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25-Sep-01 | Deep Space 1 gets up close and personal… with a comet

On Saturday, 22 September, Deep Space 1 became the second spacecraft ever to capture close-up images of a comet. DS-1 passed within 1,200 nautical miles of comet Borrelly at a relative speed of about 37,000 mph. The encounter occurred at 22:30 UTC, with the first data reaching Earth about 13 minutes later.

Amazingly, not only did the unshielded spacecraft survive the potential impacts of cometary dust as it passed through the coma — a mission for which it was never designed — it significantly expanded the state of comet observation. With perfect aim and using all four of its advanced technology (i.e. experimental) instruments, DS-1 captured the most detailed black-and-white photos yet of a comet’s nucleus; that same camera package (MICAS) carries an infrared imaging spectrometer. PEPE (Plasma Experiment for Planetary Exploration) collected ion and electron data from the coma and observed its interaction with the solar wind. Measurements of the magnetic field were also taken. Much of the data will continue to be downloaded over the next few days.

The preliminary results — showing a complex, elongated nucleus spouting asymmetric jets while not travelling at the center of its own coma — appear to have comet scientists perplexed, who apparently were expecting a neatly packed schoolyard snowball. The data from Deep Space 1 will beneficially influence several future comet rendezvous missions, including CONTOUR and Deep Impact, both of which will be launched on Delta II vehicles.

DS-1, which launched aboard Delta 261 on 24 October 1998, has already tripled its design lifetime and long ago successfully completed its primary mission of testing a dozen advanced technologies including a xenon ion engine and autonomous navigation system; in 1999 it survived the loss of its (off the shelf, non-experimental) star tracker thanks to the tireless efforts of the project team led by Marc Rayman. Saturday’s fly-by was considered little more than the stem on the cherry on top of the banana split that was an already-stellar mission; the fact that it succeeded beyond anyone’s wildest dreams is a testament both to the robustness of the hardware and the hard work of the team.


     

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