Slashdot Mirror

← Back to Stories (view on slashdot.org)

First modernized GPS satellite Launched

Posted by Hemos on from the keeping-up-with-the-neighbors dept.

A reader writes "The first GPS 2R-M satellite has launched from Cape Canaveral, Florida on top of a Boeing Delta 2 rocket. The government is now competing with Europe's Galileo system, and has added two additional military channels and one civilian channel, which will increase the accuracy and performance of GPS - as well as increase its resistance to jamming."

51 of 221 comments (clear)

  1. You Will Be Assimilated! by AKAImBatman · · Score: 5, Interesting

    You know, I was about to ask the rocket scientists hanging around here (hi guys!) about how small new generation comsats were going to be. After all, there has been a tremendous increase in miniturization and technology since the original GPS sats were launched. (e.g. better microprocessors, denser batteries, more efficient solar panels, better propulsion, etc.) If we could get these sats small enough, it might be possible to deploy a GPS system for Mars in one or two launches.

    Then I saw the borg cube that assimilated the Willy Wonka Chocolate Factory (Mirror) Excuse me while I pick my jaw up off the floor.

    On another note, the picture makes it look like the design hasn't changed much from the original NAVSTAR configuration. I assume that these satellites are merely sharing the same chassis, and have very different internals?

    --
    Javascript + Nintendo DSi = DSiCade
    1. Re:You Will Be Assimilated! by madaxe42 · · Score: 2, Interesting

      You find a way of fitting a Caesium fountain clock in a smaller case.

    2. Re:You Will Be Assimilated! by jurt1235 · · Score: 4, Informative

      Depending on the rocket which launches the satellite, there will be a general base for the satellite to be build on. You need to be able to mount the satellite on the rocket. Total reuse of the framedesign will save a significant amount of money, so there will be attempts to reuse the frame, solar panels, and general control systems. This ofcourse if the power signature of the new equipment matches with what the frame can deliver.

      One thing is a bit weird though about the first photo. Usually these satellites are assembled in clean rooms with people wearing all kinds of protection against static electricity build up and anti dust covers. So I wonder if the satellite in this picture is just a mockup to make a testfit of the equipment (never trust the drawings).

      --

      My wife's sketchblog Blob[p]: Gastrono-me
    3. Re:You Will Be Assimilated! by lbmouse · · Score: 4, Informative

      Looks like a device for something out of a Dr. Seuss book. Anywho :), here are some specs.

    4. Re:You Will Be Assimilated! by pr0nbot · · Score: 3, Interesting

      If we could get these sats small enough, it might be possible to deploy a GPS system for Mars in one or two launches.

      OT... something I've been wondering about, with regard to long-range communication with satellites: we know how to do networks now, why aren't we peppering space with small node probes that travel away from Earth (i.e. aren't orbital satellites) but keep in touch with eachother and so can route the data from real science probes back to us from further and further out?

      I suppose the number of nodes required would grow at the same order as the volume of a sphere (assuming we want to spray them in all directions) but we actually probably only want to send them out in specific directions.

    5. Re:You Will Be Assimilated! by AKAImBatman · · Score: 4, Informative

      OT... something I've been wondering about, with regard to long-range communication with satellites: we know how to do networks now, why aren't we peppering space with small node probes that travel away from Earth

      1. Nanoprobes wouldn't have a large enough transceiver dish.
      2. We are. Have you heard of the NASA Deep Space Network? Every sat and probe we launch becomes part of NASA's network in space. That's why when they had communications problems with the Mars Rover, they were able to send reset commands from a probe heading elsewhere. As long as they can find a number of sats with the necessary line of sight, NASA can communicate with any probe, anywhere. Even if it's on the other side of the Sun. :-)

      (No, I am not privy to the exact locations of anything. So take this with a grain of salt. We have a lot of hardware up there, but space is a big place.)

