Plans for the first all-female spacewalk in history have been scrapped for lack of a second space suit, the US space agency Nasa says.
Christina Koch and Anne McClain had been scheduled to step outside the International Space Station (ISS) on Friday to install batteries.
But it turned out they both needed a medium-size spacesuit and only one was ready for use.
Koch will now exit the ISS with male colleague Nick Hague instead.
She will wear the medium-size suit used by McClain on a spacewalk with Hague last week.
McClain trained in both medium and large-size spacesuits but only realised after her actual spacewalk that the medium-size suit fitted her best, Nasa said.
She is scheduled to perform her next spacewalk, on 8 April, with another male astronaut, David Saint-Jacques.
What exactly is the problem with the suits?
The issue relates to the spacesuit's hard upper torso or "shirt".
Nasa has two medium-size hard upper torsos on the ISS but only one of them has been properly configured for a spacewalk.
To get the other ready would have taken hours and Nasa decided it would be easier and safer to change the astronauts.
Brandi Dean, a spokeswoman for the Johnson Space Center in Houston, explained that size requirements could change once astronauts were in space.
"Individuals' sizing needs may change when they are [in] orbit, in response to the changes living in microgravity can bring about in a body," she was quoted as saying by AFP news agency.
We’ve seen your tweets about spacesuit availability for Friday’s spacewalk. To clarify, we have more than 1 medium size spacesuit torso aboard, but to stay on schedule with @Space_Station upgrades, it’s safer & faster to change spacewalker assignments than reconfigure spacesuits. pic.twitter.com/tPisBHaF2p— NASA (@NASA) March 26, 2019