A NASA mission to Mars, launched on 7 November 1996 for arrival in September 1997, effectively as a replacement for the failed Mars Observer. It was successfully put into a high elliptical orbit around Mars on 11 September 1997. In the following months, it was gradually manoeuvred into an almost circular near-polar orbit from which to carry out systematic mapping between March 1998 and January 2000. The technique used to change the spacecraft’s orbit was aerobraking, in which the drag of the martian atmosphere was used to reduce the orbital speed of the craft. Mars Global Surveyor was designed to serve as a communications satellite for future missions after completion of its mapping mission.