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Delta 2 Rocket Launches 50th GPS Satellite
wetshoe writes "This CNN article reports that 'the 50th U.S. Global Positioning Satellite has lifted off aboard a Boeing Delta 2 rocket.' It was sent into space to replace an aging GPS satellite. One more reason why geocaching is so much fun."
Its just you (and maybe some friends), no real pressure. Plus its an actual trek (ranges from in-city, to some caches are ones that need Scuba or moutain gear or whatever).
;-)
And with geocaching you've just got your GPS, a compass, and maybe a topographic map (if you can get one). None of this fancy cell phones with internet to tell you answers stuff
There is no god
Doesnt say if this is capable of GPS-2 or whatever its called. As someone who uses GPS to manage infrastructure, I'd like to see some more precise GPS without having to spend $20,000 on Trimble or Leica equipment.
The Doormat
If you're not outraged, then you're not paying attention.
I'm not sure how much fuel is required to break orbit and send a satellite to the sun, but I'm pretty sure that an old GPS I satellite doesn't have it. It's easier just to slow the satellite down a bit so it burns up in the atmosphere as it falls to earth, which is what they do. Every US Air Force satellite that goes up nowadays has some sort of end-of-life plan.
I guess that it costs quite a lot of money to set up and run the system, and that funding would be a lot easier to get if there was some benefit to taxpayers other than indirectly through improved military capability.
It is good that the US has made the system available effectively without restriction, however now that other nations have realised the value of such a system, it is understandable that they want to be able to operate something similar without whatever political considerations are affecting the US to affect it.
Wouldn't it be more accurate to say that the GPS satellites make geocaching *possible*? Whether or not it's fun has little to do with a rocket launching a satellite. Of course, you could say that it wouldn't be fun at all without a GPS system, since you'd have to navigate with less convenient methods. :)
"Destroy science and religion. Science would re-emerge exactly the same; but not religion." - Penn Jillette, paraphrased
The article says the satellite costs $45 million. I Googled a bit and found that the launch cost for a Delta 2 is around $50 to $60 million. The article also said the satellite being replaced is 11 years old, and at the end of its useful life, and that there are 50 GPS satellites.
Crunching the numbers, we have about $105 million to put up a GPS satellite, with about 11 useful years; call it $10 million per year. Multiplying by 50 satellites, we have $500 million per year cost for GPS. I never knew. Also, on average, each year 4 or 5 launches must happen to replace aging GPS satellites.
Note that the launch costs are actually higher than the cost of the satellite. Also, the satellite could probably be made more cheaply if launch costs were lower (instead of over-engineering it to never break, they might just launch a cluster of two in the same orbit, or just design it to be easily repaired). If and when private companies build reusable spacecraft that can carry a GPS satellite, the cost of GPS will go down a lot. A Boeing Delta 2 is completely used up in each GPS launch right now, so truly reusable spacecraft should be able to dramatically cut launch costs and still make money.
steveha
lf(1): it's like ls(1) but sorts filenames by extension, tersely
I used to work with Guidance & Navigation systems (late '70s, early '80s). One of the test sites was in the Pacific Islands. Most of the maps were originally made by the Japanese Military during WW2. It was fun finding some landmarks so we could get accurate data -- then use this data to extrapolate coordinates for the rest of the map. There's a lack of permanence to sand & coral, especially since it had been subjected to naval bombardment.
It really was great fun searching the islands for these sites, and I got paid for it too!
"Glory is fleeting, but obscurity is forever." --Napoleon Bonaparte
Differential GPS sends corrections for errors in the pseudoranges for each satellite (and in some cases, sends improved ephemerides for predicting the sat's orbit).
It can be mathematically shown that "Poor man's DGPS", i.e. "This is the lat/long the GPS says I'm at, this is my real lat/long" does not work, and may even degrade accuracy.
