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50th Space Wing completes Phase 1 of E24

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Old January 26th 11, 04:02 AM posted to sci.geo.satellite-nav,rec.aviation.ifr
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Default 50th Space Wing completes Phase 1 of E24

On Jan 25, 8:56*pm, Sam Wormley wrote:
50th Space Wing completes Phase 1 of E24
Schriever Air Force Base
19 January 2011

The 50th Space Wing is pleased to announce the completion of phase one of a two phase
Global Positioning System constellation expansion known as "Expandable 24." *When fully
complete, this expansion will increase global GPS coverage and provide civil, military
and commercial GPS users with more robust satellite availability and a higher probability
of signal acquisition in terrain challenged environments.

The GPS constellation consists of 24 operational slots positioned within six equally-spaced
orbital planes surrounding the earth. *This plane/slot scheme and enhanced satellite
placement ensure GPS users receive the most accurate navigation data at any time, at any
place around the world.

Expandable 24 is a U.S. Strategic Command commander directed initiative, executed by the
wing, specifically the 2nd Space Operations Squadron, to reposition six satellites in the
current GPS constellation. *Given the strength and number of satellites in the current
constellation, Air Force Space Command was in a unique position to enact this revolutionary
strategy to benefit global users. *AFSPC acted on this opportunity to increase the
robustness of satellite availability by expanding three of the baseline 24 constellation

Phase one of Expandable-24 began Jan. 13, 2010 when 2 SOPS performed maneuvers to reposition
three GPS satellites, one of which took *351 days to maneuver. *The last of the satellites
completed repositioning on Jan. 18, 2011.

Phase two of Expandable-24 began in August 2010 and is expected to be complete in June 2011.
During Phase two, three other GPS satellites will be repositioned. When complete, the GPS
constellation will attain the most optimal geometry in its 42 year history, maximizing GPS
coverage for all users.

"Our primary focus is to execute flawless operations to maintain GPS as the world's gold
standard for positioning, navigation, and timing," said Lt. Col. Mike Manor, director of
operations for 2 SOPS. "By repositioning a handful of our satellites to optimize their
locations in space, we've not only improved the accuracy for military users in disadvantaged
terrain like Afghanistan, but also improved the accuracy for all GPS users worldwide."

So far overall there were improvements. But nothing that can be called
impressive or that gives the impression that optimizing GPS
performance is that important to the GPS wing. The impression that is
their own perception is that it's good enough, so let's do some
improvements, show some results. But above all, just leave them
wanting more. Let's always hold something back.
PRN30 Delta V timing was very disappointing. 2-3 months ago PRN 30 was
in a great position midway between PRN16 and PRN25. Today it's a
useless for PDOP, in shouting distance from PRN16. If they cared, they
would have positioned PRN30 optimally. It's likely one of the birds
not far from dying of old age anyways.

"When complete, the GPS constellation will attain the most optimal
geometry in its 42 year history, maximizing GPS coverage for all
I'd like to see that. Maximizing ? With PRN3/6 that close, with
PRN11/24 that close, with PRN9/27 that close ? If in 6 months things
will be so great, some delta Vs to achieve that would have been
performed already or be in the schedule already.

I'm not trying to do a hatchet job with GPS. They can improve it
substantially more if they want to. It's in their hands. Just two
months ago performance was noticeably better than it is today.

Hopefully with 4 Galileo launches in the next 24 months (satellites
that will actually be part of the constellation, with operational L1C/
L5 signals), and those birds coming online with L5 and L1C in testing
mode (message 0) will raise the ante. Passive Hydrogen Maser clocks
should redefine GNSS clock stability. Even though Galileo time won't
be precisely the same as GPS time, I understand the specs include a
time offset to GPS, so it should be possible to use Galileo satellites
to improve GPS geometry as soon as message zero is removed (or using
special firmware that uses message zero satellites normally).

Ok, I'm going to now shut the hell up until they declare their work
done. No more criticism until June 2011.

A true friend is not who says what you want to hear. It's he who says
what you don't want to hear, but does so hoping to make you better !

Marcelo Pacheco

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