Ariane 5 Flight 501
| Mission type | Magnetospheric |
|---|---|
| Operator | ESA |
| Spacecraft properties | |
| Launch mass | 1,200 kilograms (2,600 lb) |
| Start of mission | |
| Launch date | 12:34:06, June 4, 1996 |
| Rocket | Ariane 5G |
| Launch site | Kourou ELA-3 |
| End of mission | |
| Disposal | launch failure |
| Destroyed | June 4, 1996 |
| Orbital parameters | |
| Reference system | Geocentric |
| Regime | Highly elliptical |
| Epoch | planned |
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ESA quadrilateral mission insignia for the Cluster mission.
Cluster was a constellation of four European Space Agency spacecraft which were launched on the maiden flight of the Ariane 5 rocket, Flight 501, and subsequently lost when that rocket failed to achieve orbit. The launch, which took place on Tuesday, 4 June 1996, ended in failure due to an error in the software design caused by assertions having been turned off, which in turn caused inadequate protection from integer overflow. This resulted in the rocket veering off its flight path 37 seconds after launch, beginning to disintegrate under high aerodynamic forces, and finally self-destructing by its automated flight termination system. The failure has become known as one of the most infamous and expensive software bugs in history. The failure resulted in a loss of more than US$370 million.
Cluster consisted of four 1,200 kilograms (2,600 lb) cylindrical, spin-stabilised spacecraft, powered by 224 watt solar cells. The spacecraft were to have flown in a tetrahedral formation, and were intended to conduct research into the Earth's magnetosphere. The satellites would have been placed into highly elliptical orbits; 17,200 by 120,600 kilometres (10,700 by 74,900 mi), inclined at 90 degrees to the equator.
The Ariane 5 reused the inertial reference platform from the Ariane 4, but the Ariane 5's flight path differed considerably from the previous models. Specifically, the Ariane 5's greater horizontal acceleration caused the computers in both the back-up and primary platforms to crash and emit diagnostic data misinterpreted by the autopilot as spurious position and velocity data. Pre-flight tests had never been performed on the inertial platform under simulated Ariane 5 flight conditions so the error was not discovered before launch. During the investigation, a simulated Ariane 5 flight was conducted on another inertial platform. It failed in exactly the same way as the actual flight units.
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