GPS Test Successful From Outer Space

An anonymous reader writes: "AMSAT reports that the GPS experiment on the international amateur radio spacecraft AO-40 has undergone successful testing." A note on the site reads in part: "This experiment supplied and sponsored by NASA, is to determine if it is possible to get positional data outside of the GPS ring of satellites. There are two GPS receivers on AO-40, the A receiver for receiving signals around apogee and the B receiver for signal reception around perigee. ... A signal on the apogee receiver from about 52 Thousand Kilometres out with good signal levels has been received, further data is being gathered and those downloaded so far are being analysed. If this experiment goes the way I expect, it will revolutionise the way we use GPS in Space. Many future HEO spacecraft will be able to take advantage of GPS for autonomous navigation and stationkeeping." This is one of the most interesting applications of GPS technology I've heard about -- nice way to reuse what was intended as a terrestrial navigation aid.

Comments

Re:Nice....

[rice_burners_suck]

"Also, so much is said about the problems of space debris. GPS recievers can be small, small enough to attach to debris. Yes, placing it on every little thing could suck, but on the larger things that pose a real hazard."

Several months ago, I listened to a radio show where they talked about space debris from all sorts of previous missions. As it turns out, they currently track objects that are quite large, as well as objects the size of a soda can. IIRC that's the smallest they can track. All space debris, even smaller than what they can track, poses a serious hazard to satellites and more so to larger vehicles. Imagine something the size of a golf ball hitting the space shuttle at the speed of a bullet and you've got an idea of the danger. Chances are, the shuttle is designed to get hit by all sorts of stuff, but it can still cause serious damage.

Destroying the space trash isn't the answer either, as it would simply smash larger pieces into smaller pieces, and that's an even bigger mess.

For some reason, I don't think a GPS receiver can be placed on all but the largest pieces of trash. It's like mice who wanted to place a bell around the cat's neck for advance warning. They all cheered about the great idea until an old, wise mouse came along and asked, "And who will put the bell on the cat?" Besides, to attach a receiver to a piece of space debris, you'd have to intercept the debris with a vehicle. If you're going to go through all that trouble, you may as well send a garbage truck^H^H^H^H^Hshuttle and collect all the pieces.

Wild idea: How to deal with space debris.

[Bruce Perens]

I wonder if space debris could be deorbited by using laser light as a sort of retro-rocket? Light exerts pressure, and although this is a very small amount of pressure, it will accumulate if you keep pushing. So, put up a satellite with lasers, not powerful enough to melt debris but powerful enough to give it a little push. Push on the debris with the laser light from ahead of its orbit. The satellite gains some orbital energy, the debris loses some. Eventually, the debris deorbits.

Bruce

Re:Wild idea: How to deal with space debris.

[MarkusQ]

Bruce --

Great idea. One quibble though:

Push on the debris with the laser light from ahead of its orbit. The satellite gains some orbital energy, the debris loses some. Eventually, the debris deorbits.

If the goal is to deorbit the debris, we can take the fact that it loses energy as given. However, depending on the relative orbits, it isn't clear that the laser platform will gain energy. If they are appoching each other head on, for example, they both lose energy. In most cases, I suspect the effect on the platform would be a mild course correction with little change in total energy. One strategy might be:

Rule 1) Don't shoot at targets that would reduce our orbital energy (eliminating 1/2 the potential targets).

Rule 2) Only shoot at half the remaining targets, chosen so that we consistantly precess our orbit, bringing previously ignored targets onto our active list.

Another thought is that we get the delta-V even if we don't hit the target, so we can always shoot at nothing (after confirming that there is in fact nothing there) to adjust our course.

-- MarkusQ