US military would jam GPS in a future conflict

The US military will jam the global positioning system (GPS) in any future conflict, to prevent hostile use of the satellite-based navigation system.

The Department of Defense (DoD) has launched several initiatives to equip its forces to use the GPS signals in a jamming environment, including a new military code broadcast by higher-power satellites and protected by improved cryptography.

Programme director Col Doug Loverro says the DoD is developing precision GPS jamming techniques that will "preserve civil use outside the theatre of operations". At the same time, the DoD is developing ways to improve the anti-jamming performance of its own receivers.

One initiative will add a "spectrally separate" military (M) code in nulls in the existing civil signal. This will allow the civil signal to be jammed without blocking the military code. The last 12 Lockheed Martin-built GPS Block IIR satellites and the first six Boeing-built Block IIFs are to be modified to add M-code, allowing initial operational capability by 2008.

Full operational capability is set for 2016, after the launch of higher-power Block III satellites. The DoD plans to begin a risk-reduction phase with two contractors in 2002, with one to be selected to develop and launch the Block IIIs from 2009. The spot-beam satellite "will provide a 20dB [anti-jam] performance increase in M-code", Loverro says.

While it waits for M-code and the Block III satellites, the DoD is pressing ahead with fielding an improved cryptographic module - SAASM - to enhance protection of the GPS military code. "The current security...is susceptible," he says. The DoD has decreed that, after 2002, only SAASM can be used in GPS receivers.

Recognising that retrofitting thousands of platforms with M-code and SAASM is a massive undertaking, the DoD is developing a combined receiver and security module "on a card". This will be installed in aircraft during avionics upgrades. Meanwhile, production of M-code receivers may be accelerated so that "day one" platforms such as the Lockheed F-117 can be equipped as early as possible.

Source: Flight International