Another Step To May 15th Launch
NASA is marking a major step in assembling the Space Shuttle for
its Return to Flight mission. Last week, workers successfully
"mated," or attached, the redesigned External Tank and twin Solid
Rocket Boosters (SRBs). The fuel tank and booster rockets will help
launch Space Shuttle Discovery on its mission to the International
Space Station, currently targeted for May 15-June 3.
The Space Shuttle's External Tank was lifted by a giant crane
and joined to the already assembled, or "stacked," boosters in the
52-story Vehicle Assembly Building (VAB) at NASA's Kennedy Space
Center, FL. Mating the tank with the boosters is another major step
in readying the Space Shuttle system for flight.
Following integration and final checkout of the External Tank
with the SRBs, orbiter Discovery will join its propulsion
components in the VAB. Discovery will roll over from its hangar,
the Orbiter Processing Facility, later this month to mark the
completion of Return to Flight processing. The orbiter then will be
attached to the stack in the VAB.
The External Tank will fly with several modifications, including
two new forward bipod heaters at the forward attach fittings that
connect the tank to the orbiter. NASA and Lockheed Martin Space
Systems Co. spent nearly two years modifying the tank to make it
safer.
During ET-SRB mating, the left and right boosters are bolted to
the tank at both the forward, or top, and the aft, or tail, ends.
At the forward end, a vertical bolt mechanism attaches each booster
to the tank. On launch day, approximately two minutes after
liftoff, the SRBs will separate from the ET when pyrotechnic
devices fire to break the 25-inch, 62-pound steel bolts. One half
of the bolt is caught in canister-like "bolt catchers" located on
the tank; the other half remains with the boosters.
Discovery will also be the first flight with a modified bolt
catcher, which was upgraded from a two-piece welded design to a
one-piece, machine-made design. By eliminating the weld, the
modified bolt catcher is structurally stronger than the original
design.
Prior to orbiter Discovery joining the stack, final closeouts on
the External Tank will include attaching the new bolt catcher and
electrical cable connections, as well as installing an aerodynamic
fairing and the bi-pod struts, which are the attach points for the
nose of the orbiter to the tank.
The External Tank is the largest element of the Space Shuttle
system, which also includes the orbiter, main engines and SRBs. It
measures 27.6 feet wide and 154 feet tall. Despite the tank's size,
the aluminum skin covering it is only an eighth of an inch thick in
most areas. Yet it still withstands more than 6.5 million pounds of
thrust during liftoff and ascent. The tank is the only Shuttle
component that cannot be reused.