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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
The launches you should worry about are the launches they don't announce! But I guess it's no fun being paranoid if you can't point to actual new items that "justify" your paranoia!
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No, i wonder about the one's we do know about...much easier to sneak a toy or two into space. ;-)
damn, this foil is itchy.
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.
Have you ever thought that conspiracy theories are a conspiracy to make you buy tin foil? I'd worry about why it itches!
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.
What the fuck do you think the NRO does?
I'm well aware that the EU has plans of a GPS type system, however it does seem a bit unfair that the United States foots the bill for virtually the entire world's navigation system. While the system is primarily there for military means, the US could have encrypted the system from day one to avoid non-military use (which is what many other nations would do), or have offered decryption codes to US organizations to give them a competitive advantage. Instead they've offered it free of charge worldwide, even turning selective availability off so that geocaching adventure is even less of an adventure. Perhaps there's an insidius underlying motive (for example getting the world hooked on GPS while keeping their finger on the conceptual power button), but overall it's a praiseworthy thing they've done.
Alright, time for handholding:
"The NRO designs, builds and operates the nation's reconnaissance satellites. NRO products, provided to an expanding list of customers like the Central Intelligence Agency (CIA) and the Department of Defense (DoD), can warn of potential trouble spots around the world, help plan military operations, and monitor the environment."
From their site
We have our moments.
Do you guys ever have to go out into the ocean or some small unihabited island (if there is such a thing)? In the Canadian wilderness? That could be a real adventure!
Geocaching is fun because they replace old GPS satellites with new ones? wtf?
Burn the land and boil the sea, you can't take the sky from me
if there is any one appropriate physical activity appropriate for geeks
stop right there; short circuit the rest of the statement.
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 last sentence of this post should have made everyone go wtf... it makes absolutely no sense and is a completely offtopic line in itself.
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.
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 think he just hid his cache in the satellite before it went up. Darn, that is going to be hard to get.
"There is no teacher but the enemy."-Mazer Rackham
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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
The fact that this satellite is the 50th is obviously just a temporary aberration. After all, it's replacing an existing one, right? As soon as they decommision the old one, then this becomes the 49th one again.
"Software is too expensive to build cheaply"
Do you have a reference please, or did you come up with this on your own?
Although I've heard, and certainly believe, that it's possible for the US to screw up GPS, I've never heard of them actually doing it.
Do you have some reference for this? I'd be very interested to see more information about these incidents. In particular, I'd like to see what President (I'd assume the decision would be made by the commander-in-chief) allowed it and if he explained his reasoning to the public.
DGPS is more a concept than anything (use nearby readings to cancel out as many forms of GPS error as possible), and can provide anywhere from WAAS-level accuracy to centimeter-level accuracy if you're willing to take readings over several days and process them on a computer after the fact.
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
My Garmin iQue is WAAS compatible. The manual says that it is available in coastal areas. I live in San Diego and have never ONCE encountered a WAAS-enhanced signal, even while driving down the coast highway.
As the previous post would suggest, WAAS seems to only work at high altitudes... or maybe it is just prone to interference at lower altitudes. Anyone care to clue us in on this?
Yep it's off with the ability to turn it back on should the need arise. However, the political backlash would probably cost a president his re-election, so Bush wouldn't do it till after the election.
A couple more GPS IIR then the upgrade GPS will be launched, then several years after that another upgrade will start going up.
It was a very nice launch on a beautiful Florida day.
Our founding fathers removed the guys in charge. Be American. Vote incumbents out.
[For the dorks grading articles, give this a minus 10 right now. ]
Differential GPS is nice, it does depend on how close your base station is to the "rover" which is gathering the data you are really interested. If your base station is close, you can count on precisions as small as 10cm. If the rover can average some given location over many "time periods", you can probably get better than 10cm. Typically, vertical precision is about twice of horizontal precision, but this depends on the "constellation" you are seeing.
I've seen quite a few more than 4 (the minimum to calculate (X,Y,Z,T)) at any given time. Where I have run into difficulties, is at the edges of agricultural fields where there is a stand of trees next to the field. Just guessing, I would think the highest number of satellites in view was around 8. But the constellation is much more important than the number! If many of the satellites are vertical (and hence about the same z distance away from the rover), they all give about the same information and hence don't really contribute to the accuracy of the solution.
