Status Report

STS-109 Grunsfeld Report #4 – 7 Mar 2002

By SpaceRef Editor
March 7, 2002
Filed under , ,

STS-109 Extravehicular Activity

  • STS-109 Mission Guide
  • EVA Operations Reference

  • STS-109 EVA Timeline

  • Spacewalk Number One, Flight Day Four: Replace -V2 Solar Array and
    Diode Box Assembly, Install Diode Box Controller Cross Strap Harness

  • Spacewalk Number Two, Flight Day Five: Replace +V2 Solar Array and
    Diode Box Assembly and Reaction Wheel Assembly-1

  • Spacewalk Number Three, Flight Day Six: Replace Power Control Unit

  • Spacewalk Number Four, Flight Day Seven: Replace Faint Object Camera
    with the Advanced Camera for Surveys, Install Electronics Support Module
    and Perform Power Control Unit Cleanup Tasks

  • Spacewalk Number Five, Flight Day Eight: Install the Near-Infrared Camera
    and Multi-Object Spectrometer (NICMOS) Cryogenic Cooler and NICMOS
    Cooling System Radiator

  • EVA Day 3
    PCU day, the power control unit changeout. The PCU is the main power
    relay box for the whole Hubble Space Telescope. A problem with the
    old one threatened to end the telescope’s life early, so it was
    decided by NASA to change it out. The interesting part is that the
    box is not really designed for change-out by space walkers.

    Early this
    morning (space morning) Rick Linnehan, my space walking partner,
    and I got into our space suits. This was the third EVA of the flight,
    the first two being the change-out of the solar arrays with new
    more powerful arrays. After my space suit was started it began to
    leak water out of the cooling water tank. We quickly changed out
    the upper part of the space suit with one of the other team’s suits,
    and off we went, just a couple of hours late.

    Finally out
    in the clear vacuum of space, Rick and I started working on preparing
    the telescope for a complete power-down, the first time in 12 years
    on orbit! I put thermal covers on some of the temperature sensitive
    bays (it gets cold in space without heaters). Rick began disconnecting
    batteries, and I lowered light covers over the star tracker cameras.

    Then, the meat
    of our task-at the PCU worksite. In one of the electronics bays
    is the PCU. It has 36 circular connectors, one after another, on
    the left side of its large black box. Inside are electronics and
    relays to power the telescope. Our job was to disconnect all of
    the connections, and then swap the PCU for a new one, called PCU-R,
    for replacement, and then connect all the wires back up. Sounds
    easy, except that we are in the very bulky stiff space suits, and
    the connectors are too close together to use your hand.

    We have a special
    wrench/connector tool developed just for this task, and one after
    another, Rick disconnected the wires. With just a few to go, we
    swapped out positions on the Shuttle robotic arm, and I finished
    off the last few. After driving the bolts to remove the old PCU
    from HST, I met Rick in the payload bay, picked up the new PCU,
    and left Rick to stow the old one. Off to HST, riding on the Shuttle
    robot arm driven by Nancy Currie, I put the new PCU in the Hubble.

    For the next
    two hours I attached one connector after another. Because of their
    location on the side of the box, I often only had a view of the
    interface with my left eye. Parallax is a significant aid, which
    I had to do without. Each connector took a couple of minutes to
    do, with inspections of the little pins and sockets, alignment and
    then turning the collar. Many of the wires were quite stiff, and
    I had to simultaneously align and turn. While it doesn’t sound hard
    in principle, in practice it was really hard in the space suit with
    the stiff bulky gloves.

    During training
    I joked that my task was “Zen and the art of connectors”
    in that to perform this task Rick and I needed extreme concentration,
    patience and a little bit of skill. At one point I looked at one
    particular connector and started laughing, thinking, “This
    is it, the PCU task ends here.” I didn’t think I could get
    access and align and mate the connector with my big gloves on it.
    After trying a couple of different approaches I finally used my
    connector tool, and zip, it went on. Seven more connections and
    I was all done.

    We reconnected
    the HST batteries, powered the telescope back on, and went back
    to the barn, in this case the barn being the airlock on the Space

    Overnight the
    ground commanded the Hubble systems back on line, and with a day
    of work in space we now have a Hubble power system that will allow
    the telescope continued operation well into the future.

    On board Columbia
    I went to sleep satisfied I did an honest day’s work, and very tired.

    SpaceRef staff editor.