Thermal Tests

Manoeuvring the Shuttle into various attitudes to better understand its thermal characteristics before declaring it operational was a key objective of STS-4. ''We had been assigned to do a bunch of thermal tests,'' Mattingly said later, ''where you put the orbiter in an attitude and get one side hot, and then one side cold and then spin it around. They were collecting the data [because] after this flight we wouldn't have the instrumentation to do that. It was kinda something that had to be done, but was really not a glamorous kind of test that you can run.''

Rookie astronaut Mike Coats, who was sitting in Mission Control monitoring these tests, called the Shuttle's thermal behaviour ''the banana effect''; during orbital flight, the entire vehicle was bending like a banana, as its 'hot side' expanded and its 'cold side' contracted. During a practice opening and closure of the payload bay doors under extremely cold conditions, problems arose after one period in the belly-to-Sun attitude. A 'closed' indication on one of the doors was not achieved, prompting Coats to advise the astronauts to reverse their attitude and warm up Columbia's topside instead of her belly.

This procedure, as well as 10 hours of 'barbecue roll' and two hours in a tail-to-Sun attitude, rectified the problem and door opening and closure was demonstrated several times thereafter. A thorough understanding of factors affecting the satisfactory closure of the payload bay doors was essential before the Shuttle could be declared operational; if a crew was ever unable to close them properly, they could not return home. For the rest of her mission, Columbia spent 67 hours in a tail-to-Sun attitude and on 3 July undertook a 10-hour barbecue roll to thermally stabilise herself prior to re-entry.

In effect, the astronauts could place the Shuttle into the required attitude and leave her alone until it became necessary for another orientation change; in the meantime, they had a multitude of other tasks to accomplish. Chief among these were the final series of RMS tests and, to highlight the importance of the arm on this and future missions, a new console had been set up in Mission Control: that of the 'RMS, Mechanical Systems and Upper Stages Systems Officer', known by the callsign of 'RMU'.

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