Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/shuttle/shut_mnu.txt

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FLASHBACK FOR THE SPACE BACKPACK

Reprinted from the February 3, 1989, issue of
Space News Roundup,
a publication of NASA's Lyndon B. Johnson Space Center,
Houston, Texas

Manned maneuvering unit celebrates fifth anniversary

     On Tuesday, it will be exactly five years since astronaut
Bruce McCandless pushed a lever and became the first space walker
to fly freely above Earth.
     McCandless' untethered flight with the manned maneuvering
unit (MMU) was the fruition of a dream that had been moving
toward reality since the early 1960s, a dream enjoyed by many at
JSC. This center managed and performed much of the work on the
MMU, which was built by Martin Marietta.
     On Feb. 7, 1984, McCandless piloted the nitrogen-jet
propelled MMU a little more than 100 yards from Challenger,
creating a scene of space-age freedom that became immediately
famous as it fired the public imagination. McCandless was
accompanied by astronaut Bob Stewart who flew a second MMU.
Together, the two tested the units and found their performances
flawless.
     It was a triumphant moment for both McCandless and Ed
Whitsett, project engineer for the MMU and a man involved with
the concept since his graduate thesis in 1960. The two had worked
together on the MMU off and on for about 16 years.
     "We had a lot of confidence in it. We knew it was a good
machine," Whitsett said recently. "But, obviously, the first time
he flew away from the Shuttle, a lot of people were uptight."
     That was not the case for McCandless. "I had lot of
confidence in the hardware," he said. "I knew that the laws of
physics hadn't been repealed recently."
     McCandless said he experienced no new physical sensations as
he became, essentially, a second spacecraft. After having been in
orbit aboard Challenger for four days, the only difference he
felt in the MMU was "a sense of professional satisfaction."
     "I did not feel alone or isolated," he remembered. "I
attribute that largely to excellent radio communications. Vance
(Brand) and the guys were reading off ranges and talking to me,
so I didn't feel I was isolated."
     The first flight was the result of development work that
began with an awkward, difficult-to-control, hand-held
maneuvering unit used during the Gemini program. The work
proceeded through the Skylab missions, where crew members
evaluated another hand-held unit, a device called "jet shoes" and
the first backpack thruster unit. Among these three, the
backpack, flown by five different astronauts for a total of 14
hours within the orbital workshop, easily won.
     Development of the MMU during the Shuttle program was
spurred, at first, by a desire to have a method the crew could
use to inspect the bottom of the Orbiter in flight, Whitsett
said. But its major use, and the event that put its operation in
high gear, was a need for satellite retrieval and repair.
McCandless' flight was a dress rehearsal for repairs of the Solar
Maximum Mission satellite.
     The MMU was used on two following Shuttle flights to work
with three satellites_Solar Max, Westar VI and Palapa B-2. All of
the flights took place within a year, and, in total, six
astronauts have flown MMUs for a combined 10 and a half faultless
hours.
     MMUs aren't currently scheduled for any future flights,
although it is possible they will be used for a Space Station
Radiator Assembly Demonstration (SRAD) flight experiment sometime
in 1993. Still, Whitsett said, one can never tell when the need
could arise for an MMU mission.
     "The Westar and Palapa mission wasn't planned far in
advance. It just happened that the MMU was needed," he explained.
     The MMUs, proven dependable fliers, are in storage now at
Martin Marietta. "They're in good shape, able to be used whenever
the need arises again," McCandless said.
     Completing development of the MMU, a project that spanned so
many years, was a little bittersweet for those devoted to it.
"Everybody who worked on it was extremely enthusiastic. People
were nearly fighting to get on the project," Whitsett said. "It's
sort of like raising a child. When they go off and get married,
you're still proud of them. But they're not there anymore."
     Many of those involved with development and flight of the
MMU plan to honor the fifth anniversary of the first flight on
Tuesday.
     The MMUs remain ready and waiting as they are, but they may
be improved by work now under way on the Extravehicular Activity
(EVA) Retriever, a fetching space robot being developed at JSC.
"A lot of the retriever work will feed into MMU updates, such as
a fault detection system and caution and warning lights," said
Whitsett, who now works as systems integration manager for space
station EVA systems.
     McCandless also has special ideas for the future of the MMU.
"I'd dearly love to see us mount the IMAX camera on the MMU for a
flight," he said. "You could get stand-off imagery of the Orbiter
with Earth in the background. I think that would be very
dramatic."
     McCandless said he does have one minor regret about the
first MMU flight. "I had intended when I got out 30 feet or so to
stop and face away from Orbiter and look at the cosmos," he said.
"I forgot; I was concentrating on watching the Orbiter."
     McCandless is now deeply involved in preparing for another
Shuttle flight, STS-31. Scheduled for December, the mission's
primary objective will be to deploy Hubble Space Telescope.

     -END-