Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: TUESDAY, May 1, 1990 TAG: 9005010511
SECTION: NATIONAL/INTERNATIONAL PAGE: A/1 EDITION: EVENING
SOURCE: Associated Press
DATELINE: GODDARD SPACE FLIGHT CENTER, MD. LENGTH: Medium
The telescope's No. 2 high-gain antenna, wedged in one position since last Friday, was free and sending data through relay satellites.
The National Aeronautics and Space Administration expected calibration and other normal start-up work to begin by tonight and to receive its first pictures from the telescope by next weekend.
"The moral of the story is that there is no solution that's too humble," said David Skillman, who built a model of the jammed antenna.
"We were faced with a problem on the telescope that involved quite intricate geometry," he said. "A number of us realized we could benefit greatly from a model. Someone suggested that even a Tinkertoy model could be useful."
He drove to a toy store Sunday afternoon and bought two boxes of the construction toy. He got the other items in a drugstore and put the model together in 15 minutes with another engineer, John Decker.
The telescope has two dish-shaped high-gain antennas that are designed to transmit science data to two orbiting relay satellites at speeds equivalent to sending the contents of a 30-volume encyclopedia in 42 minutes.
The No. 2 antenna jammed on Friday when engineers were turning it left and right. Sensing something wrong and trying to prevent damage, the telescope's computer shut down the whole system.
One engineer noticed that the inch-thick electrical cable on the back of the antenna was slightly out of position. With that in mind, they looked at telemetry data for signs that the cable could interfere with the counterweights when the dish was turned to certain positions.
The model that Skillman and Decker built showed that to be the case and that, in turn, would cause the motors to work too hard and be automatically halted.
Troubleshooters had thought the cable might be a possible problem after studying photographs of the telescope while it still was on the ground and nestled in the cargo bay of space shuttle Discovery.
Data from the telescope indicated the dish's position and, said Skillman, "when we set the model to angles in the computer screen, we could see the interference in antenna parts and cable."
What they visualized with the model was matched with computer drawings at Lockheed Missiles and Space Co. in California. "They didn't have the cable in them," Skillman said. "Once we sketched in the cable, they saw the interference."
Armed with that knowledge, computer commands were sent to the telescope directing exactly the way the dish should move to back out of its jam.
"The antenna moved beautifully and easily out of its problem and back to normal," Skillman said. "Many times a simple solution is the best solution."
Until, perhaps some day, an astronaut goes to the antenna and bends the cable out of the way, NASA's solution also is a simple one. It sent up commands to the telescope's computer ordering it to avoid the position where it could come in contact with the cable.
by CNB