Fact sheet number: FS-2001-02-31-MSFC
Even in the quiescent, virtually gravity-free, environment of the International Space Station, tiny potential vibrations or disturbances -- such as those caused by crew exercise — can upset sensitive science experiments. The Active Rack Isolation System (ARIS) acts as a vibration absorber to help isolate them. By acting as a buffer between the experiment and these vibrations, ARIS will protect delicate experiments housed in EXPRESS Rack No. 2 from outside influences that could potentially affect research results. The EXPRESS Rack, which stands for EXpedite the PRocessing of Experiments to the Space Station, is a standardized payload rack system that transports, stores and supports experiments aboard the International Space Station.
A related experiment to the ARIS system -- the ARIS ISS Characterization Experiment (ARIS ICE) -- is a separate payload created to characterize ARIS' on-orbit performance. In addition to generating controlled disruptions on and off the rack, ARIS ICE will enable real-time monitoring of the on-orbit vibration isolation capabilities of various ARIS configurations. Since ARIS is one player in an integrated ISS vibration isolation strategy. It is critical that we understand its capabilities and limitations on orbit.
The ARIS system will be installed in EXPRESS Rack No. 2 — a standardized payload rack that transports and houses experiments aboard the International Space Station. ARIS attenuates — or reduces -- external vibration disturbances at selected payload locations.
ARIS achieves this disturbance reduction using a combination of sensors and actuators. When sensors detect disturbances from the Space Station, the actuators work to counter the effects of vibrations by delivering a reactive force between the payload rack and the laboratory module. In this way, it performs like a powered shock absorber, acting as buffer between the experiments and any outside disturbances.
Much more complex than traditional shock absorbers, ARIS is a finely tuned system with multiple components. Among these are accelerometer assemblies that measure vibration disturbances and send data to the ARIS electronic unit; pushrods that apply force against the framework of the Space Station; and a microgravity rack barrier that prevents accidental disturbance of the active ARIS rack.
The ARIS system will be installed in the International Space Station during the STS-100 Space Shuttle Mission, part of Expedition Two, ISS Mission 6A, in April 2001. This is the same mission that will carry the Express Rack No. 2, in which the ARIS unit will be installed.
ARIS will be primarily controlled from the ground by the Payload Rack Officer (PRO) on-duty at the Payload Operations Center, located at NASA's Marshall Space Flight Center in Huntsville, Ala. Seven days a week, 24 hours a day, a rack officer will be on-hand to operate ARIS as an EXPRESS Rack subsystem to support payloads in the rack.
Although it will be primarily controlled from the ground, the ARIS system requires some crew interaction to install it in EXPRESS Rack No. 2 and to complete its activation and initial checkout phases. After installation, the ARIS system at any time can be commanded to Active Isolation mode — the mode in which it actively reduces external disturbances -- with minimal crew time. Using laptop computer displays, the crew will be able to activate or deactivate ARIS hardware, perform pushrod alignment procedures or change ARIS states of operation.
States of ARIS operations include:
ARIS ICE: The ARIS ISS Characterization Experiment is a separate payload created to test ARIS performance. During ARIS-ICE operations, ARIS experiments will be conducted daily in 16- and 24-hour blocks for a 12-week period during Expedition Two and Three.
During these experiments, scientists will monitor the on-orbit vibration reduction capabilities of the ARIS system. To accomplish these objectives, ARIS will be operated during different Space Station activities, including those that cause vibration disturbances, such as crew exercise.
The ARIS-ICE ground team will control most experiments from the Payload Operations Center. One tool at their disposal is the ARIS ICE shaker unit. This component, located within the EXPRESS Rack No. 2 aboard the International Space Station, provides a precise measurable disturbance in order to simulate possible disturbances within the Space Station environment.
A prototype of the ARIS system was tested during the Space Shuttle STS-79 mission, a 1996 flight during which Space Shuttle Atlantis docked with the Russian space station Mir. To simulate the weight of future scientific payloads, five lockers within the ARIS rack on STS-79 were filled with 375 pounds of Russian food packages delivered to the Mir crew during the mission. After the ARIS system was activated, the astronauts conducted an extensive series of tests that indicate ARIS was successful in reducing the impact of off-board disturbances.
The NASA Microgravity Research Program strives to increase the understanding of the effects of gravity on biological, chemical and physical systems. The International Space Station will permit long-duration microgravity experiments in an environment otherwise more similar to Earth-based laboratories -- minus the gravity.
The ARIS system will enhance the ability of scientists to conduct these experiments. By countering vibrational disturbances that could potentially damage the research results of certain delicate experiments, ARIS will play a key role in the success of this permanent laboratory in space.
More information on the ARIS system and the International Space Station can be found at: