Active Rack Isolation System (ARIS) ISS Characterization Experiment (ICE) Results

Results

The
ARIS system became "operational" in April 2002. This means that
the system, which consists of eight actuators and pushrods that dampen
vibration, now provides full-time support to sensitive experiments installed
in EXPRESS Rack 2. During the week of May 13,
operations were transferred from Seattle and Houston (where the developer
and program manager, respectively, are located) to the Payload Operations
Center at Marshall Space Flight Center (MSFC). The members of the ARIS-ICE
science team gathered at MSFC to help with the transfer.

The
science team and Expedition 4 crew conducted extensive tests throughout
March in preparation for ARIS’s operational debut. The crew replaced a
faulty actuator/pushrod earlier in the month. ARIS was designed to work
with as few as six, so normal function was not interrupted. Since then,
ARIS has successfully responded to hammer tests, where the crew taps on
the rack with a small mallet, and normal crew movements around the module.
"We have spent the past year running tests to learn whether we could
perform the level of isolation required," said Naveed Quraishi, project
manager. "We passed those tests and now we can begin in earnest contributing
to scientific research aboard the Space Station." ICE, which was
used to monitor and calibrate ARIS, will be returned to Earth on STS-111,
scheduled to fly in May.

ARIS
was set up during the week of May 25, 2001. ICE was activated on June
12, before ARIS was brought online. ICE successfully recorded both low-frequency
vibrations, created by crew exercise and Station reboost, and broad-frequency
vibrations, caused by hammer testing, dockings, and undockings. On September
4, the crew installed a shaker device on EXPRESS Rack 2. The device allows
ground control to deliberately send vibrations through the rack, allowing
ICE to measure ARIS’s ability the prevent the shaking motion.

Testing
conducted at the end of October focused on how cables that connect the
ARIS rack to the Station Z Panel, a power and utility interface panel,
affects ARIS’s vibration-dampening capabilities. Cables are capable of
transmitting vibrations. By altering cable material, thickness, stiffness,
and position, the amount of vibration transmitted can be increased or
reduced. The replacement "vibration-free" cables are 200 to
300 percent more flexible than those originally used. "The majority
of vibration to the rack comes from the Z Panel through the umbilicals
into the rack," explained Naveed Quraishi, ARIS-ICE project manager
at Johnson Space Center. "Now we are in a very aggressive testing
mode until the end of [Expedition 3]. The new cables have improved performance
quite a bit."

Applications

One
of the benefits of conducting scientific research in space is the quiescent
environment.  Fragile structures, such as protein crystals, which
may be damaged by their own weight and ambient vibrations on Earth, can
be grown to impressive size and quality in microgravity.  However,
even in space, these sensitive experiments can be affected by small disturbances
moving through the Station framework. ICE and other acceleration
characterization experiments will allow research teams to predict events
that would create vibrations, and ARIS provides the ability to prevent
the potentially damaging effects of these vibrations.

These two capabilities are critical to making the ISS a laboratory for
unique, world-class research.