Major Overhaul – Replacing the Ammonia Pump Module on the ISS

August was a busy month for the crew of the International Space Station and the support teams on the ground.

On Saturday, 31 July 2010 the Loop A Ammonia Pump Module (pictured at right) on the External Thermal Control System (ETCS – pdf) on the S-1 truss on the Integrated Truss Structure (Starboard side – diagram below) failed, cutting the main cooling capacity of the United States portion of the International Space Station by 50%. The Russian modules have their own cooling system.

Station managers began shutting down a variety of systems and experiments on board the ISS in order to reduce the heat load to a level manageable by the Loop B ETCS on the P-1 truss (Port side).

Two EVAs were scheduled to remove and replace (R&R) the Pump Module. The first for Thursday 5 August and the second no earlier than two days later.

Ammonia Pump Module
Ammonia Pump Module
Flown on STS-129
Image Credit: NASA

structure
Image from the Interactive Guide to the Integrated Truss Structure
Image Credit: NASA

Planning for the first EVA eventually caused the spacewalk to slip to Saturday. The EVA tasks required working with numerous electrical cables and both internal and external cooling fluid lines prior to being able to remove the Ammonia Pump.

The first EVA was scheduled to disconnect cooling lines and remove the failed pump module from the S-1 truss. Problems were encountered with one of the quick disconnect units on an ammonia line, and removal of the pump module was postponed until the second EVA.

Doug Wheelock and Tracy Caldwell-Dyson began the second EVA at 7:27am Central time (9:27 EDT) on Wednesday 11 August. This time the quick disconnects for cooling and electrical connections went as planned. The two astronauts then successfully removed the failed pump module and stowed it.

Pump Diagram
Ammonia Pump Module Diagram
Image Credit: forum.nasaspaceflight.com

ETCS Truss Diagram
External Thermal Control System Truss Diagram
Image Credit: forum.nasaspaceflight.com

The third EVA began on Monday 16 August at 5:20am Central Time. Astronauts Doug Wheelock and Tracy Caldwell-Dyson then set out to unbolt the replacement Pump Module (PM) and place it in position on the S-1 Truss. Wheelock removed the bolts holding the new PM to ESP-2 (External Stowage Platform) and the Space Station Remote Manipulator System (SSRMS) then translated Wheelock and the 780 pound PM to the S-1 truss.

Wheelock bolted the PM into place and Caldwell-Dyson mated several electrical connections, “waking up” the PM. Initial electrical testing prove the new PM was ready to go. Various fluid lines were reconnected and ammonia was reintroduced into the system.

By Wednesday 18 August, the International Space Station was beginning to get back to normal. There were no yellow or red system lights on the status board.

On Wednesday and Thursday, the major effort involved bringing the Columbus science module and the Japanese Experiment Module (JEM – “Kibo”) back online.

The remainder of the month has involved bringing the various experiments back on line and testing the coolant systems in Loop A. Congratulations to the ISS team for successfully working the Pump Module failure. With three additional back up PMs on the Space Station, we can expect to see this scenario repeated. Lessons Learned will be carried forward by the ISS team. Current expectations are that the ISS will be in operation until 2020, and perhaps beyond that. There will be a lot more R&R of various systems as the years pass.

Let us know what you think. What do you want to know about? Post a comment.

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One thought on “Major Overhaul – Replacing the Ammonia Pump Module on the ISS

  1. Pingback: Atlantis – The Last Space Shuttle Flight « The National Space Society of Phoenix

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