Friday marks a milestone at the International Space Station. Two NASA astronauts, Peggy Whitson and Flight Engineer Jack Fischer, will perform the 200th spacewalk at the ISS.

It's yet another landmark in space for Whitson, who recently broke records for most spacewalks by a woman and most hours spent spacewalking with more than 50. The pair will install and replace equipment during the planned 6.5-hour spacewalk.

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