The International Space Station has shed two more pieces of debris into space, sparking concern among NASA officials.
The station has cast off at least three objects since 5 February, with the latest space junk seen drifting away on Sunday. Mission managers are scrambling to identify the objects and assess any risks from their loss or potential collisions with the station.
A visible ID number helped managers trace one object seen Sunday to a 6 centimetre “eyebolt” from the Russian cargo vehicle Progress, which docked with the station on 31 January.
Progress and the docked Soyuz transport vehicle each use four of these bolts to keep their solar panels folded after launch. When the panels are deployed by other explosive bolts, these eyebolts are no longer needed, but they are designed to remain fixed to the spacecraft.
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Images sent from the station reveal the second object to be a washer. But the thin strip-like object seen floating away from the station on 5 February, soon after some tests on Progress’s thrusters, has not yet been identified.
Radar network
US astronaut Mike Foale, one of the station’s two crew members, watched the stray eyebolt through a window for several minutes as it passed in front of the station at a relative speed of 5 centimetres per second, according to an MSNBC report.
The bolt’s relatively low speed compared to typical debris impact speeds of 10 kilometres per second eased engineers’ fears of colliding with the bolt. But this still prompted NASA to request a track on the object by the US military, which used a worldwide radar network to search for the bolt. However, the search was unsuccessful.
Cameras on the station’s robotic arm have also been trained on the station to check for damage from collisions with space junk, but none has been found, according to a NASA spokesperson. Both crew members will also visually inspect the station’s exterior while installing new science experiments on a 5-hour spacewalk scheduled for 26 February.
Heavily shielded
“There isn’t a concern to the vehicle or crew safety,” Kylie Moritz, a spokeswoman for NASA’s Johnson Space Center in Houston, Texas told New Scientist. “All systems continue to function well on board.”
Nonetheless, NASA has an office devoted entirely to studying the risks of orbital debris to spacecraft. More than 100,000 objects between one and 10 centimetres long orbit the Earth and most travel at speeds of about 8 kilometres per second. During the Russian space station Mir’s 15 years in orbit, space debris caused most damage to its unprotected solar arrays.
According to NASA’s orbital debris office, critical components of the ISS – the most heavily shielded craft ever flown – will normally be able to withstand the impact of debris as large as one centimetre across.
Risk of impacts with larger objects is said to be “slight”, and the station can manoeuvre to avoid hitting known objects. In 2001, the station was redirected with rockets to steer clear of a tool dropped during a spacewalk.
