Archive for the 'Launch' Category

Last GPS Block IIR Satellite now in Orbit

August 17th, 2009 | Category: Launch

Monday, August 17 at 10:35 GMT, the last Lockheed Martin built Block IIR satellite lifted off.  There were a lot of lasts with this launch:

  • This is the last Block IIR satellite
  • This was the last time the Air Force would use the Delta-II rocket
  • This is the last scheduled launch from pad 17A, in use since the 1950's

SVN 50 (PRN 05) will be located in the same orbital slot as SVN 40 (PRN 10), eventually taking its place.  SVN 40 is on its last clock (of four original clocks) and it also has a reduced navigation payload capability.  It's User Range Error (URE) is not too bad though, as can be seen from these graphs:


This plot shows the ephemeris error for SVN 40 (PRN 10) for the last three days.


This plot shows the clock error for SVN 40 (PRN 10) for the last three days.


This last bar chart shows a three day history of the RMS URE for all satellites in the constellation.  PRN 10 is a nice, middle-of-the-road satellite.  I'd expect to to remain in use until it can no longer perform it's duties.  There may even be some benefit in moving it within plane to optimize the Dilution of Precision (DOP) for the entire constellation.

Job well done on the Block II Replenishment satellites!

Next up: Block IIF with the first launch for this new series of satellites scheduled for early 2010.

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SVN 49, PRN 1 URE too high

May 03rd, 2009 | Category: General Navigation,Launch

After the last Nog, someone pointed me to the following picture, published by the GPS Operations Center from this site:, (pick the Position Errors By Satellite value in the drop down box)


This shows that PRN 1, on April 30, 2009, had a very large User Range Error (URE), larger than any other satellite in the entire GPS constellation. If you've been following the Nog for awhile, you know that a URE this big can lead to large navigation errors.  This is certainly the reason PRN 1 is not healthy yet.  URE's are calculated using ephemeris and clock errors.  Ephemeris errors are rarely a problem, so it's likely that this satellite has a clock problem.


SVN 49 – not healthy yet – what’s up?

April 29th, 2009 | Category: General Navigation,Launch

SVN 49, PRN 1 was launched Mar 24 and if previous experience is any guide, it should have been set healthy quite awhile ago.  The standard time frame for this activity is a month, but we're over that mark now.  This satellite is also broadcasting the new L5 signal.

The GPS Operations Center says that the Air Force is continuing testing on that satellite and will be releasing a statement regarding this issue.

So what are the possible issues?  Caution, speculation ahead!

The satellite is on-slot, it's been in the almanac since late March.  It started broadcasting L5 on April 10, but still remains unhealthy for navigation using L1-L2 C/A-P(Y).  The time between when it's on-orbit and it becomes healthy is usually spent characterizing the on-board clock - the heart of the navigation and timing function of the satellite.  Once the clock has "settled down" (a technical term), it can be set healthy for navigation.  So, one could speculate that there is a problem with one of the clocks (there are three Rubidium atomic clocks on-board each GPS IIR satellite), or possibly an issue with the addition of the L5 signal.  If you have a receiver that tracks through the unhealthy setting on the satellite, you could watch the how the signal changes over time and make some conclusions.  If you do, I'd love to hear from you!

Until we get an official word from the Air Force, we'll just have to be content with our 30 healthy satellites.

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Block IIR-20 launch successful

March 24th, 2009 | Category: Launch

At 0434 EDT this morning a Delta II launch vehicle carried the next GPS satellite into space.  The flight lasted 68 minutes, according to United Launch Alliance.  From this point, the satellite will maneuver into it's designated slot.  See the previous Nog for further details.

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Block IIR launch Imminent and Block IIF Woes

March 21st, 2009 | Category: General Navigation,Launch

InsideGNSS and Patrick AFB are reporting that the latest Block IIR satellite (IIR-20) is ready for launch.  The launch is scheduled for March 24, 2009 between 0434 and 0449 EDT.  The GPS Operations Center reports that IIR-20 also known as SVN 49, will take PRN 1 and be placed in slot B2.  This slot is currently occupied by PRN 30, so this new IIR is probably a replacement.

SVN 49 has an L5 payload aboard and is intended to secure the L5 spectrum GPS is planning to use for civil signals.  According to InsideGNSS:

Meanwhile, the U.S. Air Force is in a race against the clock to get the new L5 signal on the air by August 26, 2009, in order to meet an International Telecommunications Union (ITU) deadline for securing a preferential L5 frequency allocation for GPS operations.
Problems have pushed the GPS program much closer to the deadline that expected.

The first and probably only opportunity to meet the deadline: a modernized GPS Block IIR-M satellite — IIR-20(M) — with an experimental L5 signal demonstration payload scheduled for a March 24 launch.

But if there are problems with the launch or the vehicle - ?:

“Originally, the U.S. planned to meet the deadline with the first IIF satellite,” said the [GPS Wing] spokesman. “The IIR-20 demo payload was developed as the back-up plan.”

If GPS cannot secure the L5 spectrum before August 26, 2009, ITU regulations state that GPS risks losing unconditional use of that band - instead providing priority usage of that spectrum to which ever GNSS system begins broadcasting on it first - so hopes are high on this launch and success of this vehicle.

Block IIF problems

The Block IIF program has suffered a recent setback - a power anomaly affecting all signals on the L2 frequency discovered during testing.  According to InsideGNSS:

Discovery of a power anomaly in signal generator of the first GPS Block IIF space vehicle (SV) has thrown a new wrinkle into the long-delayed follow-on generation of spacecraft.

In the words of a GPS Wing spokesman at the Space and Missile Systems Center (SMC), Los Angeles Air Force Base, California, “In reviewing test data from the final phase of SV1 thermal vacuum test, [government and Boeing mission assurance teams] identified a new concern that a component in the L2 transmitter may not have sufficient design margin to operate at its highest required power throughout the satellite lifetime.”

