All-female spacewalk scrub: Here's what went into NASA's decision

CAPE CANAVERAL, Fla. – NASA astronauts Anne McClain and Christina Koch both trained for years before their first spaceflights, but despite all the training to mimic the effects of zero-gravity, neither woman had been to space before. That is why McClain learned exactly what size her Extravehicular Mobility Unit, or EMU suit, best fit her during her first spacewalk outside the International Space Station last week.

McClain and Koch were set to conduct the first all-female spacewalk in history this week. NASA officials said Monday that because both women need to wear the same torso or shirt of the spacesuit, Koch will now conduct the March 29 spacewalk with NASA astronaut Nick Hague instead of her female counterpart.

Social media users had some thoughts on mission managers postponing the first all-female extravehicular activity, known as an EVA, -- even former Secretary of State Hillary Clinton.

The spacewalk would have been historic. Of the 214 EVAs conducted since 1998 only 13 included women. In the last two years, McClain and NASA astronaut Peggy Whitson are the only women to work outside the space station.

Both Koch and McClain are part of the 2013 NASA astronaut class, the first class at the space agency to be half women and half men.

However, the spacewalk change was not because NASA did not provide enough suits -- there are no male or female suits -- the call came down to safety and comfort for both astronauts as well as time.

Let's go over the preparations astronauts and mission managers undergo before a six and a half hour spacewalk.

Spacewalks are planned years in advance

According to Art Thomason, the EVA controller and instructor, once NASA determines what task they want to complete with a spacewalk the planning for the EVA begins a year or more in advance. 

NASA’s podcast, “Houston We Have a Podcast,” recently addressed the planning that goes into a spacewalk with Thomason and Tara Jochim, the project manager for the EVA repair of the Alpha Magnetic Spectrometer in 2017.

Astronauts have been living and working on the space station for almost two decades. Like a used car, it needs a tuneup every now and then.

The EVA Koch and Hague will complete Friday continues the work started by Hague and McClain last week swapping old nickel-hydrogen batteries with new lithium-ion batteries on the station. 

"It's been on orbit for a long time, and so now we're starting to see that maintenance time period come up, and we go out and, you know, fix things that maybe have some issues or go install new science payloads for, you know, new science to get completed on (the) Space Station," Jochim said on the podcast.

The change really came down to time, NASA officials said. The spacewalk on Friday was delayed from last fall.

How astronauts train to work in space

The spacesuits astronauts wear outside the station, known as Extravehicular Mobility Units or EMUs, are essentially their own personal spacecraft. The suits provide life-support, mobility, keep the astronauts cool and have communication systems.

Astronauts train on the ground using POGO, a suspended system at the mockup facility in Houston, which allows them to practice the cause and effect of working with tools in zero-gravity. They also train in the Neutral Buoyancy Laboratory, a 6.2-million-gallon pool in Houston where astronauts can train for spacewalks wearing a full EMU suit.

“No one training environment can fully simulate performing a spacewalk in microgravity, and an individual may find that their sizing preferences change in space," Brandi Dean, with Johnson Space Center's Public Affairs Office, said in an email to News 6.

That is the case with McClain, who trained in multiple sized suits on the ground before experiencing the real thing.

“Based her experience in the first spacewalk in the series, McClain determined that although she has trained in both medium and large torsos, the medium was a better fit for her in space,” Dean said.

To accommodate that preference, Koch will wear the medium torso on March 29, and McClain will wear it on April 8.

After the response to the spacewalk assignment change McClain sent out a tweet Wednesday to explain the decision.

"This decision was based on my recommendation," McClain said. "Leaders must make tough calls, and I am fortunate to work with a team who trusts my judgement. We must never accept a risk that can instead be mitigated. Safety of the crew and execution of the mission come first."

A spacesuit's fit matters

If you’re thinking, “How can there not be multiple spacesuits of the same size?” The short answer is there are, but multiple pieces make up a single spacesuit.

The particular portion McClain and Koch both share the same size is the torso, or the top half of the suit.

NASA officials said there are six EMU suits on the space station including two medium, two large and two extra-large upper torsos.

“However, one of the mediums and one of the extra larges are spares that would require additional time to configure for a spacewalk,” Dean said. Configuring an EMU suit would take time further delaying the spacewalk.

To configure the other medium torso for a spacewalk it would take about 12 hours of crew time, according to NASA. 

NASA spokesperson Stephanie Shierholz told News 6 partner Florida Today it was safer to change the spacewalk assignment than to configure the suit.

"It's less risky," Shierholz said. "This way, all spacewalks can stay on schedule and the astronauts can still do the number of spacewalks they are scheduled for."