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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.
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
Well then we must OUTLAW ALL FORMS OF IT and discontinue any research on the subject!!
...wait a second, you said terrestrial navigation aid. Heh. I thought it was terrorist navigation aid.
Keeping
Maybe it's time to rename the thing to the "Galactic Positioning System." Seriously, this thing seems to have the potential to make space probe control and navigation much easier and more accurate. It should be very interesting to see what applications come of this.
"No, no, no. Don't tug on that. You never know what it might be attached to."
This opens up so many possibilities! Like the article mentioned, satellite station keeping for one. Also, we would know exactly where they were (well, down to a few dozen meters at least) for avoidane and things like that.
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. I know there is a project to map the sky's debris, forgot the link. Now, astronauts could know in real time where this stuff is.
Using this for navigation might not work now. As far out as you are, the satellites are really close together, and any errors you see now are going to be much larger. But, we could place GPS satellites orbiting other bodies to use for solar system navigation. LIke i said, lots of possibilites.
http://www.google.com/search?hl=en&lr=&ie=UTF-8&o
OH NO!!!!!
now what am I going to do?
now i am not safe anywhere from the government tracking me with GPS
They must have grown suspicous during my occasional trips to the mother ship
now we will be found out
*sigh*
i knew the anal probing days had to come to an end
The Borg assimilated my race & all I got was this lousy T-shirt
Maybe I'm missing something here, but what makes the results so astounding? Did the experimenters think the GPS satellites transmitted/responded in one direction only (toward Earth)?
Attach GPS transmitters to space debris? Once you find the debris, why not clean it up :)
If they know where the debris is to tag it, how come they don't know where it is before it hits something?
Also, although I am no expert, this sounds as feasible as keeping inventory of a wheat field.
It seems more feasible to advance our radar technology and evolve computers to track and keep tabs on potential collisions with unknown objects...
isnt this sort of backwards-engineering against the DMCA?
is the RIAA going to sue NASA now?
Bruce
Bruce Perens.
Most of our space craft ARE in orbit around the earth. This would be great for satellites, especially microsatellites. These are usually under 100kg and could be used for anything from satellite observation and diagnostics to cheap comm sats to HDTV mobile cameras. This experiment could help drive their cost down as it would mean that they could use a cheap GPS receiver for guidance instead of some clumsy, custom method. The US Air Force has some interesting ideas. As does this New Scientist article.
People usually just moderate me down because I'm the grammar nazi. I deal with it. You should deal with it too.
Keeping
My Cache is located at N 37 50.047 W 122 13.809 A 56,000 km. It contains a compass, a dollar bill and a 5kg nuclear core. Please sign the log.
"Get them before they get....
Bruce
Bruce Perens.
Now maybe NASA can tell whether their probes are 100 meters or 100 feet away from smacking into Mars.
----------
I am an expert in electricity. My father held the chair of applied electricity at the state prision.
I don't know much about how GPS works, but I have a basic idea. The system determines the time it takes to bounce signals to a few different satellites and then triangulates where you are based on the determined distance from each satellite.
That works great when the distance between you and one of the satellites is the same or somewhat less than the distance between the satellites themselves. But out in space, even if they only go a small fraction of the way to the moon, the distance to ANY GPS satellite is going to be so much further that the difference in "ping" time from one satelitte to the next is going to be minimal.... which means your ability to triangulate where you are gets worse and worse. In fact, I don't think this would be reliable except for orbiting satellites. And I am sure orbiting satellites have been doing the same thing via ground stations (non-GPS signals) for years. So how useful is this? Unless we plan on setting up hundreds or thousands of GPS sattellites on the way to Mars (or to the moon for that matter)... but there's already this cool triangulation thing you can do with a few big natural satelittes... the sun, earth, and nearby planets. Last I checked that's totally free.
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.
;-)
"It is a greater offense to steal men's labor, than their clothes"
O No! Now the aliens will be able to use them against us!
Better start sending positionning signals into space TODAY, because when we'll reach warp drive capabilities, we'll travel faster than the radio signal, and I don't want any excuses for those people to be Lost and waiting for the signal to catch up on them.
--- Metamoderating abusive downgraders since my 300th post.
"...Testing this experiment has been a long time in coming, and we were worried that radiation may have damaged the GPS receivers."AMSAT President Robin Haighton, VE3FRH
Off-the-shelf components promise to decrease the cost of missions, but what risks are we taking by doing so?
