Star Fleet; Picard had to keep telling him when to go pee.

I love that this was tagged as insightful. God bless slashdot!

I prefer... (1)

fyngyrz (762201) | more than 4 years ago | (#33072300)

...beer [fantasticfiction.co.uk]

Re:I have a CRT (0)

Anonymous Coward | more than 4 years ago | (#33074454)

photon actually

Re:I have a CRT (0)

Anonymous Coward | more than 4 years ago | (#33072968)

You're gad dang'd right!

The day I seen Trinitrons powering space flight, THEN I'll be impressed.

Re:I have a CRT (0)

Anonymous Coward | more than 4 years ago | (#33074228)

I have dual CRTs.

Attitude Control (1, Funny)

Anonymous Coward | more than 4 years ago | (#33072148)

My wife needs that just about every month.

Re:Attitude Control (5, Funny)

Abstrackt (609015) | more than 4 years ago | (#33072234)

I can imagine. Living with a husband who makes comments like that must be stressful.

Re:Attitude Control (-1, Troll)

Anonymous Coward | more than 4 years ago | (#33072348)

You've either never been married or are a women. Comments like that only come due to the attitude, otherwise I wouldn't be commenting on her attitude.

Re:Attitude Control (0)

Anonymous Coward | more than 4 years ago | (#33072858)

A women? What does that even mean? I guess it's like amen. So be it.

Re:Attitude Control (0)

Anonymous Coward | more than 4 years ago | (#33073286)

It's like a Chinamen, only worse.

Re:Attitude Control (1)

Hylandr (813770) | more than 4 years ago | (#33073586)

changing the spacecraft's orientation."

Apparently this spacecraft doesn't need women...

- Dan.

Re:Attitude Control (0, Offtopic)

Profane MuthaFucka (574406) | more than 4 years ago | (#33079386)

It appears that at least in the near term my position as the sole Slashdot poster who has actually put his cock into a vag remains secure.

Re:Attitude Control (1)

supertrinko (1396985) | more than 4 years ago | (#33084330)

I love that people consider that offtopic.

Re:Attitude Control (1)

suomynonAyletamitlU (1618513) | more than 4 years ago | (#33072954)

You've either never been married or are a women.

No, I can definitely say that common sense is not limited only to women... but I can't say I know if marriage causes men to lose the ability. I may have to take your word for that.

Re:Attitude Control (1)

morgauxo (974071) | more than 4 years ago | (#33073966)

Maybe losing the ability leads to marriage?

Re:Attitude Control (1)

osu-neko (2604) | more than 4 years ago | (#33074416)

No, I can definitely say that common sense is not limited only to women...

[citation needed]

A Crookes Radiometer? (1, Interesting)

Mad-Bassist (944409) | more than 4 years ago | (#33072228)

It's neat to see this phenomenon being used for a spacecraft.

Crookes Radiometer is NOT turned by light pressure (4, Informative)

Bruce Perens (3872) | more than 4 years ago | (#33075752)

Crookes believed that his radiometer was turned by light pressure, but he was wrong! It's actually a phenomenon of low-pressure gas moving around a temperature differential. If you pump your radiometer down to a really good vaccumm, it stops working! The light pressure is not sufficient to conquer the bearing friction.

There's a good explanation in Wikipedia [wikipedia.org] .

Re:Crookes Radiometer is NOT turned by light press (1)

Mad-Bassist (944409) | more than 4 years ago | (#33079380)

Interesting! I didn't know a radiometer needed a partial instead of hard vacuum to work properly. I bought the "light pressure theory" as well. It makes sense—solar wind couldn't get through a glass bulb.

It seems to me the effect of the LCDs interacting with the solar wind would be pretty small, but it's a neat idea since there are no moving parts.

Ya learn something new every day.

Ya'har! (0)

Anonymous Coward | more than 4 years ago | (#33072260)

I like the cut of your space gib!

Clever (1)

starfishsystems (834319) | more than 4 years ago | (#33072276)

Come on, you have to admit that's a pretty clever design element.