But, technical considerations ignored; if geocaching or the Digital Confluence Project gets people to get some exercise, it is all worth it.
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 get a signal from the WAAS birds all the time with my Garmin 60C. Heck, I can even pull a signal down indoors sometimes. With my 76S, I never once got a WAAS signal. I guess newer gps's are getting better at recieving...
As I said in a previous comment, the best reference are the aviation magazines. Sadly few put all the stories online.
Most places want to move to free airspace, rather than pre-designated corridors. To do so requires better knowledge of where the planes are, and where they are going (this is way more than just TCAS). They also want to improve precision of approaches to runways (where a few meters matters a lot).
An obvious component of such a system is something like GPS but with greater accuracy. Europe, Russia and others have been using this as one reason to deploy their own systems. Read the press for what the US has been doing.
(Note I am not saying that the US is doing anything illegal or immoral, just that it is trying to ensure everyone uses its system.)
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.
Selective Availability has mostly been turned off, but it still comes on occasionally, during military exercises or whatever. Warnings are issued over marine radio etc. when SA is to be in effect.
Most of the time, accuracy is indeed better than 10 feet. In my experience, it's actually about a meter.
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.
THe Slective availability option is always available. They jiggered with it as a matter of operating procedure until 2000. They can always turn it back on. Plus they try to optimize accuracy in areas of military operations (Iraq, Afghanistan). By just doing the reverse, they could increase the inaccuracy in regions. However, I doubt this could be used to large effect without impacting US military operations in a larger region. Plus, using too many such maneuvers would reduce the lifetime of the satellites (fuel is the precious, limited commodity)
Our founding fathers removed the guys in charge. Be American. Vote incumbents out.
During Gulf War 1 they had SA cranked up to the max (~300m error) until they realized that 1) the Iraqi's didn't have any GPS units and 2) there were not enough military GPS units available for all the troops. So they completely turned off SA and handed out quickly requisitioned civilian GPS units to the troops.
There are 4 boxes to use in the defense of liberty: soap, ballot, jury, ammo. Use in that order. Starting now.
narc. your just put here so that people will be thrown off.
narc
Do handheld GPS units actually "send" data, or signal or -ANYTHING- out?
Or is it 100% "silent"?
Paranoid minds want to know!
Anyone have a good general GPS book recommendation with all the latest tech and explanations ? Maybe roll your own guide too? I'd love to learn this stuff
Yeah, you're right. Over at spacetoday.net they list it as being GPS 2R-11. (For the record, the IIR is 2370 pounds.)
I went caching in the desert (where in most cases a clear view of the entire sky results in very high GPS accuracy - I've seen my GPS be accurate to within 5 feet on some caches...), and there were cases where I would literally be standing on top of the cache and not see it.
.4 miles up the canyon and then .4 miles back along the rim to reach it. Once you got to it, it was a buried can sitting under a rock.
One of the best was a cache at the top of a canyon. The first time I went there, I thought my GPS was just being inaccurate and the cache was at the bottom. That would've been too easy.
You could park 100 feet from the cache, but you had to hike
There are lots of rocks - Even close-up, this one was almost indistinguishable from any other.
East Coast geocachers are usually not so evil, probably due to the fact that those caches are in the woods and they know that their GPS units and those of the cache finders won't be as accurate. I know of one cache that can only be found at certain times due to the fact that it's in a gorge and over half the time you can't receive signals from enough satellites for even a 2-D fix down there.
retrorocket.o not found, launch anyway?
I believe the "GPS-2" referred to above is proposals I've heard to put the C/A (coarse acquisition) code on the second GPS frequency (L2) in addition to L1.
Currently only military receivers and special receivers that use extra processing tricks (aforementioned $20k Trimbles, NoVaTels, etc.) are capable of using the current L2 transmissions.
The advantage of a dual-frequency receiver is that ionospheric delay (a significant contributor to GPS error now that SA is turned off) is a linear function of frequency. Measure the difference in arrival between the pseudocodes on two different frequencies, and you can figure out the absolute ionospheric delay at a given frequency.