Few companies use Gallium Arsenide (GaAs) as a substrate in the manufacture of their semiconductors due to its cost. It is brittle, and does not possess a native oxide (used as an insulating layer). Consequently most companies use good ol' Silicon (Si). One of the benefits of devices built on GaAs, is their capability to function normally in a high-radiation environment. They are said to be radiation-hardened.
Should a device need to be radiation-hardened, it would most likely need to be manufactured in another company's fab, using/developing a new process.
Even if the software was written today, and a satellite was ready to be deployed tomorrow, it'd be a long time before we had an autonomous and station-keeping satellite...simply due to the time needed to build a radiation-hardened device. It'd just be a matter of time (and statistics) before a Si-based device malfunctioned and took out several other satellites along with it.
Existing satellites will likely be fine, but as they are EOL'd I would expect their replacements to have this technology. In the interim, maybe satellites can be built with the capability for an upgrade module that NASA can intall for them at a later date? --providing another market and decrease TCO for companies/governmments that require satellites.
Bruce, How about asking HP to set up a page for ideas. There are many ideas out here, that HP could look at and take up iff they are feasiable. You know that many in the O.S.C. simply want to see our ideas make it.
Making use of Earth-Sun Lagrange points, couldn't we develop a second tier of strong-signal positioning satelites to aid navigation? Is this something that could be made feasible or would the distances involved and the relatively low number of reference points make it imprecise and ineffective?
I think this is something that needs to be done for the benefit of Man. With the advent of an effective and universal system of navigation in space, its privitization would be ever more likely.
Pax Digitalia
- Using software to wash SEU's out of cheap flight-RAM
- the use of the adapter-ring as a satellite in it's own right
- The entire MicroSat concept in toto
and etcetera, as one of the techniques routinely employed thruought the non-amateur aerospace industry. Thanks again.Now, get out of the way while we sell all your spectrum to the highest bidder!
73, de Gus
Eight Papa Six Sly Mongoose
I'm skeptical of the practical uses of GPS by space objects. Here's my reasoning:
By using GPS, you are limited to the locational accuracy of the GPS satellites. How old are those satellites? Surely some aspect of the technology they use to determine/maintain their own position has advanced in the time since they were launched. Hence, I would expect a new satellite to be better able to know its position without using GPS.
But hey. Research whatever you like, usually some good will come from it.
I had the pleasure of working on some of the first test satellites (circa 1991)... These worked at LEO orbits (LEO is below the GPS satellites, which is below geostationary), so they had the advantage that they operated in a manner relatively similar to earth-bound units.
Three major differences:
- speed and altitude limitations removed (the government doesn't want these guiding missles)
- satellite reacquisition time reduced. Going fast means that you'll have to change satellites used for the calculation much more often. Back in the day of single-channel receivers, this was a major concern.
- vehicle dynamics set to assume an orbit, not some low earth speed.
Here's a great page with some info & diagrams of what's going on. It also shows how a signal can be received from a higher orbit: it listens to satellites on the other side of the earth. This is refracted through the ionosphere, and a lot of math is probably used to compensate (actually the military version of gps uses two frequencies - the ionosphere modifies each one differently and, knowing this, can be corrected better).
The RADCAL satellite took measurements, but didn't use the GPS signal for navigation. REX-II actually used a closed loop system to stabilize the entire satellite. The attitude control system is an essential part of any satellite, since it points the antennas to the ground and the solar cells at the all-important sun. Usually, there are many different types of sensors (horizon sensors, magnetometers that compare the current field with a predetermied map of the earth, star sensors, and gyros), and typically none of these sensors alone provides a complete attitude. The fusion between all these sensors, with various levels of error and fault tolereance, is a really tough job! So, a small, light gps adds a lot of good information to the equation, and can serve as the primary sensor, or as a good backup.
We used a modified trimble gps unit with 4 antennas. This unit was originally designed to determine the attitude of fighter planes, but we used modified software to work in space. One antenna read the main GPS signal, while the other three measured the phase difference between themselves and the main signal to find the difference in distance to the satellites.
Side note about the fighter jet version of the software: The differential positions of the antennas were used to calculate the attitude. I know what you're thinking: why 4 antennas to solve 3 unknowns (pitch, yaw, roll)? It turns out that wing flex (since these were spread out as far as possible, which meant 2 were on the wings) had to be taken into account. Besides that, the extra antenna provided improved coverage in case the fuselage blocked an antenna.
We used these units sucessfully in many leo satellites...
