Spaceflight Now: Fixing Hubble

PAGE 4
Shuttle Discovery poised for urgent Hubble repair
BY WILLIAM HARWOOD
Posted: Dec. 14, 1999

  Replacing the RSUs
The first task will be to replace Hubble's failed gyroscopes with the RSU packages. Photo: NASA
 
The first item on the agenda for the first spacewalk, or EVA, is replacing all six of Hubble's gyroscopes, housed two each inside three compact devices called rate sensing units.

"On the RSUs, the task itself is not intrinsically difficult," Grunsfeld said. "You climb inside the telescope, you disconnect some connectors, run some bolts out and swap out the gyros. But ... everything around us is tremendously fragile. You can't move your arm in other than a very pre-planned way when you reach for a connector. So from the ballet aspect, it has to be a highly choreographed activity."

Smith will actually float completely inside the telescope's aft section, anchoring his feet in temporary restraints.

"I'll put his feet in while he tries to avoid touching anything except a handhold in the telescope," Grunsfeld said. "Then he will gently rotate so his mini work station, which is the part that holds all the tools on his stomach, is inches away from one of the fixed head star tracker light shields, which we're told we absolutely cannot touch. Then on his left side, as he's doing RSU 3, will be a couple of hundred-million-dollar scientific instruments and an optical bench, which we can't touch."

Smith will detach electrical connectors and physically hold each RSU while Grunsfeld, reaching in with a large power tool extension, drives out the bolts holding each device in place. Smith will then pass the old unit out and position its replacement so Grunsfeld can drive in the necessary bolts.

Concern about brittle internal insulation is a major issue. The focal plane structure "is covered with some MLI (multi-layer insulation) to protect it and what the Hubble community is concerned about is when a crew member climbs in there, if he rubs up against it, particulate is going to come loose and we're going to contaminate the telescope," said Kieth Johnson, the lead spacewalk trainer for SM-3A. "That's our biggest fear."

Voltage/Temperature kit installation
Installation of the Voltage/Temperature Improvement Kit. Photo: NASA
 
 
Once the three RSU boxes are connected, engineers on Earth will begin a series of "aliveness" tests to make sure they are working properly. While those tests are going on, Smith and Grunsfeld will move to the bottom of the telescope and open a valve to vent any traces of nitrogen in the NICMOS cooling system that might interfere with operation of the replacement cryocooler in 2001.

Grunsfeld and Smith will close out the first spacewalk by installing six voltage regulator kits, or VIKs, to improve battery conditioning and to protect against an unlikely failure scenario that could lead to a battery rupture. Finally, protective covers will be installed on a handrail near fine guidance sensor No. 3 to prevent possibly peeling paint from flaking off the second spacewalk.

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Explore the Net
NASA Human Spaceflight - Space agency Web site dedicated to International Space Station and space shuttle programs.

Press kit - Official STS-103 mission press kit.

Shuttle Media Reference Guide - Complete in-depth look at space shuttle systems and facilities.

Shuttle Countdown Online - NASA Kennedy Space Center site with pre-launch information.

Hubble Space Telescope - Home page of NASA's first Great Observatory.

HST Servicing Mission 3A - NASA site focused on this servicing mission of Hubble.

European Space Agency - partner in HST program and has two astronauts flying on STS-103.

United Space Alliance - prime contractor responsible for daily shuttle processing work.

Thiokol - Manufactures the shuttle's solid rocket boosters.

Rocketdyne - Division of Boeing that builds shuttle main engines.

Lockheed Martin - Corporation that builds the external fuel tank.