Keeping a rocket motor cool

When Orbital ATK needed to test the Development Motor-2, or DM-2 (NASA's second, fully developed Ares five-segment solid rocket motor), they faced a problem.

A cold motor test was vital to prove the motor could perform at low temperatures, but this meant keeping both the motor and propellant at 40ºF (5ºC). With ambient temperatures at the Utah testing ground exceeding 100ºF (38ºC), maintaining this temperature would be tough. The team at Orbital ATK asked us to design a cooling system that would simulate near freezing conditions in the temporary test buildings housing the motor and propellant.

Sub-zero water in this type of system has a tendency to condensate and frost up the coils, so we needed electric defrosting built in. Another challenge was that the buildings were small, so our cooling equipment would have to sit outside.

Finally, the team on the ground would need to roll the buildings back and forth from the rocket, so our system would have to be flexible enough to keep the air at the right temperature in spite of these challenges.

We designed an air-cooling system, including chillers, with three stacks of two low-temperature air handlers that could also defrost. One of the pairs of air handlers drew air from inside the building, cooled it to 20ºF (-6.7ºC) and then sent it back in, while the other unit was on standby or in defrost mode. We then installed a seventh air handler to send in fresh air and raise the air pressure to keep warm, moist air out.

Just before the live test, we detached the equipment from the building and ran a custom air conditioning duct system to cool the DM-2 joints up until one minute before the rocket fired. 

The tests were carried out on schedule, a huge achievement for everyone involved. There's no doubt that our close cooperation with Orbital ATK, combined with our specialist approach, played a large part in the project's success – testing the largest and most powerful solid rocket motor designed for human flight.