PASADENA, Calif. Reaching across 179 million miles (288 million kilometers) of space, engineers will shortly begin beaming new software to a NASA spacecraft in a last-ditch effort to ready the idle probe for a 2001 rendezvous with a distant comet.
The innovative software, hastily written and tested over the past five months, will allow NASAs Deep Space 1 to recast the role of its science camera into that of navigational instrument. The original instrument, called a star tracker, ceased functioning in November 1999.
That loss, still unexplained, left the spacecraft without a way to use the stars to orient itself in space. Since then, the spacecraft has remained in a near slumber.
But that slumber must end soon if Deep Space 1 is to resume its course so it can pull off a bonus September 2001 flyby of the comet Borrelly.
The unexpected loss of the star tracker has already forced NASA to cancel another rendezvous with the comet Wilson-Harrington which flight planners had penciled in for March 2001. The spacecraft did, however, fly by the asteroid 9969 Braille on July 28, 1999.
Although the main $152 million mission ended last fall, the two additional flybys were much-anticipated gravy for scientists.
"Wed still like to capture as much from this mission as we can," said Marc Rayman, Deep Space 1s chief engineer at NASAs Jet Propulsion Laboratory. If the new software fails to work, the mission could come to an end.
NASA will begin loading the new code into Deep Space 1's computer over a 10-day period beginning May 30, test it for the balance of the month of June and then if all goes well instruct the spacecrafts futuristic ion-propulsion engine to resume thrusting. The schedule is extremely tight.
"If we had another two months we could make the software work with a very high degree of reliability, but we dont have the time," Rayman said. "We need to start thrusting with the ion-propulsion system in July."
The software fix will allow Deep Space 1s science camera to pinpoint target stars that will aide in determining the spacecrafts attitude, or orientation, in space.
The spacecrafts star tracker allowed it to image its surroundings, which it then compared to an on-board catalog of thousands of stars to determine where it was pointed.
Without it, the spacecraft can only find one star our sun using another sensor on board. Since the November 11, 1999 failure, engineers have also succeeded in plotting the signal strength of Deep Space 1s low-gain antenna during a series of calculated spacecraft rotations. The work has allowed engineers on the ground to infer the spacecrafts orientation, including when it is pointed directly at Earth.
Since Deep Space 1 can already find the sun on its own, adding the ability to locate Earth allows the spacecraft to recalculate its bearings that vital bit of knowledge it lost in early November.
With those two cosmic landmarks firmly located, engineers hope the spacecraft will next use its new software and science camera to begin hunting stars. Once the probe has found at least one known star, it can then skip from star to star and resume navigating its way to its tryst with Borrelly.
"Its a pretty neat method, and I think its one of the things thats so fun in working on problems like this its what engineers and scientists love to do: Its working on something thats seems impossible," Rayman said. "By all rights, we should have declared the extended mission dead."
Deep Space 1s primary mission came to a successful conclusion in September 1999, having tested the dozen innovative technologies it carried into space. The testing validated the use of the technologies, including the ion-propulsion engine, an autonomous navigation system and solar arrays that rely on special lenses to focus the suns rays, on future, higher-risk science missions.
Deep Space 1 was launched October 24, 1998. The mission was the first under NASAs New Millennium Program.
Deep Space 2, the twin microprobes lost at Mars in early December along with the Mars Polar Lander, was the programs second mission.
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