WATCH: NASA astronauts conduct 200th spacewalk at International Space Station

Update: This event has ended.

NASA astronauts Peggy Whitson and Jack Fischer will perform the 200th spacewalk at NASA's International Space Station on Friday, marking a historic milestone for U.S. space exploration.

The astronauts will be replacing a large avionics box and hardware stored outside the facility, while also installing a connector to route data to another craft. Whitson -- who holds the U.S. record for most spacewalks by a female astronaut -- will be performing her ninth excursion, while Fischer will be conducting his first.

Friday's spacewalk coverage began at 6:30 a.m. EDT, and is expected to take 6.5 hours in its entirety.

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