The International Space Station partners are keeping a close eye on two pieces of debris that could potentially come within the safety perimeter maintained around the station. An avoidance maneuver is planned for Thursday using ATV-3′s engines.
One piece of debris is from a Russian Cosmos satellite, the other from an old Indian rocket. Neither one is expected to actually collide with the station but by ISS rules, avoidance maneuvers are initiated when an article is expected to enter a region of space 50x50x1.5 km centered on the station. The debris in question may just hop over the edge of this box.
With the European Space Agency’s cargo ship ATV-3 still docked to the station following an aborted departure on September 25, it was decided to use that ship’s spare propellant to execute the maneuver.
ATV-3 was supposed to leave the station on September 25, but following hatch closure and hook release, it was discovered that commands sent to one of the cargo ship’s panels from a computer on ISS were not reaching their target. ATV-3 was therefore resecured to the station while an investigation took place. Although initially the laptop in question was blamed for signal interference, it subsequently turned out that the command being sent was simply using the wrong ship code; none of the hardware involved has malfunctioned. With the avoidance maneuver planned, ATV-3′s departure cannot take place earlier than Friday.
ISS last experienced a near miss in March when an erratic remnant of the 2009 Cosmos 2251-Iridium 33 collision was spotted too late to perform an avoidance manuever. In that instance, the crew took shelter in their Soyuz capsules as the debris passed 11-14 km from the station. Collision hazards have occured every few months for the past two years, a frequency increase that some blame on the approaching solar maximum.
Below, a 2011 debris incident that was detected too late for an avoidance maneuver, passing within 250 m of the station: