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Mysteries of the Milky Way
Europa
Beyond Hubble
A look inside the universe
Apollo
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| DEEP SPACE 1 |
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January 21, 2000 Deep Space 1, which successfully completed its prime mission of testing advanced technologies late last September, has added a new accomplishment during its extended mission. On January 14, the mission team directed the spacecraft to point its main antenna toward Earth in a complex and innovative maneuver. This challenging maneuver allowed the spacecraft to transmit a large volume of important science and engineering data to the operations team at NASA's Jet Propulsion Laboratory. Further, the maneuver was accomplished without the use of one of Deep Space 1's primary sensors, the star tracker. The star tracker, which failed in November, was used to help determine the spacecraft's orientation by tracking the positions of stars. It was a new and advanced sensor, but was not one of the 12 advanced technologies that were the focus of Deep Space 1's successful primary mission. Prior to this maneuver, Deep Space 1 was pointed toward the Sun. Without the star tracker, the spacecraft did not know which direction to turn to search for another target; in this case, the Earth. Working with NASA's Deep Space Network, the operations team watched the radio signal grow in strength as the spacecraft antenna pointed closer to Earth and then fade as it went past. After two sweeps, engineers calculated what time the next one would occur. Then, accounting for the time it takes a radio signal sent from Earth to reach the spacecraft and for how long it takes to tune to the correct frequency and transmit an instruction, a code was sent to trigger commands stored in the spacecraft's computer that would halt the rotation. Spacecraft, like sailboats, cannot "stop on a dime." But engineers had taken that into consideration and designed the commands to include an instruction to rotate back to the desired point. The design worked perfectly and the spacecraft was right on target. Commands were sent to Deep Space 1 to transmit stored onboard data at a high rate. Some of the information returned included observations of Mars from November. "This was an exciting and interesting problem to solve and represents another challenge for the mission that has so successfully accomplished so many remarkable feats. And our success in keeping the antenna pointed toward Earth shows that we are well on the way to developing an effective solution," said Dr. Marc Rayman, Deep Space 1's chief mission engineer. Now that the spacecraft can point its main antenna reliably toward Earth for extended periods, the mission team will be able to develop new computer programs to operate Deep Space 1 without the star tracker. Deep Space 1 is now over one and two-thirds as far from Earth as the Sun is and over 650 times as far as the moon. At this distance of more than 252 million kilometers (about 156 million miles), radio signals traveling at the speed of light take almost 28 minutes to make the round trip. -JPL |
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