Imagine if the entire sail surface could be selectively modulated in this way.

Re:Clever (1)

Ungrounded Lightning (62228) | more than 4 years ago | (#33073236)

Come on, you have to admit that's a pretty clever design element.

I agree. It's brilliant. (No pun intended, though one is available.)

(Downsides: You need to keep 'em from freezing (or design 'em to survive it) and you probably need to build the actuators as a large number of independent units, so a meteorite puncture or other damage doesn't take too much of the control area out of service (or "stick" it in an undesired mode).)

Imagine if the entire sail surface could be selectively modulated in this way.

Though it would improve the maneuverability it would drastically increase the sail's mass, thus decreasing its performance for propulsion. You only want enough of this to accomplish the control necessary for the mission profile.

Re:Clever (1)

Gilmoure (18428) | more than 4 years ago | (#33075472)

And if you could form it in to a dish...

Re:Clever (1)

Bruce Perens (3872) | more than 4 years ago | (#33076068)

And focus it.

Blink and it's a weapon, blink again and it's a communication system, blink once more and it's a star drive.

I think that's from A Mote in God's Eye or The Gripping Hand.

Re:Clever (1)

Gilmoure (18428) | more than 4 years ago | (#33076262)

I was thinking of using it to deflect space debris. By modulating it, you could induce many fanciful beams and radiations to the surrounding area.

Holography (2, Interesting)

Bruce Perens (3872) | more than 4 years ago | (#33076370)

How about using computed holography driving embedded LCDs to make a light sail act as a sort of synthetic-aperture device? You could have multiple steerable beams, receive with multiple steerable reflections, etc.

Color me impressed (3, Funny)

metiscus (1270822) | more than 4 years ago | (#33072368)

I wonder what amount of torque they were able to develop with this? It seems like it was pretty effective.

Re:Color me impressed (4, Funny)

JustOK (667959) | more than 4 years ago | (#33072430)

just some light torque, i would think.

Re:Color me impressed (1)

metiscus (1270822) | more than 4 years ago | (#33072562)

Well played good sir.

All the torque that's needed (3, Informative)

mangu (126918) | more than 4 years ago | (#33075868)

I wonder what amount of torque they were able to develop with this? It seems like it was pretty effective.

IAARS (I Am A Rocket Scientist). If there are no fluid leaks anywhere, as there shouldn't be in a properly functioning spacecraft, then *all* of the torque that changes the attitude of a spacecraft comes from solar radiation pressure alone. Therefore there should be not much problem in controlling attitude by modulating solar radiation pressure.

As a matter of fact, this effect is already being used today in commercial satellites. Some of them have adjustable panels that can be turned so that the solar radiation torque is zeroed. The new idea here isn't using solar radiation for attitude control but using LCD panels to modulate the radiation pressure.

The problem in understanding how such a small pressure as solar radiation can cause a spacecraft to rotate is that we are used to thinking about things here on the earth surface, where there are many other forces around us. In orbit, the spacecraft is in free fall in a vacuum, there's no friction and no wind, it will move to the slightest impulse applied. A typical commercial geostationary satellite may need attitude maneuvers a few times a week.

Re:All the torque that's needed (1)

metiscus (1270822) | more than 4 years ago | (#33076026)

My original query was more in relation to what degree of control authority that they could exert based on differential pressure. If one side was turned off completely and the other completely on, what moment would be generated?

Also, I'm guessing they use the on-board supply of hydrazine for delta-v only then?

Re:All the torque that's needed (2, Interesting)

mangu (126918) | more than 4 years ago | (#33076760)

As I understood from the press release, the purpose of the test was to find a viable way to control the attitude of the sail itself. Being so thin, it would flutter and probably be ripped apart if handled roughly. An LCD is an interesting idea in this context, although I believe the LCD would be orders of magnitude thicker and heavier than the solar sail.

As for the momentum needed, it would be very small, because the disturbing momentum itself is very small. Since all the perturbation comes from radiation pressure, it's no big deal to get the correction from radiation pressure as well.

