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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.
Or am i missing something?
Gravity.
Disclaimer: Won't work if you accelerate beyond escape velocity.
Finally! A year of moderation! Ready for 2019?
Still time to chip in your contribution towards the Planetary Society's second attempt to do a working solar sail.
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).
We're all born with nothing.
If you die in debt, you're ahead.
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.
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Tilt the sail. In one direction, it will increase your tangential velocity, and raise your orbit. In another direction, it will decrease your tangential velocity, and lower your orbit.
That's the easy part. A couple of electric and magnetic fields and it'll work out.
The hard part is creating the antimatter. By the way, for warp drives we need something more exotic than antimatter. Matter with negative mass or something.
As long as there are slaughterhouses, there will be battlefields.
Only problem with that being that a million miles a second is roughly five times the speed of light. Last time I heard, it's not possible go that fast.
This ain't rocket surgery.
Almost right. The revised version of 3 pages of technobabble became "Reverse Course!", not "Turn around!'
General Relativity: Space-time tells matter where to go; Matter tells space-time what shape to be.
At the risk of replying to myself, I believe that story was first related in Whitfield's "The Making of Star Trek".
General Relativity: Space-time tells matter where to go; Matter tells space-time what shape to be.
Solar sails are nothing but gossamer (light weight) sails. If it was that easy to get something like that to generate electricity with something as thin as standard garbage-bag plastic I'm sure we would have done it before. Solar panels are pretty much a similar process related to CPU/microchip fab == silicon chip == expensive and heavy.