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\u201cWindows1 R&R is complete less 24 hr re-torque. Window #7 R&R complete,\u201d noted the latest processing information (L2). \u201cFuel Cell 2 voltage reduction test complete. OMS Pod Functional is in work. S-Band antenna troubleshooting in work.<\/p>\n
\u201cPayload download is in work. FRCS (Forward Reaction Control System) functional is complete. Wheel and tire installation continues to be in work.<\/p>\n
\u201cWeekend Work: Remove Bay 11 & 12 longerons. Waterproofing Sunday (Bay Clear).\u201d<\/p>\n
Atlantis has at least two more missions ahead of her prior to the retirement of the fleet \u2013 pending a final decision on shuttle extension \u2013 along with the assignment as the STS-135 LON (Launch On Need) support role of the final mission on the current manifest.<\/p>\n
Currently targeting launch No Earlier Than November 12, the STS-129 mission will see Atlantis deliver the Express Logistics Carriers 1 & 2 (ELC-1 and ELC -2), along with SASA and MISSE (Materials on International Space Station Experiment) 7A and 7B, to the Space Station.<\/p>\n
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ASA Root Cause:<\/p>\n
![\"a61\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2009\/06\/a61.jpg\" "\\"a61\\"")
Work started on the ASA channel 1 failure \u2013 a system required for carrying commands from the flight computers to the aerosurfaces such as the elevons and tail \u2013 shortly after Atlantis landed in California at the conclusion to STS-125.<\/p>\nThe issue was first registered during SSME ignition, which \u2013 it has since been revealed via Flight Readiness Review (FRR) documentation \u2013 had the potential to cause a RSLS (Redundant Set Launch Sequencer) hold with just seconds remaining on the countdown.<\/p>\n
\u201cDuring SSME ignition an electrical short occurred on DC buses MN-A and MN-B which resulted in the loss of ASA-1 and caused several MDM (Multiplexer Demultiplexer) FA1 and OA1 measurements to become erratic momentarily,\u201d noted a 260 page Agency FRR presentation from the Orbiter Project, available to download on L2.<\/p>\n
\u201cIf this failure were to occur prior to T-10s, the result would be a violation of GNC Launch Commit Criteria. If this failure were to occur between T-31s and T-0s, the potential for an RSLS hold or abort exists (however, \u201cInstrumentation shift only \u2013 not true cap voltages,\u201d allowed Atlantis to launch and continue to orbit without concern).<\/p>\n
\u201cAt ~T-3s FC currents indicated a current-limited short of ~12.5A on FC1 (MN A) and ~7.5A on FC2 (MN B). At ~T-0s the short circuit was isolated from the main busses (total short circuit time of ~3s). At ~T+1s the event indicator for APCA4 RPC 10 (10A) transitions from ON to OFF followed by the event indicator for APCA5 RPC 12 (5A) at ~T+2s.<\/p>\n
\u201cFC (Fuel Cell) current short circuit signatures were consistent with RPC trip characteristic signatures (150 percent for 2-3s). APCA4 RPC 10 and APCA5 RPC 12 provide redundant power to Aerosurface Servoamplifer-1 (ASA-1). Follow on flight control signatures support loss of ASA-1.\u201d<\/p>\n
![\"a28\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2009\/06\/a28.jpg\" "\\"a28\\"")
The short itself was caused by the noise of the SSMEs powering up injecting into Atlantis\u2019 aft, and causing some disruption of Atlantis\u2019 avionics.<\/p>\n\u201cReview of Bus Monitoring Unit (high rate) data showed that during the time of the short circuit a distorted, 400Hz sinusoidal wave was injected onto the MDM FA1 and OA1 signal return buses,\u201d added documentation.<\/p>\n
\u201cThis resulted in measurements which use the MDM signal return bus as a reference to become erratic (single ended). Differential measurements were not affected. Once the short circuit was isolated all measurements on MDMs FA1 and OA1 returned to expected values.<\/p>\n
\u201cReview of historical data uncovered a very similar event during the STS-37 (104 Flight Eight) ground flow (1991). Short circuit was determined to be caused by an exposed conductor contacting vehicle structure on the 26Vac excitation circuit between ASA-1 and a left wing elevon actuator<\/p>\n
\u201cWire was pinched in the non-insulated portion of a wire harness clamp that shorted while personnel were in the area. MDM interference was determined to be due to the grounding scheme of the ASA box.\u201d<\/p>\n
In-flight short circuits associated with orbiter wiring are rare, with the previous incident occurring during Columbia\u2019s highly eventful STS-93 launch<\/p>\n
![\"a73\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2009\/06\/a73.jpg\" "\\"a73\\"")
*Click image for a clippedd video sample (full video on L2) showing flight controllers reacting to the STS-93 event.*<\/em><\/p>\n\u201cThere have been seven previous in-flight short circuits which were later isolated to Orbiter wiring damage.<\/p>\n
\u201cThe last in-flight short circuit isolated to Orbiter wire was the AC-1 phase A short during ascent of STS-93 (1999). This resulted in a stand down period during which all vehicles were inspected for previously undetected wiring discrepancies.\u201d<\/p>\n
Following the STS-93 short, corrective actions were implemented that both reduced the potential for wire damage and heightened detection capability should it occur.<\/p>\n
\u201cInspection Processes Enhanced Following STS-93. Wire inspections are now performed by two independent quality inspectors anytime wire bundles or connectors are opened for any type of work (category 1),\u201d outlined documentation.<\/p>\n
