At 33 minutes after 4 p.m. PDT today, NASA's Stardust spacecraft finished its last transmission to Earth. The transmission came on the heels of the venerable spacecraft's final rocket burn, which was designed to provide insight into how much fuel remained aboard after its encounter with comet Tempel 1 in February.
"Stardust has been teaching us about our solar system since it was launched in 1999," said Stardust-NExT project manager Tim Larson from NASA's Jet Propulsion Laboratory in Pasadena, Calif. "It makes sense that its very last moments would be providing us with data we can use to plan deep space mission operations in the future."
The burn to depletion maneuver was designed to fire Stardust's rockets until insufficient fuel remains to continue, all the while downlinking data on the burn to Earth some 312 million kilometers (194 million miles) away. Mission personnel will compare the amount of fuel consumed in the burn with the amount they anticipated would be burned based on their fuel consumption models.
Fuel consumption models are necessary because no one has invented a reliable fuel gauge for spacecraft when in the weightless environment of space flight. Until that day arrives, mission planners can approximate fuel usage by looking at the history of the vehicle's flight and how many times and for how long its rocket motors have fired.
Mission personnel watched the final data from the burn come down at JPL's Space Flight Operations Facility and at the Stardust-NExT mission support center at Lockheed Martin Space Systems in Denver.
"Stardust motors burned for 146 seconds," said Allan Cheuvront, Lockheed Martin Space Systems Company program manager for Stardust-NExT. "We'll crunch the numbers and see how close the reality matches up with our projections. That will be a great data set to have in our back pocket when we plan for future missions."
The Stardust team performed the final burn to depletion because NASA's most senior comet hunter is a spacecraft literally running on fumes. Launched on Feb. 7, 1999, Stardust had completed its prime mission back in January 2006. By that time, Stardust had already flown past an asteroid (Annefrank), flown halfway out to Jupiter to collect particle samples from the coma of a comet, Wild 2, and returned to fly by Earth to drop off a sample return capsule eagerly awaited by comet scientists. NASA then re-tasked the spacecraft to perform a bonus mission to fly past comet Tempel 1 to collect images and other scientific data. Stardust has traveled about 21 million kilometers (13 million miles) in its journey about the sun in the few weeks since the Valentine's day comet Tempel 1 flyby, making the grand total from launch to its final rocket burn about 5.69 billion kilometers.
With all that mileage logged, the Stardust team knew the end was near. Now, with its fuel tank empty and its final messages transmitted, history's most traveled comet hunter will move from NASA's active mission roster to retired.
"This kind of feels like the end of one of those old Western movies where you watch the hero ride his horse towards the distant setting sun – and then the credits begin to roll," said Larson. "Only there's no setting sun in space."
Stardust-NExT was a low-cost mission to expand the investigation of comet Tempel 1 initiated by NASA's Deep Impact spacecraft. JPL, a division of the California Institute of Technology in Pasadena, managed the Stardust-NExT project for the NASA Science Mission Directorate, Washington, D.C., which was part of the Discovery Program managed by NASA's Marshall Space Flight Center in Huntsville, Ala. Joe Veverka of Cornell University, Ithaca, N.Y., was the mission's principal investigator. Lockheed Martin Space Systems, Denver, built the spacecraft and managed day-to-day mission operations.