ESA Sentinel 1A: Collision Avoidance maneuvre to avoid dead satellite

At the end of the first day after the launch (4 April): all deployments have been executed during the night and completed early in the morning at the beginning of the first ‘day shift’.

As the first day shift nears its end, a serious alert is received: there is a danger of a collision with a NASA satellite called ACRIMSAT, which has run out of fuel and can no longer be manoeuvred.

A collision avoidance manoeuvre during LEOP has never been done before, and has not been simulated.

The satellite had not yet reached its ‘normal pointing mode’, the ESA team could not manoeuvre it before this milestone was reached.

But there was no alternative. After a brief team consultation Juan, the ‘day shift’ Deputy Flight Operation Director, decided to start preparing the satellite in case a manoeuvre was needed, and it was to be executed by his colleagues on the night shift.

It is decided to manoeuvre Sentinel-1A. Its orbit altitude needs to be changed to escape the chaser satellite (debris).

The manoeuvre takes 39 seconds. The sequence of commands was uplinked during pass 37 over Alaska/Svalbard/Kiruna/ at 04:33 UTC for execution at 05:14 UTC, outside visibility.

The atmosphere was tense and the Main Control Room was filled with suspense.

All eyes were watching the big screens on the wall, waiting for a sign, good or bad.

As the satellite approached Troll ground station on the next pass and the telemetry started to scroll down in the twilight of the control room, the team held their breath.

But there was no need for concern. The satellite was in Orbit Control Mode and the GPS on-board showed a change in its orbit status.

The manoeuvre had been a complete success. The collision and premature end of the mission had been avoided. Just another day in the office for the ESA Flight Operations team.

But it does highlight the need for continued vigilance in the debris littered orbits around the Earth. A more permanent solution is vital to allow the continued use of Earth orbits for scientific research.

Russian Progress Module Unable to dock with ISS

An unmanned Progress supply ship during approach to the space station May 1. The spacecraft was docked using a manual system after its KURS automated navigation system malfunctioned.

(Credit: NASA)

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.

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