NASA astronauts Anne McClain and Christina Koch were set to make history on March 29th as the first all-female crew to perform a spacewalk at the International Space Station.

But NASA has announced that the spacewalk has been delayed, "due in part to spacesuit availability on the station."

On March 22, McClain and astronaut Nick Hague conducted the first of three spacewalks for Expedition 59. It was during this spacewalk that NASA says McClain learned "that a medium-size hard upper torso – essentially, the shirt of the spacesuit – fits her best."

But since only one medium-size torso suit will be ready by March 29, the women will not be able to perform the second spacewalk together. Instead, Koch will wear that spacesuit and conduct the spacewalk with Hague.

Twitter

"McClain now is tentatively scheduled to perform her next spacewalk — the third in this series — on Monday, April 8 with Canadian Space Agency astronaut David Saint Jacques," NASA said in a statement. "Assignments for this spacewalk will be finalized following completion of the second spacewalk."

Spacewalks are relatively rare, and are usually conducted for the purpose of doing experiments, test new equipment or repair satellites or spacecraft already in space. Since December 1998, there have been only 214 spacewalks at the International Space Station, according to NASA.

McClain and Koch's spacewalks will mark 35 years since Svetlana Savitskaya became the first woman to walk in space in 1984. NASA reports that 59 women have flown to space as of 2017, "including cosmonauts, astronauts, payload specialists and foreign nationals."

Although McClain and Koch will now be traveling separately, they will still make history by being the 13th and 14th women to perform a spacewalk. It will be McClain's first time in space and Koch's first spaceflight.

Both McClain and Koch are graduates of NASA's 2013 class, which had the second largest number of applications NASA has ever received, over 6,100. That class was also 50 percent women, as was NASA's most recent class of flight directors.

Like this story? Subscribe to CNBC Make It on YouTube!

Don't miss: Two NASA astronauts will conduct the first all-female spacewalk in history