Red Letter Day after smooth EVA 2

by Chris Bergin

The hugely complex re-wiring of the International Space Station took a major step forward today, following a successful EVA 2 on Flight Day Six of STS-116.

It was expected that the spacewalk would take six and a half hours, but was completed ahead of time, as Christer Fuglesang and Robert Curbeam successfully carried out all their on orbit tasks, ahead of EVA 3 – which will finalize the re-wiring process.

**Over 2100mb of STS-116 onwards related presentions and mission documentation available on L2 ** Daily MMT/MER STS-116 Presentations and same day ISS On Orbit Status reports on L2 helped collate this article.

**LIVE news updates on Discovery STS-116 – FOR EACH FLIGHT DAY**

Ground controllers thanked the crews of Discovery and the ISS for what they called a ‘red letter day for the ISS,’ following the smooth transitions through the tasks – both on the spacewalk and through the huge amount of commands that were sent to the ISS during the reconfiguration work.

The major objectives of the EVA included the reconfiguration of the ISS EPS (Electrical Power System) to the permanent architecture, drawing power from the P4 solar panels, beginning with the EPS’ Channel 2/3 side.

The relocation of two CETA (Crew and Equipment Translation Aid) carts from their current locations on the S1 truss to the S0 on top of the Lab to allow the MT (Mobile Transporter) to move to the S1 WS-2 (Worksite 2) for next year’s installation of the S3/S4 truss elements (13A/STS-117).

The installation of a thermal blanket on the SSRMS LEE (Space Station Remote Manipulator System/Latching End Effector) force moment sensors, and also to carry out the reconfiguration of power to the Z1 truss electrical patch panel 6.

EVA 2 also retrieved the starboard and port QD (quick disconnect) bags, filled with maintenance hardware and tools, from the A/L and relocate the bags on top of the A/L.

The purpose of the EVA is part of STS-116’s mission to all the station to draw power from the new solar arrays that were installed on the previous shuttle mission, STS-115.

The re-wiring allows the station to have multiple options on drawing power from the arrays in a different configuration, in the event of problems with one source of power, whilst increasing the total capacity in preparation for new modules that will arrive on future shuttle flights.

The EVA was preceded by a carefully choreographed program of power-down commanding by flight controllers,’ according to Thursday’s On Orbit Status Report.

‘Their purpose is to place all associated equipment in a safe condition before opening the DCSU RBIs (Direct Current Switching Unit/Remote Bus Isolators) and thereby powering down the MBSUs (Main Bus Switching Units) and DDCUs (DC-to-DC Converter Units).

‘Turning the MBSUs back on again afterwards is a prerequisite for powering the EATCS (External Active Thermal Control System) to cool the MBSUs in the first place before they overheat (it is estimated that they can run OK without cooling for an hour). Filling the EATCS Loop B with NH3 (ammonia) coolant, pressurized by N2 at 390 psi, has been successfully completed overnight.’

Today is also the second of two big cargo transfer days for the shuttle and ISS crew, with several hours scheduled again for Shuttle-to-ISS and ISS-to-Shuttle transfers.

‘As of this morning, 39 percent of transfers were completed, plus the transfer of two CWCs (Contingency Water Containers) from Shuttle to ISS. Return cargo is being configured in the Shuttle Middeck and in the Spacehab module.’

The success of today’s events comes after the difficulties of Flight Day 5, which saw the troublesome retraction of the P4 solar array, which could lead to a fourth EVA to aid the completion of the full retraction process.

‘Solar Array Wing 4B retraction last night stopped short when guide wires snagged on the grommets, and could not be completed,’ added the On Orbit report. ‘Retraction came to a halt at bay 17.5. This provides enough clearance to allow a nominal SARJ (Solar Alpha Rotary Joint) rotation (which successfully executed).

‘However, permissible loads on the partially retracted structure would be exceeded during the docking of Soyuz TMA-10/14S after its planned relocation to the FGB nadir port in April 2007.

