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| Science Forum Index » Geology - Satellite Navigation Forum » GPS Constellation Management: Playing not to lose... |
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| Sam Wormley... |
 Posted: Thu Oct 22, 2009 9:15 pm |
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Guest
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GPS Constellation Management: Playing not to lose
http://www.gpsworld.com/gps/gps-constellation-management-playing-not-lose-9062-0?print=1
October 22, 2009
By: Eric Gakstatter
In sports, there is a phenomenon that sometimes occurs when a team is leading towards the
end of a game. It’s called “playing not to lose”.
For example, there’s five minutes left in a basketball game and a team is leading by ten
points. The leading team wants to run the clock down as much as possible and still
maintain their lead. There are two basic strategies the leading team can take. One is to
continue being aggressive and using the strategy that put them in a winning position to
begin with. The other strategy is to try to “play it safe” until the time clock expires.
The problem with the latter strategy is that the other team can sense the change in
mentality and feed off of it. It’s called “playing not to lose” instead of “playing to
win”. I’ve seen it happen over and over again in team sports and in business. Once an
organization has achieved a level of success, they lose the edge that brought them their
success.
The reason you are seeing high HDOP warnings from the NAVCEN and GPS “brownouts” during
the day when RTK (GPS-only) isn’t working is because the GPS satellite constellation is
sub-optimal. The current design of the GPS constellation is not focused on “playing to
win”, but rather “playing not to lose”.
Even the original GPS Program Manager, Dr. Brad Parkinson, has voiced his concern about
GPS brownouts and discussed possible solutions. You can read one of his presentations
here. In 2006, noted GNSS consultant John W. Lavrakas published a GPS World article
entitled Managing the GPS Constellation for Today’s Needs discussing the disparity between
the professional user community needs and GPS constellation management.
Today, there are 28 operational satellites. There were 30, but PRN08 is offline for
maintenance and PRN24 was placed in active reserve after an “unusual failure”. The 31st
one, PRN01/SVN49, never has been declared operational since its launch last March due to
the issues discussed here before. The current GPS ground control infrastructure can only
handle 30 or 31 satellites.
Given these limitations, GPS looks grim for the GPS-only RTK user, right?
Not necessarily.
The GPS constellation is optimized for 24 satellites. When there are more than 24
satellites in orbit, like there has been for many years, the extras are not positioned to
benefit the users but rather to be in a position to replace satellite failures. They are
sometimes referred to as “paired orbits”. Simply put, the active spares are orbiting very
near other satellites that are most likely to fail. This does very little for the user
community.
The current discussion is not whether to launch more satellites, but rather how to
reconfigure the satellites that are in orbit. Launching more satellites is a complicated
issue. It’s not just an US Air Force (the GPS stewards) technical issue, but a political
one because it’s expensive (~$150M per GPS satellite launch). That leaves the Air Force
with the option of adjusting the GPS constellation to benefit the user community. Doing
this is not completely void of political implications I’m sure, but certainly not near the
risk of launching a new satellite and certainly a better bang for your buck to the user
community.
See the rest of the article, and the links implied above, at:
http://www.gpsworld.com/gps/gps-constellation-management-playing-not-lose-9062-0?print=1 |
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| HIPAR... |
| Posted: Fri Oct 23, 2009 5:13 am |
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Guest
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On Oct 22, 11:15pm, Sam Wormley <sworml... at (no spam) mchsi.com> wrote:
[quote]GPS Constellation Management: Playing not to lose
http://www.gpsworld.com/gps/gps-constellation-management-playing-not-...
October 22, 2009
By: Eric Gakstatter
In sports, there is a phenomenon that sometimes occurs when a team is leading towards the
end of a game. Its called playing not to lose.
For example, theres five minutes left in a basketball game and a team is leading by ten
points. The leading team wants to run the clock down as much as possible and still
maintain their lead. There are two basic strategies the leading team can take. One is to
continue being aggressive and using the strategy that put them in a winning position to
begin with. The other strategy is to try to play it safe until the time clock expires.
The problem with the latter strategy is that the other team can sense the change in
mentality and feed off of it. Its called playing not to lose instead of playing to
win. Ive seen it happen over and over again in team sports and in business. Once an
organization has achieved a level of success, they lose the edge that brought them their
success.
The reason you are seeing high HDOP warnings from the NAVCEN and GPS brownouts during
the day when RTK (GPS-only) isnt working is because the GPS satellite constellation is
sub-optimal. The current design of the GPS constellation is not focused on playing to
win, but rather playing not to lose.
Even the original GPS Program Manager, Dr. Brad Parkinson, has voiced his concern about
GPS brownouts and discussed possible solutions. You can read one of his presentations
here. In 2006, noted GNSS consultant John W. Lavrakas published a GPS World article
entitled Managing the GPS Constellation for Todays Needs discussing the disparity between
the professional user community needs and GPS constellation management.
Today, there are 28 operational satellites. There were 30, but PRN08 is offline for
maintenance and PRN24 was placed in active reserve after an unusual failure. The 31st
one, PRN01/SVN49, never has been declared operational since its launch last March due to
the issues discussed here before. The current GPS ground control infrastructure can only
handle 30 or 31 satellites.
