STS-124 spacewalkers Ron Garan and Mike Fossum will debut a new modification to the EMU (Extravehicular Mobility Unit) gloves they will use during their three EVAs.
This comes in the form of Turtleskin patches, sewn into the thumb and index finger regions of the gloves, a modification that is classed as an alternative to the overglove protection – which was implemented following a number of worn and cut glove incidents.
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STS-124 FRR Review 1 – EMU Glove Modification:
Classed as ‘Glove TMG (Thermal and Micrometeoroid Garment) Protective Patches’, the modification has been phased into making its debut with STS-124, following several instances of glove damage during EVAs since STS-116.
Most notable was the incident with STS-118 spacewalker Rick Mastracchio, who was sent back to the Quest airlock after a cut was observed in his glove during EVA-3.
However, that cut was spotted during a regular check, a process that is now baselined into EVAs. This process came about after damage was seen on Robert ‘Beamer’ Curbeam’s EMU (Extravehicular Mobility Unit) gloves, after STS-116 had landed. Engineers have been working on improved safety ever since.
With the overglove debuting on STS-120 – and modified for STS-122 – the Turtleskin patches are likely to be the final safety modification option to be implemented onto the EMU gloves, which is also being targeted for use with US spacewalks during International Space Station EVAs.
This new modification – according to the associated STS-124 EVA Flight Readiness Review (FRR) presentation – will also provide benefits by removing the requirement to wear overgloves, should EVA work require increased dexterity during tasks.
‘TurtleSkin is significantly tougher than Vectran. No requirement to wear overgloves when wearing the modified EMU gloves,’ noted the presentation. ‘Any RTV (coating) loss will not be reason to don overgloves.
‘Periodic glove inspections will occur and post-EVA glove photos will be taken and downlinked for assessment. EVA will be terminated for a visible cut or hole.
‘If crewâ€™s prime gloves are considered no-go after post EVA inspection is completed, crew backup gloves are not modified so crew will wear overgloves for all remaining EVAs, but will remove them if needed for the following reasons, including tasks that are impractical to perform with overgloves.’
Turtleskin is a tightly woven Vectran that has a significantly higher cut and puncture resistance than the knit Vectran currently used in the glove palm.
The Turtleskin patch is a field retrofitable modification that is sewn over the existing RTV pad. Individual patches will be installed on the prime gloves in the areas of concern (i.e. the thumb and index finger), which will provide up to four times the resistance to cuts than the previous glove design.
‘The patch consists of TurtleSkin fabric wash-coated with RTV 3145, a Teflon pleated back, and an additional strip of RTV 3145,’ added the FRR presentation. ‘Two to four times more cut resistant than the Phase VI glove knit Vectran. Higher puncture resistance than the Phase VI glove knit Vectran.’
Testing of the patches was carried out with the crew in the NBL (Neutral Buoyancy Laboratory), which led to a couple of modifications being carried out on the gloves, prior to full flight certification.
‘Glove box evaluations conducted to gain crew concurrence prior to retrofitting STS-124 and Increment 17 crewmembers training gloves with initial patch design. NBL evaluations concluded that the design was acceptable for flight with the addition of some minor modifications:
‘Crew and engineering requested the addition of a thin RTV strip to the top of the patch to increase grip. Crew also requested that the patch be made slightly smaller in order to decrease contact between the patch and the lower RTV pad.
‘Successful glove box evaluations were conducted to evaluate the modifications. Crew and engineering comments were incorporated into the final design.’
Now believed to be the cause of most of the recent glove damage, MMOD (Micrometeorite and orbital debris) impacts on ISS hardware – such as recently observed on the handrail of the Quest Airlock – were also evaluated in the testing of the new modification.
The results, outlined in the FRR presentation, favored the gloves with the Turtleskin modification, though it also showed the risk of such MMOD induced hardware damage, if left unnoticed.
‘Objective: Evaluate and compare damage created by simulated MMOD hits on handrails to knit Vectran and Turtleskin. WSTF (White Sands Test Facility) shot handrails with hypervelocity particles simulating on orbit impacts. Knit Vectran and Turtleskin were exposed to the MMOD strikes in a pressurized suited event attempting to induce glove damage.
‘Phase VI Glove Knit Vectran (Molded Palm) Results: Cuts were induced on Knit Vectran after a single exposure. Subject was not able to cut the Vectran with slow high force gripping motions. Subject cut Vectran using a quick sliding motion across the MMOD impact site while pushing into the handrail.
‘TurtleSkin Patch Results: Attempted to cut the TurtleSkin using the same motion that cut the knit Vectran. One attempt broke off a large burr that caused a 3/4 inch cut in the knit Vectran. No damage beyond surface abrasion and RTV loss (after 10 attempts on each glove).
