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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."
Uh, No. SA has been turned off since the Clinton administration and hasn't been turned back on. Ten feet or so is the best accuracy you're going to get without using differential gps.
First.. Space Junk.
GPS is launched into an orbit some 12,000 miles above the Earth's surface. That orbit has a grand total of about 50 satellites split into 6 different, non-overlapping planes and slightly different altitudes. There are very, very few satellites that go out that far and none have a circular orbit within a few hundred miles of the GPS satellites. Very, very little chance of a collision.
Also, from that height, the satellites lack enough fuel to deorbit or be sent into the sun. In 1992, my Univ of Colorado aerospace engineering lab went down to the control center and we had a nice tour. I asked the officer giving the brief if they intended to establish some sort of parking orbit for dying satellies as they get phased out. He indicated that it was something they would consider as the constellation gets built out.
Secondly..
Paying the bill.
GPS was encrypted from Day 1. The lower resolution receivers we use just are allowed to decrypt the satellites. It is very difficult to get the higher resolution channel.
The US government is perfectly willing to let the other countries contribute to the costs associated with running GPS.
But..
You might want to consider why the other countries are willing to spend billions on a redundant system rather than pay into GPS or use it for free.
When someone spend billions rather than use a free service, something is up.
The US military adamantly refuses to free any of the control of the system up. It is a US *military* asset. As such, it has military utility. They have completely thrown off the commercial channels in the past while engaging in military activities in a region by jiggering with the output to cause the locations to be off. (They can also turn off all the commercial channels on satellites flying over Afghanistan, then turn them back on before the reach the US, for example).
The rest of the world seems to have some qualms about handing the world's major navigation system to a single provider, for some reason.
all the sattelites do is send out signals of what time it is. they all have atomic clocks on board and just send it out. each device knows where the sattelites are (if i'm not mistaken, either they know or they ALSO send out a signal of where they are, but how are they supposed to know where they are? GPS?) last i heard there were 26 or 27 sattelites operating (50 is how many have ever existed, i'm guessing). So your GPS device also has a clock on it, and it gets a signal from 3 or 4 sattelites (4th for altitude if you want it, or more just for more accuracy) and it compares the time to its own and this way it can know exactly how far away each sattelite is, and it triangulates its position. The clocks work in hundredths of seconds, but the recievers can make these times more accurate by looking at when each hundredth of a second starts and ends blah blah blah. it's a lot more simple than you would think if you just learned about them.
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How naive of you.
US, and specifically those who wrote and otherwise endorsed PNAC have been doing everything possible to stop the development/deployment of Galileo - GNSS (EU GPS initiative). US isn't providing the rest of the world with global navigation technology out of its heart's content. It's a tool which gives corporate interests as well as military complex a dominant role. There are billions of dollars involved ($12bn and growing), as well as geo-political element of control. Imagine if there was a conflict between China and US in the next decade. Do you honestly believe Pentagon would let the Chinese to utilize GPS in order to strike US targets?
Paul Wolfowitz was one of those people who was (and still is) opposed to any kind of GPS which isn't under direct jurisdiction of United States. Now that the deal has been reached, it leaves no choice for the hawks to accept the fact that US GPS hegemony will be broken in few years. Competition helps everyone.
There is also the commercial aspect to it. Galileo, once fully operational by 2007, would suck a huge amount of revenue from GPS. US officials had many reasons to stifle competition in order to ensure GPS monopoly.
Read the paper on detailing some of the drama and US' sabotage of EU independent GPS system here
There are multiple bits of information buried in the data.
g ps /gps_f.html
There is the carrier frequency.
Then each satellite has a specific identifying signal for each channel called a psuedo random number.
Then, it layers in a telemetry data packet as part of the actual data transmitted
http://www.colorado.edu/geography/gcraft/notes/
Get over the ambiguous wording.
2. The satellite launched was a Block IIR vehicle. Block IIR-M and IIF vehicles are still in a very low orbit (close to sea level..haven't been launched.)
3. We can't burn satellites in from semi-synchronous orbit (the GPS orbit) using today's technology. When they're disposed of we kick them away from the earth a couple of hundred kilometers. Orbital degradation is slight at semi-synchronous, but the satellites will interfere with each other in about 6,000 years. I hope we'll be able to clean it up before then.
4. GPS Signals arrive on two frequencies, L1 (L1 = 1575.42 MHz) and L2 (L2 = 1227.6 MHz). C/A code (which is FREE as in air to civil users) is modulated onto the L1 carrier signal. It has never been encrypted. It has been degraded (selective availability, the method of degradation, was turned off in 2000) but is now every bit as accurate as the military signal. The only significant advantage the military receivers have is the ability to correct for ionospheric defraction using both frequencies.