      --
      Javascript + Nintendo DSi = DSiCade
    6. Re:You Will Be Assimilated! by GileadGreene · · Score: 2, Interesting
      On another note, the picture makes it look like the design hasn't changed much from the original NAVSTAR configuration. I assume that these satellites are merely sharing the same chassis, and have very different internals?

      No, they're substantially different designs. Different manufacturers even (Rockwell vs Lockheed). But if you have a spacecraft performing the same mission, odds are it's going to have a similar configuration. The thing that makes them look most similar is the navigation signal antenna array (the "Willy Wonka Chocolate Factory"). Even those are slightly different between the two models. But since they're fundamentally performing the same function, thye look very similar ("form follows function").

    7. Re:You Will Be Assimilated! by cpu_fusion · · Score: 2, Insightful
      So I wonder if the satellite in this picture is just a mockup to make a testfit of the equipment (never trust the drawings).

      Given the military nature of the project, perhaps it is just a "PR model" for secrecy.

    8. Re:You Will Be Assimilated! by speculatrix · · Score: 3, Interesting
      there has been a tremendous increase in miniturization and technology since the original GPS sats

      your statement is naive in that it supposes that mil-spec and rad-hardened technology has advanced at the same rate. Once, it was the military who led the way and consumer devices followed; now, it's the other way round, and in fact the military/space people have big problems with obsolescence, especially with the recent EU rules on Reductions Of Hazardous Substances (often known as "lead free", but actually covers other things as well). In some instances, military kit is being forced to use automotive-spec components as replacements, because that's all that's available and at least the devices have a wider temperature range.

      so, yes, mil- and space-spec hardware is advancing, but the testing cycle is far longer - think months rather than weeks. when you're spending $M's in launch fees, you've got to get it right!

    9. Re:You Will Be Assimilated! by josecanuc · · Score: 5, Informative
      Speaking of which, I am wondering what the heck those things on the antenna array are.

      Those *are* the antennas. See the spiral bits on both kinds? That's a conductive strip. It's a helical antenna -- common on satellites. The body that looks like the main bulk is just to give the thin metal something to hold shape.

    10. Re:You Will Be Assimilated! by ChrisA90278 · · Score: 4, Informative

      You've been reading to much science fiction. Yes there are some cases where spacecraft use inderect means of communication through a relay but this is not done ad-hoc using some general purpose capability built into every spacecraft. In every case wherwe relay is used the capabilty is plaanned from the beginning. The idea of selecting some random spacecraft to use as a relay to soe other random spacecraft just can't work. The orbiters currently on mars were design specifically to relay. Closer to Earth TDRSS acts as a relay between low Earth orbit and the ground. Notice (1) that TDRSS is the relay, thaey are NOT sending data between randon spacecraft and (2) the data are passed only between LEO and the ground, not through out the solar system or even to geosync. orbit. http://msp.gsfc.nasa.gov/tdrss/oview.html

    11. Re:You Will Be Assimilated! by LandKurt · · Score: 2, Informative

      Have you heard of the NASA Deep Space Network? Every sat and probe we launch becomes part of NASA's network in space. That's why when they had communications problems with the Mars Rover, they were able to send reset commands from a probe heading elsewhere.

      Did you even read the Wikipedia article you linked to? The Deep Space Network is an earth based network of large radio dishes that listen to deep space probes. It's not located in deep space. It's almost always easier to talk to a distant probe with a huge dish on earth than to try and use the small dish on another probe.

      The closest thing to what you're discussing is NASA's TDRS system. That relays signals from earth orbiting satellites to the ground.

    12. Re:You Will Be Assimilated! by GileadGreene · · Score: 2, Informative
      What you say is true. In particular, the "hot new" rad-hardened processor is the RAD750, a hardened PowerPC 750. And yet...

