STS-123’s countdown for Tuesday morning’s opening launch attempt has begun, with no major issues being worked on the shuttle – though a concern relating to a quick-shoe mount has been discussed.
With the UHF radio problem cleared to fly as-is, and the weather forecasted as favorable, Endeavour now heads into the complex ballet of pre-launch operations, which will hopefully conclude with her launch at 2:28 am on Tuesday.
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STS-123: UHF Radio:
At the noon board meeting on Friday, shuttle managers requested a better understanding of the UHF radio issue – specifically ensuring they had capability for scenarios such as communication with launch abort sites – prior to approving the system to fly as-is.
While not an LCC (Launch Commit Criteria) breach in its current state, a full understanding of its ability during powered flight and the latter part of re-entry was required.
As previously noted, the radio has a level of functionality, in low power mode. The fault occurs when operated in high power mode, despite the replacement of certain elements of the radio system via donations from Atlantis.
‘MOD is GO for launch with UHF in Low Power. Nominally UHF is available through powered flight and is picked up during Entry at about Mach 9 (around 15 minutes prior to touchdown). UHF is required for TAL and ECAL Aborts,’ noted one of two expansive presentations on the issue.
‘During an abort, crew uses UHF to speak directly with airport tower personnel for runway and weather information. UHF is also required for dissimilar redundancy to S-Band system.
‘If the UHF system fails pre-launch, MOD would be NO-GO for launch per the LCC (CT-05).’
The presentations also outlined how the problem was found, which led to issue being elevated from the Engineering Review Board (ERB) to the Leroy Cain led Noon Board.
‘The UHF ATC transceiver was being tested on single bus power. COM checks on main C followed by main A were successful with the power amp (PA) off and measured transmit power was (-)83 dBm.’
‘The next test was on main A with the power amp on. The radio experienced a complete shutdown and IPR (Interim Problem Report) was initiated. Troubleshooting then removed all power and repeated the single bus power amp off com checks. The main C and main A checks were good on both simplex frequencies.
‘With main A on and main C off, the power amp switch was turned on and a one-way uplink voice check from the C&T station was good. The orbiter transmitter was keyed and again the radio shutdown.’
Clearing the system to fly in its current state was delayed until Friday, due to additional data being required on the system’s ability during launch aborts.
This saw data being presented to managers, where communications were initiated in all relevant scenarios via flight history – simulated with the radio in low power mode – on the Dynamic Environment Communications Analysis Testbed (DECAT).
DECAT, is an in-house developed simulation tool, used to analyze dynamic communications coverage and link performance based on vehicle trajectory and attitude and the relative geometries, which proved that there was still enough power for communications to be made via the orbiter and required ground stations and abort sites.
Had the results been negative for flying as-is, a back-up plan was in place, which would have involved Discovery’s UHF radio being donated for Endeavour. While the re-test would have only taken four hours, access to Discovery’s radio would have taken a fair amount longer.
‘Cannibalization of the OV-103 (Discovery) UHF radio. AV-Bay 3A access is required and there could be an impact to the flight crew equipment stowage. Retest requires 4 hours. A test was performed today on OV-103 which verified full operation of its radio.’
However, now the radio has been cleared for flight, this plan is no longer required.
PRCB Evaluations of Quick-Shoe Mount:
The next major meeting of shuttle managers will take place at the L-2 MMT (Mission Management Team) meeting, with one additional item of interest likely to be further evaluated.
That relates to a discussion started by the all-powerful Program Requirements Control Board (PRCB) on Thursday, which saw a large presentation being made on a potential problem with a ‘quick-shoe mount’ in the crew module that has a ‘remote’ risk of causing a breach in the canopy’s skin.
The mount – and attached Bogen Bracket and Arm – will hold a Payload and General Support Computer (PGSC) in place on the flight deck, and it has been recommended that the mount, which ‘shows negative margins due to crew induced moment loads imparted by the Bogen Bracket attached to the Quick-shoe,’ should be relocated.
‘The stress community does not know the failure mode or hole size generated should the skin fail,’ noted the PRCB presentation, citing the worst case scenario being ‘External Leakage Of The Crew Module/ODS Resulting In Loss Of Habitable Environment: Catastrophic Severity.’
Given the findings are technically an increase in risk to the vehicle and crew for STS-123 – ranging up to the worst case scenario of LOVC (Loss Of Vehicle and Crew) – a waiver may be required for this mission.
More importantly, now that the potential issue has been spotted, options and mitigation efforts have been presented ahead of launch.
‘(1) Accept Risk and Fly-As-Is: Recommend STS-123 Crew use minimum torque to tighten Bogen Arm to lessen the likelihood of imparting moment load on the Quick-shoe. Approve flight waiver,’ listed the options.
‘(2) Clamp the PGSC Desk to the R13 panel per backup plan.
‘(3) Use Loc-Line Bracket in place of Bogen Bracket: Preliminary information suggests that the force required to impart a moment is 10 times less (13 in-lbs assumes 18 inch moment arm) than the Bogen Bracket.’
The recommendation to relocate the Quick-shoe bracket was supported by the majority of departments involved in the discussion.
‘Crew Systems, Safety, CM Structures, and OPO (Orbiter Project Office) recommend Option 2 and to remove Quick-shoe from mounting plate. Relocate Quick-shoe to non primary structure for future flights.
‘Crew Office recommends Option 1: Level 2 Loads Panel does not support a waiver: Waiver rationale and current margins should be provided for further discussion.’ The Crew Office cited the relocation as ‘different from crewâ€™s trained baseline, adding Panel R13 must be accessible.
This article will be updated when further information on the quick-shoe evaluations are available.
L2 members: All documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, updated live.
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