Two NASA astronauts set for spacewalk to replace faulty space station antenna

Two US astronauts were set on Tuesday to venture out of the International Space Station for a spacewalk to replace a failed antenna, facing what NASA officials say is a slightly elevated risk from the debris of a Russian anti-satellite missile test.

NASA TV planned to provide live coverage of the 6-1/2-hour spacewalk, scheduled to begin at 7:10 am Eastern time (1210 GMT) as astronauts Thomas Marshburn and Kayla Brown exit an airlock of the orbiting research lab some 402 km above Earth.

The outing is the fifth spacewalk for Marshburn, 61, a medical doctor and former flight surgeon with two previous trips to orbit, and the first for Barron, 34, a US Navy submarine officer and nuclear engineer on her debut spaceflight for NASA.

Their objective is to remove a faulty S-band radio communications antenna assembly, now more than 20 years old, and replace it with a new spare stowed outside the space station.

The malfunctioning antenna recently lost its ability to send signals to Earth. Though other antennae on the space station can perform the same function, mission managers decided to install the replacement to ensure communications redundancy, NASA said.

Marshburn will work with Barron while positioned at the end of a robotic arm operated from inside the station by German astronaut Matthias Maurer of the European Space Agency, with help from NASA crewmate Raja Chari.

The four arrived at the space station November 11 in a SpaceX Crew Dragon capsule launched from the Kennedy Space Center in Cape Canaveral, Florida, joining two Russian cosmonauts and a NASA astronaut already aboard the orbiting outpost.

Four days later, an anti-satellite missile test conducted without warning by Russia generated a debris field in low-Earth orbit, and all seven crew members took shelter in their docked spaceships to allow for a quick getaway until the immediate danger passed, according to NASA.

The residual cloud of debris from the blasted satellite has dispersed since then, according to Dana Weigel, NASA deputy manager of the International Space Station (ISS) programme.

But NASA calculates that remaining fragments continue to pose a "slightly elevated" background risk to the space station as a whole, and a 7 per cent higher risk of spacewalkers' suits being punctured, as compared to before Russia's missile test, Weigel told reporters on Monday.

Although NASA has yet to fully quantify additional hazards posed by more than 1,700 larger fragments it is tracking around the station's orbit, the 7 per cent higher risk to spacewalkers falls "well within" fluctuations previously seen in "the natural environment," Weigel said.

Still, mission managers cancelled several smaller maintenance tasks under consideration for Tuesday's spacewalk, Weigel added.

Tuesday's exercise marks the 245th spacewalk in support of assembly, maintenance and upgrades of the space station, which this month surpassed 21 years of continuous human presence, NASA said.