      • When the GPSIIR-M started the design process the RAD750 was nonexistent - major USAF satellites can take on the order of a decade to design and deploy.
      • As I've said elsewhere in this thread, electronics are not necessarily that large a contributor to spacecraft mass.
      • More capable processors may suck down more power, which tends to make other parts of your spacecarft (e.g. the solar arrays) larger.
      • Li-Ion batteries are still considered relatively unproven in a spacecraft context. They've only been used on a few missions, and the performance and lifetime data we have on them is limited. They are unlikely to be selected for a critical system like GPS at this point.
      • Li-Ion batteries were speculative "future technology" at the time the IIR-M was being designed. I'm pretty certain they aren't being used in the next-gen GPSIIF satellites. I'd be surprised if they made it into the GPSIII (which isn't due to deploy for another 6-8 years).
      • Arcjets and other forms of electric propulsion have indeed proved themselves. They are in regular use on GEO comm satellites. However, whether or not EP makes sense for a given mission depends on many things. One key issue is solar array size. Using EP for an orbit transfer makes sense on a GEO comm bird because they have huge solar arrays that won't be used during the transfer - that spare power can be used to run an ion engine. In the case of GPS it's not clear that the arrays are large enough that you wouldn't need to add extra array area just to support an EP transfer - you'd end up saving propellant but making a more massive spacecraft. EP for stationkeeping is another question. But again, there are many tardeoffs involved.
      • Satellite structures are still mostly made from aerospace-grade aluminum. There's been some work on using composites, but there are issues with outgassing in a vacuum environment, and ease of manufacture.
      • There's been little in the way of advancements in spacecraft thermal control technology in the past couple of decades.
      • Spacecraft antenna and RF technology hasn't changed a whole lot. Especially for precision applications like navigation signalling. Where it has changed, it's been used to add more capability rather than lower mass.
      • Solar array technology has advanced quite a bit. But again, that just provides scope for higher-power applications (greater comm bandwidth, more processing power).

      None of this means that the IIR-M couldn't be smaller and lighter (I personally believe it could be). But doing so requires careful design and assessment of the tradeoffs involved. Just throwing technology at the problem is not the answer. In fact, it's often the cause of the massive cost and schedule overruns that happne in DoD space programs.

    13. Re:You Will Be Assimilated! by GileadGreene · · Score: 3, Insightful
      IMHO it comes down to 3 things (one of which you've already captured):
      1. It takes a long time to get a satellite up, and chasing new technology will just make it take longer.
      2. It is not a given that a new technology will provide benefits for a given mission. There are interactions between different elements of the design that may mean that a certain technology is not appropriate for the mission in question (the demands of EP on solar arrays being a prime example of this kind of negative interaction).
      3. The temptation is always to cram as much capability as possible into the satellite, instead of providing the minimum capability required. This is especially true of government satellites since the requirements are typically ill-defined to begin with (at least in my experience).

      These reasons apply to US government space programs. For an alternative approach, you might look at Surrey Satellite Technologies Ltd in the UK. They build and launch things quickly, have a well-defined strategy for integrating new technologies into spacecraft in a low-risk fashion and getting rapid flight-test information on them, make good use of the technologies appropriate to a mission instead of getting wedded to any one tech, and are extremely good at nailing down their requirements and building only what is needed. IMHO they are the best, and most innovative satellite manufacturer in the world today (and no, I don't work for them - although I'd do so in a heartbeat if I ever moved to the UK).

      To being things slighly back on-topic, it's probably worth noting that SSTL has the contract to develop a testbed satellite for the Galileo system (the European competitor to GPS).

  2. Compatibility by slimey_limey · · Score: 3, Interesting

    Will this improved accuracy come at the cost of compatibility? I already have a GPS reciever, and I don't want to have to buy a new one to make my data more accurate. (Magellan hasn't released new firmware for the SporTrak Basic since 2002, and I'm not holding my breath.)

