From: Johns Hopkins University
Posted: Monday, August 19, 2002
CONTOUR Team Listens For A Signal
With electronic eyes and ears pointed to the sky and a fix on CONTOUR's location more than 1.3 million miles (2.1 million kilometers) from Earth, the mission team continues checking for a signal from the spacecraft.
"The plan is to watch and monitor," says Mission Director Dr. Robert Farquhar of the Johns Hopkins University Applied Physics Laboratory, which built CONTOUR and manages the mission for NASA. "We realize the possibilities are small, but we can't discount the idea that the spacecraft is still operable. We have to determine that before we give up."
Since Friday the team has received telescope images from several observatories showing two objects traveling along CONTOUR's predicted path - which engineers believe is CONTOUR and part of the spacecraft that may have separated from it when CONTOUR's solid rocket motor fired on Aug. 15. Mission operators at APL and navigators at NASA's Jet Propulsion Laboratory are using these images to pinpoint the spacecraft's orbit and are aiming the Deep Space Network's powerful 70-meter and 34-meter antennas along that trajectory.
"Without knowing how big the objects in the telescope images are, we're going to work on the assumption that the spacecraft may still be largely intact," Farquhar says. "You need at least three separate observations to determine an orbit, and we have that. We know we're looking in the right place."
This week, mission operators are listening to determine if CONTOUR is alive and can carry out a timed command to cycle and attempt to transmit through three of its four antennas. The sequence is timed to start 96 hours after CONTOUR receives its last command. Because the team can't determine which commands the spacecraft may have received late last week, the cycling between transmitters and antennas could have started as early as 4:09 (EDT) this morning or could start as late as 10:09 (EDT) tonight.
The 60-hour sequence begins with the first of CONTOUR's two transmitters cycling 10 hours each through the low-gain and multidirectional (pancake) beam antennas on CONTOUR's aft side - opposite the dust shield - and the forward-side low-gain antenna. (Because of its narrow beamwidth and the unlikely prospect of its facing Earth, CONTOUR's high-gain dish antenna is not part of the sequence.) The second transmitter then repeats the pattern.
"It may be difficult to hear anything because, depending on the spacecraft's position and condition, the antennas might not have a direct line of sight toward Earth," says CONTOUR Mission Operations Manager Mark Holdridge. "But we'll be listening."
If the team doesn't hear from the spacecraft this week, Farquhar says, a final concentrated effort will be implemented in December when the antennas are in a more favorable orientation. "We're obligated to give it this last try," he says. "And who knows, we might get lucky."
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