STS-131: Discovery berths MPLM and completes DLI ahead of undocking

by Chris Bergin

Discovery’s crew have raced through their Flight Day 12 tasks, completing the berthing of MPLM Leonardo and the Docked Late Inspections (DLI) over three hours ahead of schedule. The crew are now into the final transfers between Station and Discovery’s middeck, ahead of undocking on Saturday morning.

STS-131 MER Status:

No new MER (Mission Evaluation Room) items or funnies (minor issues) have been added of late, as crewmembers overcame issues with the unberthing of the MPLM from its Common Berthing Mechanism (CBM) on Flight Day 11.

“The mission continues to progress satisfactorily. KSC Landing is currently scheduled for Monday, April 19th at 0853 EDT with a second attempt at 1028 EDT,” noted the NASA Test Director (NTD) status on Friday. “Flight Days 11 & 12 (4/15-4/16) Completed: MPLM egress. Post EVA EMU reconfiguration. MPLM uninstall from ISS and installed in the Orbiter payload bay.”

The problem with unberthing related to the Control Panel Assembly (CPA) on the CBM, with one of the 36 connectors suffering from an electrical issue.

“While activating the CBM for MPLM uninstall, we experienced a communication error between the Int MDM and CPA 4. This was preceded by a Latch 2 failure annunciation,” noted Flight Director Bryan Lunney via a memo acquired by L2. “Attempted to reactivate on CPA 1, but was no joy.

“After (we) unpowered the system, the crew demated and remated all of the connectors. They noted that a set screw on the Port CPA connector had sheared off. They reported the wiring was intact, so they taped up that connection and reported it was not moving (ie. Good tape job).

“Reactivated the system on CPA 3 and is communicating with CPA 3. However there (was) some conflicting data, (worked) through malfunction procedures to resolve the unexpected indications.”

Eventually, engineers were confident the system was in a nominal condition to continue with the unberthing, which was completed late in the Flight Day. The CBM will continue to be checked out ahead of its next role, hosting a Japanese HTV cargo ship in 2011.

“The MPLM grapple and uninstall was successful. The MPLM has been maneuvered to the MPLM Low Hover position and will remain there during crew sleep,” noted GNC notes. “The SSRMS grappling of the MPLM was delayed approx. 6 hours due to ISS Common Birthing Mechanism (CBM) issues and troubleshooting.”

Meanwhile, mystery still surrounds the identity of the object seen departing from the aft of Discovery’s Payload Bay during EVA-3. Likely to be insulation from the returning Ammonia Tank Assembly (ATA), NASA advised the United States Strategic Command (USSTRATCOM) of the incident, in order to potentially track the object.

“At 103/09:35:58 GMT (07/23:14:33 MET), a bright object was observed on video departing from the aft Payload Bay (PLB). The object appeared to be moving quickly with a departure direction of radial up and out-of-plane with possibly a small posi-grade component,” noted the MER manager.

“Identification of the object was not possible. The crew has verified that all Extravehicular Activity (EVA) tools have been accounted for and the United States Strategic Command (USSTRATCOM) was notified in an attempt to track the object. Tracking may not be possible, but USSTRATCOM is expected to provide an answer within a couple days.”

Discovery herself continues to perform extremely well, with all major systems showing no sign of problems ahead of departure from the ISS on Saturday morning.

“All DPS (Data Processing System) systems performing nominally. All passive thermal control systems are currently maintaining temperatures within acceptable temperature limits,” added MER status to the Mission Management Team (MMT).

“All thermal systems are performing nominally and all temperatures are within acceptable limits. Cycling has been observed on the “A” system on the airlock structural zone 1 heater. The heater was enabled to “B” only as part of the checkout of this heater system.”

And despite the troublesome return of the MPLM, the extra docked day has allowed for the transfer tasks to continue on schedule, with just minor middeck returns from the ISS being worked by the crew, along with the return gift of water from the orbiter.

“The first Payload Water Reservoir (PWR) was filled at 104/10:01 GMT [08/23:39 Mission Elapsed Time (MET)] with 20.3 lbm of water. The sixth Contingency Water Container (CWC) was filled at 105/07:55 GMT (09/21:33 MET) with 96.0 lbm of water. A total of 889.5 lbm of water have been transferred to the International Space Station (ISS) in the five CWCs, eight CWC-Iodines (CWC-Is), and one PWR thus far in the mission.”

STS-131 Specific Articles:

DLI Complete:

Most impressive was the completion of Docked Late Inspections (DLI) three hours ahead of schedule, especially considering the very late finish to the previous Flight Day.

With procedures uploaded and discussed with the crew in a timely manner, surveys of the starboard and port wings – along with the nose cap – showed no signs of concern with the potential challenges of tight clearances between the booms and Station modules.

DLI was called for after the Ku downlink ability was lost on Discovery, requiring the use of the Station’s Ku assets for downloading the vast amount of imagery of the orbiter’s Thermal Control System (TPS).

“The main activity for FD12 will be the Docked Late Inspection (DLI) survey for the Reinforced Carbon-Carbon (RCC) Leading Edge Surfaces. This survey is normally conducted after undocking,” added the MER. “However, the failure of the Ku-Band antenna earlier in the mission precludes video downlink of survey imagery while undocked, and performing the survey while docked allows the video imagery to be downlinked using ISS assets.

Challenges were 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) – which required managers to work on procedures.

While a previous DLI had taken place with Endeavour on STS-123, the addition of the JPM to the Station complex required additional thought for the robotics teams on the ground.

Utilizing a plan that was set to debut on the final mission to the ISS – which will end with the OBSS being left on Station – a plan was soon created, and carried out to the letter early on FD12.

“On behalf of the ground control team, we really appreciate all the hard work. Outstanding job,” noted Mission Control in Houston at the conclusion of DLI, with STS-131 pilot Jim Dutton returning the thanks. “Thanks to the team for the early procedures and yesterday’s tag up.”

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