    --
    ☠
    1. Re:Compatibility by AKAImBatman · · Score: 4, Interesting

      The new civilian channel is in addition to the existing channel, so your existing equipment should work. As more of these sats go online, you can expect to see gear that provides access to the second civilian channel. (Source)

      What I have to wonder, though, is what will they do with the two new military channels? It seems that all the field soldiers tend to use civilian gear because the military gear is too heavy, unfriendly, ugly, and is in short supply. I suppose it would make the missiles hit their targets better, but it would be nice to know that our entire military can use the equipment.

      --
      Javascript + Nintendo DSi = DSiCade
    2. Re:Compatibility by Wyatt+Earp · · Score: 3, Informative

      In each squad I think there is a military grade GPS reciever, since Afghanistan and more so, Iraq, more and more soldiers are carrying thier own GPS hand held which is good enough for field work.

      The new military channels will be more for JDAM/Cruise Missiles and other targeting systems.

  3. Spaceballs by q-the-impaler · · Score: 5, Funny

    Jammed? Raspberry. There's only one man who would dare give me the raspberry. Lone Starr!

    --
    Sierra Tango Foxtrot Uniform
  4. Jamming by whom? by moz25 · · Score: 3, Informative

    As I understand, one of the jamming related problems with GPS is not by criminals/terrorists, but by the government when they see the need. It seems more of a political than a technical nature. That's one of the potential benefits of the Galileo system: to have more than one "supplier" of such information.

    --
    see a Text Widget
    1. Re:Jamming by whom? by Gaima · · Score: 2, Informative

      http://science.slashdot.org/article.pl?sid=05/08/0 8/1350218&tid=160&tid=103

    2. Re:Jamming by whom? by AKAImBatman · · Score: 3, Informative

      As I understand, one of the jamming related problems with GPS is not by criminals/terrorists, but by the government when they see the need.

      No, it's more complex than that. Yes, the government can fine tune the results to cause problems for enemies, and even turn off the unencrypted civilian bands if they so choose. However, real methods exist for sending confusing signals that will effectively jam a GPS signal. This jamming can force so called "smart bombs" to rely on internal guidance instead of GPS. The result (hopefully) is that the less precise guidance would cause the bomb or missile to miss the target.

      In practical terms, it seems a bit harder than that to prevent US munitions from reaching their targets. Our guidance computers were well developed prior to the general use of GPS coordinates, and we have the capability to manually deliver ordinance wherever it may be needed. So in the end, this is about keeping the efficiency of our weapons in good order so that we have to risk fewer lives in missed targets and strafing runs.

      --
      Javascript + Nintendo DSi = DSiCade
    3. Re:Jamming by whom? by Dun+Malg · · Score: 4, Insightful
      However, real methods exist for sending confusing signals that will effectively jam a GPS signal. This jamming can force so called "smart bombs" to rely on internal guidance instead of GPS. The result (hopefully) is that the less precise guidance would cause the bomb or missile to miss the target.

      Problem with active GPS jamming is that it's a "damned if you do, damned if you don't" situation. Any sort of active jamming on the battle field is a huge beacon on the battlefield screaming BLOW ME UP! It then becomes a question of whether or not to turn on the jammer at all, as at most it'll be good for slightly de-accurizing (if that's not a word, it ought to be) one bombing run before being obliterated. If they were cheap enough, maybe, but even still...

      --
      If a job's not worth doing, it's not worth doing right.
    4. Re:Jamming by whom? by w42w42 · · Score: 4, Informative

      I remember watching a press conference with a military general at the opening of the last gulf war. The press was all lathered up about reports that Iraq was jamming GPS signals - it was assumed the Russians had given them the equipment - and the general commented that whoever was running that equipment had the worst job with the shortest life expectancy in the world at that time. Like you alluded to, any military equipment that relies on an outgoing radio signal instantly becomes a big bright target.

    5. Re:Jamming by whom? by mcd7756 · · Score: 2, Funny

      They become suicide bombees instead of suicide bombers.

