September 12, 1996
Johnson Space Center
Boeing Public Relations
When the Space Shuttle Atlantis blasts off on its fourth rendezvous and docking with the Russian Mir Space Station on the STS-79 mission, a prototype International Space Station rack will be on board designed to counter vibrational disturbances that could potentially damage the research results of certain delicate experiments planned on the permanent laboratory in space.
The Active Rack Isolation System, or ARIS, was designed and built by engineers from Boeing, the prime contractor for the International Space Station. The ARIS isolates the research payload through a sophisticated electronic sensing and control system as well as umbilical cables and actuators, allowing the rack to float within a half-inch clearance in all directions in the space station.
The ARIS rack flying on the STS-79 mission resides in the Spacehab module. On the second day of the mission, the ARIS will be activated and an extensive series of tests will be conducted before, during and after the Shuttle docks to the Russian Mir Space Station.
To simulate the weight of future scientific payloads, five lockers within the ARIS rack on STS-79 are filled with 375 pounds of Russian food packages that will be delivered to the Mir crew during the mission. After the astronauts set up the rack, testing will be conducted by Boeing engineers at the Spacehab payload control room at the Johnson Space Center, Houston, Texas. Once docking is complete, the food within the rack will be unloaded and the rack will be tested again. Test data will be stored on a payload computer. When unlocked for microgravity operation, the ARIS rack will float within a half-inch clearance, connected to the Space Station module by eight actuators and a set of utility umbilicals. The umbilicals provide power, data, fluids, gases and vacuum conditions for science payloads in the rack. The umbilicals also allow some of the module disturbances to enter the rack. The control system will use accelerometers to sense rack vibration and generate response signals to the rack actuators. Then the actuators in the ARIS rack will counter those vibrations by pushing between the rack and the space station module.
Boeing Defense & Space Group engineers began developing the ARIS rack in 1994. The ARIS flying on the STS-79 mission is a prototype system to prove its concept and design. Boeing is contracted to build nine more racks for the International Space Station, with an option for six additional racks. This special system is needed for the space station to support highly sensitive microgravity research at half its payload locations.
"There were two main challenges in developing the ARIS," said John Larson, Boeing ARIS team leader. "The first challenge was the control system itself, which must operate within tight tolerances. Another challenge was the umbilical connectors for the rack, which must be very flexible so that the control system has as little to counteract as possible."
Boeing engineers in Huntsville, Alabama, designed the umbilical connections and made mechanical modifications. The rack's graphite shell also was manufactured in Huntsville. Boeing engineers in Seattle designed and built the ARIS electronics and the control system, outfitted the system, conducted testing on the ARIS rack and shipped the system to the Kennedy Space Center, Florida, for launch on the STS-79 mission.
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