Re:All the torque that's needed (0)

Anonymous Coward | more than 4 years ago | (#33083436)

Well then you also know that everything leaks, even if you can't measure it. You can't stop leaks you can only limit the allowable leakage.

Also, you talk about orbit in which case you know there are gravity gradient torques, not much aero torque at GEO but significant at LEO, and of course magnetic effects. Solar radiative effects are mostly due to mass ejections from the sun, using photons is what JAXA is claiming.

Next up... (3, Interesting)

peacefinder (469349) | more than 4 years ago | (#33072420)

Downwind faster than the solar wind!

Re:Next up... (2, Informative)

MozeeToby (1163751) | more than 4 years ago | (#33074132)

I may be wrong, but going downwind faster than the wind is only possible because sailboats have a keel which transfers some of the sideways force into a forward force. Not possible in space I'm afraid so unless the light pressure is higher than the solar wind pressure I don't think you're gonna be able to do it.

Re:Next up... (1)

gurudyne (126096) | more than 4 years ago | (#33074400)

Well, you are wrong as far as land cars are concerned.

Check out http://www.fasterthanthewind.org/

They have gone over 2.5X faster than the wind, DIRECTLY DOWNWIND.

No side forces on the wheels. Straight downwind

Re:Next up... (2, Informative)

Anonymous Coward | more than 4 years ago | (#33075050)

Rather than using a keel to convert sideways forces forward they are using wheels to convert torques forward. Therefore this isn't applicable either.

The analogy here would need to be a wind powered plane traveling faster than the wind (and not using gravity).

Re:Next up... (2, Insightful)

electrostatic (1185487) | more than 4 years ago | (#33075284)

"...faster than the wind, DIRECTLY DOWNWIND."

There's a bit of a cheat in the directly downwind assertion.

While it true that the vehicle is going directly downwind, its propeller is rotating in the wind. This causes to blade to experience the wind at an angle, just like a sailboat tacking into the wind. And in addition to the "lift" force perpendicular to the blade forcing the car forward, its rotation is used to drive the wheels.

Very clever nonetheless.

Re:Next up... (1)

DragonFodder (712772) | more than 4 years ago | (#33074462)

Or, if we could set the gravity keel to provide that sideways force diversion in relation to the solar flux.

Oh yea, wrong century... resetting my temporal resonator to a more reasonable timeline.

Re:Next up... (2, Insightful)

osu-neko (2604) | more than 4 years ago | (#33074522)

This is essentially true. However, it's probably simpler to note that solar sails are pushed along by light pressure, generated by the photons hitting the sail. The photons, being light, tend to travel at light speed (by definition). There are other considerations besides the lack of a keel for why a spacecraft won't be exceeding that speed.

Re:Next up... (1)

peacefinder (469349) | more than 4 years ago | (#33076008)

For what it's worth, I wasn't actually serious. :-)

(Especially given that - if I understand my relativity rightly - photons would still be traveling at C in the frame of reference of the vehicle.)

Re:Next up... (1)

IndustrialComplex (975015) | more than 4 years ago | (#33075260)

may be wrong, but going downwind faster than the wind is only possible because sailboats have a keel which transfers some of the sideways force into a forward force

You are close.

Sails generally act as a vertical airfoil. You point it into the wind, and the force is created due to a pressure differential. This is just a guess, as I'm not a sailor, but wouldn't the sail(s)'s surface area be the major factor in allowing a larger force to be extracted? (The keel plays a factor, but it isn't the reason why a boat can travel faster than the wind)

Your boat would accelerate until the drag forces equal the motive forces of the sail. So the velocity of the wind isn't the hard cap of your final velocity.

(However, wouldn't this mean that a wind directly at your back would prevent you from traveling any faster than it since you wouldn't be able to generate any 'lift' in your sail once you reached the velocity of the wind).

However, I'm not a sailor, and I've never been on a sailboat, so I could be dead wrong.