\u201cHarnesses are flared and a detailed inspection of accessible wire performed with 10X magnification, lighting and mirrors as required. A baseline wire inspection was scheduled to be performed on each vehicle at its next OMM (category 2).<\/p>\n
\u201cA hands-on outer-periphery inspection of ALL accessible wire bundles with criteria and methods similar to category 1 intended to capture and repair latent wire damage (i.e. baseline the vehicle).<\/p>\n
\u201cCloseout inspection criteria was updated to require two independent inspectors and inspections are now performed prior to installation of hardware that would cover wire. Arms-length inspections of wire bundles are performed as areas are backed out and closed for flight.\u201d<\/p>\n
During flight, the failure of the single channel ASA \u2013 part of a quad channel system \u2013 holds no mission impact. However, due to flight rules, a second failure \u2013 depending on the cause \u2013 forces a discussion on whether to bring the orbiter home at the next landing opportunity.<\/p>\n
Expansive plans were drawn up in the event of a second channel failure, resulting in over 20 presentations to the Mission Management Team (MMT) during STS-125\u2019s mission (all available on L2).<\/p>\n
![\"a35\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2009\/06\/a35.jpg\" "\\"a35\\"")
The need to find the root cause of the ASA failure was deemed a priority for engineering teams, although the task was daunting to say the least, due to the amount of wiring that required inspection.<\/p>\n\u201c(The ASA wire network) represents approximately 300 feet of bundled cables or approximately 800 feet of cable end to end,\u201d noted documentation, with initial resistance checks during Atlantis\u2019 stay at the Dryden Flight Research Facility (DFRC) finding no obvious fault candidate.<\/p>\n
Working through wiring from the nose of Atlantis, all the way through to connections with the Solid Rocket Boosters (SRBs) and External Tank, sections were cleared one at a time during the investigation, prior to a breakthrough last week.<\/p>\n
\u201cASA 1 Update: Troubleshooting found a Hi-Pot failure in Right Hand inboard Elevon,\u201d noted processing information, relating to a test that applies a higher than normal voltage to the signal wires, with the aim of applying a greater stress to the insulating coverings in order to uncover any weakness.<\/p>\n
The voltage is usually applied with respect to system \u2018ground\u2019 reference and any excessive current indicates a breakdown of the insulation (due to cracks, damage, etc.)<\/p>\n
Root cause for the ASA failure is thought to be a short from one of the power signal wires to ground, and further testing on the associated harness were undertaken to reveal the specific fault.<\/p>\n
![\"a43\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2009\/06\/a43.jpg\" "\\"a43\\"")
Updating status, the Orbiter Project Office (OPO) noted observations of worn-through insulation specific to the area in question, adding confidence they have found the cause of the short associated with the ASA-1 failure.<\/p>\n\u201cOn the ASA, did find the short and the wire harness was removed. Guys did a good failure analysis on it, and at NSLD (NASA Shuttle Logistics Depot) they could see the worn-through over-braid and the worn-through insulation of the wire below the over-braid,\u201d OPO noted on the latest Shuttle Standup\/Integration report (L2).<\/p>\n
\u201cThey could see the damage from the HPOTP (High Pressure Oxygen Turbopumps), but were able to find a small pit that appears to be the original short location. Have been working with Ground Ops to do the inspections on the other vehicles in similar locations and making sure we have everything protected.\u201d<\/p>\n
This associated harness will be replaced with a new version that is being built in time for installation into Atlantis next month. Endeavour was already cleared due to added in-built braiding protection on her wiring.<\/p>\n
\u201cAt the NSLD, we\u2019ve started the planning and fabrication of a new ASA wire harness to replace the one removed from OV-104 (Atlantis),\u201d added processing notes. \u201cLooking at July 10 as a delivery date.\u201d<\/p>\n
L2 members<\/em><\/em>: Documentation \u2013 from which the above article has quoted snippets \u2013 is available in full in the related L2 sections, now over 4000 gbs in size.<\/em><\/em><\/p>\n","protected":false},"excerpt":{"rendered":"
Engineers have found the root cause of the Aerosurface Servoamplifer (ASA) channel 1 failure on Atlantis, after an expansive failure analysis effort found a short in the wiring. Atlantis is being processed for STS-129, following the highly successful STS-125 mission to Hubble. As part of her turnaround, the Space Shuttle Main Engines (SSMEs) that helped […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"inline_featured_image":false,"footnotes":"","_links_to":"","_links_to_target":""},"categories":[2],"tags":[8290,9199,8951],"class_list":["post-41072","post","type-post","status-publish","format-standard","hentry","category-news","tag-sts-125","tag-sts-129","tag-sts-93"],"acf":[],"_links":{"self":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts\/41072"}],"collection":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/comments?post=41072"}],"version-history":[{"count":0,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts\/41072\/revisions"}],"wp:attachment":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/media?parent=41072"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/categories?post=41072"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/tags?post=41072"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}