Handprints on Hubble 
 
June 26, 2015: It's funny, the things you notice hanging upside down in space.
 
Astronaut John Mace Grunsfeld remembers a quirky discovery back in 1999. He
had just arrived at the Hubble Space Telescope and climbed out of the airlock
of Space Shuttle Discovery to begin a servicing mission. Clinging to a
handrail running down the side of Hubble's gleaming exterior, he ran his eyes
over the blue planet 350 miles below and tried not to think too hard about the
yawning starry expanse behind him.  The astronaut, Hubble, and Discovery,
connected together, raced around Earth at 17,000 mph.
 
That's when he noticed the handprints.
 
"The outside surface of Hubble is covered with them-scuff marks and other
signs of handling by astronauts," says Grunsfeld.
 
A ScienceCast video explores the deeper meaning of superficial 'handprints' on
Hubble.
 
http://youtu.be/R9fYj1YCGJ0
 
Astronauts visited the orbiting telescope five times since it was launched in
April 1990, conducting 23 spacewalks to repair and improve it. The
"handprints" come from oil and silicon on the astronauts' gloves, which make
an impression on Hubble's exterior foil.  Initially invisible, these residues
darken over time as they are exposed to solar ultraviolet radiation.
 
The prints Grunsfeld saw are more than chemical scuff marks, though.
 
"They are a symbol," he says, "of a unique human-robotic partnership."
 
Hubble's designers intended for astronauts to lay hands on Hubble.  The
telescope is festooned with knobs and handrails, hinged doors, and crawl
spaces fit for astronauts to visit and tinker. This has allowed Hubble to do
something no other spacecraft has done before-evolve.
 
When Hubble left Earth 25 years ago it was equipped with reel-to-reel data
recorders, 1980s-era microprocessors, and some of the earliest digital
cameras.  Fast forward to the present:  Almost every scientific instrument
onboard the telescope has been replaced at least once. Hubble now has
solid-state recording devices, upgraded computers, and astronomical detectors
that far outperform the older technology it originally took to space.
Astronauts have also replaced the telescope's aging solar arrays, batteries,
gyroscopes, some reaction wheels and fine guidance sensors. Keeping pace with
technological advances on its home planet, Hubble is very much a creature of
the 21st century.
 
Astronauts have done more than just upgrade Hubble.  They have also saved it.
 
The first time was in 1993.  When Hubble reached orbit, images revealed that
the telescope's mirror was flawed.  It suffered from a distortion called
spherical aberration.  Hubble could still take pictures of the cosmos but not
with the sensitivity or resolution its designers envisioned.
 
"The first servicing mission in 1993 took care of that," says Grunsfeld. That
December, seven astronauts flew to the telescope onboard Space Shuttle
Endeavour.  Over a period of 11 days, the crew conducted 5 spacewalks and used
more than 100 specialized tools, many of which were invented specifically for
the mission.  They installed corrective optics, a new main camera, new solar
arrays, and two new gyro packages.
 
Not everything went smoothly.
 
During the mission, spacewalkers Story Musgrave and Jeff Hoffman opened a pair
of service doors to swap out gyros but could not get them closed again. The
door bolts would not reset. Engineers on Earth speculated that when the doors
were opened, a temperature change caused them to expand or contract.
 
"They ended up using a make-shift ratchet to squeeze those doors together,"
recalls Grunsfeld. "That was a very bad idea. It could have broken Hubble, but
at the time, they didn't know that.  Anyway, they squeezed the doors together
using brute force."
 
Evidence of the wrestling match is evident today in a confusion of
'handprints' and scuff marks around the doors.  The marks tell a silent story
of ingenuity, risk, and triumph.
 
"Without that first servicing mission, Hubble would have been a nice telescope
but not a great one," opines Grunsfeld.  "We would not have measured the edge
of the universe, validated black holes, or discovered dark energy. The
fingerprints of astronauts are all over those advances."
 
Another difficult moment came in the late 1990s. Mission planners were growing
nervous as Hubble's gyros unexpectedly started to fail-one in 1997, another in
1998, and a third in 1999. If one more gyro went offline, the telescope would
not be able to point accurately.
 
The whole telescope was on the razor's edge of failure as Grunsfeld and six
other astronauts readied themselves for Servicing Mission 3A. Indeed, just
weeks before their Space Shuttle, Discovery, was scheduled to launch, a fourth
gyro failed and Hubble science came to a screeching halt.
 
"We felt some urgency to get up there and fix the telescope," he recalls.
 
It would be Grunsfeld's first mission to Hubble, the first time he touched the
telescope, and the first time he added his own prints to those of his
predecessors. Discovery lifted off on Dec. 20, 1999. During the week-long
mission, the crew installed new gyros, replaced a Fine Guidance Sensor (FGS)
and swapped out the main computer. The new computer was 20 times faster and
had six times the memory of the one it replaced.
 
"Coming out of that mission, we left the telescope in pretty good shape," he
says. "We saved Hubble."
 
Little did he know, that rescue merely set the stage for a more thrilling one
to come.
 
In 2000, engineers working on Hubble noticed a curious anomaly: The
telescope's batteries were not charging as quickly as they should.  It was a
tiny effect, measured in units as small as micro-ohms, but over time it could
add up to catastrophe: Hubble could "go dark" as early as 2003. With detective
work that insiders still remember with awe 15 years later, engineers figured
out the problem. There was a subtle ground fault in the telescope's Power
Control Unit-or PCU.
 
The PCU is essentially a bank of relays that routes power from Hubble's solar
arrays to its batteries and other systems.  It is a very complicated device,
and the only way to service it is to turn it off.  Completely.  No power to
Hubble at all.
 
