Following the decision made by the Mission Management Team (MMT) to press ahead with a Focused Inspection (FI) on one area of Thermal Protection System (TPS) damage located on Endeavour’s belly, the Orbiter Boom Sensor System (OBSS) was used to gain imagery which has successfully allowed managers to clear the vehicle for entry. Later on Flight Day 6, his Holiness the Pope called the joint crew on orbit and gave his blessing.
STS-134 Focused Inspection:
Following Friday’s successful EVA-1, the crew was set to enjoy a largely off duty day, mixed in with some robotic procedures and preparations for Sunday’s EVA-2.
However, due diligence from the MMT – based on a recommendation from the Damage Assessment Team (DAT) – resulted in a call to use the pre-planned placeholder in the flight plan to carrying out a Focused Inspection on a relatively small area of tile damage, located on the starboard side of Endeavour’s belly, between the Main Landing Gear Door and (MLGD) External Tank Door (ETD).
The damage is historically minor, but due to a need for additional data to be plugged into DAT’s extensive computational analysis models, and less than perfect imagery of the damaged area from Flight Day 3 RPM photography, the FI option is an opportunity to add confidence in what is expected to be full clearance for entry in around 24 hours.
The OBSS instrumentation package – which rides on the end of the 50 foot boom – consists of visual imaging equipment, the Laser Dynamic Range Imager (LDRI), and the Laser Camera System (LCS). The post-Columbia modification has sensors that can resolve at a resolution of few millimeters, and can scan at a rate of about 2.5 inches per second.
Thanks to Neptec’s Laser Camera System (LCS), engineers will gain detailed high resolution images and even a 3D model to provide additional data for their thermal modelling and requirements within hours of the survey.
The Focused Inspection by the OBSS will be one of its final roles with the orbiter, ahead of the Docked Late Inspection (DLI) which will then result in the Canadian superstar being handed over to the ISS for a role as the Integrated Boom Assembly (IBA).
Although imagery requirements were refined in real time, baseline Focused Inspection requirements were provided to the MMT a few days ago, providing some procedural outlines into the dual use of two elements of the OBSS package – namely the LCS and the IDC (Digital Camera).
“Priority Location 1: Large Tile Damage: Damage ID: D-134-RPM-600_2-001. Location: Starboard side between MLGD and ETD. Location X= 1243.85, Y= 106.07 , Z= 267.33. Sensors: LCS and IDC (with LDRI illumination – Mode 6, record LDRI),” outlined a DAT procedure document (L2).
“Requested Views Details: 5 total views are required for damage assessment. The first four of the five views should be optimized for IDC imaging, but LCS data is requested as well. Views 1 thru 3 have IDC/LCS positioned slightly outboard of damage site and pointed inboard (approx 5 degrees off normal).”
Those five total views are all the DAT engineers need for their data requirements, which will refine the dimensions of the damage and should result in not just imagery, but 3D computational models, as was seen during STS-118’s Focused Inspection.
“View #1: IDC approximately 6″forward (-X direction) of damage. View #2: IDC approximately even (X direction) with damage. View #3: IDC approximately 6” aft (+X direction) of damage. View #4: IDC positioned directly above the damage pointing to the damage at normal incidence,” added the DAT overview.
“View #5: LCS positioned directly above the damage pointing to the damage at normal incidence. Need to capture 20” minimum all the way around damage site. IDC is not required for this additional data acquisition.”
The robotics operations also require the crew to follow set instructions on ensuring the imagery taken with the Digital Camera on the end of the OBSS is based on the real-time environment, as the Endeavour/ISS stack race through daylight and darkness on orbit.
“Sensor Package 2 IDC Preferred Parameters: Range: 75” for Views 1 thru 4. Boom Motion: Brakes On plus 90 second dwell before beginning data collection (NO EXERCISE). IDC Scenario: “Black Tile – Day” and “Black Tile – Night”. Crew will select proper file (day or night) per real-time environment,” the requirements added.
“IDC Lighting: Daylight (direct or earthshine) or LDRI illumination at night (daylight is preferred). IDC FOV: Fixed at 16 deg x 9 deg. Notes: The engineering and imagery teams will be satisfied with a range between 66” and 84”. There is some risk that data collected between 60” to 66” or 84” to 120” will be unsatisfactory for this inspection, but it is better than no data at all (note: assume IDC in these ranges is better than ITVC at 60”).
