Navstar 7

Navstar 7, also known as GPS I-7 and GPS SVN-7, was an American navigation satellite which was lost in a launch failure in 1981. It was intended to be used in the Global Positioning System development programme. It was the seventh of eleven Block I GPS satellites to be launched, and the only one to fail to achieve orbit.

Navstar 7 was launched at 01:10 UTC on 19 December 1981, atop an Atlas E/F carrier rocket with an SGS-1 upper stage. The Atlas used had the serial number 76E, and was originally built as an Atlas E. The launch took place from Space Launch Complex 3E at Vandenberg Air Force Base.

During preparations for launch, a seal on the number B2 engine of the MA-3 booster section of the Atlas was replaced. Sealant from this seeped into three coolant holes, plugging them. Four seconds after liftoff, the engine overheated and burned through its gas generator, severing an oxidiser line. Within seven and a half seconds of launch the engine lost thrust, causing the rocket to pitch out of control. It was destroyed by range safety, with debris landing within 150 m of the launch pad, less than twenty seconds after liftoff.

If the launch had been successful, it would have placed Navstar 7 into a transfer orbit, from which the satellite would have raised itself into medium Earth orbit by means of a Star-27 apogee motor. The spacecraft had a design life of 5 years and a mass of 758 kg.