STS-134: Endeavour completes Docked Late Inspections for OBSS handover
As the historic milestones continue to come thick and fast, Endeavour was put through her final inspections via the Orbiter Boom Sensor System (OBSS), ahead of presenting it to the International Space Station (ISS) as a farewell gift. The results of the scans – which focus on her Reinforced Carbon Carbon (RCC) panels – will be used to clear the orbiter for Entry.
Normally carried out after undocking, the Late Inspections follow a similar path to that utilized on Flight Day 2, which provide the baseline for the final checks of RCC panels, along with other critical areas of her heatshield, such as the nose cap.
With the data sent down to the ground for the Damage Assessment Team (DAT) to carrying out two levels of reviews into the findings, a final peer review would then be in progress as the DAT inform the Mission Management Team (MMT) with a recommendation Endeavour is in acceptable condition to return home early next week.
As per FD2’s opening inspections, Endeavour is in great shape. Only some minor dings on her belly ramped up the skilful evaluations by the DAT, as they cleared the final area of interest via the Focused Inspection (a full review article on the clearance will follow later in the mission).
The Focused Inspection utilized the OBSS sensor suite, which is again in action with the Docked Late Inspections. Unlike the FD2 inspections, additional challenges for the robotic teams resulted in an expansive plan for the positioning and translation of the OBSS – relating to clearances between the boom’s movements and the Station hardware Endeavour is docked with.
Notably, DLI debuted with Endeavour during STS-123, as the OBSS was left on Station for use by Discovery on the following mission. This handover related to the clearances with lofting the Japanese Kibo Laboratory with Discovery, leaving no space for the OBSS to be berthed in the payload bay.
A DLI was also used by Discovery herself during STS-131, when a Ku Band failure on the orbiter called for the utilization of ISS Ku assets to downlink the vast amounts of imagery to the DAT in Houston.
The lessons learned from both of the previous DLIs allowed for extra confidence in the planning for STS-134’s inspections.
“Structural interference from the ISS prevents running the standard FD 2 autosequences, so we will utilize docked inspection autosequences developed for STS-134/ULF-6,” noted one of several presentations on STS-131 DLI plan (L2).
“These autosequences provide full LDRI (Laser Dynamic Range Imager) coverage of RCC (Reinforced Carbon Carbon), but limited IDC (Digital Camera) coverage (IDC data will not be collected).”
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With changes to the inspection process, the DLI will take around one hour or so longer than standard Late Inspections – which are nominally a five hour process.
“Timing: We estimate the surveys will take 5-6 hours to complete: STBD (Starboard): around 2.75 hrs. NOSE: around 1 hr. PORT: around 1.5 hr. If the attitude maneuvers are required (to and from +ZVV), each will require around 1 hr for attitude handovers and the maneuvers.”
Outlining the proposed procedure, a preliminary inspection plan was produced in the main DLI presentation, starting with the Starboard Wing.
“STBD Survey: The stbd survey is divided into two parts. In the first part, the SRMS (Shuttle Remote Manipulator System)/OBSS reach over the PLB (Payload Bay) to scan the upper, forward, and some lower RCC zones. In the second part, the SRMS/OBSS reaches under the PLB to scan some lower RCC zones,” noted the presentation.
“In order to get full coverage, we will have to accept several close clearances between both the OBSS-RCC. Minimum clearance between the OBSS and RCC is expected to be 42 inches with several good available views (RSC, RMS Elbow, etc). These tight clearances require the stbd survey be heavily segmented, with several pause points with LDRI pan/tilt reconfigs as well as a few places where data is taken via a pan/tilt survey.”
Once the Starboard wing survey is complete, clearances for the two additional elements of inspections – the Port Wing and the Nose Cap – are far less restricted.
“NOSE and PORT Surveys: In the survey, the OBSS ‘wraps’ around the front of the vehicle and requires less than 5 ft clearance to completely survey the stbd side of the nose cap. The port survey requires less than 5 ft clearance to the port PLBD for some upper RCC surfaces.”
With the final plan to be sent up to the crew to allow for training briefs – which included CGI videos of the projected paths the SRMS and OBSS will take – other considerations include the attitude of the ISS during the surveys, due to the potential of LDRI shutdowns caused by the sun shining into the sensor.
The LDRI (Laser Dynamic Range Imager) is one of the stars of the OBSS sensor suite, and was involved in the earlier Focused Inspection evaluation on the small area of damage on Endeavour’s belly.
Incidentally, the LDRI raised the latest issue at the Mission Evaluation Room (MER), cited as “MER-11: LDRI Mode Timers Not Incrementing”.
“STS-134 LDRI Mode Timers: Noticed on GMT 144 that LDRI mode timers did not increment as expected. Nominally Mode 2 timer should be accumulating at least 24 hours each day. During the last mode check (GMT 144:16:14-144:16:20) the delta operational hours for all modes was 1.04 hours. Mode 2 Timer should have increased almost 42 hours,” noted a JSC Engineering presentation (L2).
“Most likely cause is an inadvertent power cycle or left in Mode 1. If LDRI is in any Mode and abruptly loses power, then all those hours of usage in that Mode are lost. Further, when the LDRI is firsts powered on, it goes into Mode 1.
“Request to perform a test of the LDRI (emulating LDRI calibration) to aid in determining the impacts, if any, to the LDRI. Data processing under very tight turn around schedule (24 hrs) due to EVA 4.”
That test was carried out at noon (Central) on Wednesday, via commands on the ground, given the crew was sleeping.
The results are being evaluated in relation to any unlikely impacts to the work to handover the OBSS to the ISS and conduct work to install it as the Integrated Boom Assembly (IBA) – its new role after supporting shuttle.
A MER report (L2) noted that similar event occurred during STS-123, after the LDRI was left in Mode 6 for 56 hrs and it resulted in a latent image. Additionally, we did not get live flat field for late inspection. These compounded events resulted in a 5 hour delay in processing the data.”
EVA-4 will be the focus of Flight Day 12, which will involve Mike Fincke and Greg Chamitoff installing the OBSS at the Starboard 0/Starboard 1 truss interface, prior to swapping out of the OBSS grapple fixtures, retrieval of the Port 6 truss segment power and data grapple fixture, and release of retention systems on the Dextre spare robotic arm.
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