on-orbit. According to Nook, the manufacturer of the ball screw, the failure was a classical fatigue failure  of a ball screw and ball nut assembly.  Testing - Development  As has been discussed, ARED is well into the testing phase of the project. Below is a summary of  ARED’s testing program.  Preliminarv Life Cvcle Units  Two life cycle test rigs were built. Rig 1 was intended to exercise the cylinder/flywheel, the main arm, the  arm base, and the pivot arm. Rig 2 was intended to exercise the ball screw and the arm base slider  housing. Rig 1 was used to evaluate different design parameters, especially in the piston/cylinder  interface. At the end of development phase, rig 1 has accumulated 320,000 cycles. Rig 2, as mentioned  in the previous section, produced 1.3 M inches on travel on the ball screw. Both Rig 1 and Rig 2 will be  modified and upgraded to serve as the qualification lifecycle test beds.  Hi-Fidelitv Enuineerinu Unit  Lessons learned from testing on Rig 1 and Rig 2 were incorporated into the design. To further increase  confidence in the design, a Hi-Fidelity Engineering Unit was constructed, using near-flight-quality  drawings. This Hi-Fidelity Engineering Unit was used for Man-In-The-Loop testing, with the intent of  evaluating human-machine interface issues and ergonomic issues. Over a period of five months, forty-  three human subjects performed 700 workout sessions on this unit, accumulating over 150,000 cycles.  The unit was also used extensively by the team to evaluate various design modifications as well as to  develop operational and maintenance procedures. In addition, astronauts with long-duration spaceflight  experience on both Shuttle and ISS were invited to exercise on ARED to identify issues unique to zero-  gravity such as the location of handrails and foot restraints.  Certification of Flight and Qualification Units  Having established high confidence through development testing on Rig 1 and Rig 2 and the Hi-Fidelity  Engineering Unit, production of three flight-quality ARED units are underway and should be nearing  completion at the time of this symposium. One unit (Dash 301) will be designated for delivery to the  International Space Station, the second unit (Dash 302) will serve as the Lifecycle Qualification Unit, and  the last unit (Dash 303) will be the General Qualification Unit.  The ARED Qualification and Acceptance Test Plan stipulates that each of ARED’s components must be  subjected to an Acceptance Vibration Test (AVT). This test is intended to be a workmanship screen. The  Flight Unit, Dash 301 will then undergo a series of functional tests and packaged for launch. Dash 302,  after a series of functional tests, will be installed on Rig 1 and Rig 2 and undergo continuous lifecycle  testing. Current requirements state that ARED must successfully complete 1.5 M cycles on the ground in  order to qualify the Flight unit for one year of on-orbit usage (6 crew members, exercising 1.5 hours per  day, and 6 days per week). Results from lifecycle testing on Dash 302 will be used to determine  maintenance and re-supply plan for the on-orbit Flight Unit. Dash 303, will be subjected to a launch  vibration test (QVT) and an acoustic emission test. In between these tests, Dash 303 will undergo a  series of functional tests.  At the conclusion of the Qualification and Acceptance Test Program, Dash 303, along with the Hi-Fidelity  Engineering Unit, will become crew training units and/or research test beds for ground-based  physiological studies.  329