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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."
Seems to be getting more and more cluttered up there... even though the old ones come down eventually. Why not set them for a collision course with the sun?? Incinerate them for less space junk floating around out there, seems like a logical solution. Kinda like what mars is gonna be like in 10 years... dead rovers all over.. haha
Even a stopped clock gives the right time twice a day.
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.
the US could have encrypted the system from day one
it was encrypted from day one. they just recently changed it. (which is good and makes the rest of your post true and insightful)
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.
Not quite:
The US offered two levels of GPS; one was encrypted and only available to the military; one was unencrypted but had something called "Selective Availability" (SA) turned on which decreased the accuracy by 200-300ft.
Recently, they have turned off one of the two SA inaccuracies. The military (encrypted) signal is still more accurate (~10 feet), but now the public signal is valid to ~30 feet.
Comment removed based on user account deletion
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/
Actually the military signal is no more accurate in practice except that it offers codes on a second frequency which helps to offset phase shift and multipath. Good commercial unit use the phase information from both the civilian channel AND the military channel (they can encrypt the code but the signal phase is still available) along with the civilian codes. General accuracy of consumer models is limited to around 10m probability sphere which is actually 5m average accuracy. Good equipment using both frequencies and two antennas can get down to about 12cm accuracy in roughly a minute and centimeter accuracy over a period of time (generally 10 minutes to 2 hours depending on necessary confidence). Btw SA has been turned off for quite a while, in fact it was May 1, 2000 that presidential order turned off SA. This was mostly due to realization that military units were too expensive and not widely enough available to common troops.
There are 4 boxes to use in the defense of liberty: soap, ballot, jury, ammo. Use in that order. Starting now.
Get over the ambiguous wording.
Have you ever USED WAAS? I have it turned on in my GPS and only get a WAAS signal if I am at about 4000' ASL or higher. And I use my GPS a lot. So far WAAS has not helped me all that much. (I also know the map & compass way too) Nick Butte County Search & Rescue
Mostly the US has declared that it is 'unnecessary' for the EU to develop their own system or that the planned sytem would disrupt GPS (the planned improvements to GPS due to similar frequencies). Recently the US has come to an agreement with the EU about how the satellites will work. So it does appear that Galileo will become a reality.
Forbes magazine
EU viewpoint
Our founding fathers removed the guys in charge. Be American. Vote incumbents out.
I went back to double-check and I misread the capacity as being in pounds when it was actually in kilograms. Curse you, conventional "English" measurement system. I go now to hang my head in shame.
As a pilot with a WAAS capable IFR GPS (Garmin 430), I've looked into this. There just aren't that many WAAS ground correction transmitters yet.
Obviously you've not been caching. FIrst off, GPS isn't accurate to within 15 feet when you're in the woods. Also, nobody puts the caches in plain sight. I've been to caches where me and my kids walked around a 50 foot diameter circle for 30 minutes before finding the cache, to find out we'd walked right past it dozens of times. Many times it'll be a camoflaged ammo box half buried with twigs and leaves over it.
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.
Yes, and GLONASS sucks. Maybe even 'sucked'--I'm not sure it's still operational in any useful capacity. As I recall (I'm going from memory here), the GLONASS constellation was optimized for high latitudes--probably a Molniya orbit, or something similar. Anyway, it's more work than just putting them in a half-sync orbit like the NAVSTAR constellation for GPS.
I know a guy that was with Space Command, working GPS since the early days. He met some Soviet Major (or something) at a conference once, years later. The guy related that his tank had both a GPS and a GLONASS reciever installed. His description of each?
"GPS--very very good. GLONASS--dogshit."
My biggest problems with GALILEO?
First, the levels of precision--the stuff they're givng their police and EMS are on par with what our military has under lock and key. Which sounds harder to steal? (This may not be an issue now--been a long time since I read that.)
Second (and more importantly), it's going to be expensive. As soon as the system is working, the EU is going to require anyone that wants to use GNSS for navigation to use GALILEO instead of GPS. Some requirement about 'safety' or somesuch. And they'll tax all the receivers. And charge for each approach (I'm told they charge you for about all they can in the European airspace system--approaches, wx reports...).
Just wait. I guarantee you it will happen. Anyone flying over Europe will have to buy a GALILEO receiver. I'd bet Collins and Trimble are already lining up dual-system receivers.
--Ribald
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.
Trilateration, not triangulation.
More info here.
We have more to fear from the bungling of the incompetent than from the machinations of the wicked.
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
As someone who helps out with the local Mountain Rescue group - one of the biggest problems they now have is people going out without proper maps and compasses and only their GPS.
They then phone (cell phone) for rescue cause their GPS batteries are flat and they haven't a clue where they are.