[reporter] What's going on right now?

We are getting ready for EVA day 2 on our servicing mission, and today is important

because we're doing two big things to extend the life of the telescope.

The first thing will be the gyros, replacing the gyros...

The gyros help keep the camera steady so you don't get a shaky picture - we're

targeting photos pretty far off so you want to keep the camera still and the

gyros help keep the telescope still, so we take clear pictures.

We've done gyros before. We've changed the procedure, we've improved the procedure

over the years, over the servicing missions, and we've developed new tools...

...and refined the procedure. So it should go smooth.

[reporter] So how difficult a task is this?

It's a pretty difficult task. When the astronauts working inside the telescope

there are plenty of surfaces that they have to avoid. Mike's going to go in,

Mike Massimino is going to go in on his back...

...there's a bunch of delicate instrumentation inside that he has to avoid, and he's got to

snake those big arms of his past all this sensitive equipment to get to the bolts

that will release the RSUs.

It's physically challenging. We've got a rather large

astronaut inside a very cramped space, but you know what? Those long arms

are going to serve him well, I think.

[reporter] Why do you keep teasing Mike like that?

Mike's a buddy...[laughs].

[announcer] Michael Good now seating the new Rate Sensor Unit.

[applause]

That was fun, huh? RSU, the first RSU installed very nicely, and with the

second one - ran into a little difficulty because we had contingency procedures

ready. We were able to fall back on those and come up with a fix.

So we got the second one installed and the last RSU installation we had to go to

retrieve our spare.

What we are looking for is debris that could be going into the telescope or coming from

the telescope - because we wonder did something break on the telescope or is

there something that could get in the way of an electrical connector that the

astronauts are going to mate.

There are a lot of reasons we need to keep it clean, and so we see something in the

video - we run back there - they have a Tivo - so we say "play that back" - they

run it back and forth a couple of times, and then we try and think about it, and

I don't know if you saw us looking at the monitors, we have models of the telescope,

and we try to see if it's coming from say this red area here it could sweep out past

the field of view - imagine that the astronauts is laying on his back inside

the telescope looking out at space while he's working and we see these particles

going by - we say where did they come from? So we start thinking in our heads, we'll

maybe it's back here - there's actually a port that water is dumped out of the

orbiter and ice crystals can build up there.

So our thought now is that maybe that's just ice crystals we saw difting by in

the field of view of the camera - didn't come from the telescope at all, didn't

go inside the telescope, so it's OK.

[reporter] This mission has been described as one of the more dangerous ones because

of the altitute at which it's flying in, you hear about space debris, and you

mentioned debris. Are we talking about the same debris?

No, the space debris is already up in orbit, and it's moving a lot faster

relative to the shuttle and the telescope, and so we wouldn't see that on a video

because it would go whizzing by so fast you wouldn't even see it, unless it hits

something in which case it would just make little pin holes if it's small,

if it's big it could be a bigger problem, but we have people on the ground with

radar that are tracking the large pieces and they actually move the shuttle out

of the way if we are going to get close to something like that.

The batteries are 19 years old. The capacity has degraded over these years, and by putting

in new batteries we will restore the original capacity of these batteries to run the

instruments.

That was a longer than expected spacewalk, but Hubble now has six new gyroscopes and

three new batteries. But on tomorrow's schedule, the first ever camera repair

to be done in space.

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