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EVA-37 spacewalkers to retract radiator, install external equipment

EVA File

For EVA-37, two astronauts will retract a thermal radiator on the P6 Truss. Photo Credit: NASA

Two weeks after installing International Docking Adapter 2 (IDA-2) on the front of the International Space Station (ISS), Expedition 48 astronauts Jeff Williams and Kate Rubins are gearing up to take another step outside the outpost. The two will retract and cover a thermal radiator as well as install a replacement lightbulb and a new high-definition camera on the station’s structure.

Extravehicular Activity 37 (EVA-37) is slated to begin at 8:05 a.m. EDT (12:05 GMT) Sept. 1. NASA TV coverage will begin about an hour-and-a-half before that. This will be Williams’ fifth spacewalk and Rubins’ second.

Williams will be designated EV-1 and wear the suit with red stripes. Rubins will be EV-2 and bear white stripes.

Heading from the Quest airlock to the work area first will be Williams. Rubins will follow shortly after. The prime objective for the EVA will be to retract Trailing Thermal Control Radiator (TTCR), pronounced “ticker”. The ticker, located on the P6 Truss, was deployed years earlier to compensate for an ammonia leak.

The P6 Truss

P6 parts EVA-37

P6 was launched in 2000 as part of the early station configuration’s power and cooling system. It included three radiators. Once P6 was moved in 2007 to its final location, only one of its three radiators were needed. Photo Credit: NASA

The P6 truss was originally launched in December 2000. It was temporarily placed on top of the Z1 truss segment just above the Unity module.

P6 is unique because it actually has three radiators on it, whereas its later launched sibling, the S6 truss – located on the starboard side of the Integrated Truss Assembly – only has one. This was because P6 was intended as a temporary all-in-one power and cooling system for ISS in its early stages of construction.

In 2007, the truss segment was relocated to the port side of the P5 truss segment. Two of the radiators, including the ticker, were stowed, as they were no longer needed.

In 2006, a slow leak in the P6 truss cooling system was noticed. Then in June 2012, flight controllers noticed a sharp increase in the leak rate. Although it was relatively small, the leak was still large enough that the ammonia channel 2B cooling loop would have hit its minimum quantity limit within six months. This prompted engineers to believe that this leak might actually be a second leak, possibly the result of a debris strike.

Contingency spacewalk

In November 2012, an emergency spacewalk, EVA-20, was conducted to isolate the leak. The ticker was deployed, isolating the primary radiator, called the Photovoltaic Radiator (PVR). However, this did not stop the leak and in May 2013, a large increase in the leak rate from channel 2B occurred prompting yet another EVA to replaced the channel 2B Pump Flow Control Subassembly.

This fixed the problem, but the ticker continued to provide the primary cooling for the P6 truss. For NASA engineers, this was not desirable as this leaves both the PVR and the ticker, which serves as a backup, exposed and at risk for debris strikes.

During EVA-33 in November of 2015, astronauts rerouted cooling back to the PVR and attempted to retract the TTCR. However, due to time constraints, the crew was not able to fully retract the radiator. As such, they had to redeploy it, putting it into a stable configuration for another set of spacewalkers to complete the job.


TTCR Location EVA-37

The TTCR, green, will be retracted. Photo Credit: NASA TV

After a quick inspection of the work area, Williams will be stationed at the ticker. He will utilize a Pistol Grip Tool to turn a bolt to retract the radiator. Rubins will position herself to view the radiator, ensuring the retraction is conducted smoothly.

After retraction, the duo will work to install four cinches, similar to lug nuts on a car tire, to ensure the radiator is fully compressed into place. They will place a thermal cover of the ticker once it is secure.

Once the ticker is retracted and covered, the prime task of EVA-37 will be complete. The spacewalkers will then move on to their secondary tasks: installing lights and new cameras.

Secondary tasks

Rubins will return to Quest to pick up a lightbulb and HD camera, while Williams will get into position at the P1 Truss for installation. He will place a foot restraint on the robotic Canadarm2 and then secure himself to it.

When Rubins returns to the area, she will pass the equipment to Williams. Then, Japanese astronaut Takuya Onishi, located inside the station, will command the arm to move Williams into a better location for installation.

While Canadarm2 with Williams is being put into the proper position, Rubins will inspect the nearby Solar Alpha Rotary Joint (SARJ) and tightens some bolts in the area.

Once Williams arrives into position at the nadir side of P1, he will replace a bulb. Once finished, he will attach an HD camera next to a standard definition camera. He will then clean up the work area and Onishi will move the arm away and return him to the station truss structure.

One final task that Rubins will do will be to translate out to the P6 Truss to uncover a few failed orbital replacement units. This will allow for the Dextre robotic manipulator to grab onto them. A future SpaceX Dragon spacecraft will bring up replacement boxes to be swapped out.

The two will then reverse their path taken at the beginning of the spacewalk. EVA-37 will conclude when they return to the airlock. Once back inside, Williams will begin preparation for return back to Earth just a few day later on Sept. 6.

Video courtesy of NASA


Derek Richardson has a degree in mass media, with an emphasis in contemporary journalism, from Washburn University in Topeka, Kansas. While at Washburn, he was the managing editor of the student run newspaper, the Washburn Review. He also has a website about human spaceflight called Orbital Velocity. You can find him on twitter @TheSpaceWriter.

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