More ET issues, STS-121 heading to July

by Chris Bergin

Following the news that a change-out of the LH2 ECO (Engine Cut Off) sensors is required – ultimately ending the opportunity to launch Shuttle Discovery in the May window – another problem with External Tank (ET-119) has come to light today.

Sources are revealing that an issue has arisen with the tank’s LOX vent and relief valve, with procedures being evaluated on replacing the valve – adding to numerous issues surrounding Discovery’s second Return to Flight test mission and NASA’s ever-changing 17 flight manifest.

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The exact nature of the problem with the V/R valve is related to data that points to concerns that the valve may be ‘a little leaky’ – with LOX tank pressure decreases noted, following shipping. The change-out understood to be ‘highly likely’ but not certain – according to sources.

While the change-out of the ECOs is expected to start soon, the replacement of the vent and relief valve alone may not have been crucial to the May window – given it is far less of a problem to access on the ET.

The ECO change-out, however, is a much longer process, given the delicate process required with the procedure, ensuring the surrounding internal mechanics of the ET are not harmed during the change-out, added to the longer process of TPS (thermal protection system) repair, once the process has been completed.

The ET – currently vertical in the VAB (Vehicle Assembly Facility) checkout cell – has to be carefully placed back, horizontally, on the transporter that carried it into the VAB. Once horizontal, Lockheed technicians can then carry out the TPS repair in the access hatch area – post ECO sensor change-out – replacing the foam removed to enter the tank through the aft access hatch.

Following TPS repair and certification, the tank will need to be raised vertically again, ready for mating with the SRBs (Solid Rocket Boosters), or back to checkout or integration cell. This has to be the process – scheduled as 17 days according to several sources – given Lockheed do not have a process for TPS repair on an ET in the VAB whilst vertical.

Discovery RMS damage update

Discovery herself is also undergoing tests, with her RMS (remote manipulator system), or robotic arm, under evaluation, following an incident in which a small area was ‘bumped’ by an access bucket, which was clearing up fragments of a broken heat lamp from a previous mishap.

It is becoming ever-more likely that the arm won’t need replacing, with the latest information acquired via sources noting ultrasound tests are producing no anomalies on the damaged area – although more tests are to be carried out.

‘Removed section of ground plane, kevlar, and honeycomb from fwd indentation,’ noted recent documents on the evaluations. ‘Performed ultrasound, no anomalies noted. Aft indentation to be performed (later).’


Latest STS manifest

With Endeavour out of action until April 2007, the latest manifest has been refined to show Discovery and Atlantis supporting each others initial 2006 missions.

Even though the March 8 ‘PRCBD S042013FN’ manifest (available on L2) is bound to change again next week – given Discovery’s STS-121 will soon be ‘officially’ moved to July 2006 – it can be estimated that NASA is still capable of three launches in 2006. Officially, NASA is still aiming for May – although, officially, NASA hasn’t even set a launch date.

On the latest manifest, all flights are classed as ‘under review’ – bar STS-121, 115 and 116.

While Atlantis LON (launch on need) date is currently static as the 4th of August (NET – No Earlier Than), a move to July for STS-121 would likely see the CSCS (contingency shuttle crew support) being incorporated into Atlantis’ scheduled launch window, starting NET August 28 with STS-115. Discovery is currently set to return the favour for her sister with a CSCS date of NET October 28, on STS-301.

Another interesting note on the new manifest is the lack of a SSPTS (Station-Shuttle Power Transfer System) upgrade for Atlantis.

Discovery is set to receive her upgrade – allowing orbiters to stay at the International Space Station for longer durations – in-between her STS-116 and 120 missions, NET 16th November and May 3, 2007 respectively. Endeavour’s upgrade is listed to occur between her STS-118 and 123 missions, NET April 19th and 23rd of August, 2007, respectively.

Atlantis’ early retirement in 2008 could be assumed as the reason the upgrade is not currently scheduled.



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