Constant microgravity conditions are essential for many ISS experiments. Very small changes in acceleration (e.g., normal crew activity) can cause subtle vibrations to echo through the ISS. ARIS can protect these delicate experiments by absorbing the shock of motion before it can affect an experiment. This capability enables accommodation of future research that is sensitive to vibration disturbances.Principal Investigator(s)
Boeing, Seattle, WA, United States
National Aeronautics and Space Administration (NASA)Sponsoring Organization
Human Exploration and Operations Mission Directorate (HEOMD)ISS Expedition Duration:
March 2001 - June 2002
2,3,4Previous ISS Missions
A precursor to ARIS-ICE was performed on STS-79 during NASA/Mir.
Constant microgravity conditions are essential for some ISS experiments. Sources of disturbance can include
minor changes in acceleration, the movement of hardware such as the space station remote manipulator system
(the robotic arm), or even normal crew activities, any of which can cause subtle vibrations to be transferred through
station. The active rack isolation system (ARIS) protects equipment by absorbing the shock of motion before it can
affect an experiment.
ARIS is installed in two EXPRESS racks on ISS (EXPRESS Rack 2 and EXPRESS Rack 3), where it reduces vibrations using a combination of sensors and actuators. When the sensors detect a disturbance, the actuators counter the effect by sending a reactive force between the EXPRESS rack and the laboratory module, much as a shock absorber on an automobile would—except this “smart” shock absorber is finely tuned to react to, and cancel out, very minute vibrations. Accelerometer assemblies measure the disturbances and send data to the ARIS electronic control unit. The electronic control unit signals pushrods to press against the framework of station, stabilizing the rack. A microgravity rack barrier prevents accidental disturbances to the active ARIS rack. ARIS is designed to isolate all frequencies greater than 0.01 Hz, and is most effective in the 0.05- to 300-Hz range.
The ARIS-ISS Characterization Experiment (ICE) was a payload activity to characterize the ARIS on-orbit performance by monitoring the ambient vibration environment and by generating disturbances. The shaker unit provided a precise, measurable disturbance that simulated possible station vibrations. The other major component of ICE is the payload on-orbit processor, which executed characterization tests and acquired, synchronized, and processed ICE and SAMS-II data for downlink.
Even though the International Space Station orbits the Earth in relative microgravity, it is subjected to various sources of disruptive movements that can compromise sensitive experiments. Simple daily activities, like crew exercise, can cause enough vibration to potentially interfere with a particular experiment's results. It becomes extremely beneficial to create a piece of hardware that will allow experiments to remain as undisturbed as possible. This is the function of ARIS. Using data collected from ARIS-ICE, engineers will be able to utilize full ARIS capability to allow for more successful science to be operated aboard the ISS.Earth Applications
Experiments ranging from protein crystallization (which can lead to vast advancements in medicine) to the way different fluids behave when mixed are conducted on the ISS. In order for these experiments to lead to improvements in our lives on Earth, they must be conducted as close to undisturbed as possible in space. The ARIS can lead to better science by protecting those experiments from sudden movements and disturbances that can occur aboard the ISS. ARIS-ICE will allow for the ARIS to better perform its function.
Control of ARIS has been transferred from the ARIS-ICE POP to the EXPRESS rack interface controller (RIC), its proper long-term configuration. When ARIS-ICE was characterizing Station vibrations, the Shaker Unit was mounted to the Z panel on the exterior of EXPRESS Rack 2 and the Shaker Electronics Enclosure (SEE) was mounted at a nearby rack location. The Shaker Unit received power from the adjacent EXPRESS Rack 1. When not in use, the Shaker components were stowed in EXPRESS Rack 2, locker 2.Operational Protocols
Now that ICE has been completed and control transferred from the ICE POP to the EXPRESS RIC, the Payload Rack Officers at the Payload Operations Center at Marshall Space Flight Center will be part of the team responsible for proper ARIS operation.
Primary control of ARIS-ICE resided at the Payload Operations Center. During normal operations, ARIS-ICE operated passively and required minimal crew interaction. However, the crew conducted routine health and maintenance checks, manual tests, and more extensive maintenance, such as replacing damaged ARIS pushrods and upgrading the cables connecting the rack to the Z panel. The crew will continue these duties now that ICE is completed and ARIS is operational.
During ARIS-ICE operations, experiments were conducted regularly where scientists monitored on-orbit vibration reduction during a variety of Station activities, including crew sleep/wake periods, Space Station Remote Manipulator System (SSRMS) use, docking/undocking, and extravehicular activity (EVA). The crew also conducted additional tests by creating disturbances and monitoring the ARIS reaction, using one of two methods: tapping the Station structure adjacent to EXPRESS Rack 2 with a small hammer, provided as part of the ARIS-ICE package, or the crew executing commands on the Shaker Unit, to send vibrations to the rack.
ARIS can be controlled by the ground-based research team or by the on-orbit crew via a laptop computer. When microgravity conditions are not required, the crew can connect a laptop directly into EXPRESS Rack 2. When microgravity conditions are required, the crew must use a "remote" laptop (since a direct interface may cause unwanted vibrations), and the data is transmitted to ARIS via the Station's Ethernet. During the first year of ICE and ARIS operations as functional facility support hardware, control was based in Seattle and Houston. Remote operations were transferred to the Payload Operations Center in Huntsville, AL, in May 2002.
ARIS-ICE operations were performed for over a year during ISS Expeditions 2 - 4. During that period more than 1700 test runs were completed, ranging from short 1-second stability tests to 5-hour isolation characterization tests. Station vibrations were isolated to levels well below the science requirements of investigations in EXPRESS racks equipped with ARIS (Bushnell et al. 2002a). The ARIS-ICE command and data handling architecture helped to streamline the operational efficiency of the ARIS system. The level of testing needed was greatly reduced by this system (Bushnell et al. 2002b). Quick-control design cycles were able to facilitate on-orbit payload operations, allowing ease of performing ARIS-ICE (Fialho et al. 2003).
The investigators determined, through a series of acceleration characterization experiments conducted during ARIS ICE, that the ARIS facility provides the ability to predict and prevent the potentially damaging effect of station vibrations. It was also determined that sensitive experiments installed in ARIS would be isolated and protected from both vibrational and acceleration movements. These capabilities are critical to make ISS a unique, world-class research laboratory in microgravity. (Evans et al. 2009)
Bushnell GS, Fialho IJ, Allen JL, McDavid T, Quraishi N. Ground And On-Orbit Command and Data Handling Architectures For The Active Rack Isolation System Microgravity Flight Experiment. AIAA 53rd International Astronautical Congress, The World Space Congress; 2002; Houston, TX.
Fialho IJ, Bushnell GS, Allen JL, Quraishi N. Microgravity Flight Characterization of the International Space Station Active Rack Isolation System. AIAA Microgravity Measurements Group Meeting, The World Space Congress; 2002; Houston, TX.
Fialho IJ, Bushnell GS, Allen JL, Quraishi N. Taking H-infinity To The International Space Station: Design, Implementation and On-orbit Evaluation of Robust Controllers For Active Microgravity Isolation. AIAA Guidance, Navigation, & Control Conference; 2003; Austin, TX.
Bushnell GS, Becraft MD. Flight Test of an International Space Station Active Rack Isolation Prototype System. Smart Materials and Structures; 1999.