The end result is increased accuracy without the need for differential corrections. (Right now, L1-only receivers must rely on DGPS to eliminate errors from ionospheric delay. A dual-frequency receiver can eliminate those errors without external information.)
retrorocket.o not found, launch anyway?
I wish that GPS would be able to penetrate about 150 or so feet of water. Underwater navigation is tough enough (visability, lack of landmarks). Being able to set the coords of the boat before diving would be nice. Love to Geocache, I have 3.5 year old caches out there in the desert.
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?
Galileo was shaping up to become a reality around May of 2000. (i.e. the Europeans were getting REAL serious about putting up their own positioning system.)
Guess when SA was turned off? Guess how fast Galileo turned into a dead project after SA was turned off?
Nowadays, even if SA is turned back on, it probably won't mean much. DGPS has become far more common than just the USCG stations. (For example, WAAS/EGNOS/whatever the Japanese call their system, all three are identical with different names, which are a form of DGPS.)
retrorocket.o not found, launch anyway?
Yup, and if you need to learn how to use a compass, I'll just plug my pages about it. It is a bit dated, I hope to be able to return to it soon.
Employee of Inrupt, Project Release Manager and Community Manager for Solid
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
Thanks for the Google cache link of that paper. Does anyone know where the PDF has been moved? Or does anyone have a copy? I'd like to print it out for reading.
Yes, the europeans are developing their own GPS.
The USA stepped in and FORCED them to reduce the accuracy of the system AND make it jammable by USA forces.
Sounds to me like the USA would prefer there was "no competition" in this area, so they can continue turning it off when they want to (civilian GPS has been disabled over wide areas where US military forces are in conflicts)
Make no mistake. Like Interstate highways, GPS is a MILITARY system. It is in the USA govt's interest to have civilians and foreigners dependant on US positioning systems _only_ for the same reason any monopolist or militarist wants sole control of an arena - once the general population is dependant on the availability of something, removing it induces severe hardship.
I've been in small aircraft hundreds of miles out to sea (island hopping) when GPS has suddenly been switched off - something which carrying a spare unit has no backup for. You can't use VHF beacons, because they don't carry that far, (even when flying at emergency altitudes of 25,000 feet, using oxygen) and shipping beacons (HF) "bend" around landmasses, so are unreliable when travelling at aircraft speed (on ships you can spend several minutes looking up corrections, etc). Even a sextant is of limited use a lot of the time - and in that case a sextant is exactly what was used. Flying a compass bearing could and probably would have resulted in missing the target by far enough that there would be no fuel to retrack (and this is despite having more than twice as much fuel onboard as the estimated time of flight. Headwinds over open ocean at 10,000 feet can easily double flight times - and 10,000 feet is the maximum safe altitude without pressurisation/oxygen.
It would have been interesting to see what the results would have been if the euros had flipped the bird to the Pentagon and continued along the intended design path. Perhaps they're still doing so while saying they're not - the USA has been known to do just that in the past.
GPS users should really appreciate my website:
http://trailregistry.com
You can create maps from old track logs, and share these maps, waypoints, trip reports, etc..
Check out TrailRegistry.com, my hiking site, Maps, altitude pr
"I'd like to see some more precise GPS"
Us Olde Europeans are waiting for Galileo ;-P
For some real information, check out the NASA space junk site. The NASA Safety Standard is on the mitigation page, and the ORDEM2000 software gives you the estimated debris environment in low-Earth orbit.
Objects with perigee above LEO (about 2000km) won't decay within "human" timescales, but we keep sending up more.
When NASA sends up probes or people or whatever into space (such as mars), do they need to take into account the position and orbit of every satelite up there to make sure they don't inadvertently drive a rocket into one?
When all is said and done, nothing changes...
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
There is still somewhat of a push to get EU and others with their own birds up. It's funny to hear these conspiracy theorists about why we tried to block it. Using their own logic, we are trying to keep Iran from developing their own nukes because we want everyone else to buy ours....WTF? Yeah...thats it...
