Space officials are keeping a watchful eye on two different pieces of space junk that may force the International Space Station to steer away from potential impact threats.
Debris from the Russian COSMOS satellite and a fragment of a rocket from India may come close enough to the space station to require a debris avoidance maneuver. If needed, the maneuver would be done using the ESA’s Automated Transfer Vehicle “Edoardo Amadi.” The ATV was supposed to undock on Tuesday night, but a communications glitch forced engineers to postpone the departure.
Both pieces of debris are edging just inside the so-called “red zone” of miss distance to the station with a time of closest approach calculated to occur Thursday at 10:42 a.m. ET. It is not known how large the object is.
An approach of debris is considered close only when it enters an imaginary “pizza box” region around the station, measuring 1.5 by 50 by 50 kilometers (about a mile deep, by 30 miles across, by 30 miles long) with the vehicle in the center.
NASA says the three-person Expedition 33 crew is in no danger and continues its work on scientific research and routine maintenance. The current crew includes NASA astronaut Sunita Williams, Japanese astronaut Akihiko Hoshide and Russian cosmonaut Yuri Malenchenko.
If the maneuver is required — and NASA said it could be called off any time — it would occur at 8:12 a.m. ET Thursday, using the engines on the ATV, which remains docked to the aft port of the station’s Zvezda service module. It usually takes about 30 hours to plan for and verify the need for an avoidance maneuver.
Debris avoidance maneuvers are conducted when the probability of collision is greater than 1 in 100,000, if the maneuver will not result in significant impact to mission objectives. If it is greater than 1 in 10,000, a maneuver will be conducted unless it results in additional risk to the crew.
If there’s not enough time to conduct an avoidance maneuver, the space station’s astronauts may be alerted to take shelter in their Soyuz vehicles. The last time that happened was on March 24, but the threatening object passed by without incident.
The space station is thought to receive small micrometeoroid hits frequently, based on the data from experiments left outside the station and on visual inspections of the station’s hull. But there have been never been any impacts large enough to cause depressurization or other problems on the International Space Station.
Tuesday’s initial attempt to undock the ATV was called off due to a communications error between the Zvezda module’s proximity communications equipment and computers on the ATV. Russian engineers told mission managers that they fully understand the nature of the error and are prepared to proceed to a second undocking attempt. That attempt has been scheduled for Friday, due to Thursday’s potential space debris threat.
Once the ATV is undocked, it will move to a safe distance away from the station for a pair of engine firings that will send the cargo ship back into Earth’s atmosphere to burn up over the Pacific Ocean.
The ATV still has extra fuel on board, and so the decision was made to use that fuel for the avoidance maneuver if necessary.