Pentagon Urged Not To Use Ability To Degrade GPS Signals
- From: Sam Wormley <swormley1@xxxxxxxxx>
- Date: Thu, 19 Jul 2007 03:25:13 GMT
Pentagon Urged Not To Use Ability To Degrade GPS Signals
By Bob Brewin
Government Executive, July 18, 2007
A newly formed multiagency advisory board argues that the Defense
Department should never again intentionally degrade the performance
of the Global Positioning System.
At its first meeting held in March, the National Space-Based
Positioning Navigation and Timing (PNT) Advisory Board decided that,
although the Air Force has the ability to degrade signals from the
constellation of GPS satellites through a process known as "selective
availability," board chairman and former Defense Secretary James
Schlesinger says he "cannot conceive any scenario in which SA has any
credibility today," according to minutes of the meeting, which the
board released this month.
The last time Defense intentionally degraded the civilian signal was
in 1990, and its reason for doing so was not made public. The Air
Force intends to add the ability to degrade the signal in its
next-generation GPS III satellites, which it plans to launch in 2013.
The PNT board includes members from the departments of Defense,
Transportation, Commerce, State, Homeland Security, and the Joint
Chiefs of Staff and NASA, as well as representatives from academia
and U.S. industry. Representatives from Australia, India, Japan,
Norway, Switzerland and Great Britain also sit on the board.
The Air Force started development of GPS during the Cold War and
included the ability to degrade the accuracy of signals sent for
civilian use, which are globally available, to an accuracy of about
100 meters instead of the current 10 meter or better level of
accuracy. In May 2000, President Clinton declared that the United
States would no longer degrade the civilian GPS signal.
President Bush issued a revised PNT policy in December 2004, which
promised "uninterrupted access" to civilian GPS signals. But Bush
added that the United States would include capabilities to deny
hostile use of the GPS system "without unduly disrupting civil and
commercial access" to GPS signals.
Chet Huber, a PNT board member and president of OnStar, a vehicle
navigation and security system that relies on the GPS system, told
the meeting that the 2 million users of OnStar need assurance of
signal stability. GPS-equipped OnStar units help responders locate
emergencies more quickly, Huber said, and "there would be a high
price due from applying SA."
Retired Air Force Gen. James McCarthy, a former pilot who currently
serves as a national security professor at the Air Force Academy and
is a PNT board member, told the meeting that SA can be eliminated
"with the right set of arguments, which have not yet been made or
articulated." McCarthy added that in his view there is no need for
SA, although he would not have said that five years ago.
The United States turned off its ability to degrade the GPS signal
seven years ago, but James Miller, a senior GPS technologist with
NASA, told the board meeting that many countries still do not trust
GPS because of "the international perception that continuing with SA
capability enables GPS to be turned off at any time."
Accuracy for both military and civilian users also will be improved
by insuring that the GPS constellation remains at its current level
of 30 satellites, according to Schlesinger and other board members.
Schlesinger said the Air Force only guarantees 24 satellites. An
increase would boost GPS accuracy, and he said 30 satellites are the
minimum needed to support ground forces operating in varied terrain.
Aviation users also say they need 30 satellites to support aircraft
navigation. Capt. Joseph Burns, director of flight standards and
technology at United Airlines and a board member, said he is
concerned about accuracy being degraded by interference.
Board member Timothy Murphy, a technical fellow with the Boeing
Commercial Airplane Group, said the company's vision is "tightly
wrapped" around the notion that there will be a "robust" satellite
navigation system based on 30 satellites.
Retired Air Force Maj. Gen. Robert Rosenberg, chairman of the Air
Force Space Command GPS Independent Review Team, told the board that
the GPS system must be robust enough to work in challenging
environments, such as mountains and urban canyons, which require more
than 24 satellites. Rosenberg said all users today are used to the
service that 28 to 30 satellites provide, and a reduction in that
number of satellites would have a potentially "enormous adverse
impact."
But it may be difficult to keep that number of fully functional
satellites in orbit in the near term, he said. By next year, 11 GPS
satellites will have reduced capabilities and the number of
satellites in the constellation may have to be cut.
Future funding for GPS may be limited and "more must be done with the
same or less finding," Rosenberg said. Col. Allan Ballenger,
commander of the Air Force GPS Wing, which is the acquisition arm for
the GPS program, says his funding runs between $900 million and $1
billion a year.
.
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