Stardust's burn to depletion: On March 24 four rocket motors on NASA's Stardust spacecraft, illustrated in this artist's concept, fired until the spacecraft's fuel was depleted.Courtesy NASA/JPL-Caltech Yesterday NASA's Stardust spacecraft performed a final burn with its main engines which effectively ended the life of NASA's most traveled comet hunter. Called a "burn to depletion", the procedure will help to answer the question of how much fuel Stardust had left in its tank. While it sounds like running your snow blower until it runs out of gas to store it for the summer, this was an important test as no one has invented an entirely reliable fuel gauge for spacecraft. Part of the process of approximating fuel use is looking at the history of the vehicle's flight and how many times and for how long its rocket motors have fired.

Stardust's burn to depletion is expected to be useful especially because the spacecraft has been proverbially "running on empty" for a long time. Stardust has been in space for over 11 years and has flown past an asteroid (Annefrank), collected particle samples from a comet (Wild 2) and returned them to Earth in a sample return capsule in January 2006. Then, after these primary objectives, it was then re-tasked to perform a flyby of comet Tempel 1, a task it completed last month.

Before the burn to depletion Stardust pointed its antenna at Earth and sent information on the burn as it happened. The command ordering the rockets to fire was sent for 45 minutes, but the burn lasted just 146 seconds. 20 minutes after the engines burned out, Stardust's computer commanded its transmitters to turn off. Without fuel to power the spacecraft's attitude control system, Stardust's solar panels will not remain pointed at the sun. When this occurs, the spacecraft's batteries are expected to drain of power and deplete within hours.

Its a fitting end to a very impressive mission for NASA.

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