Re:Next up... (1)

w0mprat (1317953) | more than 4 years ago | (#33076430)

Perfectly possible. Solar wind is a stream of charged particles. You could easily get 'traction' against this by accelerating this medium as you pass through it. See http://en.wikipedia.org/wiki/Magnetic_sail [wikipedia.org] - but to go down wind faster than the solar wind (600km/s), you would need an external energy source such as solar panels, and a way to accelerate the interplanetary medium.

In short your magnetic sail could also double as a kind of ion engine. An arrangement of electrically charged hoops would accelerate the stellar medium. By this reasoning you could also extract and store energy from the solar wind, then use this energy for thrust once your sail passes equilibrium with the solar wind.

Useful for stationkeeping? (2, Interesting)

GreenTom (1352587) | more than 4 years ago | (#33072472)

Neat. Anyone have an order-of-magnitude idea if this could be used for stationkeeping on sats in Earth orbit or for attitude control in deep space missions? Just wondering if it produces enough torque to control a real spacecraft. IIRC, for most spacecraft fuel for attitude control is the limiting factor on mission duration, and I think in some cases (e.g., Kepler) it's the only expendable. Could a spacecraft using this technique have virtually unlimited life? If you're solar powered and don't burn fuel, what limits lifetime-- dust on the solar arrays? Battery degradation?

Re:Useful for stationkeeping? (1)

strider200142 (1279440) | more than 4 years ago | (#33072608)

Radiation damage!

Re:Useful for stationkeeping? (5, Insightful)

gstoddart (321705) | more than 4 years ago | (#33072616)

Just wondering if it produces enough torque to control a real spacecraft.

What, exactly, do you mean by a 'real spacecraft'.

IKAROS is real. It's in space. It's actually using this.

Have I missed something? From what I can tell, this is about as real as you can get.

Re:Useful for stationkeeping? (2, Interesting)

GreenTom (1352587) | more than 4 years ago | (#33073398)

Fair enough, and didn't mean to imply that IKAROS is not real. But, IKAROS is a technology demonstrator. As far as I can tell, the solar sail is the payload, and it's performance requirements are based around testing the solar sail. I was wondering about the amount of torque this kind of setup produces, and if this technology is a potential alternative to thrusters for bleeding the reaction wheels on future spacecraft.

Re:Useful for stationkeeping? (1)

gstoddart (321705) | more than 4 years ago | (#33073540)

But, IKAROS is a technology demonstrator. As far as I can tell, the solar sail is the payload, and it's performance requirements are based around testing the solar sail.

Well, if it's got a working solar sail, and using LCD technology to generate torque ... wow, what a hell of a demonstrator.

But, yes, I see your point. Of course, now that they've shown both of those technologies, I'm sure someone will see what practical use they can put it to.

Re:Useful for stationkeeping? (0)

Anonymous Coward | more than 4 years ago | (#33077008)

Without seeing more data I'm not sure this has been successful. All the data I've seen is that they managed to change an attitude rate (and almost instantly it looks like) and that correlates to when they started turning on and off lcd's. There doesn't seem to be any acceleration (because the plot appears to be 2 relatively straight lines) but more of an instantaneous change in attitude rate. Maybe all they were trying to achieve was to reverse the rate and then maintain the new rate, if so why don't we get a zoomed in plot of the much more dynamic sections of the plot.

Additionally, while I know a good bit about LEO space environments I'm much weaker elsewhere. Could this have been caused by magnetic torques created by powering the lcds?

Note to previous posts-certain satellites already dump momentum (or create it depending on your perspective) using magnetic torques.

Re:Useful for stationkeeping? (1)

santiagodraco (1254708) | more than 4 years ago | (#33074084)

No offense, but I'd think it is pretty obvious that this is a proof-of-concept and any interpretation that this is in any way billed as "ready for prime time" shows a complete lack of understanding of the real accomplishment here. It also devalues what's been accomplished.

This is a MAJOR accomplishment. Like many other early stage technologies it might not be practical but will most certainly pave the way for very practical applications. You do realize that this essentially represents free energy for both powering AND maneuvering space craft, right? About the only thing you'd need with a spacecraft built using this kind of technology is thrusting mass for maneuvering in gravity wells and/or takeoff/landing from the surface of a body (looking much further out).

Certainly a number of overall technologies will need to come together for this to be applicable for anything beyond use for satellite positioning. The use of this for a space faring craft will be faced with a laundry list of other techology hurdles, such as:

1. Mass/scale engineering. What would it take to build a sail large enough to provide inertia but can remain rigid enough to actually move a spacecraft module.
2. What are the affects of long term solar radiation on the solar/lcd panels? Will they survive the hard radiation of the "solar winds" long enough to make travel worthwhile?

Another question concerns the math around the acceleration of the object. I don't have a clue myself (but it would be interesting to look into). Remembering that the solar radiation used by the sails is travelling at the speed of light we need to calculate the acceleration of the body over time. I think we'll find that even though acceleration is slow it is also continuous, so you can reach EXTREMELY high speeds over time. Here's a quote I pulled from http://www.planetary.org/programs/projects/solar_sailing/facts.html [planetary.org] :

"The real advantage of solar sailing is that, unlike a chemical rocket that applies a lot of thrust for a very short time, sunlight hitting the sail applies thrust continuously. In 100 days, a sail-propelled craft could reach 14,000 kilometers per hour. In just three years, a solar sail could reach over 150,000 miles per hour. At that speed, you could reach Pluto in less than five years."

Pretty awesome stuff.

Re:Useful for stationkeeping? (0)

Anonymous Coward | more than 4 years ago | (#33074692)

"The real advantage of solar sailing is that, unlike a chemical rocket that applies a lot of thrust for a very short time, sunlight hitting the sail applies thrust continuously. In 100 days, a sail-propelled craft could reach 14,000 kilometers per hour. In just three years, a solar sail could reach over 150,000 miles per hour. At that speed, you could reach Pluto in less than five years."

Are you assuming too much here?

Your source of power (sunlight) becomes progressively weaker with distance. The inverse square law [wikipedia.org] must come into play here.

Was that taken into account in the calculations?

Re:Useful for stationkeeping? (1)

Low Ranked Craig (1327799) | more than 4 years ago | (#33075240)

Well, then you need the launching lasers on the moon to provide supplemental thrust.

Re:Useful for stationkeeping? (1)

Anomalyst (742352) | more than 4 years ago | (#33076924)

Why sink yourself into another gravity well, or put them where this is still plenty of sunlight. Put them in the asteroids.

Re:Useful for stationkeeping? (1)

BJ_Covert_Action (1499847) | more than 4 years ago | (#33075164)

That's a good point regarding momentum dumping. I am also curious about what kind of pointing accuracy they could acquire with this method as the primary attitude control system. Apparently, it works well enough to steer the spacecraft over long, gradual thrust maneuvers, but I would be very surprised (pleasantly so) if it could achieve the kind of pointing accuracy that reaction wheels give...or hell, even spin stabilization. I suppose we'll have to wait and see.

Re:Useful for stationkeeping? (2, Interesting)

mangu (126918) | more than 4 years ago | (#33076186)

if this technology is a potential alternative to thrusters for bleeding the reaction wheels on future spacecraft.

I suppose that the idea is to make momentum dumping unnecessary. If the torque is always perfectly zero there will be no momentum accumulating on the wheels.

Re:Useful for stationkeeping? (1)

stanlyb (1839382) | more than 4 years ago | (#33072664)

Not deep space station, but close sun range station, like Venera, Mars, Mercury...

Re:Useful for stationkeeping? (1)

asukasoryu (1804858) | more than 4 years ago | (#33074100)

Magnetic torquers [wikipedia.org] are already in use and would have the same benefits/limitations as these LCD thingies.

Magnetorquers are lightweight, reliable, and energy-efficient. Unlike thrusters, they do not require expendable propellant either, so they could in theory work indefinitely as long as a sufficient power source is available to match the resistive load of the coils.

Re:Useful for stationkeeping? (1)

osu-neko (2604) | more than 4 years ago | (#33074736)

Magnetic torquers [wikipedia.org] are already in use and would have the same benefits/limitations as these LCD thingies.

Not exactly. The OP asked about satellite station keeping AND deep space missions. The magnetic torquers may work fine for the former but not for the latter. They don't have the same benefits/limitions, they are in fact much more limited, being only useful while in orbit around planets with significant magnetic fields. The LCD thingies work whereever the sun shines, which is a much larger volume of space (although still essentially limited to the inner solar system).

Re:Useful for stationkeeping? (1)

Bruce Perens (3872) | more than 4 years ago | (#33075960)

Magnetorquers need an ambient magnetic field. The terrestrial one is close and reliable. The solar varies between a zero-crossing with polarity reversal and a maximum on an 11-year cycle (a complete two-reversal cycle every 22 years). I haven't found a figure for its RMS power at earth orbit but I guess the inverse square law applies.

Re:Useful for stationkeeping? (4, Interesting)

Bruce Perens (3872) | more than 4 years ago | (#33076238)

It seems you don't get solar wind in a magnetosphere, so the two systems each work best where the other won't.

Re:Useful for stationkeeping? (1)

Bruce Perens (3872) | more than 4 years ago | (#33079498)

But I just confused solar wind and light pressure. Different phenomena.

Re:Useful for stationkeeping? (1)

Larson2042 (1640785) | more than 4 years ago | (#33074578)

Neat. Anyone have an order-of-magnitude idea if this could be used for stationkeeping on sats in Earth orbit or for attitude control in deep space missions? Just wondering if it produces enough torque to control a real spacecraft. IIRC, for most spacecraft fuel for attitude control is the limiting factor on mission duration, and I think in some cases (e.g., Kepler) it's the only expendable.

You are correct that fuel for attitude control is generally the limiting factor for spacecraft (useable) lifetime. Using solar sails for attitude control would be possible, I think, for spacecraft operating far enough away from a planetary atmosphere. Otherwise, drag from the sail would certainly overwhelm solar pressure. So, though it may be possible, I'm not sure how economical it would be to use for stationkeeping. I would be interested in seeing a trade study between electric propulsion (another low thrust over long duration type system) and solar sails. Solar sails would probably mass more and take up more volume than an equivalent EP system, but would not require nearly as much electrical power, which would reduce solar panel size and save some mass and volume there. Bottom line, though, is that with the state of solar sail tech right now, it'll be a while before anyone tries using solar sails in such a manner. Most solar sail applications I think you'll see is as the main propulsion system getting craft between planets. That's where the greatest benefit of low thrust, but long duration burns that don't require propellant or little to no electric power will be.

Could a spacecraft using this technique have virtually unlimited life? If you're solar powered and don't burn fuel, what limits lifetime-- dust on the solar arrays? Battery degradation?

Aside from propellant, the big limit is degradation of solar panel generation capacity (from atomic oxygen, radiation, etc) and battery capacity that also degrades over time. Moving parts (like momentum or reaction wheels that control spacecraft pointing) can also wear out. Space is hard on lubricants. Then there are things that can ruin your day like computer errors from radiation effects (like the Galaxy 15 spacecraft) and impacts from space debris. So while eliminating the need for attitude control propellant will improve spacecraft life and is a worthwhile endeavor, don't count on getting unlimited spacecraft life any time soon.

Re:Useful for stationkeeping? (1)

wagnerrp (1305589) | more than 4 years ago | (#33075054)

Solar pressure at Earth's orbital distance is around 4.6 Pa for absorption, or double for reflection. While the force will certainly build up over time, you're not going to be using it for direct attitude control. You would use momentum wheels or CMGs, and then use solar pressure to bleed off energy and prevent saturation.

Re:Useful for stationkeeping? (2, Informative)

mangu (126918) | more than 4 years ago | (#33076116)

for most spacecraft fuel for attitude control is the limiting factor on mission duration

Not for geostationary satellites. For those, inclination control consumes about 90% of the fuel. Drift control depends on the longitude where the satellite is, but it typically consumes 90% of the rest, so attitude control consumes only a few percent at most of a geostationary satellite fuel budget.

There are already some commercial geostationary satellites that use solar radiation pressure for attitude control. Depending on the satellite model, this can be done either by setting each solar power panel at a slightly different angle or by having small auxiliary reflective panels that can be turned to the specific angle needed to apply the needed torque to the satellite.

Actually, the needed correction is small, because satellites are designed to be more or less symmetrical to begin with.
 

Re:Useful for stationkeeping? (1)

Bruce Perens (3872) | more than 4 years ago | (#33076198)

The sail and spacecraft will receive an electrostatic charge transfer from the solar wind, I think. It might get really large over time. I guess this would tend to drive away dust.

LCD? (2, Funny)

r00tyroot (536356) | more than 4 years ago | (#33072530)

Now if only they could equip the spacecraft with some sort of LCD Soundsystem.

Re:LCD? (3, Funny)

sconeu (64226) | more than 4 years ago | (#33072626)

Not a good idea. They'd probably use Sony components, and because it has to do with audio, it would have a rootkit.

Re:LCD? (0)

Anonymous Coward | more than 4 years ago | (#33073622)

Not a good idea. They'd probably use Sony components, and because it has to do with audio, it would have a rootkit.

If Independence Day has taught us anything, the aliens will try to pirate our music and we'll take control of the mothership! Everyone (on Earth) wins!

Re:LCD? (0)

Anonymous Coward | more than 4 years ago | (#33082294)

They would be losing their edge if they did that.

Now that is advancement! (1)

PmanAce (1679902) | more than 4 years ago | (#33072594)

Good for Japan. Too bad other countries are not collaborating and taking advantage of this advancement, or are they?

Re:Now that is advancement! (1)

nobodylocalhost (1343981) | more than 4 years ago | (#33072784)

What country? It's ZAFT technology! :D

Re:Now that is advancement! (1)

osu-neko (2604) | more than 4 years ago | (#33074838)

Good for Japan. Too bad other countries are not collaborating and taking advantage of this advancement, or are they?

They will. The Japanese are not the Soviet Union, they're not going to keep the technology under wraps and prevent anyone else from learning how it was done. The Cold War is over. They'll be articles and papers and such. Welcome to the 21st century. This was invented on Earth. People on Earth will take advantage of it. The specific nationality of the inventors is largely irrelevant. Humanity benefits, and only living fossils from the previous century will get worked about where specifically on Earth it was invented...

Re:Now that is advancement! (1)

osu-neko (2604) | more than 4 years ago | (#33074866)

get worked UP, that is...

onwards to mars... (0)

Anonymous Coward | more than 4 years ago | (#33072686)

its getting hot here

It's the Loony Tunes sail! (-1)

Keyslapper (852034) | more than 4 years ago | (#33072880)

I'm not the only one that sees an analogy to Daffy Duck blowing on his little sail to make his boat go, am I?

And I thought they only watched manga in Japan ...

Re:It's the Loony Tunes sail! (0)

Anonymous Coward | more than 4 years ago | (#33073630)

Haven't read TFA but I don't think a solar sail ship could propel itself by shining a light into its own sails. Equal-and-opposite reaction and all that; the light source would try to propel the ship backwards and what photons hit the sail would propel it forward. Imagine trying to propel a fan boat by directing the fan into a parasail -- the sail would just be a drag. You can't lift yourself up by your own bootstraps. You'd do better shining the light out into space.

I believe what is being described in the summary is using LCDs to reflect photons hitting the sides of the ship into the sails at an angle, to generate torque. The LCDs are adjustable reflectors in this case.

Re:It's the Loony Tunes sail! (3, Informative)

Ungrounded Lightning (62228) | more than 4 years ago | (#33074904)

Haven't read TFA but I don't think a solar sail ship could propel itself by shining a light into its own sails. Equal-and-opposite reaction and all that; the light source would try to propel the ship backwards and what photons hit the sail would propel it forward. Imagine trying to propel a fan boat by directing the fan into a parasail -- the sail would just be a drag. You can't lift yourself up by your own bootstraps. You'd do better shining the light out into space.

