Mars Global Surveyor maps the planet Mars Observer lost
Mars Observer died three days short of orbit in 1993. Its instruments were rebuilt as Global Surveyor, which found fossil crustal magnetism and geologically fresh gullies.
Mars Observer was NASA's first Mars mission in seventeen years: $813 million, eight instruments, a commercial Earth-satellite bus. On 21 August 1993, eleven months into the cruise and three days before orbit insertion, controllers commanded it to pressurise its propulsion system. Nothing came back. A Naval Research Laboratory board blamed nitrogen tetroxide seeping past check valves into the pressurisation plumbing: when the helium valve opened it met monomethylhydrazine and ruptured a line, spinning it into a contingency mode that left the transmitter off.
Mars Global Surveyor flew Mars Observer's flight spares and rebuilt designs — Mars Orbiter Camera, Mars Orbiter Laser Altimeter, Thermal Emission Spectrometer, magnetometer, electron reflectometer — on a far smaller spacecraft: $154 million to build, $65 million to launch. It launched 7 November 1996 and reached Mars 12 September 1997.
One solar panel had not latched on deployment, and aerobraking, hundreds of dips through the upper atmosphere to shed orbital energy without fuel, loaded that hinge. Controllers cut the drag to a third, stretching a four-month manoeuvre to eighteen; systematic mapping began in March 1999.
The magnetometer found magnetised stripes, the longest over two thousand kilometres, in the ancient southern highlands, among the strongest crustal magnetism in the solar system: the fossil of a core dynamo that shut down before the Hellas and Argyre basins were excavated. MOLA mapped global topography to about a metre vertically, the northern plains exceptionally flat. In June 2000 Michael Malin and Kenneth Edgett published images of gullies in steep crater walls: alcoves, channels, debris aprons, almost no craters on top. Whether they require liquid water or dry carbon-dioxide flows can cut them is still argued.
It mapped for more than seven years and relayed data for the rovers below, last speaking on 2 November 2006. A routine command to move a solar array tripped a parameter written to the wrong memory address five months earlier; it turned to an attitude that left one battery in direct sunlight, and both drained.