NASA's next
seven astronauts to fly aboard a space shuttle have a bit of orbital hot potato
in store for them when their spacecraft reaches the International
Space Station (ISS) later this year.
Using the space shuttle Discovery's robotic arm alongside its ISS counterpart, astronauts with NASA's STS-114
mission - the agency's first since the Columbia accident - will
perform a meticulously choreographed operation to hand off a new sensor boom
and resupply the space station.
"We have
flight rules in place that say 'Thou shall not use both robot arms at the same
time,'" said Jeffrey Sugar, a NASA shuttle robotics instructor, in an
interview. "So during the hand-off, it's very clear in the procedure that you
have to get a verbal 'Go' before you can make a move."
At the center
of the tricky move is a 50-foot (15-meter) orbital boom
tipped with a camera and a laser ranging system designed to help STS-114 astronauts
evaluate the integrity of their spacecraft. The boom connects to the end of the
Discovery's robotic arm, just about doubling its reach.
While the
arm-boom combination will have an ample range of motion in the early days of
the STS-114's flight, once Discovery docks at the ISS on mission Day 3
connecting the two may be a bit more difficult.
"Because of
where we're docked, and the fact the docking mechanism is in the forward part
of our payload bay, you actually can't take the shuttle arm and reach across to
grapple the inspection boom without hitting the space station structure," said
STS-114 mission specialist Wendy Lawrence, who will be operating the ISS arm
during the hand-off. "So we're going to space station's arm."
Lawrence
and the rest of the STS-114 crew are currently scheduled to launch aboard
Discovery no earlier than May 15. As NASA's first return to flight mission, STS-114 will mark the first test of the orbital boom system, which flight controllers hope will be able to detect any damage to
Discovery's heat-resistant tiles and reinforced carbon carbon
(RCC) panels.
The STS-114
crew is scheduled to rehearse the inspection process and go through the robotic
arm motions required for the three spacewalks currently set for the mission.
Passing the boom baton
STS-114
flight director Paul Hill said that while unusual, using both shuttle and ISS
arms for a specific task is not unprecedented.
The two
robotic manipulators were a put in simultaneous play previously during NASA's STS-104
flight in 2001, when the shuttle Atlantis delivered the U.S.-built airlock and
four high-pressure gas tanks for assembly to the ISS.
"While we
don't like it, we understand how to plan for this," Hill said of the double-arm
operations.
For
STS-114, Lawrence
will use the ISS arm to pluck the orbital boom from the shuttle payload bay, then hold it up for her fellow astronauts to grab with
Discovery's own arm. Once the shuttle's arm has a good hold, the station's
manipulator will loosen its grip and the Discovery's arm-boomassembly
will be positioned to get a good camera view of docked operations and
spacewalks, NASA officials said.
"We're
going to move [the arms] one at a time," Lawrence
said. "It keeps it simple."
With the
orbital boom safely removed from Discovery's payload bay, Lawrence and STS-114 pilot Jim Kelly will use
the ISS manipulator to pull the Raffaello cargo module from the shuttle payload bay and
connect it to the space station for delivery.
A dynamic boom
Before
Discovery arrives at the ISS, shuttle astronauts will have already put the
orbiter's arm-boom combo through its paces.
On Day 2 of
the spaceflight, mission specialists Andrew Thomas, Charles Camarda
and Kelly will maneuver the boom along Discovery's wing leading edges and nosecap to inspect heat tiles and RCC panels.
"You've got
to be doing fairly careful, hand-eye coordinated motions at a time when you
might not be at your best," said Thomas, a veteran of tree spaceflights, adding
that shuttle astronauts are often still acclimating to weightlessness on the
second day of a mission. "What it's all going to be about is clearance monitoring."
While the
inspection run is automated for the most part, Thomas will have to pre-position
the boom at the start of every scan and make fine adjustments as needed while
the sensor package sweeps with two feet of the orbiter's surface at times. During
each sensor sweep, Thomas, Camarda and Kelly will
scrutinize television camera views to make sure the entire assembly doesn't
stray too close to their spacecraft.
"There is
no collision avoidance software, so it is up to the operator to make sure the
boom doesn't hit the shuttle," Sugar said.
Contingency plans
Thomas has
also trained for the possibility that Discovery's orbital boom sensors malfunction
or a repair is needed, requiring a spacewalk in which a crewmember would mount
the end of the boom and make a visual survey of the orbiter.
"He's on
the end of a 50-foot arm which is on the end of a 50-foot arm," Thomas said of
the scenario. "If he pushed with a lot of give, there can be a lot of flexing
on the boom....those dynamics you have to worry about."
Flight
controllers are also still analyzing another contingency - the failure of the
space station arm during the hand-off operations, Lawrence said. One potential alternative could
include undocking Discovery, pre-positioning the shuttle arm-boom combination, and
then redocking with the ISS, though both the orbiter
and station remote manipulators are highly robust systems, she added.
"It's a
rare day that either arm will be completely incapable of accomplishing our
needs," Lawrence
said.
Fixing NASA: Continuing Coverage of
the Space Shuttle Return to Flight
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