posted 08-28-2008 05:20 PM               

For the first time in five years, the International Space Station changed course on Wednesday to avoid a piece of space junk -- in this case, satellite debris that the Russians have insisted wasn't there.

The five-minute maneuver made use of the engines aboard the European Space Agency's Automated Transfer Vehicle, or ATV, which is docked at the Russian end of the station. As a result of the thruster firing, the space station's 18,000-mph progress around Earth was slowed by about 2 mph, lowering the average height of its orbit by about a mile.

In a status report, NASA said the course change was required because the space debris was predicted to come within about a mile (1.627 kilometers) of the station -- bringing the risk of a collision above the threshold for a "debris avoidance maneuver."

Russian news reports said Wednesday's maneuver was required to dodge "pieces of space debris" of unspecified national origin. ESA's news release stated merely that the debris came "from an old satellite." NASA's main station news page identified the threatening object as "a spent Russian rocket," but the more detailed daily report called it "part of the Kosmos-2421 satellite" (part of the payload, not part of the booster).

Launched in June 2006, the Cosmos-2421 was a naval surveillance satellite, designed for electronic eavesdropping to keep track of Western military vessels. According to U.S. tracking data, the satellite disintegrated on March 14 into hundreds of pieces -- with further fragmentation on April 28 and June 9. More than 500 objects resulted, creating one of the largest debris clouds in space history.

In recent weeks, the station has been cycling through the thickest region of the debris cloud. "It's been giving us fits," said one analyst, who asked that his name not be used because he was not authorized to speak publicly. Although the peak concentration has passed, further avoidance maneuvers may yet prove to be necessary, another source told msnbc.com on condition of anonymity.

posted 08-29-2008 09:00 AM               

Conjunction Update: Using ATV thrusters, the ISS performed a 1 m/s braking burn yesterday at 12:11pm EDT to remove the risk of collision with an orbital object,- #33246 (part of the Kosmos-2421 satellite). The retrograde firing of 5 min 2 sec duration resulted in a mean altitude loss of ~1.77 km. Propellant usage: ~98 kg of ATV prop, leaving ~190 kg in “Jules Verne” prior to undock (possibly with some margin, to be assessed by ESA) and ~320 kg of Progress/SM props for attitude control of the stack. A second possible conjunction with another piece (#33248) of Kosmos-2421 has been identified for tomorrow (8/29) at 9:09pm EDT, currently predicted to be in the RED box. This would require another DAM (Debris Avoidance Maneuver), but more tracking is required for a burn decision. Estimated prime TIG (Time of Ignition): tomorrow 7:00pm. Prop strategy is currently under study. If a second DAM is necessary tomorrow, using ATV prop, the Progress 29P undocking on 9/1 (Monday) can be supported by SM thrusters. Ballistic calculations must continue to account for future Soyuz launch, Soyuz landing and Shuttle ULF2 launch/rendezvous constraints.

posted 09-06-2008 01:47 PM               

Conjunction Update: When a conjunction prediction last night (8:00pm EDT) for a piece of Kosmos 2421 debris showed a miss distance of 0.67 km at a TCA (Time of Closest Approach) of ~10:00am this morning, leaving insufficient time for calculating & executing a DAM (Debris Avoidance Maneuver) with SM propulsion, Safe Haven instructions were uplinked to the crew. Subsequent tracking data reduced the PC (Probability of Collision) drastically, and when it approached zero this morning, "Safe Haven" was called off. [For the Safe Haven scenario, the crew would have relocated the Airlock PCS (Portable Computer System) laptop to the SM, then closed out and egressed the two Kibo modules (JLP, JPM), COL, Node-2, US Lab, Node-1/PMA-1, closing all hatches to the RS (Russian Segment), which contains ECLSS, and then retreating to the Soyuz crew return vehicle to await TCA.]

posted 10-02-2008 02:32 PM               

ISS Reboost Cancellation: This morning's planned ISS reboost by Progress M-65/30P was cancelled shortly before its scheduled time due to a post-reboost conjunction conflict. Planning of the reboost maneuver originally looked at five options, each with its respective potential for creating a conjunction with Kosmos-2421 satellite pieces and other debris. The five options were then narrowed down to two with the least likelihood for a conjunction (they showed ~1 km radial miss distance). Both options were acceptable as of 24h before the reboost since they stayed out of the 'forbidden' box, defined by 0.75 km radial miss distance, and both were pursued. But at about 2-3 h before the maneuver, the pieces' predicted flight paths had moved into the box, passing at ~0.71 km -- which triggered the cancellation for today. Backup date for the reboost is now 10/4 (Sat), with all options being screened starting 48 hrs before. Significantly (fortunately), the cancellation occurred before attitude control authority was handed over to Russian MCS (Motion Control System). The purpose of the reboost is to set up orbital phasing for the 17S/16S Soyuz launch & landing. The number of conjunctions has increased in the recent past, both due to the Kosmos-2412 debris cloud and the currently unusually quiet sun with the resulting reduced atmospheric density at high altitudes causing less orbital drag, i.e., less orbit clean-up.