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Summary:
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The third EVA, scheduled for FD 6, begins with the replacement of Data
Interface Unit-2 (DIU-2), the replacement of the Engineering/Science Tape
Recorder-1 (ESTR-1) with the Solid State Recorder (SSR), and Reaction
Wheel Assembly (RWA) change out. These tasks, as well as the clean up and
daily close out of the payload bay, are timelined for six hours.
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In His Own Words
The mission as seen by
NASA Astronaut Steve Smith
STS-82 Mission Specialist
Overview
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The third day, Mark and I go out again and this time Mark will be on the
arm. He'll perform the DIU task (the Data Interface Unit). It's a computer
box, and basically half of it has failed. So they want to replace it with
a box that has tubes inside working.
It's an interesting task. The box is about the size of a microwave
oven. It's interesting because it has so many connectors. It has about 20
cables coming into it. And cable connections are very difficult in space
because you have bulky gloves on. So in many ways this is the most
hand-intensive task and each cable, as you pull it out, has, of course,
many, many pins, on the order of 20 to 40 pins. And you have to be careful
not to bend any of them.
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Switching the Data Interface Unit
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And so we'll have to be very careful with the DIU. But it's the same
concept again: You open up a door of Hubble. You take out a box that's
broken and put a new one. This one's very time consuming because of all
the cables. And, again, Mark has a full complement of tools that you have
on the end of the arm to choose from to help release all of these cables.
We'll then switch places and do something called the SSR.
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Installing the Solid State Recorder
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And it's solid state recorders, what that stands for. You'll recall, we
replaced one of the three tape recorders earlier. That was ESTR-2. Well,
one of the other tape recorders is operating a little bit suspiciously, so
we're going to put a new tape recorder in its place too. But instead of
replacing a mechanical tape recorder with a mechanical, weÕll put
solid-state in. And, of course, there are many advantages to that:
reduction of moving parts. But more importantly, increasing the capacity
to store data tremendously. And that's important because the new
scientific instruments, STIS and NICMOS, will provide much more data. You
know, multiple times data than the old instruments. So you need better
tape recorders in there also.
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Change Out the RWA
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We will also replace one of the reaction wheels on board Hubble. It
uses 4 reaction wheels to control its attitude, and when we say attitude
in our business, we mean how the Hubble is oriented in space.
Hubble does not have any gas on board or engines, or little
rockets to position it, to point it at certain stars. It uses big
gyroscopes. If you think of that. One of those failed last Friday night,
just 5 days ago, and so they're down to 3. They had 4, and they're down to
3 now. And it needs 3 to work. So we're down to basically no fault
tolerance, that's what we call it. That's about an hour task. It's the
same philosophy.
We'll use the arm to go up to a bay or a door, open the door, take
out the reaction wheel that's broken and put a new one in. Mark would be
on the arm doing it. This reaction wheel assembly's about the size of a
color TV. Weights about 110 pounds or so.
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Steve's Challenge of the Day
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On this day for me, it will be fun to get a lot more free floating time
and to be, to have more freedom now that I will have been an experienced
space walker. I will be able to get off the arm and watch an experienced
person do a very difficult task. That's probably the highlight for me.
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