Troubleshooting and weather challenging STS-120 pad work

by Chris Bergin

Discovery’s S0007 (Launch Countdown) procedures were two hours behind schedule last night, due to a number of leaks at the pad, along with a weather delay to PRSD (Power Reactant Storage and Distributation) loading.

The loading of reactants into Discovery’s power generating systems was delayed by around two hours, as operations were ceased due to lightning in the local area. However, this has now been caught up and STS-120 remains on track for Tuesday’s opening launch attempt.

**The most comprehensive collection of Shuttle, Ares, Orion and ISS related presentations and mission documentation, plus expansive daily processing documentation and updates are available to download on L2 **

Extensive STS-120 Special Section on L2, including Flight Plans, ALL Handbooks and Checklists, Manuals, documentation and presentations. STS-122 to STS-127 documentation already available.

STS-120 L2 Special includes 20 Full FRR presentations (Oct 9-10) – the most expansive overview of the mission. **Click here for sample**

Now includes the STS-120: Joint SSP/ISS FRR Chart Presentations (over 25mbs worth), part of the LIVE MMT level mission coverage on L2.

**LIVE news updates on Discovery STS-120 PAD Processing**

**LIVE news updates on Endeavour STS-123 Processing**

**LIVE news updates on Atlantis STS-122 Processing**


Sunday’s processing at the pad included a number of scheduled procedures, such as ongoing Orbiter/SRB PIC Resistance Tests and SRB Ignition S/A Device Verification. However, it was PRSD loading that was the key event of the day.

Due to a lightning warning in the locality of the pad, PRSD loading was delayed by around two hours, placing the schedule slightly down on the timeline – although this is not uncommon and can be caught up.

As of around 10pm local time on Sunday, the schedule was two hours behind, with some pad work ceased due to the continued threat of lightning. By 11pm local time, the threat had passed, allowing engineers to start catching up with full S0007 pre-launch processing. By 8am this morning, engineers had caught up with the two hours lost.

‘As of 15:15 EDT local weather conditions were deteriorating with lightning in the vicinity threatening the continuation of PRSD loading. 15:30 EDT PRSD loading was suspended,’ noted processing information.

‘The STS-120 S0007 LCD is slightly behind in the schedule due to troubleshooting IPR’s and threat of lightning (Phase II advisory) within the LC-39 Area. We are still marching towards a launch at 11:33:18 (EDT window opening) on October 23, 2007.’

Those IPRs (Interim Problem Reports) mainly reference GSE (Ground Support Equipment) at the pad. Again, this is not uncommon in a pre-launch flow.

‘IPR: O2 Air Half Coupler (Midbody) post load fill poppet leak checks exceeded OMRS (Operational Maintenance Requirements and Specifications) limit of 2.18 psi/min on tanks (number) 3 (4.8), 4 (2.4) and 5 (2.4),’ noted processing information, which added an expanded explanation.

‘During O2 air half couplings midbody poppet leak checks, 3 of 5 tank (tanks 3,4,5) readings failed OMRSD (Operational Maintenance Requirements and Specifications Document) requirement which requires a decay less than 2.18 psi.

‘The decay on tanks 3, 4, and 5 were 4.8, 2.4, and 2.4 psi, respectively. Will wait for H2 to load and O2 to stabilize before reperforming the test again. This condition has happened on past flow – and same trouble shooting plan resolved issue.’

Another observed leak will lead to the removal and replacement of a valve on the GO2 system at the pad, after engineers literally heard the problem.

‘GO2 Leak in panel on valve in Storage Battery at Pad. There was an audible leak at a valve on panel on the GO2 System. The leak is at the stem of a needle valve on the facilities panel. The valve must be removed and replaced before continuing the pressurization of the GO2 lines.’

This process of replacing and retesting the valve will only take around an hour to carry out, and would only become a constraint during the countdown if the work isn’t completed by the time the countdown comes out of the T-11 hour hold.

‘During cross country line pressurization of the GO2 line, a panel valve was noted to be leaking from the needle externally to ambient. An upstream valve was closed to stop the leak and the clears remain in place.

‘The forward plan is to replace the valve and then resume pressurization ops. Replacement parts have been located and the estimated timeline on this valve is 45 to 60 minutes. Constraint is being moved to 15-3 (Resume count at T-11 Hours).’

**(NOW INCLUDES STS-118 Re-Entry Video) Ride home through the fire, sparks and plasma of re-entry with Atlantis, Discovery and Endeavour. FIVE Stunning high quality 2hr, 355-400mb Camcorder and HUD videos – from payload bay closure – through re-entry with a astronaut held camcorder video – to post landing – several more videos showing landing from 90,000 ft also available – Now includes HALO II Re-entry video**

Other issues of note included PRSD H2 LD (Hydrogen loading) reading of 12600 ppm on OMBUU (Orbiter Mid Body Umbilical Unit) H2 Sample Panel, which is 2600 ppm over the point such readings should be reported as an IPR.

Also, the Cabin Pressurization Air System Regulator on the FSS (Fixed Service Structure) 215 foot level was classed as ‘creeping’ – which led to it being removed and replaced.

‘The regulator should hold to 130 psi. The system was isolated when pressure reached 142 psi – would have received an alarm at 145 psi. The regulator adjustment was attempted, but it was determined that the regulator must be removed and replaced,’ noted processing information, classing this as an open issue, due to the replacement regulator also suffering a problem.

‘A new regulator was on hand, the replacement is complete, and we are in the proper configuration. However, shortly after the Primary Regulator was replaced, the pressure crept back up during retest. Suspect secondary regulator is the cause of the problem.’

At around midnight Sunday, engineers were also looking at a debonding issue with a F1D Tyvek cover. Evaluations are taking place on whether to replace the cover.

Launch weather on Tuesday remains a concern, with a 40 percent chance of being a constraint to launch, with the same probability reaching into Wednesday. By Monday morning, this had risen to 60 percent.

‘A front has stalled in Central Florida and will begin migrating north this afternoon causing a threat for showers and thunderstorms. By launch day, high pressure will be located off of the east coast of the US causing south-southeasterly flow over Central Florida, and a cold front will be moving into the Central Gulf of Mexico,’ noted official NASA information.

‘With this weather pattern, there is a threat of coastal showers, cumulus cloud development, and a low cloud ceiling at the onset of the east coast sea breeze near launch time.

‘Although meteorological models have changed the past few days on the timing of the front, they are beginning to come into agreement that the cold front that will be in the Gulf of Mexico on launch day will move through Florida on Wednesday, 24 October.’

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.

**STARLIGHT: NEW STS-117 MISSION REVIEW MUSIC VIDEO** – STS-118 Mission review video also available. 

(Video section is FREE, but you need to sign up as a member of the forum to enter the video section of the site. We only use your e-mail to send you your password. It will not be used for spam etc.)

Related Articles