Item History: SEVS was one of the first satellite simulators in the early development and testing of GPS user equipment. At the time, four prototype satellites were in orbit, providing only a few hours of coverage each day – often at very inconvenient times. Simulating the satellite signals in a range of programmable, repeatable scenarios enabled GPS developers to evaluate their systems without being hampered by the availability of orbiting-satellite signals.
In its qualification testing capacity, SEVS powered, controlled and monitored GPS receivers, providing interface signals, coordinated satellite data and host vehicle aiding data such as inertial, baro altimeter and precise time. SEVS simulated real-time flight scenarios, during which the GPS receiver would transmit its performance data into the SEVS data recording system for post-test evaluation against truth data.
SEVS simulation capabilities included:
- Masking – both terrain and body
- Antenna – different kinds of antenna technology
- Jammer – stationary or moving using closed-circuit simulation, with a maximum of two types of jammers at any time
- Satellite – up to 24 satellites (up to six at a time), with truth data used to generate satellite motion, satellite clock offset and ionospheric delay
- Host vehicle motion – predefined motion (i.e., no pilot), with separately computed attitude. Motion simulation included coordinated turns for fixed-wing aircraft, ship’s motion models and vectors fixed by velocity for land vehicles.