Excitement turned to disappointment this week when NASA announced it had to shuffle astronaut assignments, scrubbing what would have been the first all-female spacewalk in history. The reason: There wouldn't be enough medium-sized spacesuit torsos available in time for the Friday event.

NASA astronaut Anne McClain, who just completed her first spacewalk at the International Space Station on March 22, spoke out in defense of the decision on Wednesday, saying it was based on her recommendation. 

"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," McClain tweeted. "Safety of the crew and execution of the mission come first."

NASA astronaut Christina Koch and McClain were originally slated to head out into the vacuum of space together to continue work on a project to upgrade the batteries for the station's solar power system. Now Koch and NASA's Nick Hague are set to share work duties outside the ISS on Friday.

McClain made the call after her first spacewalk when she decided she would be more comfortable in a medium suit rather than a large. It takes time to properly prep a spacesuit and only one medium suit was ready to go, so Koch will wear it on Friday. 

A third spacewalk scheduled for April 8 is tentatively set for McClain and Canadian Space Agency astronaut David Saint-Jacques. 

McClain had one more tweeted message for people who are bummed about the spacewalk adjustments: "Tune in -- history is made every day up here!"