“Tasks: Move the sensor package into position. Allow boom motion to dampen out. Pointing can be confirmed by the IDC in “Scan Lo-Res”. If IDC view not used, from the LCC GUI, perform a Quickview scan to verify LCS pointing. Downlink the Desktop Downlink,” the overview notes.
“Stop IDC scan to allow LCS ops. Select the appropriate Detailed Area Scan name (as defined above), and press ‘Start Area Scan’. Restart IDC scan and select the proper scenario file. Activate ‘Acquire Set’ function. Data will finish collecting in approximately 30 seconds.
“Activate the IDC ‘Scan Lo-Res’ feature. Crew adjusts (moves/sizes) the exposure window if necessary. Check MCC. Activate “Scan Hi-Res” feature. Collect IDC data for 30 seconds. Leave the IDC on and collecting data as the boom is moved into the next view. After completion of data take, stop LDRI recorder and select ‘Power Off’ to power down the IDC to safe it from accidental exposure to sunlight.”
The Focused Inspection, which began after some troubleshooting with an associated monitor on the middeck, was completed after 55 minutes.
A similar overview was also provided for the damage on the Inboard Elevon – ahead of DAT engineers clearing it, as expected, for entry.
In fact, with the Reinforced Carbon Carbon (RCC) and all other areas of the orbiter cleared, the final clearance of the Focused Inspection area will result in Endeavour being fully cleared for Entry, pending Docked Late Inspection (DLI) results.
“Focused inspection CHIT (Documentation) developed to assess damage site: D-134-RPM-600_2-001. IDC and LCS sensors will be utilized. IDC will provide details of the tile cavities. No color,” noted a DAT presentation to the MMT (L2).
“LCS will provide point cloud data of the tile cavities and surrounding TPS. Surrounding TPS topography req’d for overlay repair option for 600_2-001. Elevon damage site removed from request based on 3D thermal model and command TPS Stress model utilized on assessment. TPS and Stress tile margins remain positive.”
The additional data will also provide managers – via computational models – with extra confidence the damaged area will still provide – as if fully expected – the protection for the underlying structure, with DAT showing numerous images of the inside of the orbiter in the damage location.
“Structure in damage region is aluminum skin with mechanically attached aluminum stringers and structural fittings. Skin panel thickness is 0.146” constant under damage with minimum thickness 0.114” within 6” inches of damage location,” the always-impressive DAT presentation added.
“Mechanically fastened stringers and fittings provide additional 0.08” to 0.23” structure thickness in portions of the damaged region. Yo105 MID Fuselage Longeron and Xo 1249 Wing Spar provide additional structure mass.”
Although no sub-system components are located on the lower skin in the wing region between Xo1191 and Xo1307 inboard of Yw167, DAT’s recommendation for a Focused Inspection is outlined in their findings.
“Initial analysis indicate that if Filler Bar is exposed, Structure temperatures will exceed 350 degrees F. Structural exceedances of 350 degrees F require detailed assessment. Detailed Stress assessment will not be available prior to Focused Inspection.
“Mitigations to overcome modeling issues for exposed Filler Bar are continuing in preparation for Focused Inspection. Damage Assessment Team split over value of determining crack tile in damage site. Portion of team recommending Focused Inspection regardless of thermal results. DAT recommends execution of Focused Inspection.”
With the FI is complete, engineers on the ground got to work on the data within hours, with Mission Management Team (MMT) chair expecting a 24 hour process to clear the area for Entry. No preparations were carried out for any further action, such as an EVA repair.
UPDATE: However, given the clear margins of safety based on the results of the point cloud data from the FI, the DAT gave a recommendation to clear the area of damage – and as a result the entire vehicle – for entry, with the MMT agreeing with no dissenting opions.
Later in the Flight Day, his Holiness the Pope addressed the astronauts aboard the International Space Station. ESA astronauts Roberto Vittori and Paolo Nespoli and their colleagues talked for 20 minutes with His Holiness Benedict XVI, who was in the Foconi Room of the Vatican Library.
During the call, the Pope asked several questions, and blessed the crew.
STS-134 Specific Articles: http://www.nasaspaceflight.com/tag/sts-134/
The crew then completed their proceedure reviews and tool checkouts for the second of four EVAs scheduled for STS-134, which will be the focus of Flight Day 7.
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