      --
      Am I not destroying my enemies when I make friends of them? --Abraham Lincoln
    6. Re:Jamming by whom? by nsayer · · Score: 2, Informative
      any military equipment that relies on an outgoing radio signal instantly becomes a big bright target.

      Yup.

      And I rather suspect that HARMs are not limited to air defense radar systems...

    7. Re:Jamming by whom? by Dun+Malg · · Score: 2, Interesting
      Can they not use multiple stations to make it appear the signal is coming from a place where it is not?

      No, all that would do is present multiple individual targets. Modern direction finding equipment uses such advanced digital processing that it can separately identify two transmitters right next to each other based on subtle differences between them caused by things like inherent manufacturing variations in the transmitters' modulation circuitry.

      --
      If a job's not worth doing, it's not worth doing right.
  5. Its about time by dj245 · · Score: 2, Insightful

    The sattelites up there are fairly old. Some of the newer ones were launched only a couple years ago, but some have been up there since the early 90's or before. We've had the math equations and the computing technology to be able to put up satelites with around 1m accuracy and better signal strength for a couple years now. Forget about the better jamproofing; with the newer eqipment you can sum the error of your integrals with newer algorithms and faster and determine position that much better less error-prone initial conditions.

    --
    Even those who arrange and design shrubberies are under considerable economic stress at this period in history.
    1. Re:Its about time by spankus · · Score: 2, Insightful

      Do you upgrade your computer every time a new processor comes out????

      Same reasoning (sorta) applies to GPS. Why throw away a $100,000,000 satellite when it hasn't died yet?

      The newer satellites do have some expanded capabilities, but don't plan on seeing those operationally for 5 to 8 years. (It's a long story of governmental mismanagment and strife)

    2. Re:Its about time by gunnk · · Score: 2, Funny

      Do you upgrade your computer every time a new processor comes out????

      Bad analogy, there, you're posting on Slashdot after all...

      --
      Life is short: void the warranty.
  6. How do you compete with vaporware (Galileo)? by Anonymous Coward · · Score: 5, Insightful

    " The government is now competing with Europe's Galileo system "

    Lets see :
            Galileo has not launched yet.
            Galileo will not be free.
            The 2R-M was planning before Galileo was anounced.
            Galileo operational capibility is not planned until 2008.

    I'm failing to see the link to the vaporware...

    1. Re:How do you compete with vaporware (Galileo)? by Anonymous Coward · · Score: 3, Informative

      Having worked on the Galileo internal operating software, i can say operation in 2008 is somewhat optimistic.

    2. Re:How do you compete with vaporware (Galileo)? by aperezbios · · Score: 3, Informative

      Wrong. Do your homework before you make idiotic claims such as "Galileo will not be fre"

      From the Galileo Wikipedia Article: (http://en.wikipedia.org/wiki/GALILEO_positioning_ system)

      "An encrypted higher bandwidth Commercial Service with improved accuracy will be available at an extra cost, while the base Open Service will be freely available to anyone with Galileo compatible receiver."

  7. which # by allelopath · · Score: 2, Insightful

    Is there a way to know which # (1..24) this one is replacing?
    Just curious...it would be fun to know when i turn on my GPS receiver.

    1. Re:which # by Ossifer · · Score: 3, Informative

      From TFA:

      GPS 2R-M1 will assume the Plane C, Slot 4 position, taking over for the GPS 2A-20 craft launched in May 1993.

    2. Re:which # by Toaste · · Score: 2, Interesting
      From the article: "GPS 2R-M1 will assume the Plane C, Slot 4 position, taking over for the GPS 2A-20 craft launched in May 1993."

      From the designation of the old satellite, I presume that this position is number 20 on GPS receiving equipment. Just a guess.

      By the way, does anybody know how they plan to move the old one out of the way? According to info found here the origional was a 3-axis stabilized NAVSTAR, but I doubt it will be able to move significantly with only its thrusters.

