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."

A Crookes Radiometer?

[Mad-Bassist]

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

Next up...

[peacefinder]

Downwind faster than the solar wind!

Useful for stationkeeping?

[GreenTom]

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?

[GreenTom]

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?

[mangu]

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?

[Bruce Perens]

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

Holography

[Bruce Perens]

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.

Re:All the torque that's needed

[mangu]

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.