Given these limitations, GPS looks grim for the GPS-only RTK user, right?
Not necessarily.
The GPS constellation is optimized for 24 satellites. When there are more than 24
satellites in orbit, like there has been for many years, the extras are not positioned to
benefit the users but rather to be in a position to replace satellite failures. They are
sometimes referred to as paired orbits. Simply put, the active spares are orbiting very
near other satellites that are most likely to fail. This does very little for the user
community.
The current discussion is not whether to launch more satellites, but rather how to
reconfigure the satellites that are in orbit. Launching more satellites is a complicated
issue. Its not just an US Air Force (the GPS stewards) technical issue, but a political
one because its expensive (~$150M per GPS satellite launch). That leaves the Air Force
with the option of adjusting the GPS constellation to benefit the user community. Doing
this is not completely void of political implications Im sure, but certainly not near the
risk of launching a new satellite and certainly a better bang for your buck to the user
community.
See the rest of the article, and the links implied above, at:
http://www.gpsworld.com/gps/gps-constellation-management-playing-not-...
[/quote]
NAVSTAR was and is a system conceived to support the warfighters.
System reliability /availability is more important in that role than
absolute accuracy. An accuracy degradation from three meters to four
meters doesn't make much difference when delivering high explosive
ordnance. That's why the satellites are being clustered to back up
the key orbital slots.
I'd bet if you could get the system operators to offer an 'off the
record' comment, they would say we civil users have become a major
distraction.
--- CHAS |
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| matt weber... |
| Posted: Fri Oct 23, 2009 1:04 pm |
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Guest
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On Fri, 23 Oct 2009 03:15:16 GMT, Sam Wormley <swormley1 at (no spam) mchsi.com>
wrote:
[quote]GPS Constellation Management: Playing not to lose
http://www.gpsworld.com/gps/gps-constellation-management-playing-not-lose-9062-0?print=1
October 22, 2009
By: Eric Gakstatter
In sports, there is a phenomenon that sometimes occurs when a team is leading towards the
end of a game. Its called playing not to lose.
For example, theres five minutes left in a basketball game and a team is leading by ten
points. The leading team wants to run the clock down as much as possible and still
maintain their lead. There are two basic strategies the leading team can take. One is to
continue being aggressive and using the strategy that put them in a winning position to
begin with. The other strategy is to try to play it safe until the time clock expires.
The problem with the latter strategy is that the other team can sense the change in
mentality and feed off of it. Its called playing not to lose instead of playing to
win. Ive seen it happen over and over again in team sports and in business. Once an
organization has achieved a level of success, they lose the edge that brought them their
success.
The reason you are seeing high HDOP warnings from the NAVCEN and GPS brownouts during
the day when RTK (GPS-only) isnt working is because the GPS satellite constellation is
sub-optimal. The current design of the GPS constellation is not focused on playing to
win, but rather playing not to lose.
Even the original GPS Program Manager, Dr. Brad Parkinson, has voiced his concern about
GPS brownouts and discussed possible solutions. You can read one of his presentations
here. In 2006, noted GNSS consultant John W. Lavrakas published a GPS World article
entitled Managing the GPS Constellation for Todays Needs discussing the disparity between
the professional user community needs and GPS constellation management.
Today, there are 28 operational satellites. There were 30, but PRN08 is offline for
maintenance and PRN24 was placed in active reserve after an unusual failure. The 31st
one, PRN01/SVN49, never has been declared operational since its launch last March due to
the issues discussed here before. The current GPS ground control infrastructure can only
handle 30 or 31 satellites.
Given these limitations, GPS looks grim for the GPS-only RTK user, right?
Not necessarily.
The GPS constellation is optimized for 24 satellites. When there are more than 24
satellites in orbit, like there has been for many years, the extras are not positioned to
benefit the users but rather to be in a position to replace satellite failures. They are
sometimes referred to as paired orbits. Simply put, the active spares are orbiting very
near other satellites that are most likely to fail. This does very little for the user
community.
The current discussion is not whether to launch more satellites, but rather how to
reconfigure the satellites that are in orbit. Launching more satellites is a complicated
issue. Its not just an US Air Force (the GPS stewards) technical issue, but a political
one because its expensive (~$150M per GPS satellite launch). That leaves the Air Force
with the option of adjusting the GPS constellation to benefit the user community. Doing
this is not completely void of political implications Im sure, but certainly not near the
risk of launching a new satellite and certainly a better bang for your buck to the user
community.
See the rest of the article, and the links implied above, at:
http://www.gpsworld.com/gps/gps-constellation-management-playing-not-lose-9062-0?print=1
I am a long time GPS user, I go back to a period when there were only[/quote]
about 14 sats in the constellation. My experience was that by the time
there were 18 sats up, coverage world wide was 24/7 (it certainly
wan't with only 14). Sometimes the PDOP's were very bad (2 digit), so
while positional accuracy suffered (sometimes considerably), the
system was still usable. So as long as there are 24 operable birds
(and we have considerably more than that available today, and will for
the forseeable future), 2/7 coverage with reasonable PDOP is just
about a given. |
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