Space Shuttle Discovery’s external tank (ET-119) was to be shipped to Kennedy Space Center (KSC) in Florida from NASA’s Michoud Assembly Facility near New Orleans on 24 February, despite ongoing issues with tank and ramp foam loss.
Flight environment tests and analysis at the Michoud facility will carry on until April, when the tank will be mated with Discovery in preparation for its roll-out to launch pad 39A for mission STS-121. But concern over the test outcome could delay the mission beyond the currently planned 10 May launch date.
Shuttle programme sources have told Flight International about delamination issues with the ET’s liquid hydrogen (LH2) ice/frost ramp located 47m (150ft) from the tank’s nose - a ramp referred to as Xt1851 by NASA engineers.
Michoud is unable to comment on the claims, but says: “The PAL [protuberance air load] ramp is off. We have added super lightweight ablative SLA-561 to the [Xt1851] ice/frost ramp [to strengthen it] and made the surface more aerodynamic. We will always have some foam loss.”
The tank on Discovery/STS-114 lost foam from aft LH2 ice/frost ramps, LH2 tank acreage, the intertank/LH2 tank flange, the bipod fitting and the LH2 PAL ramp, which has been removed. Ramp Xt1851 is now in a tougher environment since NASA decided to remove the PAL ramp above it. The test concerns could also delay delivery of the next tank, ET-118, to be used for Atlantis/STS-300 – the rescue orbiter under NASA’s return-to-flight rules.
NASA also confirmed it may retire Atlantis. According to internal NASA planning documents obtained by Flight International, if STS-121 does not launch until the third quarter then Atlantis’ last flight will be in May 2008 after five more missions. It would then be used for spare parts. The plans also show that Endeavour, which is currently finishing an overhaul, ends its operational life in the third quarter of 2009 and Discovery makes the very last Shuttle flight in the fourth quarter.
ROB COPPINGER / LONDON
Source: Flight International