      Another interesting point: the page lists the design life of this series at 7.5 years. Which means this satellite was replaced a mere 4 years, 10 months, and 13 days beyond its expected service life.

    3. Re:which # by Hrdina · · Score: 4, Informative

      Actually, it will appear as PRN (pseudo-random noise) #17 on receiving equipment. That PRN is currently unused. The current vehicle in slot C4 is PRN07, and it will keep that PRN assignment until it is decommissioned by the USAF.

  8. Too Little Too Late by qwp · · Score: 3, Funny

    I would have been able to post first post,
    had i known about this great achievement. The problem is
    I was suck in my car cause I took a wrong turn due to my
    dam'ed gps navigator. Maybe they haven't turned it on yet..

  9. Re:Look everyone! Somone who didn't RTFA! by AKAImBatman · · Score: 3, Interesting

    Yeah, I did read it. The part that stuck out to me was that the new sats were about 60 pounds heavier than the old ones. Now I understand that they couldn't have gotten all the new features in for only 60 pounds without modern technology. Still, I can't help but think that it could have been a lot smaller than that.

    Then again, I'd like to see a day when we can create useful PongSats, for this stuff but I supposed that won't be happening anytime soon. (Especially not when you need a large tranceiver!)

    --
    Javascript + Nintendo DSi = DSiCade
  10. Re:Look everyone! Somone who didn't RTFA! by cerberus4696 · · Score: 5, Insightful

    You have to remember that they're overengineering these things by terrestrial standards, because the satellites have to withstand some fairly harsh conditions while in orbit (such as radiation, EM storms from solar flares, etc). I imagine they're also hardened to some degree against human-generated interference, given all the worrying the Air Force has been doing lately about space warfare. Given all that, I'm not surprised that they seem excessivly bulky by the standards of present technology.

  11. Specs? by adminispheroid · · Score: 2, Interesting

    Anybody know what's on the new civilian channel? e.g. is it the same kinda stuff as the two existing channels, on a new carrier? Or is it a new code?

    1. Re:Specs? by Anonymous Coward · · Score: 4, Interesting

      The new civilian code is probably a longer signal that repeats less often. This gives better accuracy but takes longer to determine position when first switched on. Using the lower accuracy signal would allow for a rapid first estimate of postion while the GPS would become more accurate once the position using the new signal was calculated. The military GPS systems use the civilian signal to estimate their position more quickly.

    2. Re:Specs? by stienman · · Score: 2, Funny

      Anybody know what's on the new civilian channel? e.g. is it the same kinda stuff as the two existing channels, on a new carrier? Or is it a new code?

      According to one of the press conference questions:

      "We are not going to confirm the content of the new channel at this time. We can state, however, that due to recent FCC regulations affecting our public broadcast, we will not be including Howard Stern for the initial lineup."

      I hope this helps.

      -Adam

  12. Re:Look everyone! Somone who didn't RTFA! by GileadGreene · · Score: 4, Insightful
    The thing is making a satellite slightly lighter doesn't buy you much. You need a substantial drop in mass in order to get down to a cheaper launch vehicle. So given that you're already constrained to launch on a particular LV, why not pack in as much capability as possible? The Air Force in particular has a habot of keeping upgraded satellite designs at the same (or similar) mass as their predecessors, but adding lots of extra functionality.

    The other thing to keep in mind is that there are many things that contribute to the total spacecraft mass in addition to the electronics. Not all of them have undergone the same kind of Moore's law reductions in mass (or improvements in capability) that electronics have.

  13. I see jamming in action regularly by RebornData · · Score: 4, Informative

    I use a laptop-integrated GPS in my car, and I drive by the Pentagon regularly for work. The GPS goes nuts on certain roads that pass near the building... the "position" of the vehicle jumps all over the place. Same thing happens near the capitol building. No suprise of course...

