CAPE CANAVERAL - NASA aims to start connecting a redesigned external tank and two rocket boosters today while managers consider data that shows extra safety modifications might be needed before the agency's next shuttle flight.
But any additional work on the tank, if required, can be completed in time to launch Discovery on NASA's second post-Columbia test flight in early July, agency officials say.
"We've already booked five to seven days for those activities if we decide they are necessary," said Kyle Herring, a spokesman for Johnson Space Center in Houston. "We can accomplish any additional work and still meet the schedule we've laid out for July 1."
A decision on whether to order up extra work could be made as early as Thursday.
NASA took a big step toward launch Monday as crane operators hoisted the 154-foot-long tank off a transporter in the Kennedy Space Center Vehicle Assembly Building.
After carefully lifting the tank into a vertical position, the technicians were ready to ease it between two 149-foot solid rocket boosters already stacked on a mobile launcher platform.
Mechanical connections were scheduled early today. Electrical connections will follow over the next 17 days.
The mating operation "is a critical milestone to launch in early July," KSC spokeswoman Jessica Rye said. "It's always nice to have all the hardware here at Kennedy and to start assembling a shuttle."
The orbiter Discovery remains scheduled to move May 12 from its hangar to the assembly building, where it will be connected to the tank and its attached boosters.
But first, NASA managers must decide whether to modify foot-long segments of foam insulation designed to prevent ice from building on metal brackets that hold fuel pressurization lines on the outside of the tank.
Some managers propose to reshape the "ice-frost ramps" to reduce the amount of foam that could be shed from them during flight. Wind tunnel test results have been mixed.
In one series of tests, foam broke free from a reshaped ice-frost ramp on a mockup at the Air Force's Arnold Engineering Development Center near Tullahoma, Tenn.
Insulation also was lost during separate tests of ice-frost ramps identical in design to those on the tank being readied for Discovery's flight. But the amounts were considered within allowable limits -- that is, not large enough to cause catastrophic damage.
Slight modifications subsequently were made to the reshaped ice-frost ramps, and more tests were run. The results in those cases were encouraging, Herring said.
The tests are part of an effort to eliminate sources of foam debris large enough to down an orbiter. The 2003 Columbia accident was blamed on foam debris, and a large piece of insulation nearly struck Discovery after launch in July.
The Discovery debris came from a 38-foot foam ramp (11-meter) that served as a windshield for fuel pressurization lines and electrical cabling on the outside of the tank. Wind tunnel tests are being conducted to make sure the shuttle can be flown safely without it.
Engineers remain concerned that ice-frost ramps such as those on Discovery's tank might be susceptible to internal cracking when supercold propellants are loaded into it. Such defects could weaken the ramps and make it more likely they could pop off in flight.
Any extra work on Discovery's tank likely would be done in the assembly building between May 2 and May 9, Herring said.
Discovery still is scheduled to move out to its launch pad May 19. A fuel-loading test is tentatively scheduled for June 1, but managers still haven't decided whether to conduct it.
The test would enable engineers to see whether replacements for suspect fuel-depletion sensors in the tank work properly. It also would subject the tank's foam insulation to super-cold temperatures that could cause internal cracks.
A decision on whether to proceed with the test is expected in early May. Discovery remains scheduled for launch during a window that will extend from July 1 through July 19.
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