Failed Power Unit Leads to Spacewalk Changes, First All-Female EVA Will be This Week

Failed Power Unit Leads to Spacewalk Changes, First All-Female EVA Will be This Week

NASA announced changes today to its series of five spacewalks to replace batteries on the outside of the International Space Station (ISS).  After two successful extravehicular activities (EVAs) last week, a power unit connected to one of the new batteries failed.  NASA is not sure why and is pausing this sequence of EVAs until engineers have some answers. Instead, Christina Koch and Jessica Meir will make a spacewalk on Thursday or Friday to replace the failed power unit.  That will be the first all-female spacewalk, moving that milestone up several days.

The ISS is powered by large solar arrays that charge batteries that feed into ISS systems.  In 2017, NASA began a process of replacing all 48 of the original nickel-hydrogen batteries with 24 more efficient lithium-ion batteries.

Illustration of the International Space Station configuration as of October 3, 2019. The solar arrays are shown in yellow. Credit: NASA

The batteries connect to 24 battery charge/discharge units (BDCUs).  After replacing one of the batteries in April 2019, its BDCU failed.  In that case NASA was able to use the robotic Canadarm2 to replace it.  This time, the failed BDCU is too far away so astronauts will have to do the job.

During a teleconference today, ISS Mission Operations Integration Manager Kenny Todd said it will take Koch and Meir about 3-3.5 hours to complete the swap-out.  EVAs typically last about 6 hours and they will use the rest of the time to perform other tasks.

Todd said the resulting loss of power on the station is manageable, but they “don’t want to live with it long term.” He is confident this week’s EVA will solve the immediate problem, but is worried about why the BDCUs failed. The BDCU that failed in April blew the fuse on the new battery to which it was wired, so it failed, too.  Fortunately that did not happen this time.  The battery itself is OK.

NASA only has 3 or 4 spare BDCUs on the ISS and none on the ground, so any more failures could pose a significant problem.  Todd said he does not know how long it would take to build a new one. The unit that failed in April was returned to Earth and he is hopeful it can be repaired, but they are “looking hard” at the sparing plan.

NASA has been planning a total of 10 spacewalks before the end of this year.  The first five are for the battery replacements and then five more to fix the Alpha Magnetic Spectrometer, a particle physics experiment mounted to the ISS.  Whether that schedule holds up remains to be seen.  Today he could not even say if the Koch/Meir spacewalk will take place on Thursday or Friday.

Spacewalks are fairly routine, but the first all-female EVA is a milestone that is generating a lot of buzz.  It was supposed to happen earlier this year, with Koch paired with Anne McClain, who since has returned to Earth.  McClain recommended a change in plans after she conducted an earlier EVA.  The torsos of the spacesuits aboard ISS can be configured as medium or large depending on the stature of the astronauts using them. At the time, one was large and one was medium.  McClain thought she could use the large while Koch used the medium, but concluded after her first EVA that it would be difficult for her to use the large.  Rather than spending the time to reconfigure it as medium, she suggested that her male colleague, Nick Hague, do the spacewalk with Koch since he could use the larger suit.

Although the rationale was logical, it created quite a public relations stir and heightened interest in when an all-female spacewalk would, in fact, take place.

On October 4, ISS program manager Kirk Shireman laid out a schedule for these spacewalks where that would happen on October 21, but today’s changes move that up to the end of this week.

Astronaut Megan McArthur, Deputy Chief of the Astronaut Office, insists that gender is not a determining factor in assigning spacewalks.  It is based on who has the right skills and workload balancing.

Nevertheless, ensuring diversity in the Artemis program to return American astronauts to the Moon is an important message from Vice President Mike Pence and NASA Administrator Jim Bridenstine.  They repeatedly stress Artemis will put “the first woman and the next man” on the Moon.  Bridenstine even said it may be two women.

That means lunar spacesuits must be able to accommodate people of many sizes. Bridenstine showed off the Artemis spacesuit today at NASA HQ — the Exploration Extravehicular Mobility Unit (xEMU).  After showing how flexible they are compared to the Apollo suits from 50 years ago, NASA spacesuit engineer Kristine Davis explained they can accommodate “from the first percentile female to the 99th percentile male.”



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