Endeavour undocks from ISS – Shannon pushing for May STS-124

by Chris Bergin

Following a hugely successful docked stage, Endeavour has undocked from the International Space Station (ISS) on Flight Day 15. Undocking was slightly delayed to 8:25pm Eastern.

Meanwhile, Shuttle manager John Shannon is continuing to push for a May launch date for STS-124, despite the downstream delays to the LON (Launch On Need) External Tank (ET-127) and ET-129.

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Endeavour has performed extremely well during her long stay at the Station, and – thanks to a nominal SSPTS (Station-Shuttle Power Transfer System) – could have even stayed ‘days longer’, had there been a requirement.

With all primary mission objectives completed, including the final transfers between the two vehicles, Endeavour was cleared to proceed towards an on time undocking, which will be followed by the always-stunning flyaround. However, undocking was slightly delayed.

‘Shuttle Endeavour’s undocking from the station has been slightly delayed. Mission control just notified the shuttle crew that the delay could last up to 15 minutes. There is a difficulty with latching two beta gimbal assemblies on the outboard end of the P6 truss.’

No major issues are reported with the orbiter in Monday morning status information, which noted what originally appeared to be an excessive number of ‘hits’ registered by Endeavour’s port wing WLE IDS (Wing Leading Edge Impact Detection System) during Late Inspection.

These hits – or triggers – have since been cleared as noise in the sensors. This is not uncommon, with the majority of triggers registered by the WLE IDS occurring due to the finite sensitivity of the sensor system that is mainly used to register impacts to the wing leading edges during ascent and MMOD (micrometeoroid/orbiting debris) strikes during the docked phase of a mission.

‘WLEIDS Memory Overflow. During MMOD monitoring during late inspection, sensor S/N 1150 within Group A on the port wing had excessive triggers,’ noted Monday morning NTD information. ‘All sensors on port Group A were cancelled. Initial data review concluded that the excessive hits were due to noise on the sensor. Most probable cause is component failure in the sensor circuitry.’

Under evaluation by JSC’s Mission Evaluation Room (MER) is the make-up of the air concentrations onboard Endeavour. This is also not unexpected due to the length of mission – with the only requirement to assess when the LiOH (lithium hydroxide) canisters will be implemented.

‘High local LO2 Concentrations. Post undock, insertion of the LiOH canisters may be implemented earlier in the timeline,’ noted the MER Item.

Incidentally, these canisters – used to control the CO/d2 levels in the crew cabin – were the center of a large scale investigation by the all-powerful PRCB (Program Requirements Control Board) last year, following the discovery that the dust in the canisters was causing respiratory irritation for crew members who worked in the near vicinity (on the middeck).

Three such events were noted (STS-114, STS-115 and STS-118) which led to a flight waiver being placed on STS-122 and STS-123. The forward plan called for additional masks to be taken uphill with the crew, along with additional crew training on handling the canisters to avoid the risks of dust inhalation.

The only other entry on the MER list relates to the Laser Dynamic Range Imager (LDRI) – part of the Orbiter Boom Sensor System (OBSS), which is now stowed on the Station.

‘LRDI Latent Image. LRDI was left in scan mode for 54 hours which resulted in some burn in. Continued use will dissipate the effects. No impact to image quality but did increase processing time. No further action planned.’


The OBSS isn’t returning with Endeavour due to payload bay clearance issues with the next mission – STS-124 with Discovery – that will be carrying the huge Pressurized Module of the Japanese Experiment Module.

That mission is currently targeting May 25 as a NET (No Earlier Than) launch date – still under review due to issues with the External Tank delivery dates downstream of the mission.

The relation to STS-124 – which has its flight tank (ET-128) just about within the required flow schedule for making the May date – is the LON tank (ET-127), which has to be on a schedule to support a rescue mission – to be carried out by Endeavour – in the event of a serious problem with Discovery during her mission. Currently, this is not the case.

A review of the delivery dates is due a few days into next month when the Michoud Assembly Facility (MAF) have completed an evaluation of their downstream schedules. However, Shannon has already stated he does not wish for this mission to be delayed.

This call, very much in the style of his predecessor Wayne Hale, does not in any way relate to pressure being placed on MAF’s doorstep, instead it calls for pre-emptive mitigation to be built into the schedules.

One major factor will be the CSCS (Contingency Shuttle Crew Support) levels – which are a timetable of consumable status on the ISS – used to support a stranded STS-124 crew ahead of the arrival of Endeavour on a rescue (LON) mission.

Every day the CSCS can be extended ahead of STS-124’s launch is another day MAF will have in their back pockets on the delivery and – subsequent flow timetables at KSC – for ET-127.

With the soon-to-arrive ATV and an upcoming Russian Progress supply ship all boosting the ISS’ consumable reserves, the hope is a lengthy CSCS of around three months would be possible – thus creating a buffer zone for the delayed delivery of ET-127, and ultimately allowing STS-124 to launch on schedule.

It becomes more complex ahead of STS-125, which is the mission ET-127 has a primary role with, due to the requirement of ET-129 also needing to make up some downstream schedule at MAF, ahead of being sat with Endeavour at Launch Pad 39B at the time Atlantis launches from Pad 39A.

CSCS plays no factor in that scenario, due to the lack of “safe haven” ability during the Hubble mission.

As far as Discovery herself, the flow to rollover remains on track, with a imminent review hopefully concluding with a rollover to the Vehicle Assembly Building (VAB) on Friday.

“OPF (Orbiter Processing Facility) schedules are green; have work to do, but no significant issues,” added the latest Shuttle Stand-up/Integration report. “Plan to close PLBDs (Payload Bay Doors) for roll by March 28. Will stand by to get ET, which is critical path to launch.

“Working a couple IPRs (Interim Problem Reports) under engineering evaluation, which should not be an issue.”

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