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12-Jan-05 | Delta flight 311 – Deep Impact

The first launch from Planet Earth in 2005 was a Delta II, as flight 311 set Deep Impact on course to intercept Comet Tempel 1 later this year.

It was a picture-perfect launch as the Delta team threaded the needle of an instantaneous launch window at 13:47:08.574 EST on 12 January 2005. The three-stage Delta 7925, looking very much like a GPS satellite carrier with its standard 9.5-foot-diameter payload fairing, leapt from the pad at SLC-17B and rose into a clear Florida sky.

Upper level winds that had been a concern during the countdown had subsided, and the Delta second stage shut down after 9 minutes 46 seconds in a nearly-circular parking orbit of 89.95 by 90.28 nautical miles with an inclination of 29.735 degrees. The stage’s Aerojet AJ10-118K engine fired for a few seconds longer than planned to compensate for a first stage underperformance of unknown cause, but this too was well within flight parameters.

After about a fifteen minute coast phase, the second stage restarted for another burn, this one of about 1 minute 40 seconds, that raised the apogee of the orbit. This was followed by the third stage burn which sent Deep Impact into a hyperbolic escape orbit, on course for a comet.

Once again the telemetry downlink was spotty, a problem exacerbated by a flight apparently devoid of on-board cameras. The link with Ascension Island was lost toward the end of the second AJ10 burn, causing a swarm of people to crowd into the telemetry lab to attempt to read something that wasn’t there. The signal was restored by an Air Force tracking ship called OTTR near the west coast of Africa in time to see third stage spin-up and ignition, and telemetry was maintained through spacecraft separation.

The nail-biting wasn’t over for the Deep Impact team, however, as signals received at Canberra, Australia, were indeterminate as to whether its solar panels had deployed, an event that should have occurred soon after separation. Then, since no one had bothered to include Goldstone, California, in the tracking network, it was feared that controllers would have to wait until Deep Impact passed over Madrid, Spain, for further information — but a last-minute hook-up at Goldstone sent word that the panels were deployed and all was well, for the most part. It turns out that catalyst bed heaters in the spacecraft’s propulsion system briefly caused some temperature sensors to send an alert, which put the probe into safe mode until ground control could take a look at it. (The resulting shift to low-gain communication led to the difficulty in ascertaining the status of the craft.) Project managers suspect that the temperature limits were set a bit too low, and are confident that no hardware was damaged.

Deep Impact is the eighth mission* in NASA’s highly successful Discovery Program. Its principal investigators are with the University of Maryland, and the spacecraft was built by Ball Aerospace in Boulder, Colorado, under the management of the Jet Propulsion Laboratory. On 04 July 2005 it will send its “impactor” subassembly into a collision course with Comet Tempel 1, while the “flyby” module collects transmitted data and watches closely with sensors of its own. It is hoped that the impact will release ejecta that will provide clues to the composition of comets and, by extrapolation, the early solar system.

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