NASA to Launch Solar Sail

arbitraryaardvark writes "Physorg reports that NASA will launch a solar sail around the end of July. It'll be the first of its kind; a previous attempt blew up. It's a small proof-of-concept gizmo, not a full-on spaceyacht. Solar sails operate on photon pressure from sunlight. They are well known to science fiction readers, otherwise not so much." C-net has coverage, too.

Comments

Re:Ah, sigh

[Anonymous Coward]

"Yeah well, Hollywood and {science, art, engineering, law, philosophy, history, fantasy, ...} haven't ever mixed well, for the most part."

There. Fixed it for you.

I'll give you a hint. Hollywood is like a marketing department at an engineering firm. They have learned very well that they don't need to understand the product to sell it. Package a movie with a couple of hunks and babes as well as some explosions and dramatic music, and nobody is going to care about its accuracy.

Re:Ah, sigh

[neokushan]

Package a movie with a couple of hunks and babes as well as some explosions and dramatic music, and nobody is going to care about its accuracy.

Well, except sad bastards like us.

Re:Let me guess...

[DigiShaman]

while FedEx is traversing through worm holes

Oh great! So FedEx will now tell me that my package was delivered. The bad news: it was delivered to me in an alternate reality. With my signature to prove it no doubt. Never mind the fact that "I" didn't get the damn package.

Beating against the solar wind?

[DerMatsi]

From TFA: "And like a marine sail, a solar sail could also bring you home. You could use the solar sail to tack your vessel, making it travel "against the wind," back to Earth." I don't see how this would be possible.. sailboats can do this because of a keel which exerts force on the water, which cannot be done in the near vacuum of space. Or am i missing something?

Re:Beating against the solar wind?

[bcrowell]

Gravity.

No, that's incorrect. In space travel, the vehicle is in some orbit, and in the absence of a force other than gravity, it's just going to continue in that (typically elliptical) orbit forever. Say you're going to Mars, for instance. You needed to match orbits with Mars, which means you're in the same nearly circualr orbit around the sun that Mars is in. (Of course you also have to insert yourself into orbit around Mars, and get yourself out of that orbit as well, but let's not worry about that for now.) Once you're ready to leave, you don't just wait for the sun's gravity to pull you downhill back to Earth. You're in a circular orbit whose radius is greater than that of the Earth's orbit, so you're not coming back toward the sun unless you can reduce your velocity.

To understand how you'd really use a solar sail, let's start with the case where you just want to increase your distance from the sun. Intuitively, you'd think that you'd just orient the sail perpendicular to the sun's rays, and let it thrust you outward. However, that doesn't work, because the thrust from the sunlight is orders of magnitude less than the sun's gravitational force. Doing that would be sort of like dialing down the strength of the sun's gravity by some tiny percentage, which would alter your orbit for a given velocity vector, but only by a tiny amount.

What you actually do is to point your sail at an angle. The sunlight's thrust then has both a radial component and a tangential component. The tangential component does mechanical work, because it operates in the same direction as the motion of the vehicle. That means it increases the vehicle's kinetic energy. The higher-energy orbit takes you farther out away from the sun.

When you want to come back, you do something similar, but you tilt the sail the opposite way. The tangential component is now in the opposite direction compared to your motion, so it does negative work, reducing your kinetic energy.

This web page has an example that calculates the optimal angle to tilt the sail at.

Re:Let me guess...

[Anonymous Coward]

Meanwhile, UPS will just launch the damn thing into a black hole and say customer service is 'working on it.'

Re:Ah, sigh

[Iron Condor]

Is there anything wrong with the idea of combining solar sails WITH Ion thrusters? Both should be light weight, not require a large energy source, and theoretical light speed acceleration.

Ion engines still need fuel. Ions, to be precise. Just because they use electricity to accelerate them (instead of some kind of combustion process) doesn't mean that the energy doesn't have to come from somewhere, so now you need an energy source. Which is either solar (cutting into your available area for a sail and becoming increasingly infeasible when you get away from the sun) or nuclear (which means enormously heavy: RTGs are many kg per Watt and a full-blown reactor weighs tons before you've generated the first Watt).