‘Continued to cycle the same area of the TurtleSkinÂ® against MMOD hits. The left thumb patch showed only abrasion damage and RTV loss after 50 cycles. After 50 cycles an abrasion hole was created on the right thumb patch. Cycling as tested is more abusive than nominal glove use on orbit.’
With test results from five NBL runs, and confidence cycling (10 EVAs) indicating that the gloves integrity remained intact, along with the MMOD engineering evaluations indicating the patch is significantly more robust than the original glove material, the modification was certified for flight.
‘STS-124 and Increment 17 prime gloves have been retrofitted with the Turtleskin patch. Crewmembers have completed Class I glove fit checks and have accepted their patched prime gloves for EVA.’
Such is the level of confidence in the new modification, no use of overgloves will be required on STS-124’s EVA-1. In fact, overglove use will only come into play if back-up gloves are required on EVA-2 and 3, along with crew preference for work on replacing a faulty Nitrogen Tank (NTA).
‘Prime EMU gloves worn on EVA 1 have Turtleskin patches, therefore no overgloves are required. If back-up gloves are required on EVAs 2 and 3, overgloves will be worn per the approved Overglove Policy as follows:
‘Overgloves removed for all tasks on the JPM (new hardware). Overgloves may be removed per crew preference for the following NTA prep tasks: QD (Quick Disconnect) ops and thermal cover installation. Electrical connector ops.
‘EV2 will not wear overgloves while holding the NTA on the SSRMS (Space Station Remote Manipulator System) arm. Safety issue – lack of tactile feel during SSRMS maneuvers with NTA increases risk of losing NTA and possible subsequent vehicle damage.
EV1 may remove overgloves during ESP3 NTA removal/temp stow (same reason as EV2 above). Overgloves will be worn at all other times during the EVA unless crew fatigue/safety is at risk.
‘For prime or back-up gloves, the glove inspections will occur at the completion of major tasks/translations or every 90 minutes, whichever is sooner, as documented in the EVA procedures.’
The FRR document, one of 25 FRR presentations available on L2, also covered EVA related tasks such as SARJ (Solar Alpha Rotary Joint) Tasks and SARJ Cleaning DTO (Detailed Test Objective) requirements – including images and info on certifying a new SARJ scraper, along with the late addition of Battery Charger Module (BCM) R&R task.
STS-124 Pad Flow Latest:
With most of the shuttle workforce taking time off over the long Memorial Day weekend, engineers at the pad have been pushing towards ‘S0007.100’ Launch Countdown prerequisite operations, ahead of the countdown beginning next week.
‘Aft confidence checks were completed yesterday. Orbiter aft closeout (S1287) is complete,’ noted Friday processing information on L2. ‘Mass Memory Unit (MMU) load complete in preparation for flight.
‘Lift and installation of the crew escape pole was delayed until this morning while Flight Crew Systems investigates proof load paperwork. SRBs: the forward skirts are closed for flight and aft IEA closeouts are finished.’
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A new item of interest was the observation of a crack on the External Tank, though an engineering evaluations cleared the tank of any concerns relating to the discovery, given that it holds no concerns of liberating any debris during the ride uphill.
‘During a walkdown of the external tank an ‘irregularity’ in the Super Lightweight Ablative (SLA) of the cable tray cover on the upper LOX ogive,’ added the processing information.
‘After thorough photo analysis and engineering evaluation, this irregularity was determined to be a crack; however, there are no concerns with respect to potential debris generation during ascent.
‘The discrepancy was documented and addressed using the appropriate off-site acceptance criteria for SLA defects of this nature. No further work is required and no constraint has been established.’
Also recently cleared was the observation of an Emergency Life Support Apparatus (ELSA) in Avionics Bay 6, which had been accidentally left in Discovery’s aft during Orbiter Processing Facility (OPF) processing, before falling into the Avionics Bay during lift/mating operations in the Vehicle Assembly Building (VAB).
Though the canister failed to cause any damage in Discovery’s aft, an investigation team was formed, which will provide a full overview of the incident to the all-powerful Program Requirements Control Board) next week.
‘Emergency Life Support Apparatus (ELSA) investigation team continued their process analysis today. Next Tuesday, at the Daily Program Requirements Control Board a presentation will highlight the flight hardware inspection results, flight rationale, and status of the on-going process evaluation.’
Pad work was deemed to be slightly behind schedule, though by Friday evening, the primary and secondary waterbag installation was completed, and the J pipes have been installed.
Fine work – as per usual – by all concerned on the flow continues to place Discovery on track for an opening launch attempt on May 31.
L2 members: All documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, updated live.