Shuttle Discovery has launched on her first attempt – the third in a row for NASA – after an eventful countdown that threatened to scrub the launch.Earlier, managers cleared observed ice that had been spotted on shuttle Discovery’s External Tank (ET-120) in the final hours of the count. The ice was classed as a violation and went for evaluation by the Mission Management Team (MMT). NASA Satefy were classing the ice as “RED”, although DAT (Debris Anaylisis Team) then noted it was not going to be an issue for launch.
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Building towards the business end of the S0007 Launch Countdown, Discovery is now on track following yesterday’s issues with the weather delaying some operations.
With the RSS revealing Discovery earlier on Monday evening, preparations are now talking place for the tanking of the External Tank, with an Ops/Eng Pre-tanking Brief at 00:45 EDT. Chilldown preps ahead of tanking started (02:13 EDT) just less than one hour ahead of slow fill of the ET at 3am. The tank went into stable replenish two hours later.
ET-120’s ECO (Engine Cut Off) sensors – problematic in early Return To Flight Missions – are working without an issue, with S&MA Booster reporting ‘ECO sensor confidence check complete. Sensors looking good.’
A 13500 PPM H2 ‘burp’ was noticed during tanking, which registered on the GUCP leak detectors, but this is not deemed an issue. ‘This burp was seen at the same time on STS-116, the last flight of OV-103,’ noted controllers.
Controllers are ‘still scratching heads and working on explanation’ on an increased motor speed on Fuel Cell 2 at present, though this is well within limits.
Another issue – related to a ‘leak’ of helium in Discovery’s middeck has recieved official dissent from Boeing Safety and NASA SM&A. NASA is, however, go for launch, pending acceptable weather.
‘The midbody is reading a steady ~50 ppm He. There usually is none. KSC stated the He is attributed to a leak in the haz gas QD in the T-0 allowing some helium intrusion. (the T-0 is purged with helium) There was no indication of helium prior to loading,’ noted live NASA information acquired by NASASpaceflight.com L2.
‘They stated additional rationale was you are not seeing it on the PLB reading. This is incorrect because the PLB is at a higher pressure than the mid body. PV&D is looking into the issue.’
However, this issue appears to have caused Boeing Safety to dissent, while the MMT feel confident this is not a constraint to launch.
‘Boeing Orbiter management is go, with one dissenting opinion from Boeing Safety. OPO (Orbiter Project Office) is ‘Go’ and acknowledges the dissenting ‘No go’ position of S&MA.’
During the opening part of observations by the Inspection Team, an iceball was seen on the tank, but this was below the debris line. More of a worry is clear ice, on the LH2 umbilical, which is a problem and requires evaluation.
‘Clear ice seen on LH2 umbilical,’ noted controllers. ‘This is a violation. Folks are looking into it.’
The ice – a 4” x 1.5” piece – is located on the LH2 Umbilical pyro can closeout. Should it fail to reduce in size – or disapear – the launch would be scrubbed at the T-9 minute mark.
The MMT is evaluating it, along with Debris teams, although at present NASA Safety are classing the ice as ‘RED’ for launch, although DAT (Debris Analysis Team) are classing it as borderline.
This then became a green light to proceed, after DAT noted the ice would not be an issue for launch as it was melting.
The Ice Inspection team has arrived back at the pad to take a closer look.
Earlier, despite the usual GSE (Ground Support Equipment) leaks at the pad, Discovery was – and still is – enjoying a smooth move towards launch, with only a Tyvek cover being noted as an issue of note, after it was found that a ‘rain cover glue line did not align properly to thruster flange.’ This has since been replaced on the orbiter.
Weather remains the biggest problem, with only a 40 percent chance for favorable weather at the time Discovery is due to launch (11:38am EDT).
A new article will follow, evaluating Discovery’s ride into orbit, and Flight Day 1.
Discovery’s 34th flight will be the 120th carried out by the space shuttle. She will be launched on a 51.6 degree inclination on a High Q launch profile, inserted directly to a 122 nm altitude. Discovery – commanded by Pam Melroy – is carrying Node 2 ‘Harmony’ to the International Space Station on a 14 day mission.
