EVA 4 required – despite heroic shakes

by Chris Bergin

EVA 3’s primary requirement – to complete the second part of the re-wiring of the ISS – was carried out successfully on Saturday, but the fascinating highlight of the spacewalk proved to be in the last few hours.

Spacewalkers Robert ‘Beamer’ Curbeam and Sunita Williams attempted to free the troublesome P6 arrays by literally shaking the giant solar panels, with some level of success. However, a fourth EVA will now take place Monday.

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After a hugely complex, yet successful completion of tasks on EVA 3’s re-wiring of the station, time was set aside to head up to the solar arrays that had unsuccessfully retracted earlier in the mission.

Upon arriving at the P6 blanket box, Mission Controllers on the ground in Houston requested a visual overview of the suspected guide wires and grommets, which were believed to be causing the bays on the array to bunch up during retraction.

The P6 truss array was left in a safe configuration after the previously aborted retraction – to about half length of 17.5 bays – which was enough to allow the SARJ rotation of the P4 arrays. However, the current configuration is potentially a problem for Soyuz dockings to the Nadir port on the ISS.

After the visual inspection initially found the wires and grommets in good shape, Beamer was instructed to push against the array to see how the bays, wires and grommets reacted to the movement.

Beamer observed that three of the grommets were a problem, noting that grommets 1 through 9 were allowing the guide wire to move freely, but 10 through 12 were out of placement and conflicting with the wires.

Beamer then carried out more pushes, between five and 10 pushes at a time, and observed that grommets 10 and 11 appeared to improve their positions and released some of the tension. Even grommet 12, which could potentially remain as a problem, appeared to be in a more acceptable position.

After a good half hour of sightseeing above the planet from their orbital vantage point, the two spacewalkers waited for the next daylight pass to observe a retraction attempt on the P6 arrays.

The troublesome left side of the array was the focus of attention, as the retraction effort withdrew the array by one bay. Beamer continued to aid the tension on the guide wires with further shakes, before another one bay retraction was attempted.

This process continued – and with a high level of success – until the right array, observed by Williams, started to show similar signs of the guide wire going slack, caused by the same issue with the grommets.

That implemented the “Suni Shake,” which unfortunately only had limited success. By the time the arrays were retracted to about 11 bays, it was obvious to the spacewalkers that they had come to the limits of their shaking, to the point that it wasn’t gaining beneficial results.

With time running out on their EVA time limits, Mission Controllers recalled the duo back into to Quest airlock, closing out what was easily one of the most fascinating spacewalks ever to have been carried out.

EVA 4 – which was confirmed during EVA 3 – will now attempt different techniques in finding a solution to the tension issues between the guide wires and the grommets on the array box, hopefully leading to the completion of the retraction process.

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