Three “significant open items” will be at the center of tomorrow’s STS-115 Flight Readiness Review (FRR), as NASA look to give final approval for the August 27 launch of Shuttle Atlantis.
TPS (Thermal Protection System) putty repair risk, issues with the Ku band attach bolts and Ice Frost Ramp risk acceptance – the latter already noting dissenting opinion – are up for discussion, in what Shuttle lead Paul Hill noted would be the highlights of the FRR.
Information collated from several documents available to download on L2.
‘The most significant open items for 115 are the Ice Frost Ramp risk acceptance, TPS putty repair risk and the OV-104 Ku band attach bolts,’ said Hill in a pre-FRR memo acquired by this site. ‘The IFR discussion is pretty much the same debate as 121’s.
‘The TPS putty repair issue is similar to the IFR and is still coming together. Putty repairs have been lost in flight, including on 121. Debris transport can cause some of these to impact critical RCC panels and tiles under some conditions.
‘Orbiter is bringing the latest status on the OV-104 Ku band attach bolts to Monday’s noon board. The goal is to get into the payload bay on the pad to inspect and confirm sufficient threads are engaged.’ (Attach bolts status will be updated). Aug 15 update 8am Eastern: “The major unresolved discussion point going into the FRR will be KU-Band thread engagement.”
The Ice Frost ramps proved to be a key issue ahead of July’s launch of Shuttle Discovery on STS-121, with NASA Safety and NASA Engineering both noting their concerns, later to be diluted by their understanding that the risk was not associated with the crew, given the ‘safe haven’ ability for the mission.
It appears NASA is wanting to reduce the rating on the risk matrix to ‘Infrequent/Catastrophic’ – however, in documents dated August 11, NASA Engineering stated their self titled dissenting opinion, noting they feel the risk should remain as ‘Probable/Catastrophic.’
‘EA does not concur with describing the debris risk from Ice Frost Ramps as Infrequent/Catastrophic. For the following reasons EA considers the risk Probable/Catastrophic. The risk assessment masses of 0.08 lbm and 0.25 lbm are several times larger than the orbiter tile impact and damage capability.
‘1: Ground testing, ET-120 dissection, and stress analyses have all confirmed the constant, repeatable occurrence of the failure mechanism.
‘2: Flight history confirms that releases occur every flight and includes masses up to the maximum risk assessment mass. STS-121 had two IFR releases larger than 2 sigma.
‘3: The release mechanism is not well understood which means time of release cannot be assured.
‘4: There are no controls in place since the failure is a design flaw.
‘5: STS-121 cable tray instrumentation results indicate that the flight environment was adequately enveloped by the design environment, reducing the concern of making too many OML changes at once.
‘6: Risk Assessment indices indicate a high probably (~ 1/100) of exceeding tile capability which depends on repair capability to not be catastrophic.’
STS-121’s clean flight is likely to help the evaluations of the FRR when it comes to the risks associated. However, an extra equation to add to the mix is STS-115’s High Q ascent profile, which is required for Atlantis’ ability to lift the heavy truss segment payload uphill. Discovery flew a Low Q ascent profile to reduce stresses on the modified External Tank. – **Low/High Q article**
Regardless, following on from presentations from the MOD FRR associated with STS-115, the meeting in Florida should pass without any major standouts, with managers then being allowed to fully focus on trying to keep STS-116 (with Discovery) on track for a December launch – currently under threat. – **STS-116 Launch date threat article**
‘We’re still on track for launch August 27 (for STS-115),’ noted Hill. ‘We follow STS-115 right away with STS-117 FOR as the 116 team is simming and preparing to fly in December.
‘This is going to be a busy and fun Fall.’