HIV Crosses Species Barrier... into Muppets
I'm just wondering if it's possible to measure the speed of the spacecraft relative to Earth using the Doppler effect.
The Raven
I bet the robinsons (lost in space) might have liked this :) (/joke)
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ping -f 255.255.255.255 # if only
1) On the now-dead experimental Delta Clipper vehicle (used to test concepts for a later single-stage-to-orbit design), 3 GPS receivers were used on the vehicle for navigation. This vehicle did not have an inertial platform - it got all of its positional data by GPS.
2) GPS guided dead-fall bombs. These bombs have steering fins, but no propulsion. Drop them from a plane, and they steer their way towards the target.
3) GPS-giuded autopilots on Coast Guard helicopters. Searching at sea is very hard - with no landmarks, flying a consistent search pattern is extremely difficult. No problem - turn on autopilot, and it uses the GPS to automatically fly a perfect search pattern. As a bonus, the pilot can spend all his time looking out the window for any survivors, instead of having to fly the craft.
The Universal Position System would sound really cool, but there's a certain kickass delivery company that already has dibs on any decent acronym.
You cannot apply a technological solution to a sociological problem. (Edwards' Law)
Swell. Cheap and accurate guidance for ballistic missiles.
This would certainly offer a way of learning how to do efficient targeting. If we really are going to develop starwars, then targeting of high speed items becomes very important. Your approach would allow us to develop this and do something useful. I use to think that a net device with ion engine could do the trick, but it would take a long time to pick up very little. Too bad NASA and USAF move slowly on just about every thing.
Seeing this artical has given my a Question, I wonder what class amateur Radio licence you need I wonder what band they are useing, ie is it the 2meter (ya right wavelegth probably to long and too low of a frequency) I know it is not the 6 meter band (not alowed to do 6 meter uplinks according to the FCC rules) so it must be eather the 70cm or the 23 cm bands. does any one know, I nearly forgot about this option of amateur radio, and now I want to try (I took the exam on the 22th and I am just wait for my name to show up in the FCC's database, it should only be a few more days.
"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."
This is the first time I've the word apogee used without reference to the developer!
But then, I'm not a native English-speaking guy.
It's amazing how many of you slashdotters don't know the first thing about how GPS works - yet you're willing to make wild guesses. The GPS satellites don't receive a signal from your hand-held GPS unit. The GPS satellites are not in geo-syncronous orbit. The GPS satellites don't have any idea about their position. The GPS satellites don't have antennae that point only at the ground.
The GPS satellites constantly transmit the time (UTC/GMT). Controllers on the ground track their positions and make position corrections with little thrusters (yes, I guess some day they will run dry). Your hand-held receiver receives the signals from all the GPS satellites it can hear from and using the minute differences in time (plus maybe Dopler shift & signal strength), and knowing where the specific satellites are supposed to be, it can calculate it's own position within a 3D cube. This 3D position is then translated to a spherical position relative to the surface of Earth.
Surveyors use DGPS (Differential GPS) to get measurements down to centimeters or less. They set up a station at a known position on the ground nearby and it sends position correction data to the surveyors GPS unit.
GPS is so much better than Loran, Omega and RNAV.
This little test showed that objects in Earth orbit can use the GPS system to determine their position. It does not prove that the GPS system can be used to navigate into the solar system - it might, but this test didn't cover that idea. We'd need to launch some probes into the solar system (outside of Earth orbit) to test this idea.
I expect flames for accusing slashdotters of being ignorant, so I choose to remain anonymous.
But, we could place GPS satellites orbiting other bodies to use for solar system navigation.
But that would wreck that old cliche of Science Fiction: "Lost on an alien world, with no idea of how to get back to base."
And don't talk to me about Cell Phone satellites!
One line blog. I hear that they're called Twitters now.
Apogee is not a brand name or company of the GPS receiver they used. "Apogee" and "Perigee" are used to describe orbits of satellites in an elliptical orbit around the earth. Apogee is the far distant position in the orbit, say 60.000km and Perigee is the closest, say 500km.
Another one I've thought of for awhile: orbit large sheets of very strong thin cloth (say tight woven kevlar) going in the other direction. Spin them to keep them opened out. Debris will hit, be swept up into one place, lose energy and deorbit. it would be the same effect as hitting a curtain with a stick - the forward motion would be checked, turned into deformation motion of the fabric sheet. One sheet could catch one big item or many small ones.
If nothing else the swept-up debris will be in a more convenient form to laser and deorbit.