Discovery docks with ISS – has problems

by Chris Bergin

Shuttle Discovery has arrived at the International Space Station (ISS), following the visually stunning RPM (Rbar Pitch Maneuver) underneath the orbital outpost.

The orbiter is arriving with growing concerns over the Flash Evaporation System (FES) and Shuttle Remote Manipulator System (RMS) faults, both of which received an elevated problem status.

**Over 2100mb of STS-116 onwards related presentions and mission documentation available on L2 ** Around 15 documents and images helped collate this article – all downloadable on L2.

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The Primary B Controller on the FES Flash Evaporator System failed to come out of standby mode – but is operational on its Primary A Controller. The system is used to provide additional cooling to the orbiter radiators.

Initially, the fault was played down by Deputy Shuttle manager John Shannon at the end of Flight Day 2. However, this has now been elevated to the status of a MER (Mission Evaluation Room) problem.

‘Loss of FES Primary-B controller leaves one level of redundancy beyond Primary-A,’ noted a NASA memo acquired by this site. ‘If Primary-A fails and Primary-B can not be recovered, an MDF (Minimum Duration Mission) will be declared per Flight Rule.’

Current recommendations point to continued evaluations of the fault, and proceeding with the mission as normal.

‘The FES in Pri B Controller in topping mode failed to come out of stand-by during the crew sleep period,’ NASA information stated. ‘During topping mode, the FES supplements cooling primarily provided by the radiators. There were no immediate impacts to the crew or the mission. Prior to this event, the FES had been working with no anomalous signatures.

‘There are no immediate impacts to mission success or safety. The FES system can be operated in the using redundancy provided pri A controller and feedline A system if required. Presently the radiator cooling is sufficient to maintain the required heat load while the crew is sleeping. The FES controllers are 1R3.

‘There are no other anomalies that affect this problem.

‘On FD 02 MOD performed an on-orbit troubleshooting procedure towards the end of the supply water dump operating on FES Pri A. The attempt to continue the supply water dump using the FES Pri B failed.’

The other main issue noted, the loss of RMS End Effector Auto Release Capability, is also one failure away from requiring – in the worst case scenario – an EVA to ‘deal with certain contingency scenarios.’

The fault was spotted during SRMS checkout, when the end effector failed to extend the snare ring carriage (derigidization), indicating a potential problem with the RHC capture/release switch, 10V contact. Despite attempts by the crew of Discovery to repeat the command, the device failed to respond.

However, other steps performed manually by the crew confirmed the RHC’s capture/release switch is functioning properly.

‘Recommendation is to continue to use Manual Release, and Backup Release in the event of subsequent RHC capture/release switch failure,’ added memos.

‘There will be a nuisance Uncommanded Release annunciation when the crew ungrapples the OBSS during berthing as the MCIU will no longer receive the 10V release signal. MOD is putting together notes and work around info for the crew.

‘Further investigations will occur once the hardware is available after the mission.’

Redundancy again comes into play with this fault, but NASA has worked up a plan to consider a space walk, should the situation deteriorate.

‘The current risk and worst-case risk are that one of three levels of redundancy has been lost for End Effector Capture/Release due to the malfunction of the Capture Switch on the Rotational Hand Controller, or a circuitry problem,’ NASA memos state.

‘The next failure could lead to an EVA to deal with certain contingency scenarios outlined in the flight rules.’

Also observed on Flight Day 2 was a loose blanket on the RMS’ Wrist Pitch joint. Further images are being evaluated.

‘During RMS operations on FD2, it was noticed that the blanket around the Wrist Pitch (WP) joint was loose,’ NASA memos note. ‘The crew took pictures of the blanket.’

Not deemed a problem on orbit is a failure on the O2 Flowmeter, which failed on Fuel Cell 3, caused by a blown fuse. A post flight troubleshoot is being drawn up by NASA, but the fault is not classed as detrimental to the Fuel Cell’s operation on this mission.

‘FC 3 O2 Flowmeter went to an OSL reading. The OSL indication correlated to a 1.6 Amp increase, for a 2 second duration, on Mid Power Control Assembly #3(MPCA #3). FC 3 O2 Flowmeter circuit is protected by a 1 Amp. Based on the signatures and the specified fuse maximum blow current of a 1.5 Amp load, the fuse blew.

‘The increased O2 Flowmeter amperage load was most likely caused by overstressed EEE components located in the flowmeter circuitry. The O2 Flowmeter indication is crit 3/3. It is used primarily to indicate increased O2 flowrates during FC purges.

‘Other parameters can also aid in verifying purges such as the H2 flowmeter, Purge Line temperatures, cryo pressure decay and fuel cell performance. The loss of the FC 3 O2 Flowmeter is no impact to fuel cell 3 operation.’

On a lighter note, the imfamous ‘bird poop’ may be making a reappearance on this flight. Early images acquired from the OBSS (Orbiter Boom Sensor System) inspections on Flight Day 2 show what appears to be the remains of one of a Florida bird’s lunch.

The image came with an associated note from NASA managers, calling it ‘Suspected bird poop.’ This will burn off during re-entry.

For RPM and Docking, please refer to our live update pages.

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