5. The major driver behind Galileo (EU GPS) is economics. Basically the US has a handle on a 12 billion dollar industry and the EU wants its share. They're expecting to charge money for the same service the US gives out for free! Somebody failed economics.
Feel free to respond with any questions, I'd love to answer them.
You are WAY off.
But in reality, space does not clear after an explosion near our planet. The fragments continue circling the Earth, their orbits crossing those of other objects. Paint chips, lost bolts, pieces of exploded rockets--all have already become tiny satellites, traveling at about 27,000 kilometers per hour, 10 times faster than a high-powered rifle bullet. A marble traveling at such speed would hit with the energy of a one-ton safe dropped from a three-story building. Anything it strikes will be destroyed and only increase the debris.
With enough orbiting debris, pieces will begin to hit other pieces, fragmenting them into more pieces, which will in turn hit more pieces, setting off a chain reaction of destruction that will leave a lethal halo around the Earth. To operate a satellite within this cloud of millions of tiny missiles would be impossible: no more Hubble Space Telescopes or International Space Stations. Even communications and GPS satellites in higher orbits would be endangered. Every person who cares about the human future in space should also realize that weaponizing space will jeopardize the possibility of space exploration.
and
These satellites are already at increasing risk from space debris. At any moment, only about 200 kilograms of meteoroid mass are within 2,000 kilometers of the Earth's surface. But within this same altitude range are roughly 3 million kilograms of orbiting debris introduced by human activities, most from about 3,000 spent rocket stages and now-inactive satellites. Most of the approximately 4,000 additional objects several centimeters in size or larger resulted from the fragmentation of more than 120 satellites.
That's from Bullitin of the atomic scientists, the article is talking about the impact of SDI defense on increasing the danger but the general problem exists even without the additional clutter from ABM technology.
There are 4 boxes to use in the defense of liberty: soap, ballot, jury, ammo. Use in that order. Starting now.
The constellation has 4 slots per orbit, with six orbital planes. Since the satellites are at a semi-sync orbit around 12,000 Nm (nautical miles), there is no way to deorbit or send the shuttle up to fix. The shuttle only goes up around 50-100 miles, from what I've read.
Early GPS satellites, commonly referred to as Block I, were experimental and only expected to last around 5 years. These babies turned out to be over achievers and a few lasted 13 years (SVN 3, if my memory serves correct). It usually came down to degradation of the solar arrays. The Cesium and Rubidium clocks will still have one or two operational (they launched with 4), but the solar arrays couldn't generate enough electricity to last through Solar Season (a point in orbital mechanics, where the satellite spends a good amount of time in the sun or moon's shadow). On a few, they made the mistake ( or didn't anticipate) of not insulating one of the batteries well enough, and it failed faster.
Anyway, with technology, they started packing more and more extra crap on the satellites and it didn't seem to make the birds any better. I used to give the Rockwell engineers a hard time by saying, "Strap on a Block IIa solar array on a Block I bird and it'll last 20 years".
The launch schedule is planned around these predicted end of life time periods. We collect State of Health (SOH) data on every pass, since we go up on each satellite at least once or twice a day. This data helps with long term trending and will alert the engineers if it looks like a bird is going to die early.
When the bird gets to the point it can't maintain its attitude (Z-Axis pointing +/- 2 degrees, at the center of the Earth), or the electrical system is failing (either due to batteries and/or solar arrays), then a end of life burn is scheduled. The satellite is spun up, so that eletricity and hyrodzine is no longer needed to keep the satellite stabilzed, and then it's boosted as far out as it's feasible as to make it's operational slot in the orbit reusable.
In case anyone is curious about the stabilization, the satellites use 4 reactor wheels mounted on a pyramid shaped structure. Basicly, picture 4 flywheels spinning on the Egyptian Pyramids (but smaller, course!). One wheel can fail, and the other three can still keep the satellite 3-axis stabilized. GPS satellites keep the "bottom" of the satellite always pointing to Earth, as that's where the primary L-Band (what you use to get your GPS positioning) and S-band (what the AF uses to perform command and control, etc) antennas. There are electro-magnets that use computer modeling of the magnetic fields around the earth to dissipate stored energy in the reaction wheels. Otherwise, the wheels would eventually spin up to their max and no longer be correcting. Thruster firings are not an option, as it's too drastic a manueuver to maintain a precise positioning signal. A thruster firing will cause the satellite to flag it's data as not usable (almanac data).
Hope this was interesting....
John