    -R

    1. Re:I see jamming in action regularly by Kjella · · Score: 2, Interesting

      How effective would that jamming really be.... since anyone smart enough to build a cruise missile that could use GPS for guidance would be equally intelligent enough to build a cruise missile to simply home in on the jamming single it's self. Or even with out that could simply free fly the last little distance around the jammer and still hit extremely close to the target.

      1) He might not know it is there
      2) The jamming dish (or array of jammers) is presumably far away from any critical installation. If the military managed to radio mark their own targets, I'd classify that as gross incompetence. (also, that'd be "the jamming signal itself")
      3) "Simply"? Yes, you could make a system that would try to determine a "last known good position/direction", calculate direction and distance to target and fly it in blind, but it'd be a rather major modification. A much more likely scenarion is that someone gets their hands on a GPS-guided missile (american, russian, whatever), program it up with coordinates and launch it only to fail miserably.
      4) Who's to say the system can't actually deflect missiles? Instead of going wild (that's just the default state), an incoming missile detected on radar can be "redirected" to a designated detonation area, simply by making it believe it is hitting the target.

      Kjella

      --
      Live today, because you never know what tomorrow brings
  14. Russians using GPS by Thagg · · Score: 2, Interesting

    I was fairly astonished to see in the recent issue of Aviation Week that Russia is now building GPS-guided bombs. Presumably this is just using the civilian signal, which could be disabled or degraded in a conflict theater -- but still, it was an fairly amazing development. I suppose that it's conceivable that AvWeek got the facts wrong, and that it was a GLONASS-guided bomb, but they're usually pretty good about that sort of thing.

    Thad Beier

    --
    I love Mondays. On a Monday, anything is possible.
    1. Re:Russians using GPS by ran-o-matic · · Score: 4, Informative

      GLONASS is a GPS (global positioning system), so Aviation Week is right. One of the first examples of Russian GPS-guided bombs is the KAB-500S-E with a 1500 lb device also available.

  15. We need more GPS satellites by Animats · · Score: 4, Informative
    We've recently been struggling with a Novatel GPS that receives Omnistar High Precision corrections, and supposedly provides 15cm accuracy. The problem is that it needs to see at least five GPS satellites for Omnistar HP to work. Regular GPS requires only four, but the ionospheric corrections for Omnistar require some redundancy. Five sats are the minimum; six are better.

    Unless you're in a very flat area, in the air, or on an ocean, you won't see five or six sats 100% of the time. 70-80% is more like it. If one of the sats is down (which happens; PRN #5, plane B, slot 4, wss down for 8 days recently), the outages are longer.

    GPS uses six rings of four satellites each, with all rings in polar orbit. The four satellites in each ring are 90 degrees apart. So, when a satellite in a ring is near the zenith, it's usually the only one visible in that ring. The original design called for more satellites per ring; with six per ring, you'd always have at least two satellites visible per ring, as long as you could see to within 30 degrees of the horizon. But there was a budget cut in the early days of GPS.

  16. How soon? by Ced_Ex · · Score: 2, Interesting

    How soon do we realize the benefit of this new satellite? Should we be able to see results right away just from one satellite? Or will we have to wait for 2 more satellites and hope that our GPS connects to the 3 newest ones in order to get the better resolution?

    --
    Live forever, or die trying.
  17. Re:Jamming, eh? by iamlucky13 · · Score: 3, Funny

    I don't get it. My first instinct was to try to find a secret code in the capitalized letters, but that didn't work out. Are you attempting to appeal to the slashdot moderators that appear to be scripts by tossing in keywords? If so you're going about it all wrong. You should start with, "I'm gonna get modded down for this," and include the words space elevator, soviet russia, nucular, linux, and intelligent design. Adding in AJAX, ubuntu, and evolved expanded launch vehicle will bump you up from funny or interesting to insightful.

  18. Television as GPS by tocs · · Score: 2, Interesting

    Why do you need newer and fancier GPS satellites when you can just use satellite television signals.