"This was kind of a big deal," says Grunsfeld. "If we didn't repair it, Hubble
would die in about 3 years.  On the other hand, if we tried to fix it, Hubble
might die right away. Powering down Hubble had never been done before.
Hundreds of relays would be switched to their powered-off state. A clock would
be ticking because Hubble would get cold.  There was a window of only a few
hours to do the repairs because overnight Hubble would freeze,the optical
bench would warp, and Hubble would no longer be functional."
 
NASA decided to go for it, and Grunsfeld started training for the most
challenging mission of his career: Hubble Servicing Mission 3B.   Flying Space
Shuttle Columbia one last time before the disaster of 2003, the mission's crew
would ultimately invent new tools, new training procedures, and new repair
techniques to tackle the PCU problem.  "We really upped our game," says
Grunsfeld.
 
Around NASA, many experts worried about the PCU repair. Could it really be
done? The astronauts themselves were worried.  Sleepless in space, Grunsfeld
and Rick Linnehan woke up early on March 2, 2002, and started prepping for
their spacewalk more than two hours ahead of schedule. NASA prepared to cut
power to the telescope as soon as they were ready to step outside.
 
"Keep in mind that as soon as power was off, we were on a ticking clock," says
Grunsfeld. "There was a real sense of urgency, no question about it."
 
Immediately something went wrong:  "Astronauts Mike Massimino and Jim Newman
were preparing us to go outside," he says. "When Jim released me from the
latches on the wall of the airlock, he noticed that my backpack was wet. A
valve inside my spacesuit had failed and was leaking water.  That's very bad.
Had I gone outside, that water would have frozen, cracked an airline, and I
could have been killed."
 
Suddenly the spacewalkers were behind schedule. Tick. Tock. Tick. Tock.
Working quickly, astronauts in the airlock helped Grunsfeld out of his suit
and assembled a new one from parts of other suits that fit him.
 
"In less than two hours-record time, by the way-we were able to get me back
into a spacesuit.  By the time we started the EVA, we were about two hours
late. There was some mild panic on the ground because Hubble had been cooling
off," he recalls.
 
The astronauts, however, were even cooler.
 
"You might think, 'Oh gosh, Rick and I must have been in a panic because we
had already lost two hours of the day,'" says Grunsfeld, "But no. We went out
the hatch as if everything was completely normal.   We had that kind of focus
from the training we had done.  As soon as I was in the spacesuit again, I
totally forgot that we had had all of those earlier problems. Rick and I went
out and did it in 6.5 hours, exactly as we had trained."
 
The PCU was repaired, and the telescope powered up in good condition. Hubble
was saved again.
 
NASA retired its Space Shuttle fleet in 2011, but not before one last visit to
a telescope Grunsfeld now considered "an old friend."
 
Originally, plans called for Hubble to be serviced in February 2005, but the
Columbia tragedy of 2003 changed everything.  A trip to Hubble was deemed too
risky, and for a while, it seemed that the telescope might never be serviced
again.
 
"That would have spelled the end of Hubble," says Grunsfeld.  "The telescope's
batteries were 13 years old, and they were beginning to fail. Without
replacements, the mission would have ended as early as 2007."
 
And it would have ended, except for the ensuing public outcry.  Not only did
astronomers wish to save Hubble but also millions of ordinary people did too. 
For more than two years, 2004-2006, school children wrote letters to the
President, public hearings were held in Congress, and the "human connection"
to Hubble became as clear as the glove-marks on its gleaming foil.
 
NASA reconsidered.
 
In May of 2009, Space Shuttle Atlantis blasted off for one last mission to
Hubble.  On the ground below, Space Shuttle Endeavour waited on the launch
pad, ready to fly to the rescue if the crew of Atlantis got into trouble. This
is how NASA managed the risk of flying the soon-to-be-retired spacecraft.
 
"By 2009 a ton of things were going wrong on Hubble," says Grunsfeld. "We did
5 EVAs to fix those things."
 
As usual, the astronauts had to invent new procedures and do the
unprecedented-"like removing hundreds of tiny screws in bulky space suits," he
recalls. They replaced batteries, swapped out all six gyros (again), installed
a new Fine Guidance Sensor, repaired two of Hubble's scientific instruments
and completely replaced two others. Mindful that astronauts might never visit
Hubble again, the spacewalkers installed a soft-capture mechanism that would
allow a future robotic spacecraft to grapple Hubble to ensure a safe
conclusion to its operational lifespan.
 
For one last time, Grunsfeld saw the marks of the Hubble repair crews, the
handprints of 16 spacewalkers: Story Musgrave, Jeff Hoffman, Kathryn Thornton,
Thomas Akers, Mark Lee, Steve Smith, Greg Harbaugh, Joe Tanner, Mike Foale,
Claude Nicollier, Rick Linnehan, James Newman, Mike Massimino, Andrew Feustel,
Michael Good, and Grunsfeld himself.
 
"Leaving Hubble in 2009 was bittersweet," says Grunsfeld.  "I was sad to see
my old friend go.  However, as a crew we were thrilled that we had
accomplished all of our goals and a little more, sending Hubble off in the
best shape ever."
 
Current estimates suggest that Hubble will continue doing great science until
2020 and possibly longer.  All thanks to the human touch.
 
Credits:
Author: Dr. Tony Phillips | Production editor: Dr. Tony Phillips | Credit:
Science@NASA
 
 
Regards,
 
Roger

--- D'Bridge 3.99
 * Origin: NCS BBS - Houma, LoUiSiAna (1:3828/7)