Subject: [International Space Station] ISS DEBRIS COLLISION AVOIDANCE ALERT!

NASA monitors space debris, possible close approach to International Space Station with initial decision to put crew in Soyuz craft for debris encounter.

Pending additional analysis, flight controllers told the six-member crew of the International Space Station to plan on taking refuge in the lab’s two three-seat Soyuz lifeboats late Friday for the expected close approach of a piece of space debris around 10:48 p.m. EST. (11/6/09)

The debris, of unknown origin or size, could pass within about six-tenths of a mile of the lab complex toward the end of the crew’s normal sleep period. Because all objects in low-Earth orbit, including the space station, are moving at roughly five miles per second, close encounters, or “conjunctions,” are carefully monitored and subjected to extensive analysis.

During the evening planning conference Friday afternoon, the astronauts were told to plan on getting up a few minutes early so they can make their way to the Soyuz lifeboats by around 10:30 p.m.

“The ballistics are saying they are looking at conjunction with space debris,” Russian mission control radioed. “As you know, this is something we are prepared for. In the past, we have performed avoidance maneuvers, but this time maneuvering away from the path of the debris is not an option.

“Because we cannot perform avoidance maneuver, you will have to ingress Soyuz vehicles. Both Soyuz crews should be in their vehicles. This is what we have. We are going to work on the ballistics data to get greater precision, but right now we are in the red box. The probability of collision is non zero.”

NASA flight controllers told the astronauts the tracking data is uncertain and that engineers did not yet have confidence in the trajectory projections. But pending an additional analysis later in the afternoon, the crew was told to play it safe and plan on boarding the Soyuz lifeboats after shutting internal hatches in the U.S. segment of the lab complex.

“We have data that indicates we might be heading to a conjunction, however we do not have enough data to have any confidence in the outcomes we’re predicting at this point,” Ricky Arnold told the crew from mission control in Houston. “We’re hoping we’re going to be a lot smarter at 2200 (GMT), but right now we have to plan for an indication that we will have a conjunction.”

If the initial predictions hold up, “we would like to close all the hatches inside the station,” Arnold said. “We’re also going to be configuring our cooling to two loops. We’re going to need you guys to do some steps on board to get to dual-loop mode.”

With both of the station’s cooling systems active, the lab would be protected against an impact that might cause a leak in one of the lab’s critical ammonia coolant lines.

Under the current plan, cosmonaut Roman Romanenko, Canadian astronaut Robert Thirsk and European Space Agency commander Frank De Winne would make their way to the Soyuz TMA-15 spacecraft docked to the Earth-facing port of the Zarya module between 10:15 p.m. and 10:30 p.m. EST. Cosmonaut Maxim Suraev and NASA astronauts Jeffrey Williams and Nicole Stott would seek safe haven in the Soyuz TMA-17 spacecraft docked to the aft port of the Zvezda command module.

Flight controllers plan to make a final decision on how to proceed around 5 p.m., after getting another update on the object’s trajectory.

“Unfortunately, the particular object is not easy to track, it’s not visible by all the different tracking stations every time, and so there’s not a lot of confidence in the data on the exact location of this piece of debris,” NASA spokesman Kelly Humphries said earlier Friday.

Last March, the station’s three-man crew – Mike Fincke, Yury Lonchakov and Sandra Magnus – faced a similar situation and briefly took refuge in the lab’s single Soyuz lifeboat when another piece of debris from an old rocket motor made a close approach.

There are more than 18,000 pieces of space junk in low-Earth orbit the size of a baseball and larger. U.S. Strategic Command prioritizes radar tracking to protect manned spacecraft first, followed by high-priority military and civilian payloads.

NASA monitors an imaginary volume around the space station roughly the shape of a pizza box measuring 0.466 miles thick and 15.5 miles square.

“Initially, we have a screening box, which is .75 kilometers radial miss, which would be up or down, by 25 kilometers in cross track, which would be left or right, by 25 kilometers down track, which is either in front or behind us,” space station Flight Director Ron Spencer said in September.

“Space Command will alert us of any debris objects out there that are going to get that close to us. Then they increase tasking on those objects to try to get a better solution and decrease the uncertainty. Then we calculate a probability of collision based on the data Space Command gives us.”

Spencer said NASA has two levels of concern.

“We have two thresholds, yellow and red,” he wrote in an email exchange. “The yellow is 1-in-100,000 and the red is 1-in-10,000. We will not take any action if it is below the yellow threshold. If it between the yellow and red, we will only take action if it is easy to do so without impacting the mission. For a red threshold violation we will take action in most cases.”


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