GPS World: The Year of IIR-M: Five May Rise in 2007
- From: Sam Wormley <swormley1@xxxxxxxxx>
- Date: Thu, 02 Nov 2006 13:31:56 GMT
GPS World: The Year of IIR-M: Five May Rise in 2007
http://www.gpsworld.com/gpsworld/article/articleDetail.jsp?id=382449
Oct 26, 2006
GPS World
GPS IIR-M-2 PRN31/SVN52, the second replenishment modernized satellite,
launched on September 25 and was set usable on October 12. A third, GPS
IIR-16/M3 PRN15/SVN55, is scheduled to launch on November 14. Five more
of this generation remain Earth-bound, at various stages along the line
between Lockheed Martin's production facility and the U.S. Air Force
storage barn.
An Air Force commander informally told GPS World that the GPS Wing has
prepared a plan to boost all five of these into orbit next year. If all
goes well, this would make 2007 the Year of IIR-M. Official
confirmation of this plan had not appeared by press time for this
issue. At one point, three or four IIR-Ms were to be launched in 2006;
if current plans proceed unchecked, two will have risen.
If the second does follow the first, and if five further IIR-M launches
take place next year, this would clear the launch pad for delivery of
the first GPS Block IIF satellite in December 2007, and its currently
scheduled launch in May 2008.
32 Skidoo. The Air Force issued a memorandum stating that the November
launch will set a new mark of 31 operational satellites, assuming no
satellites are decommissioned -- and says it may even reach 32. The
second IIR-M will continue dataless code on L2. Operational control
could go beyond 32 satellites; as most current civil receivers are set
at 31, this has important ramifications that manufacturers should
consider.
The U.S. Air Force GPS Operations Center is seeking feedback on
potential impacts the largest-ever GPS constellation may have on users
and equipment. Interface specification IS-GPS-200D lists 32 operational
pseudo-random noise (PRN) codes.
"As we go over 30 operational satellites, our concern is with potential
impacts to existing fielded GPS receivers that may not properly account
for up to 32 operational PRNs," states the memo. The center asked users
to assess potential effects on their systems and respond to the 50th
Space Wing by October 20 -- though indications were that feedback
would also be evaluated after that date.
"Although future versions of our interface spec, IS-GPS-200, will
accommodate a larger constellation for the next-generation GPS, the
most pressing concern is with potential impacts to existing fielded GPS
receivers that may not properly account for up to 32 operational PRNs,"
reads the memorandum. The encrypted Wide-Area GPS Enhancement (WAGE)
message, used by the military, is specifically noted in the memorandum,
as its users are likely to have a PRN limit of 30 in their
implementation
The memo is signed by James C. Hutto, Jr., Colonel, USAF, Commander,
50th Space Wing, and Wesley A. Ballenger, Jr., Colonel, USAF,
Commander, Global Positioning Systems Wing.
.
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