This will be the first flight of OI-32 Flight Software, which includes many new capabilities, including automated SSME (Space Shuttle Main Engine) Throttle Down during launch.
Following her eight and a half minute ride into orbit, a new ET Door Closure procedure will be in effect. This was brought in after an anomaly was observed during STS-118 with Endeavour.
‘ET Door manual close procedure resulted in a hardware damage concern due to uplock latches being driven prior to the doors being fully closed,’ noted a NASA Mission Evaluation Room (MER) pre-launch presentation.
‘Procedure has been updated and flight crew trained to remove any threat of latching the doors before the door motors reach end of travel.’
Also related to launch is an updated Prelaunch Conjunction Screening protocol, to reflect accepted on orbit philosophy. This method is being utilized to clear the vehicle through MET (Mission Elapsed Time) 2hrs. The previous method utilized an action box only and was not properly sized, noted the presentation.
SSPTS debut for Discovery:
Discovery will also be debuting her SSPTS (Station-Shuttle Power Transfer System) – which performed without issue on its first flight with Endeavour during STS-118. The SSPTS allows the orbiter to receive power from the International Space Station, thus providing the ability for longer mission duration.
‘SSPTS is activated on the evening of FD3 (Flight Day 3) after docking and remains powered until just prior to EVA 5 during which the SSPTS cables are physically disconnected in preparation for PMA-2 relocation,’ noted the STS-120 Flight Plan.
‘SSPTS is also deactivated via ground command during EVA 3 and H2O dumps due to concerns with ISS power generation. SSPTS is deactivated via ground command during all other EVAs due to concerns about the crewâ€™s proximity to powered connectors.
‘For the initial activation (FD3) and final deactivation (FD11), the crew performs actions to act/deact the Orbiter Power Control Unit (OPCU) converters. MCC-H commands SSPTS connectors unpowered/powered by opening or closing ISS Remote Power Controllers (RPCs) which provide 120v power to the OPCUs. EGIL will include a message in the Flight Plan Revision leaderhosen for the crew to expect Spec 179 OPCU CH VOLTS messages.’
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‘No change from SSPTS plans and procedures on STS-118,’ added the MER overview. ‘SSPTS will be turned off during EVAs to protect crew from ungrounded cables (identical to STS-118). If SSPTS fails, then mission duration is reduced from 14 days to 12 days.’
ET-120 ready to fly – finally:
Finally making it into space – albeit for a short while before it is disposed of, not long after being separated from Discovery – will be ET-120.
The tank is one of four that were sent back from KSC for Return To Flight (RTF) modifications, a huge and complex undertaking which challenged a Michoud Assembly Facility (MAF) workforce, a workforce that is still – even today – recovering from hurricane Katrina.
ET-120 arrived back at the Kennedy Space Center (KSC) in time to support STS-118 as the LON (Launch On Need) tank, should Discovery of been moved into a rescue mission. However, more work was required before it made the STS-120 stack.
Issues with ‘resistance’ problems with LO2 level sensors caused some post-arrival work in the Vehicle Assembly Building (VAB) along with a large amount of modifications to the tank’s LO2 17 inch feedline brackets – following the foam liberation event during STS-118.
‘This tank had sections of its thermal protection system, known as TPS, removed and dissected as part of an investigation following the STS-114 significant foam loss event,’ said Tim Owen, an engineer in the External Tank Project Office, who led the effort to repair the tank and recertify it for flight.
‘The question became, ‘Can this tank be restored to flight configuration or is it destined to be a test article or museum piece?’
‘The Lockheed Martin ET team has done an excellent job, not only in returning ET-120 to flight status, but also in exceeding the Shuttle Program’s requirement by restoring the tank to a much better condition than the 2005 version.’
Now sporting a complete set of post-Return To Flight modifications – and its role beforehand as a test article in post STS-114 evaluations into foam liberation – ET-120 is ready to finally ride into space.
‘It’s now our best tank ever,’ said John Chapman, manager of the External Tank Project Office. ‘We’ve learned more from ET-120 than from any other flight tank in the program, and the knowledge gained from the dissection and study of ET-120 will impact the design on all future tanks.’
L2 members: All documentation and quotes – from which the above article has quoted snippets – is available in full in the related L2 sections, updated live.