posted 06-15-2011 03:00 PM               

Atlantis fueled for preflight tanking test

NASA fueled space shuttle Atlantis Wednesday (June 15), conducting a pre-flight "tanking test" to verify the integrity of the shuttle's external fuel tank.

The launch team at the Kennedy Space Center in Florida began the test at 11:15 a.m. CDT, filling Atlantis' external tank, ET-138, with about 535,000 gallons of liquid hydrogen and liquid oxygen, just as they will when Atlantis launches the STS-135 mission, now targeted for July 8.

For today's test, instead of lifting off, the tank will be drained overnight after being allowed to sit filled with the cryogenic propellants for two and a half hours.

The tanking test is to confirm if the rib-like stringers in Atlantis' tank are able to endure the super-cold temperatures it will be exposed to before and during launch without developing cracks like those that delayed Discovery's STS-133 launch last year.

Last night, teams changed the start of today's test from 6 to 10 a.m. after severe storms delayed their preparations. Overnight, a power substation that supports the launch pad went offline at about 2 a.m., which caused a number of systems to lose electrical redundancy.

Engineers have been working to fix the problem and in the meantime have developed a method to get the redundant power feed restored to critical systems. That extra work this morning caused the further delay in starting the tanking test.

During the fueling process, the main fuel valve (MFV) on Atlantis' main engine three (SSME No. 3) saw temperatures below normal levels, possibly indicating a leak. Teams isolated the engine valve and continued to fuel Atlantis with no issues. Temperatures returned to normal readings.

Engineers will evaluate any necessary work on the engine fuel valve following the tanking test.

The last time that a main engine fuel valve needed to be replaced, STS-73 in October 1995, the work delayed the launch about a week.

Should an inspection team find no other issues with Atlantis or its external tank, NASA plans to rollout STS-135's payload to the launch pad on Thursday evening.

The cargo, the multi-purpose logistic module Rafaello packed with supplies and equipment for the International Space Station, will be loaded into the pad's payload changeout room on Friday morning, in preparation for it being loaded into Atlantis' bay.

Questions about the tanking test? See: STS-135: Viewing, questions, and comments

posted 06-15-2011 06:53 PM               

External tank draining, no new issues seen

NASA's final inspection team, or ice team, completed its walkdown of Pad 39A at NASA's Kennedy Space Center in Florida following this afternoon's tanking test. Preliminary reports indicate no issues.

Teams are now draining about 535,000 gallons of liquid hydrogen and liquid oxygen from space shuttle Atlantis' external fuel tank.

Starting Saturday, technicians will take x-ray scans of the tank's support beams, called stringers, on the shuttle-facing side of the tank.

Earlier this year, managers directed teams to make the same stringer reinforcement modifications to Atlantis' tank, ET-138, as they had after cracks in the support beams of shuttle Discovery's STS-133 mission external tank were discovered. ET-138 is a similar tank to the one that used for the STS-133 mission.

Managers scheduled the tanking test to help verify there are no issues.

During the tanking test, the main fuel valve for Atlantis' No. 3 space shuttle main engine recorded temperatures below normal levels, indicating a possible liquid hydrogen leak. Teams isolated the engine and continued to fuel Atlantis with no issues. Temperatures returned to normal readings.

Once technicians are able to gain access to the engine after the area is cleared from tanking test operations on Thursday, engineers will evaluate any necessary work on the fuel valve.

Even if the valve needs to be replaced, managers expect that work could be done at the launch pad and still support Atlantis’ July 8 target date.