The good news is it's getting easier and easier to create a DGPS source. In the past, it was impossible to get raw pseudorange data from economical receivers. But nowadays, many sub-$200 OEM units are capable of it, as are some handhelds.
These are "cheap" receivers that I know of that allow for raw pseudorange and carrier phase logging:
Garmin 12-channel (Undocumented and unsupported, but it can be done. I've done it myself. Do a search for gar2rnx).
Rockwell Jupiter (Best example is the Delorme Earthmate, which Delorme advertises as being able to provide raw pseudorange/carrier data if you buy their software, GPS PostPro)
u-blox modules, I believe.
retrorocket.o not found, launch anyway?
It's not ambiguous though: this is the 50th GPS satellite, and it's being launched.
Actually, it's not even the 50th GPS satellite up there; prior to this launch, there were only 28 operational satellites. None of the original 11 are still in service, and one of the other 38 blew up on the launchpad.
So, while this is the 50th GPS satellite, it's only the 49th launch.
"Software is too expensive to build cheaply"
However, back in the 80's when Russia shot down that civilian airliner that strayed off course, President Reagan made the decision to make GPS publicly available.
DoD fought off turning off the system all together because we didn't want our enemies to use the system against us. However, with the EU wanting to launch their own and the spreading use of DPGS (differential GPS), it eventually became moot. So DoD turned it off in the mid-90s (I think it was 94...I was still a GPS operator and I remember helping doing it....just can't remember what year that was). They do, however, reserve the right to turn it back on. FWIW, DOT (Department of Transportation) wanted to add their own signal (L5), but I don't know if that got anywhere.
OK....trivia time for those who care: GPS comes with Selective Ability/Anti-Spoofing (SA/AS), which allow the signal to be jam-proof, encrypted and for only authorized users. The frequency can hop, and the signal's accuracy be purposely degraded. It was a security breach to speculate who High Accuracy Users were, but we joked it was a guy on a camel in the middle of the desert. I won't go into detail about how the above works, since I'm waiting for my Top Secret clearance for my new job flying Milstar Satellites (Air National Guard).
The satellites are basicly beacons, transmitting their current position and time to accuracy of a nanosecond. This is why the satellites are launched with 4 frequency standards, although the latest generation (Block IIF, I believe) was slated to only have 3. I haven't been involved with GPS lately, so my info is about 3 years old. There is a chance the Guard may become a backup for GPS, but I'm told its unlikely. Back to the topic. The frequency standards for the Cesium and Rubidium clocks are very precise, with the Rubidium clocks being a little better, however they were also more temperature sensitive. You can appreciate the difficulty keeping a clock +/- .1 degree celcius in space, where temperatures swing greatly from full-sun to being in the Earth or moon's shadow.
The signal leaves the satellite and travels to your GPS unit at the speed of light. The ionosphere and other atmospheric conditions will refract or delay the signal, but that can be corrected. SO if the satellites saying, "I'm HERE at this TIME," and you know the speed it traveled, you can determine the distance (roughly) from you to the satellite. 3 satellites give you 2-D position, and the 4th adds altitude. You actually triangulate to two (2) points. One on the earth, and the other about 22,000 miles in outer space. That outerspace point is thrown away. Today even the cheapest GPS units can track multiple satellites at the same time (early units tracked one at a time) and throw away some for reasons of GDOP. To get the most precise measurement, you want the Geometric Dilution of Precision (GDOP) to be the least by having the greatest angles between yourself and the satellites. If you have two satellites right next to each other (relative to your overhead view...not physically), you throw out the one that creates the narrowest angle with respect to the other satellites.
The other post is correct, 50 is the number of satellites launched (so it would be referred to as SVN50...SVN being Satellite Vehicle Number). The operational constellation only needs 24 satellites, however we'll put additional units up in anticipation of a satellite nearing its End of Life.
Remember....these are DoD assets...we don't give a rat's ass about businesses. Our job is to break the other guy's toys, save US lives and let the other guy die for his country.
John