Neutral Buoyancy Laboratory Evaluations
During the Hubble Space Telescope Third Servicing Mission Neutral Buoyancy Laboratory (NBL) engineering development tests of NBL 98.2 (NBL 98.2-1 and NBL 98.2-2), we evaluated the extravehicular activity (EVA) three-dimensional (3-D) roller wrench.
The test setup, shown in Figure 1, consisted of a 24" wide by 36" high by 1/8" thick task board mounted to a test stand with foot restraints. The distance from the bottom of the test stand to the top of the task board was 84". The foot restraints were mounted parallel to the task board and pitched forward 15°. The task board, shown in Figure 2, consisted of four tasks which are described below. The work envelope containing the four tasks was centered on a line parallel to the floor that extended 55" from the centerline of the bolt pattern on the foot restraint. The board was placed 23" from a line perpendicular to the floor extending through the center of the same bolt pattern.
Figure 1 ¥ 3-D Roller Wrench Test Setup
Figure 2 ¥ 3-D Roller Wrench Task Board
For the NBL 98.2 wrench evaluations, the following tools were available (part numbers are in parentheses):
- 3/8" Drive International Space Station (ISS) Ratchet (SEG33106927-303)
- 3/8" Drive 3-D Roller Wrench (SSL-RW-17-0200-02)
- 3/8" Drive 3-D Roller Wrench (SSL-RW-17-0200-03)
- 7/16" x 3" GFE Socket (10159-10084-01)
- ISS Ratchet Cheater Bar (TBD)
- Tape Measure
Task 1. Confined work site range-of-motion
Task 2. Maximum EVA free-floating torque
Task 3. Ability of an EVA subject to manually control high-inertia, low-friction interfaces
Task 4. Aft Shroud Door Latch work site simulation
Torque Data Acquisition System
Torque was measured with a 3/8" square drive socket extension reaction torque sensor. The sensor consisted of a full, four-arm Wheatstone Bridge circuit, with an elastomer coating to protect against mechanical damage, attached to a standard 3/8" drive socket extension. The gages were attached to a 100 foot, four conductor, shielded water resistant cable designed for submersion in 50 feet of water. The sensor, also designed for submersion in 50 feet of water, was covered with a special water resistant coating. The cable was routed to the surface, along the deck away from the waterÕs edge, and up to the hallway outside the control room and under the control room door. The pigtail terminations were plugged into the back of a strain gage meter with built-in transducer excitation and an isolated RS-232 communications link. An RJ11 4-wire serial line ran from the strain gage meter to a DB25 serial connector which connected to a DB25 to DIN 8 cable. The cable was plugged into the serial port of a Macintosh laptop computer. Power for both the strain gage meter and Macintosh PowerBook was provided through an AC power cord which was plugged into a Ground Fault Circuit Interrupter. The data acquisition system used is shown in Figure 7.
Figure 7 ¥ Torque Sensor Data Acquisition System
Accuracy of the torque sensor is 0.18% of the 600 in-lbf full scale value or 1.1 in-lbf. The accuracy of the strain gage meter is 0.005% of the recorded value. Pre-test calibration plots for both sensors appear below.
A paper summarizing the test was written: