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LCD 'Engine' For Spacecraft Attitude Control
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."
"yes, like in your video monitor"
No, I have an old fashioned Sony CRT monitor.
My wife needs that just about every month.
It's neat to see this phenomenon being used for a spacecraft.
"The only legitimate use of a computer is to play games." - Eugene Jarvis
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.
Parity: What to do when the weekend comes.
...beer
I've fallen off your lawn, and I can't get up.
I wonder what amount of torque they were able to develop with this? It seems like it was pretty effective.
Downwind faster than the solar wind!
With reasonable men I will reason; with humane men I will plead; but to tyrants I will give no quarter. -- William Lloyd
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?
Now if only they could equip the spacecraft with some sort of LCD Soundsystem.
What country? It's ZAFT technology! :D
Where is the "Ignorant" mod tag?
... and changing the reflective characteristics of parts of the sail from specular to diffuse...
I knew it. They photoshopped it.
When our name is on the back of your car, we're behind you all the way!
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.
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...
"Convictions are more dangerous enemies of truth than lies."
get worked UP, that is...
"Convictions are more dangerous enemies of truth than lies."
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?
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
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.
Bruce Perens.
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.
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.
Bruce Perens.
You can tack using reflection. What you say would be true if it only worked by absorption.
Bruce Perens.
"Eat at Joe's"
Table-ized A.I.
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.
"The only legitimate use of a computer is to play games." - Eugene Jarvis
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.
Bruce Perens.