Mars Observer was meant to end a seventeen-year gap. No American spacecraft had gone to Mars since the Vikings, and this one carried an ambitious payload — a camera, a thermal emission spectrometer, a laser altimeter, a magnetometer — intended to map the planet's surface, atmosphere and gravity field for a full Martian year.
It was also a product of a particular management philosophy: build it on a commercial communications-satellite bus to save money, then discover that adapting the bus for deep space costs more than a purpose-built design would have. The budget roughly tripled during development to some $813 million.
On 21 August 1993, three days before orbit insertion, the spacecraft was commanded to pressurise its fuel tanks in preparation for the burn. It never answered again. There was no telemetry, no partial signal, nothing — an instantaneous and total loss at the worst possible moment.
The investigation concluded that the most likely cause was a rupture in the fuel pressurisation system: nitrogen tetroxide had probably leaked past a valve during the long cruise and mixed with the fuel, and the pressurisation command detonated it, either destroying the spacecraft or setting it spinning too fast to recover. Nobody will ever be certain.
The loss reshaped NASA's planetary programme. The response was the faster, better, cheaper doctrine — many small missions instead of one large one, so that no single failure could erase a decade. Mars Global Surveyor flew most of the lost instruments four years later and succeeded brilliantly; two other missions of the new philosophy failed outright in 1999, which prompted a rethink of its own.
