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

Today's word is Triangulation

[Alien54]

how is this helpful?.. unless the spacecraft are in orbit around the earth, the geosync gsp satelites are going to rotate with it, so any approaching spacecraft won't really be able to use it effectivley 'cept to find out their distance from the earth, which can be done by easier means :P

So how does GPS work on Earth? The Geometry of Triangles, be it distance, angles or whatever. In GPS, it is easier to use the differance in distance for multiple satellites. Note You need more than one.

Secondary neat important fact: The Satellites orbit around the earth, and do not stand still at all relative to the earth. They are NOT geosync at all.

The Question is one of elementary geometry.

Imagine the orbits as a circle on a piece of paper, and satellites as points on the circle. If you can use triangles to find the location of a point inside the circle using those points, you can also use triangle to find locations outside the circle.

In the case of GPS and the Earth the problem is mostly one of signal strength.

With slight modifications, the logic also works in 3D.

;-)

Re:This IS useful

[phil reed]

This sounds like it would raise the issue of single point of failure; if someone managed to knock one of the GPS satellites out of orbit, a bunch of other satellites that were relying on it would then follow it out of the sky. That doesn't sound like such a great idea to me.

Unless, of course, there were multiple GPS satellites, and each satellite relyed on the positioning information returned by the majority of them. The odds of all of them being knocked out at once are much lower than just one being knocked out.

There are 24 (plus or minus 1 or 2) GPS satellites in orbit at any one time. In order for your GPS receiver to work at all, it has to receive signals from a minimum of three satellites, four if you want to get a fix that includes altitude. My commercial-grade Garmin 12XL generally shows signals from 7-8, and I've seen as many as 12 at one time.

Still, if someone were interested in knocking out communications in the united states, they would still only have to knock out the GPS ones in order to knock out the rest.

Not hardly. Satellite designers are exceedingly paranoid, and they would never rely on a single method of positioning information.