NASA astronauts successfully conduct spacewalk postponed due to debris risk

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Credit: NASA

(CNN) — During a six and a half hour spacewalk Thursday, NASA astronauts Thomas Marshburn and Kayla Barron replaced a malfunctioning communications antenna and achieved other "get ahead" tasks.

The duo began their spacewalk at 6:15 a.m. ET and ended at 12:47 p.m. ET.

NASA postponed the spacewalk until Thursday, originally scheduled for Tuesday, after receiving a space debris warning for the International Space Station. Just hours before the astronauts were due to venture out of the ISS, the agency said on its Twitter account that "due to the lack of opportunity to properly assess the risk," it had decided to delay the November 30 spacewalk until more information was available.

It was unclear whether the warning was related to the space debris created by a Russian anti-satellite test two weeks ago that forced crew members on the International Space Station to scramble into their spacecraft for safety.

"After receiving additional information about a late notification debris event on Monday, NASA determined the orbit of the debris does not pose a risk to a scheduled spacewalk by Thomas Marshburn and Kayla Barron or to International Space Station operations," the agency posted on its website Tuesday night. "Delaying the spacewalk provided an opportunity for NASA to evaluate the risk from the debris notification."

The astronauts left the hatch earlier than expected Thursday morning and successfully worked through all of their tasks.

They replaced an S-band Antenna Subassembly by using a spare that was already attached outside of the space station. The S-band radio frequencies are used to transmit low-rate voice and data from the space station more than 220 miles (354 kilometers) to flight controllers on the ground, according to NASA.

After being operational for 21 years, the antenna recently stopped sending signals to Earth using NASA's Tracking and Data Relay Satellite System. Mission managers discovered the issue in September, said Vincent LaCourt, NASA spacewalk flight director.

"That timing allowed us to have Tom and Kayla go into our neutral buoyancy laboratory, or big pool where we practice spacewalks, and practice our exact spacewalk," LaCourt said.

Overall, the loss of this antenna has a low impact on space station operations. However, maintaining antennas like this one allows for a redundancy in communications. Installing the spare, which has existed outside the station since 2010, will allow that system of backups to continue. The station has other low-rate S-band systems and high-rate KU-band systems that relay videos back and forth.

During the spacewalk, Marshburn was on the end of the Canadarm2 robotic arm, which European Space Agency astronaut Matthias Maurer controlled from inside the space station.

Marshburn wore the spacesuit bearing red stripes as extravehicular crew member 1, and Barron wore the unmarked suit as extravehicular crew member 2. This was the first spacewalk for Barron, who described it as "awesome," and it was the fifth outing for Marshburn.

Marshburn, Barron and Maurer arrived on the space station along with NASA astronaut Raja Chari in a SpaceX Crew Dragon capsule on November 11.

Thursday's spacewalk was the 245th conducted to assemble, maintain and upgrade the space station, which has served as a continuous low-Earth orbit hub for humans for 21 years.

Debris concerns

US Space Command said Russia tested a direct-ascent anti-satellite, or DA-ASAT missile, striking a Russian satellite and creating a debris field in low-Earth orbit of 1,700 pieces of trackable orbital debris that is also likely to generate hundreds of thousands of pieces of smaller orbital debris. It will take months to catalog all of the new debris created by the test.

NASA Administrator Bill Nelson said in a statement that he was "outraged by this irresponsible and destabilizing action. With its long and storied history in human spaceflight, it is unthinkable that Russia would endanger not only the American and international partner astronauts on the ISS, but also their own cosmonauts. Their actions are reckless and dangerous, threatening as well the Chinese space station."

While the debris field was very concentrated at first, it has dispersed over time, said Dana Weigel, NASA deputy manager of the International Space Station Program, on Monday. The team planning the spacewalk ran models and predictions to understand the environment the astronauts will be in during their spacewalk.

It raised the risk to the spacewalkers by 7%, which "is not a large increase and that's well within what we see with normal atmospheric fluctuations and the normal amount of debris that kind of moves through," Weigel said. "What it really tells us is EVA (extravehicular activity) has always been risky."

This risk concerns any debris with the potential to penetrate the spacesuits or the space station itself. The pieces that could penetrate the spacesuits are much smaller than anything they are able to track, Weigel said.

"It does mean penetration but it doesn't mean it's a catastrophic penetration," Weigel said. "There's a certain size of penetration that is supportable. There's an emergency oxygen package on the suit that would feed it for a while. When we talk about EVA risk, it's generally around 1 in 2,700, so that's considered the risk of having some size of a penetration over the course over the duration of the six and a half hour EVA."

Amid the elevated risk and increased uncertainty due to the new debris, "we didn't want to leave the crew out longer for items that we didn't consider critical," Weigel said.

This story was first published on CNN.com NASA astronauts successfully conduct spacewalk postponed due to debris risk