Redocking of station cargo ship will be tricky affair
BY WILLIAM HARWOOD
Posted: December 21, 2000
U.S flight controllers will provide oversight and make a U.S. video conferencing system available to relay live television views from the Progress to the ground during final approach.
But only the Russians can order an abort if the final rendezvous goes awry.
"This is a Russian vehicle, the Progress, docking to the Russian end of the international space station," said station flight director John Curry. "We are heavily involved in providing a command link. But I cannot physically push the (abort) button. We cannot talk directly to the Progress, that has to come when we're over (Russian) ground sites from either Korolev (mission control) or the on-board crew."
The Progress M1-4 cargo ship was launched from the Baikonur Cosmodrome Nov. 16 and docked with the Zarya module's Earth-facing, or nadir, port two days later. The Progress was unloaded and undocked Dec. 1 to make way for arrival of the space shuttle Endeavour two days later.
Russian engineers believe the original KURS approach failed because of a software glitch that prevented the ship's computer system from smoothly switching from guidance data transmitted by antennas on the Zvezda module to signals transmitted from Zarya.
A software patch has been uplinked to the Progress to correct that problem and Curry said engineers are confident the guidance data "handoff" will go smoothly next week.
But the KURS system can only bring the Progress to a point 200 meters or so from the station. A KURS antenna needed for the final push to docking was retracted during the initial approach and it cannot be re-extended.
The TORU system has no backup and NASA managers initially opposed the redocking. But Russian engineers have demonstrated at least three abort modes, any one of which would prevent any chance of a collision even if the TORU system malfunctioned.
First, Curry said, Russian flight controllers can uplink an abort command to force an automatic fly-away maneuver. The KURS system on its own could not attempt to complete the final push to docking because of the retracted antenna. And Gidzenko could order an abort from the station if necessary .
Concern about the possibility, however remote, of a collision between the Progress and the space station is an unavoidable consequence of a catastrophic collision in 1997 that severely damaged the Mir space station.
During a manual TORU-system approach, a Progress vehicle crashed into Mir and punctured one of its modules.
But Curry said today that test was an altogether different sort of operation from the one that will be attempted next week. And he should know. He was in the Russian control center the day the collision occurred.
"They were trying to completely eliminate the KURS system from the equation," Curry said. "The KURS system is a very reliable automated rendezvous and docking tool and we're using that Tuesday to get us from long range distance in to that station keeping distance at the 200-meter point.
"None of that exists here," Curry said, "because of the fact that we're taking the reliable KURS system and letting it do the stuff to get us to the station-keeping point. Every TORU docking that was performed on Mir from the close in distance was successful. Every single one."
The space station will be in a solar inertial attitude, or orientation, for the Progress M1-4 vehicle's redocking Tuesday. To visualize this attitude, imagine a drawing of the station pinned to the minute hand of a wall clock so that the station is free to rotate as the hand moves around the clock face.
Now imagine the Earth drawn on the face of the clock and the sun shining from the left. The KURS system will bring the Progress to its station keeping point at orbital noon, that is, when the station is roughly in the nine o'clock position with the Progress poised on the sunward side.
The docking will take place when the station is in the 12 o'clock position with the Progress approaching from the left and the Zvezda module facing the Earth.
NASA will provide live video of the redocking attempt on NASA television and we will post running play-by-play coverage in our mission status center as events unfold. A detailed wrapup story will be posted once the procedure is complete or as conditions warrant.
See the Status Center for full play-by-play coverage.