WASHINGTON — NASA is hoping to get as many as six spacewalks performed outside the International Space Station through late July to replace batteries in the station’s power system, taking advantage of the additional astronauts on the station during the Demo-2 commercial crew mission.
The first in a series of spacewalks by astronauts Bob Behnken and Chris Cassidy is scheduled for June 26, starting work to replace existing nickel-hydrogen batteries at one end of the station’s truss with lithium-ion batteries delivered to the station in May on a Japanese cargo spacecraft. A second spacewalk to continue that work is scheduled for July 1.
NASA hopes that those two spacewalks will be sufficient to complete the battery replacement for one of the station’s eight power channels. If not, a third spacewalk would take place around July 6 to complete the work.
Behnken and Cassidy would then perform a second set of spacewalks later in July to do similar battery replacement work on a second power channel there. Kenny Todd, deputy ISS program manager, said at a June 24 briefing that specific dates for those second set of spacewalks haven’t been finalized, but would likely be around the middle of July.
The spacewalks would wrap up a multiyear effort to replace the batteries in the station’s power system, which provide power when the station is in Earth’s shadow. The schedule for those spacewalks was uncertain because of the limited crew on the station: prior to the arrival of Behnken and Doug Hurley on the Demo-2 Crew Dragon spacecraft May 31, only three people were on the station.
Todd said at the briefing that the has worked closely with Steve Stich, the new manager of the commercial crew program, about the status of the Demo-2 mission and the availability of those astronauts to support the spacewalks. “We’d like to get as many of these EVAs done as we can,” he said. “We think it’s somewhere between four and six to get both of these power channels swapped.”
The uncertainty in the number of spacewalks is based on the amount of work required. “We just barely fit within a four-EVA box” for completing the battery replacement on the two channels, said Allison Bolinger, ISS spacewalk flight director. Some of the spacewalks will run slightly longer than the standard duration of six and a half hours, she said.
What gives NASA optimism that the work can be done in four spacewalks is the experience of both Behnken and Cassidy, who have done a combined 12 spacewalks. “The ace up our sleeve, if you will, is the crew that we’re sending out the door,” she said. Both astronauts got spacewalk training before their launches, including some refresher training for Behnken in the Neutral Buoyancy Lab pool at the Johnson Space Center weeks before the Demo-2 launch.
The performance of the Crew Dragon spacecraft is enabling Behken and Hurley, who will support the spacewalks from inside the station, to stay on the ISS long enough to complete the battery replacements. “The vehicle is doing extremely well as we put it through its paces,” Stich said.
That’s included the solar panels on the spacecraft, which NASA previously identified as the life-limiting factor for the mission. “Dragon is generating more power than expected,” he said, concluding those panels should generate sufficient power for at least 114 days.
Current plans call for the Crew Dragon to remain on the station until at least Aug. 2. When the spacecraft does depart, it will take between six and 30 hours to deorbit and splash down, he said, depending on the timing of the spacecraft’s departure from the station.
NASA has identified several splashdown locations off the Florida coast, both in the Atlantic Ocean and the Gulf of Mexico. The prime splashdown site is notionally the one off the coast from Cape Canaveral, since it would be easiest for transporting the astronauts back to the Kennedy Space Center, but Stich said a landing site decision will depend on how the orbits line up as well as weather.
As the Demo-2 mission continues, SpaceX is completing the Crew Dragon spacecraft for the Crew-1 mission, the first operational mission to the station with four astronauts on board. Stich said the spacecraft should ship to KSC by the end of July.
“We’ll be in a good position for a Crew-1 launch later this year,” he said. While NASA announced shortly before the Demo-2 launch that Crew-1 would launch as soon as Aug. 30, he said there is an “iron bar” of six weeks between the Demo-2 splashdown and Crew-1 launch in order to review the data from the Demo-2 mission and complete reviews for the upcoming launch. That would push the Crew-1 launch to no earlier than mid-September if the Demo-2 mission ends in early August.