STS-131: NASA managers plan out extra docked day late inspections

by Chris Bergin

With an additional docked day – already allowed for in the mission timeline options – now approved by the Mission Management Team (MMT), efforts on designing a preliminary plan for a Docked Late Inspection (DLI) have resulted in a 5-6 hour survey procedure, which is challenged by clearances of just 19 inches in areas between the Starboard Wing survey, and the Japanese Pressurized Module (JPM).

STS-131 Status:

Discovery continues to perform extremely well whilst docked to the International Space Station (ISS), with the only additional items of interest relating to the Damage Assessment Team (DAT) findings with the orbiter’s Thermal Protection System (TPS).

“MER Items: MER-05: Rudder Speed Brake TPS liberation. MER-06: TPS anomalies. Funnies: No new,” listed the Mission Evaluation Room (MER) status (L2), which continues to list the Ku Band issue on Discovery as the only real hardware issue with the orbiter.

Both Solid Rocket Boosters (SRBs) are currently being evaluated at Port Canaveral, with no problems listed during their retrieval from the Atlantic. Current status notes that only three issues – known as “squawks” – were found during inspections, which is a very low number.

“SRB Retrieval Status: Open assessment is complete; three minor squawks,” added the NASA Test Director (NTD) status report (L2) on Friday.

Flight Day 6 is focusing on the transfers between Discovery, the recently installed MPLM (Multi-Purpose Logistics Module), and the ISS – with current status showing five percent of Leonardo’s cargo has been moved on to Station, while 90 percent of middeck transfers have been completed.

With no Focused Inspection (FI) required on Discovery, a large part of Flight Day 6 is being dedicated to transfer tasks, placing them in a good stance for the rest of the mission.

In clearing the orbiter from a FI, the DAT engineers cleared the missing tile from the Rudder Speed Brake (RSB) as no concern for entry, while also taking time to evaluate a protrusion noted on Discovery’s FRCS (Forward Reaction Control System).

“STS-131 – On-Orbit: The DAT has completed the assessment of the early mission imagery and has identified no Focused Inspection requirements,” added NTD status. “The FRCS protrusion assessment resulted in NO concern for critical damage if liberated during entry.”

Overall, the vehicle is very clean, thanks again in part to the performance of External Tank ET-135, which suffered from very few areas of liberation, and more importantly – from a mitigation success standpoint – no significant intertank losses, as seen on Hi Res ET photography. An article will be published on the tank’s performance, once official findings are produced.

STS-131 Specific Articles:

Docked Late Inspection (DLI) Plan:

The MMT made the decision on Friday to extend Discovery’s docked mission by one day, moving undocking to Flight Day 13. Such a decision was likely, following the failure of Discovery’s Ku-band, and relation to Late Inspections.

While inspections can be carried out without Ku – as was the case with Flight Day 2’s inspections – the vast amount of data requires the Ku’s high bandwidth levels to send the imagery to the ground for the DAT engineers to inspect.

FD2’s inspection data download was simply delayed by a day, prior to docking and the utilization of the Station’s Ku assets, which aren’t available once the orbiter undocks.

The plan now calls for the inspections to be changed to a DLI (Docked Late Inspection) scenario, inserted on Flight Day 11, so that the ISS Ku band assets can be used to downlink the imagery.

The MMT decision included such considerations as downlink rates of the imagery, time for ground assessment of the imagery, additional downlink requirements after a TPS repair (if required), clearances between robotic arms during the DLI, and Orbiter re-dock capability after separation from ISS.

With additional challenges noted for the positioning and translation of the Orbiter Boom Sensor System (OBSS) – relating to clearances between the boom’s movements and the Japanese Pressurized Module (JPM) – managers have been busy drawing up plans for the DLI’s procedures:

“Due to the Ku failure, we are looking into performing late inspection prior to undocking. 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).”

With changes to the inspection process, the DLI will take around one hour or so longer than standard Late Inspections – which are nominally carried out several hours after undocking.

“Timing: We estimate the surveys will take 5-6 hours to complete: STBD (Starboard): ~2.75 hrs. NOSE: ~1 hr. PORT: ~1.5 hr. If the attitude maneuvers are required (to and from +ZVV), each will require ~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 – the MPLM must be berthed in the PLB for this. 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 and SRMS-JPM. The minimum clearance expected between the SRMS and JPM is 19 inches with several points within 36 inches; SPDM camera two provides excellent views of this clearance.

“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 & PORT Surveys: Both the nose and port surveys have the SRMS under the JPM. 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 will include 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 LRDI shutdowns caused by the sun shining into the sensor.

“Open and Noteworthy Items: Lighting: Nominal surveys are done in an optimized attitude for lighting, but docked surveys are limited to the TEA (Torque Equilibrium Attitude) attitude,” added the presentation.

“In TEA attitude the sun may enter the LDRI FOV causing it to shut down (a self-protect feature). Any passes/points where this may occur will have to be performed during a night pass. A maneuver to orbiter +ZVV may reduce the number sun violations. This needs to be assessed.”

A DLI has taken place before, when Endeavour’s surveys were completed whilst docked to the ISS, due to clearance issues during the installation of the Japanese modules on Station. Following Endeavour’s DLI on STS-123, the OBSS was left on the S1 truss, prior to being picked up by Discovery on the following mission.

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