"This is an oven size component. It's a big square box and its got some electrical connections and it's got some plumbing connections on it. And it's a little bit like changing out your oven, where you have to change out the electrical connection and the gas connection."
The walk was originally supposed to take place on Friday. But NASA decided they needed an extra day of planning. Replacing the part will take two days. So astronauts will do as much as they can Saturday and then finish the job the following Wednesday.
"This is a challenging g spacewalk, there's no doubt about it. We haven't done one of these replacement for these pumps yet. However we did do a lot of the ammonia connections on these kinds of things earlier on and so they have worked with these connectors."
Humphries says they have people practicing the mission in huge water tanks to simulate what it will be like in space. So far, the practice missions have worked according to plan. And, they expect the same during the spacewalk.
Bill Stamps, KUHF News.