“Boeing has identified multiple options for addressing the concern and is working parallel solutions to deliver redesigned transmitters this summer,” said the GPS Wing spokesman.

The launch of the first IIF satellite was expected in October of this year, but that has now been moved to "late 2009" with a second launch not to be scheduled for at least 6 months afterward.

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New GPS IIR Satellite set healthy in record time

March 26th, 2008 | Category: Launch

The new GPS Block IIR-M satellite (PRN 7, SVN 48) was set healthy in record time on Monday March 24, 2008. According to GPS World:

That is apparently a record timeframe for a satellite being set to usable after launch. The previous satellite launched, SVN57, which went into orbit December 20, 2007, and was set to usable January 2 — a matter of 13 days — had also set a record at that time. After the successful launch of SVN48, the Air Force originally said that it anticipated it would set the satellite to usable sometime next month.

The standard timeframe for setting a satellite healthy after a launch is a month, but if all goes well, it will usually be set healthy when it's ready.

So, why the delay once it's on orbit? 

Once the GPS satellite gets into the correct orbital slot, turn on procedures are followed to activate the payload, upload programs and navigation data.  The rubidium atomic clock is also turned on.  The atomic clock plays an important role for navigation users, you wouldn't know where you are without it.  Once the clock is turned on, it has to be set to the correct time.  This isn't as easy as turning the dial on your watch - these clocks are accurate to nanoseconds.  The GPS satellite operators go through processes with arcane names such as baseband reset and PRN sync to get the timing set correctly.  Then they have to watch the clock.  The control segment Kalman filters process the clock states continuously, watching and waiting for the initial start-up clock errors to settle down.  Once all the payloads are on and functioning correctly, all the data is uploaded and current and all of the clock and ephemeris Kalman filter states have settled down, the satellite can be set healthy for all to use.

The fact that this process takes so little time now, is a testament to the manufacturers of the satellite and the clocks and to the operators in the GPS Control segment. Well done!

Now if only I could get a dentist appointment that fast...

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UPDATE: GPS Block IIR-M 19 launch successful

March 15th, 2008 | Category: Launch

SpaceFlightNow is reporting a successful launch and deploy of the latest Block IIR-M GPS satellite.

Spacecraft separation confirmed! The U.S. Air Force's Global Positioning System Block 2R-19 spacecraft has been released from the Delta 2 rocket's third stage to complete this late-night launch from Cape Canaveral.

The deploy occurred at 2:18:03 a.m. EDT this morning.

Launch timeline and more details available from their web site.

IIR-M 19 Launch


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GPS Block IIR-M Launch Imminent

March 14th, 2008 | Category: Launch

gpsiir-lo A U.S. Air Force modernized Global Positioning System Block IIR (GPS IIR-M) satellite built by Lockheed Martin is ready for launch aboard a Delta II rocket on March 15 from Cape Canaveral Air Force Station, Fla. The Block IIR-M spacecraft series is designed to provide enhanced navigation capabilities for military and civilian GPS users around the globe.The satellite, designated GPS IIR-19M, is the sixth in a line of eight GPS IIR satellites that Lockheed Martin Navigation Systems, Valley Forge, Pa. has modernized for its customer, the Global Positioning Systems Wing, Space and Missile Systems Center, Los Angeles Air Force Base, Calif.

When the latest launched GPS satellite is set healthy, another GPS record will be broken. For the first time since its inception, GPS will have 32 active satellites. A similar record was broken when 31 satellites became active back on February 26th of this year. That was a significant milestone in two ways. First, it was the first time more than 30 GPS satellites have been active at the same time. Second, it's the first time that more than 30 GPS satellite could have been active at the same time. In August of last year, the legacy Master Control Station (MCS) ground hardware and software was replaced by the new Architecture Evolution Plan (AEP) system. The new system is a client server-based computing system that has the capability to handle more than 30 satellites. The legacy system could only handle a maximum of 30.

32 active satellites is significant because only 32 of the original 37 1-week long segments of the original gold code were selected to be used by the GPS satellites. PRN (Pseudo Random Noise) codes are further explained by another author:

The mentioned PRN-codes are only pseudo random. If the codes were actually random, 21023 possibilities would exist. Of these many codes only few are suitable for the auto correlation or cross correlation which is necessary for the measurement of the signal propagation time. The 37 suitable codes are referred to as GOLD-codes (names after a mathematician). For these GOLD-codes the correlation among each other is particularly weak, making an unequivocal identification possible.

The new GPS satellite will use PRN 7 according to the GPS Operations Center, the last remaining PRN currently unused. When the new satellite is active, I'll put up some statistical DOP accuracy information up.

Last but not least I want to wish everyone a happy PI day! Grab your ruler and head towards your nearest circle to celebrate.

That reminds me of a funny story involving masking tape, my office floor and trig several years ago. Ask me about it!

UPDATE (3/15/08):

InsideGNSS is reporting that when PRN 7 becomes active, 2 additional GPS satellites will be deactivated:

As a result, the GPS constellation will have more functional spacecraft in it than ever — 32 if this week’s launch goes as planned. Two of those satellites, however, will be switched off and kept as spares, including SVN27 that IIR-M 19 will replace. The “baseline” GPS constellation or fully operational capability (FOC) calls for only 24 on-orbit satellites — 4 in each of 6 planes.

additionally, DOP will not be optimal, considering many of the satellites are in spare slots:

Because many of the satellites are clustered together in the orbital planes (see figure at beginning of article) to ensure back-up capability rather than spread out in an optimal configuration, DOP values look more like those of a constellation with fewer satellites.