Micro-disturbance tests were carried out throughout the month of March in the Properties Test Room of the Spacecraft Integration and Test Building at the Tsukuba Space Center.
ASTRO-H will be equipped with certain devices which will be a source of mechanical vibrations, among which are elements of the refrigeration system and the gyros and reaction wheels of the attitude control system. Testing was done to measure how much of an impact on the satellite these small vibrations will cause. For example, these vibrations may cause a blurring of the X-ray image of an astronomical object under observation, or they may impact on the performance of the detectors on-board. During the tests carried out, real and mock-up versions of these devices that will act as sources of mechanical disturbance were operated, and the resulting levels of acceleration they caused were measured throughout the satellite. Accelerations were measured at 90 different locations located in and around the telescope and the observation sensors.
In order to accurately evaluate the effects of micro-disturbances, the device being tested must have the same mechanical characteristics as the actual device that will be on-board the satellite. Just as for the tests of the Thermal Test Model, a flight model, which is a full mock-up version of the sensors and other devices on-board the satellite, was constructed. All of the mechanical properties (including the mass and center of gravity) of the satellite and its instruments were included in this engineering model. Once everyone had worked to put together the full satellite model for testing, the alignments of all the instruments were measured. More than two months were required to build the proper configuration!
Because ASTRO-H has strict requirements for its pointing accuracy, measurements made of the gravitational acceleration were required to be accurate to within one part in one-thousand. As even the slightest external vibrations can have an effect on the measurements, a series of counter-measures were taken to avoid external sources of vibration as much as possible. Thus the satellite was suspended from the ceiling, the air-conditioning system was shut down, and only the smallest number of people required to carry out the experiment were allowed to participate. For measurements requiring the most precise level of accuracy, the measurements were made during the evening, and careful attention was paid to avoid the influence of experiments being carried out in the same building on other satellites. Only one month was available to carry out the tests. In addition, the use of both material and human resources was restricted. Therefore, discussions were held day and night to carefully select and plan individual experiments. In this way, both the quality and the quantity the data obtained were maximized. Beginning in April, a detailed analysis of these data was under way.