More Debris on Possible Collision Course with ISS

Following last week’s close call with a piece of space debris coming near the International Space Station, NASA is keeping an eye on another piece of debris which could come even closer to the station. Current estimates say the debris will approach the ISS early Tuesday morning, at about 3:14 a.m. EDT (0714 GMT) at a distance of only 2,600 feet (793 meters).

“The piece of debris which is expected to come close to ISS early tomorrow is from an explosion of a Russian navigation satellite in 1981,” NASA’s Chief Scientist for Orbital Debris Nicholas L. Johnson told Universe Today. NASA will decide by later today (Monday) if they will use the thrusters on the Zvezda module to move the ISS away from the debris. If so, the thrusters would fire for a short maneuver at 9:54 p.m. EDT tonight (01:54 March 17 GMT). Since space shuttle Discovery is on its way to rendezvous with the station on Tuesday, changes would have to made to the shuttle’s rocket firing sequence to compensate.

Johnson said that small pieces of debris have already collided with ISS on many occasions, but these debris to date have not affected the safety of the crew or the operation of the mission. “The dedicated debris shields on ISS can withstand particles as large as 1 cm in diameter,” he said.

Update: (5:35 CDT) NASA is now reporting that a maneuver will not be necessary for the ISS to avoid the orbital debris.

The ISS is said to be the most heavily shielded spacecraft ever built.

Johnson added that on average, close approaches to ISS occur about three times a month. An approach of debris is considered “close” only when it enters an imaginary “pizza box” shaped region around the station, measuring 0.75 kilometers above and below the station and 25 kilometers on each side( 2,460 feet above and below and 15.6 by 15.6 miles). NASA the size of the debris is not precisely known as yet, and how close it will come to the station. “This piece of debris and that which passed close to ISS last week are not associated with any recent events, such as last month’s satellite collision,” Johnson said.

Last week a rather large 12.7 cm (5-inch) piece of debris from a spent rocket motor came within 4.5 kilometers (2.8 miles) of the station. Usually, when debris is seen as on a possible collision course with the ISS, the station is able to fire thrusters and maneuver out of danger. However, because of the late notice, there wasn’t time to perform the thruster maneuvers, and the crew closed all the hatches on the station and retreated to the Soyuz capsule until the threat had passed.

According to MSNBC, the space station’s crew has taken refuge in the Soyuz as many as five times before today due to concerns about passing space debris, and the ISS has had to perform 8 collision avoidance maneuvers in the past 10 years.

Wired reported that information from a NASA database details 1,951 debris impacts to the space shuttle through 2006, requiring windows and radiators to be replaced.

“It’s yet another warning shot that we really have to do something about space debris now. We have to do something on an international level,” Harvard astrophysicist Jonathan McDowell told the Associated Press.

“As we continue to put stuff up there, the predictions are that the rate (of close calls) will increase,” added William Ailor, director of the Center for Orbital and Reentry Debris Studies at the Aerospace Corp. in El Segundo, Calif.

The U.S. Space Command tracks 13,943 orbiting objects 4 inches or larger. Only about 900 of those are working satellites, McDowell said. The rest is litter. There are thousands more smaller pieces of junk that can’t be tracked as easily.

We’ll keep you posted on the lastest space debris issue.

Sources: Email exchange with Nicholas Johnson, MSNBC, AP, Wired