The Centrifuge Rotor (CR) system, presented at the last ICES (Ohtomi et al., 1999) and scheduled to be launched in 2004, provides an artificial gravitational environment for biological specimens housed in habitats on the International Space Station (ISS).
This paper presents the concept and investigation for realizing the micro-gravity (micro-g) performance, that is, the vibration suppression performance of the CR system which is the artificial gravity generator.
The CR is a significant new development that will provide artificial gravity for gravitational experiments involving relatively large biological specimens such as small animals and plants. The CR rotates habitats located radially around the axis and generates centrifugal force, imposing artificial gravity of arbitrary magnitude up to 22.0 m/s2 (about 2.2 g) on the specimens housed in the habitats.
The CR should be maintained at the selected acceleration (gravity) within a tolerance of 0.01m/s2 or 1 percent of the selected value, whichever is larger. The selected acceleration (gravity) is 0.0 to 22.0 m/s2 (2.2 g) in increments of 0.1 m/s2. The vibration of the CR habitat interface and the CR/ISS interface should be less than the micro-g level. However, in practice, it is difficult to realize a CR design that satisfies these requirements, because there is no example to meet the micro-g requirement in such a big rotating machine as the CR. The CR is unique in the world as the actively vibration controlled rotating machine.
We developed a passive Vibration Isolation Mechanism (VIM) and an Active auto-Balancing System (ABS) for the CR so as to near the above-mentioned requirements. The VIM and ABS suppress outbound disturbances to the ISS and inbound disturbances from the ISS. These devices were installed in the Engineering Model (EM) test apparatus and their performance was confirmed.
The EM test has been performed to clarify the micro-gravity performance of the CR system by using test equipment, which has the same structural configuration as the Flight Model (FM) with additional ground support equipment to counter the 1-g effects.
The EM test results show that the CR can be maintained at the selected gravity within a tolerance and the CR system has sufficient vibration suppression performance. However, the vibration level of the current EM test does not meet the micro-g requirement. The development of the ABS control algorithm and the optimization of the vibration suppression system are indispensable to realize the micro-g performance of the CR system.