Preparing for Launch and Beyond_ Testing Roman s Outer Barrel Assembly

The Outer Barrel Assembly, or OBA, is a key part of the Nancy Grace Roman Space Telescope. It is made of two main parts: the shell section, a baffled carbon-fiber tube that surrounds the telescope to keep the temperature stable and project it from stray light; and the support struts, which extend past the instruments to connect the shell section to the rear spacecraft bus where all the support systems are located. Although the OBA is one of the less complicated parts of the overall observatory, the testing process for it is anything but simple. This time-lapse covers one tiny part of the intricate dance that all of Roman’s systems have been working their way through on their path to joining together as the complete observatory.

Just one of the many tests the OBA undergoes is static load testing in NASA’s Goddard Space Flight Center’s 120-foot-diameter centrifuge. The two parts of the OBA are separated and tested individually, with aluminum weights called mass simulators, or mass sims for short, taking the place of other parts of the spacecraft and creating the correct center of gravity. Nearly 100 sensors are connected throughout the structure to carefully measure the strain on each part of it. The OBA is attached to a metal plate which can tip and rotate hydraulically to change the position of the test hardware. These changes in position ensure that every component of the hardware experiences the full launch load.

The struts are tested in six different orientations first. Tilting for the sixth, and final test, is where this time-lapse begins. After the final test, the multi-day process of removing the struts and replacing them with the shell section begins. All of the mass sims and sensors need to come off of the struts, while, at the same time, different mass sims are added to the shell section, which is in a separate clean room. The shell section is also wrapped in protective Kapton film to reduce contamination in the non-clean environment of the centrifuge.

The struts are topped with a metal interface ring that connects them and gives structural stability. This same ring is needed to connect the shell section to the adjustable test platform and so it must be transferred from the struts to the shell. The simplest way to do this is to connect the two pieces in, with the interface ring between them, in an adjoining “high-bay” with plenty of vertical room and floor space for the two pieces to sit side-by-side on dollies. The complete OBA is then hand-pushed into the centrifuge, to a different crane, and the shell section is lifted off with the interface ring now attached only to it. The struts are pushed out and taken to the next testing step.

The OBA is attached to the centrifuge test platform and has 96 sensors carefully connected at key locations. Like the struts, it will have six spins of different intensities and positions, culminating in a final spin at 18.4 rpm and 7.1 Gs. At that speed, the wind around the edges of the centrifuge