‘Ground teams are currently assessing IVA (Intravehicular Activity) and EVA options, either a 12A.1 EVA-4 or a later Stage 12A.1 EVA (but prior to 14S relocation). For the first case, consideration is currently given to a back-to-back EVA after EVA-3, i.e., on next Sunday (17th December).’

Other notes of interest included the detection of solar flare activity from the Sun. Such events have potential constraints on spacewalkers and certain hardware in orbit.

‘On 12/12, a solar flare was detected after the EVA-1 crew’s nominal ingress into ISS. In order to avoid a possible overnight wake-up call to alert the crew, the ground provided them with a list of recommended locations in the ISS and the Orbiter before sleep time,’ continued the On Orbit report.

‘Subsequently, high energy particles have diminished from the previous flare event. If there were another significant solar event tonight, EVA get-ahead tasks would not be performed, an earlier ingress would be considered, and the use of the SSRMS (Space Station Remote Manipulator System) would be prohibited if its radiation limit is exceeded (there are no concerns with the Shuttle’s SRMS usage).’

At the start of Flight Day Six, NASA’s MMT (Management Mission Team) noted no extra issues are being worked on orbit with Discovery.

Bar a few minor communications issues, the only other recent addition of interest by the MMT has notes referring to a OBSS (Orbiter Boom Sensor System) thermal blanket seam causing minor interference with its shoulder joint, and a small amount of loose blanketing in the doom area near the SSMEs (Space Shuttle Main Engines).

‘An on-orbit photograph revealed an OBSS thermal blanket seam is touching the bottom of the Fwd Shoulder Bumper,’ noted an MMT presentation. ‘Blanket seam interference between the OBSS Shoulder Bumper and the OBSS X-Guide could result in asymmetric loading of the OBSS to Shoulder joint.

‘The 5/8 inch high blanket seam contacts the bottom of the bumper. Slight possibility exists that the seam could contact the bumper load bearing surface. The OBSS Shoulder Bumper is fully contacted (less shimmed clearance) by the time the X-Guide would contact the blanket seam. This would ‘wipe’ and/or push the blanket away from interfering with the mate.’

However, the seam proved to have no constraints during the berthing of the OBSS prior to docking, which occurred after the imagery was taken of the area in question. Added to flight experience with the same blanket, it is unlikely to prove to be an issue for the remainder of this flight.

‘No anomalies were noted during berthing of the OBSS after FD 2 inspections,’ added the presentation. ‘No berthing issues have occurred in flight or during ground processing. The blanket seam would be pushed/wiped away by the X-Guide Leg if it moved to the mating load bearing surface.’

However, once Discovery is back on the ground and undergoing processing in her OPF (Orbiter Processing Facility), modifications will take place.

‘The blanket will be modified for all future missions by removing the seam,’ ended the report.

In what is proving to be another clean flight for the Shuttle Program, Discovery’s TPS (Thermal Protection System) has been since cleared of a requirement for a Focused Inspection.

However, the amount of imagery and detailed analysis that is carried out to ensure an orbiter is indeed clear of damage is staggering.

This was proven by some of the resulting notes of interest in MMT presentations. An example of which included an image taken by the ISS crew when Discovery performed her RPM (Rbar Pitch Maneuver).

That image showed what was described as a ‘Dome heat shield blanket patch debonded.’ And whilst that holds no issues or concerns, the photographic detail of the area in question is stunning.

Located near the left hand SSME of Discovery, the tiny piece of blanket exemplifies the huge level of close detail imagery that is being achieved on these post Columbia flights.

While previous areas of interest with Discovery’s systems, such as the FES (Flash Evaporator System) remain, all issues remain stable and have no mission constraint.

Flight Day Seven will continue with the transfer of items between Discovery and the ISS, but will be largely a ‘day off’ for the crew, following a very busy week.

**LIVE news updates on Discovery STS-116 – FOR EACH FLIGHT DAY**

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