No, it's because the DoD has one objective: implement the president's foreign policy and domestic defense in the most efficient means possible. If other's launch their own satellites it creates interference (EMI, RF, etc) and increases the capabilities of our enemies. You can pant and whine about our military's economic agenda, but you'll USUALLY see this from people who've never actually put on a uniform. Does it mean it never happens. Of course not. But if it does it's usually rooted out....because, again... our #1 objectives are to make the other guy die for his country, save US lives, and break the other guys toys of death.
Did they show you the little model with the satellite rotating around the earth, keeping the Z-Axis nadir pointing, and the arrays tracking the spot-light (pseudo sun)?? I always thought that was really cool with working, tracking arrays. John
PS. No, there's not 50 operational birds. There's a min of 24 and sometimes there's 26 or so, for planned End of Life. The satellites are spun up for stability reasons, and then boosted out of the orbital plane.
You're right that the signal has not been degraded for a region. However, it is possible that we could do it if we REALLY wanted to. It would be a PITA for the crew working when they implemented it, but possible with scheduled SA/AS. The crew working would get a great write up for Crew of the Quarter (Year) and Performance Reports.... :-)
We did purposly make the signal BETTER during the first Gulf War. We only had a dozen or so satellites up, with sparse coverage over the Middle East. So we took a bird that wasn't really usable, because it couldn't maintain 3-axis stabilization, and adjusted it's Z-axis to point to the Middle East, relative to it's Nadir point when intersecting with the Earth in it's orbit. This got a couple of officers (I used to remember their names) a nice write up after the war for coming up with the idea, planning it and making it happen.
yep, gps has nuclear blast detectors. I'm not sure if it's the original purpose, but the two roles are very similar (both requiring accurate high-altitude clocks and a little trig).
I programmed for an old TRANSIT reciever and it's amazing these things ever worked. Basically, you had to listen for the satellite's signal and follow the doppler over the course of about 10 minutes. Knowing the orbit and the doppler profile would put you at one of two places on the earth, and you had to estimate from your previous position to tell which one. And you couldn't move a significant distance in those 10 minutes.
HIV Crosses Species Barrier... into Muppets
SA has nothing to do with maneuvers and wasting fuel.
GPS transmits two sets of position data. One is encrypted with a code which only the US military has, and the other is not.
The military channel gets full precision data all the time.
The civilian channel currently gets the same full precision data. However, on command the satellites can begin introducing small random errors into this data, which can throw off position calculations by an arbitrary distance. Differential GPS corrects for this - it involves ground stations at known locations which continuously compare their known location to what GPS measures, and broadcast continuous corrections. Of course, in a war those stations would be big targets, and the effect is only local to the station. To drop a bomb on a US target you'd need correction stations in the US. Presumably advesaries would only be able to utilize them within their own territory (these stations have to be precisely situated or it defeats the whole purpose of having them).
In any case, if the USA wants to put errors in GPS measurements they just have the satellites transmit bogus information - they don't change their orbits.
Note that GPS does NOT measure the location of a satellite in the sky (azimuth and elevation and all that). It measures the travel time of a signal from the satellite to the GPS unit. This creates a circle on the surface of the earth a fixed distance from the satellite. If you have three satellites you get three circles with only one intersection. However, if the satellites purposely transmit incorrect times then the circles do not intersect exactly - giving an approximate location. A GPS satellite is basically just an atomic clock transmitting the current time to high precision in a known orbit.
I don't think this is true. I think that most troops brought their own civilian GPS units because they were smaller and lighter and generally more feature-filled. And getting your hands on one is probably like being in a big company where sysadmins who need to monitor systems don't get blackberry's while CEOs who don't even read their own email do...
In addition, you need to know the precise location of your GPS antenna. This can be tough. The necessary accuracy for your reference position usually require a receiver more expensive than one capable of providing the pseudoranges from which differential corrections can be calculated.
(These days, it's possible to get a receiver capable of providing pseudoranges relatively cheaply, although sometimes in an undocumented fashion, for example obtaining pseudoranges from Garmin receivers via gar2rnx. Surveying your antenna location to within millimeters is a different story... Cheap receivers cycle-slip often enough that obtaining a millimeter-accuracy solution can be very difficult.)
retrorocket.o not found, launch anyway?