NASA Spacewalk to Go Ahead Despite Russian ASAT Debris

Two NASA astronauts will make a spacewalk tomorrow even though Russia’s antisatellite test two weeks ago increased the amount of debris in the space station’s path. A NASA official said the elevated risk is still within NASA’s accepted limits. [UPDATE: NASA later postponed this spacewalk until Thursday due to a debris issue.]

Tom Marshburn and Kayla Barron are scheduled to step outside the International Space Station at 7:10 am ET tomorrow to begin a six-and-a-half hour spacewalk to replace a faulty S-band Antenna Subassembly (SASA).

They trained specifically for this spacewalk before launching to the ISS on November 10 on SpaceX’s Crew-3 spacecraft. Marshburn has two previous spaceflights under his belt and this is his fifth spacewalk, or extravehicular activity (EVA). Barron is a rookie.

NASA Deputy ISS Program Manager Dana Weigle told reporters today about 1,700 large pieces of debris were generated by the November 15 antisatellite test when Russia launched a missile to destroy one of its own satellites. The Expedition 66 crew — two Russians, four Americans and one European — had to shelter inside the main sections of the ISS for more than a day as debris threatened the space facility on repetitive orbits.

Russia admits it conducted the test, but denies any of the debris endangered either the ISS or China’s Tianhe space station.

The space station and spacesuits are designed to protect astronauts from the micrometeoroids and orbital debris (MMOD) that populate Earth orbit. Weigle said ordinarily the risk that a particle could penetrate a spacesuit is 1 in 2,700, but that does not mean the penetration would be catastrophic.

In the aftermath of the Russian ASAT test, she said the risk is about 7 percent higher, but “that is a small increase that is well within the flux that we see in the natural environment.” “We’ve had EVAs in the past with even higher MMOD risk.”

Initially the debris from the ASAT test was “very concentrated,” but now has “dispersed out quite a bit more.”

The new 1,700 pieces of debris are still being catalogued and calculating the likelihood of collisions — conjunction analyses — is not yet possible. Very small particles cannot be tracked at all, but NASA concluded that for this EVA the “MMOD risk falls within the family of what we’ve had for EVAs over the last few years.”

Still, since the risk is slightly elevated NASA is limiting what Marshburn and Barron will do.  “We didn’t want to leave the crew out longer for items we didn’t consider critical” so some get-ahead tasks were postponed.

Repairing the S-band antenna on the port side of the ISS is considered critical. There is another on the starboard side, but the ISS is about to enter a period of time when the angle of the Sun to the space station, the beta angle, could cause the starboard antenna to exceed its thermal limits. The S-band antennas communicate to Earth via NASA’s Tracking and Data Relay Satellites. The ISS also has Ku-band antennas for video.

The first ISS module was launched in 1998. Tomorrow’s spacewalk is the 235th in support of the ISS, which just celebrated 21 years of permanent human occupancy. It is the 13th this year alone.

NASA TV coverage of the spacewalk begins at 5:30 am ET.