KENNEDY SPACE CENTER, Fla.--Russian engineers believe radio interference caused an approaching unmanned Progress supply ship to abort its approach to the International Space Station Friday, officials said Saturday. Subsequent tests showed the cargo craft is in good health and that its automated rendezvous system is working normally, clearing the way for a second docking attempt around 12:10 p.m. EDT Sunday.
The aborted approach Friday occurred about 20 minutes before the Progress 38 craft was scheduled to dock at the Zvezda command module's aft port. Instead of proceeding, the craft aborted and flew safely past the station, rotating slowly to keep its solar arrays face on to the sun.
It was the second Progress docking problem in a row for the Russians. During an approach May 1, a problem with the automated KURS navigation system aboard an approaching cargo ship forced the space station commander to take over manual control using a backup system.
Russian engineers have concluded the abort Friday was triggered by interference between the KURS automated rendezvous system and a television transmitter that is part of the backup manual system, known as TORU, that was activated around the time of the abort. The result of the interference was a "cancel dynamic operations" command that prompted the Progress flight computers to abort the automated approach.
It is not yet clear why the interference issue cropped up during this approach, but Russian engineers told their NASA counterparts that the Progress spacecraft performed normally in the face of conflicting commands, executing a safe abort and standing by for additional instructions.
The KURS system features redundant components, or "strings," and subsequent tests in the absence of any interference showed both were working normally. As a result, a second attempt to dock the Progress 38 spacecraft will be made Sunday, but the TORU system will not be activated.
The Progress 38 spacecraft, loaded with 1,918 pounds of propellant, 110 pounds of oxygen, 220 pounds of water, and 2,667 pounds of experiment equipment, spare parts, and other supplies, was launched Wednesday from the Baikonur Cosmodrome in Kazakhstan.