Given that the light would bounce off the sail it would not cancel (as in the fan/sail case) but serve as a thrust when the light reflects backward off the sail. The forward thrust on the sail would be about twice that of the backward thrust on the craft.

While you'd get essentially the same thrust firing the laser toward the rear, it would all be thrust on the craft, none on the sail. So there might be times when it makes sense to shoot the sail. Like the one below...

I believe what is being described in the summary is using LCDs to reflect photons hitting the sides of the ship into the sails at an angle, to generate torque. The LCDs are adjustable reflectors in this case.

It sounds to me like they're using it to switch areas of the sail to diffuse reflection. This reduces the thrust by scattering the reflected light in a range of directions (some of them partially canceling others) rather than reflecting it essentially straight back. By having, say, the right side of the sail develop less thrust than the left, you turn the sail to the right. It's not "on the edge" as in right ON the edge. But it's an area of the sail adjacent to the edge in order to get the most leverage from a given area of LCD material.

You could achieve the same effect by bouncing a laser (or other light source) off a patch near one side of the sail. But that would take kilowatts per square meter to get thrust equivalent to full sun at earth's orbital distance. Why burn such amounts of power when you can just modulate the sunlight you've already got hitting the sail?

I knew it. (1)

camperdave (969942) | more than 4 years ago | (#33073610)

... and changing the reflective characteristics of parts of the sail from specular to diffuse...

I knew it. They photoshopped it. [xkcd.com]

Close but not quite (1)

pozitron969 (539857) | more than 4 years ago | (#33074390)

LCD Engine not so much. LCD Rudder... yep that fits. Nevertheless it is darn impressive. It is great to see someone working with this technology.

so (0)

Anonymous Coward | more than 4 years ago | (#33074918)

all those guys with neon lights underneath their cars are actually on to something?

Fp HoMO (-1, Troll)

Anonymous Coward | more than 4 years ago | (#33075146)

The whole concept (0, Flamebait)

Dunbal (464142) | more than 4 years ago | (#33076192)

Of a solar sail is rather neat. Problem is they can never accelerate outside of our solar system. Once they hit the termination shock that's it, no more power. I wonder if someone has done the math to see what the max theoretical speed they could reach is. Of course they could probably do more if they put the sail away, slingshot around Jupiter back close to the sun and deploy the sail again once they pass the sun.

The problem however is that the "sail" only works in one direction - "away from the sun". Unlike a sailboat which can sail at an angle to the wind because it has a keel and can therefore push back against the wind, the only thing a solar sail can do is spin on its axis. It cannot change direction on its own. And the pressure you get decreases dramatically with distance from the sun, too. Still, nice to know the concept works. I'm sure practical applications will be found. This is not a method of interstellar travel, however.

Re:The whole concept (1)

Bruce Perens (3872) | more than 4 years ago | (#33076400)

You can tack using reflection. What you say would be true if it only worked by absorption.

Re:The whole concept (1)

Bruce Perens (3872) | more than 4 years ago | (#33079512)

Oh, the reason you didn't know about reflection was that you were confusing solar wind and light pressure. Easy to do. I did it too.

Re:The whole concept (0)

Anonymous Coward | more than 4 years ago | (#33078016)

In true "Mote in God's eye" style, you can push it with orbital lasers. If you really need it.
Of course, the whole point in a solar sail is to spend nothing on fuel; you can go chemical+ion otherwise.

But does it get HBO? (0)

Anonymous Coward | more than 4 years ago | (#33076234)

I have a 32-inch LCD attitude control device in my living room. It's quite effective when houseguests start getting restless. The next logical step in this technology I think would be getting the spacecraft to respond to alcohol.

It spells out: (1)

Tablizer (95088) | more than 4 years ago | (#33078932)

"Eat at Joe's"

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