Historic Deep Space Network Antenna Starts Major Surgery

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http://www.jpl.nasa.gov/news/news.cfm?release=2010-083

Historic Deep Space Network Antenna Starts Major Surgery
Jet Propulsion Laboratory
March 08, 2010

Like a hard-driving athlete whose joints need help, the giant "Mars
antenna" at NASA's Deep Space Network site in Goldstone, Calif. has
begun major, delicate surgery. The operation on the historic
70-meter-wide (230-foot) antenna, which has received data and sent
commands to deep space missions for over 40 years, will replace a
portion of the hydrostatic bearing assembly. This assembly enables the
antenna to rotate horizontally.

The rigorous engineering plans call for lifting about 4 million
kilograms (9 million pounds) of finely tuned scientific instruments a
height of about 5 millimeters (0.2 inches) so workers can replace the
steel runner, walls and supporting grout. This is the first time the
runner has been replaced on the Mars antenna.

The operation, which will cost about $1.25 million, has a design life of
20 years.

"This antenna has been a workhorse for NASA/JPL for over 40 years," said
Alaudin Bhanji, Deep Space Network Project manager at NASA's Jet
Propulsion Laboratory, Pasadena, Calif. "It has provided a critical
lifeline to dozens of missions, while enabling scientific results that
have enriched the hearts and minds of generations. We want it to
continue doing so."

The repair will be done slowly because of the scale of the task, with an
expected completion in early November. During that time, workers will
also be replacing the elevation bearings, which enable the antenna to
track up and down from the horizon. The network will still be able to
provide full coverage for deep space missions by maximizing use of the
two other 70-meter antennas at Deep Space complexes near Madrid, Spain,
and Canberra, Australia, and arraying several smaller 34-meter
(110-foot) antennas together.

NASA built the Mars antenna when missions began venturing beyond the
orbit of Earth and needed more powerful communications tools. The Mars
antenna was the first of the giant antennas designed to receive weak
signals and transmit very strong ones far out into space, featuring a
64-meter-wide (210-foot) dish when it became operational in 1966. (The
dish was upgraded from 64 to 70 meters in 1988 to enable the antenna to
track NASA's Voyager 2 spacecraft as it encountered Neptune and Uranus.)

While officially dubbed Deep Space Station 14, the antenna picked up the
Mars name from its first task: tracking the Mariner 4 spacecraft, which
had been lost by smaller antennas after its historic flyby of Mars.
Through its history, the Mars antenna has supported missions including
Pioneer, Cassini and the Mars Exploration Rovers. It received Neil
Armstrong's famous communiqué from Apollo 11: "That's one small step for
man. One giant leap for mankind." It has also helped with imaging nearby
planets, asteroids and comets by bouncing its powerful radar signal off
the objects of study.

A flat, stable surface is critical for the Mars antenna to rotate slowly
as it tracks spacecraft. Three steel pads support the weight of the
antenna rotating structure, dish and other communications equipment
above the circular steel runner. A film of oil about the thickness of a
sheet of paper -- about 0.25 millimeters (0.010 inches) -- is produced
by a hydraulic system to float the three pads.

After decades of constant use, oil has seeped through the runner joints,
slowly degrading the structural integrity of the cement-based grout that
supports it. Rather than continuing on a weekly schedule to adjust shims
underneath the runner to keep it flat, Deep Space Network managers
decided to replace the whole runner assembly.

"As with any large, rotating structure that has operated almost 24 hours
per day, seven days per week for over 40 years, we eventually have to
replace major elements," said Wayne Sible, the network's deputy project
manager at JPL. "We need to replace those worn parts so we can get
another 20 years of valuable service from this national treasure."

Over the next few months, workers will lay a new epoxy grout that is
impervious to oil and fit the antenna with a thicker runner with more
tightly sealed joints. They will then test that the rotation is smooth
before turning the antenna back on again.

"The runner replacement task has been in development for close to two
years," said JPL's Peter Hames, who is responsible for maintaining the
network's antennas. "We've been testing and evaluating modern epoxy
grouts, which were unavailable when the antenna was built, updating the
design of the runner and designing a replacement process that has to be
performed without completely disassembling the antenna. We've had to
make sure we've reviewed it for practicality and safety."

JPL, a division of the California Institute of Technology in Pasadena,
manages the Deep Space Network for NASA Headquarters, Washington. More
information about the Deep Space Network is online at:
http://deepspace.jpl.nasa.gov/dsn/index.html .

Jia-Rui C. Cook 818-354-0850
jia-rui...@jpl.nasa.gov

2010-083