SJAA Ephemeris August 2005 |
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Your first reaction: "That's impossible!" How on earth could someone simply pick up one of NASA's giant Deep Space Network (DSN) antennas-a colossal steel dish 12 stories high and 112 feet across that weighs more than 800,000 pounds-move it about 80 yards, and delicately set it down again?
Yet that's exactly what NASA engineers recently
did. One of the DSN dishes near Madrid, Spain, needed to be moved to a new
pad. And it had to be done gingerly; the dish is a sensitive scientific
instrument full of delicate electronics. Banging it around would not
do.
"It was a heck of a challenge," says Benjamin Saldua,
the structural engineer at JPL who was in charge of the move. "But thanks to
some very careful planning, we pulled it off without a problem!"
The Deep Space Network enables NASA to communicate with
probes exploring the solar system. Because Earth is constantly rotating, a
single antenna on the ground can communicate with a probe for only part of the
day, when the probe is overhead. By placing large dishes at three locations
around the planet-Madrid, California, and Australia-NASA can maintain contact
with spacecraft around the clock.
To move the Madrid dish, NASA called in a company from
the Netherlands named Mammoet, which specializes in moving massive objects.
(Mammoet is the Dutch word for "mammoth.")
On a clear day (bad weather might blow the dish over!),
they began to slowly lift the dish. Hydraulic jacks at all four corners
gradually raised the entire dish to a height of about 4.5 feet. Then Mammoet
engineers positioned specialized crawlers under each corner. Each crawler looks
like a mix between a flatbed trailer and a centipede: a flat, load-bearing
surface supported by 24 wheels on 12 independently rotating axes, giving each
crawler a maximum load of 194 tons!
One engineer took the master joystick and steered the
whole package in its slow crawl to the new pad, never exceeding the glacial
speed of 3 feet per minute. The four crawlers automatically stayed aligned with
each other, and their independently suspended wheels compensated for unevenness
in the ground.
Placement on the new pad had to be perfect, and the
alignment was tested with a laser. To position the dish, believe it or not,
Mammoet engineers simply followed a length of string tied to the pad's center
pivot where the dish was gently lowered.
It worked. So much for "impossible."
Find out more about the DSN at http://deepspace.jpl.nasa.gov/dsn/ . Kids can learn about the amazing DSN antennas and make their own "Super Sound Cone" at The Space Place, http://spaceplace.nasa.gov/en/kids/tmodact.shtml.