NASA is adding a docking ring to the
James Webb Space Telescope (JWST) just in case a visit by astronauts aboard a future
Orion Crew Exploration Vehicle is needed to complete deployment of the
multibillion-dollar orbiting observatory. The U.S. space agency made the
announcement May 10 during the unveiling of a full-scale model of the JWST on
the National Mall here.
Billed as the successor to the Hubble Space Telescope,
the JWST is slated to launch in mid-2013. By the time it is fully expanded as
it is deployed at a gravitationally stable spot some 1.5 million kilometers
from Earth, the spacecraft will be about the length of a tennis court.
Building, launching and operating the infrared telescope for 10 years is
expected to cost $4.5 billion,
making it the most expensive science mission NASA has in development.
"We cannot make the James Webb
Space Telescope fully serviceable like the
Hubble because that would cost so much money that I don't think this
country could afford it," said Edward Weiler,
director of NASA Goddard Space Flight Center, the Greenbelt, Md.,
facility in charge of the Webb telescope.
"However, what if you have a bad day when you put this thing a million
miles out and everything folds out except for an antenna ... it gets stuck? Or
a solar panel doesn't fold out completely, and you say, 'gee, I wish we could
send an astronaut just to give it a kick'?"
Weiler said NASA Administrator Mike
Griffin asked the James Webb team two years ago to examine whether it was
worthwhile to design the telescope to accommodate a visit from Orion.
According to Weiler,
it is.
"We are going to design for the
James Webb Space Telescope a little ring that the Crew Exploration Vehicle
could dock with so if we had a bad day the astronauts could go out to James
Webb and do minimal, gross things," he said. "They couldn't replace
instruments, they couldn't change out things, but they could fix things that
were obviously wrong."
Weiler said it is his hope and expectation
that an astronaut service call never proves necessary. That point was seconded
by Martin Mohan, the JWST program manager at Redondo Beach, Calif.-based
Northrop Grumman Space Technology.
"We are spending a great deal
of time in testing to make sure that JWST deploys reliably on orbit,"
Mohan said. "That is one of the core competencies of Northrop Grumman
Space Technology. That was, we believe, one of the factors in our selection.
That doesn't mean we take it lightly in any stretch of the imagination."
The decision to add a docking ring
to the Webb telescope was news to Griffin.
Asked about it May 16, he said: "A year or two ago I asked people if it
wouldn't be smart to at least have some capability to dock Orion with James
Webb such that if people wanted to service it, they could do so. It only seems
to me to make sense to not preclude that. I didn't tell them to do it. So if
they are doing it, they must have studied it and come to the conclusion that it
is a worthwhile thing to do."
Meanwhile, a NASA review board
recently determined that all 10 new technologies key to the success of the JWST
are mature enough to move into the detailed engineering phase of the program.
Among those new technologies are near-infrared detectors, sunshield
materials and lightweight cryogenic mirrors.
"The invention is done more
than six years ahead of launch," Mohan said. "That's an unprecedented
achievement."
Weiler agreed, saying that Hubble's launch
was delayed several years because its enabling technologies were not ready,
adding hundreds of millions of dollars to the cost of the project.
Mohan said that thanks to the new
technologies, Webb's 6.5-meter mirror will weigh only half of what Hubble's
mirror weighs yet will provide nine times as much light-collecting power.
The Ball Aerospace-designed mirror,
which is already in fabrication, consists of 18 separate segments that will be
unfolded during deployment and held in place by composite structures developed by
Minneapolis-based Alliant Techsystems.
Weiler said the JWST has met every
budget and technical milestone in the 20 months since NASA restructured the
project, delaying its launch two years and adding $1 billion to the life-cycle
cost estimate. The project's next major review is slated for March 2008.
As expensive as JWST might seem, Weiler said, when all is said and done it will cost roughly
half of what NASA has spent on Hubble — about $7 billion to $8 billion adjusted
for inflation and measured according to the same accounting methods that govern
Webb.
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