Weightless Environment Training Facility Inertial Training Spheres (WETFITSs) are proposed neutrally buoyant training tools that would be used in NASA's Weightless Environment Training Facility (WETF), where astronauts are trained underwater to manipulate objects in zero gravitation. Heretofore, the training in the WETF has provided astronauts accurate simulations of visual conditions but has not addressed the feel of manipulating objects. The WETFITSs are intended to address the issue of feel; more specifically, each WETFITS would be designed so that its inertial properties underwater would approximate those of a simulated object with a specified mass and six degrees of freedom in zero gravitation. A WETFITS (see figure) could be sized to simulate any large mass to be manipulated in zero gravitation, could be designed and manufactured cost-effectively, and would be reusable.

A Typical WETFITS would include a sphere sized to contain a mass of water nearly equal to that of a simulated weightless object. Internal baffles would help to approximate the rotational inertia of the object.

In WETF practice that continues to this day, the neutral buoyancy needed to simulate zero gravitation underwater is achieved by attaching polystyrene foam and lead weights to astronauts, equipment, and mock-ups of simulated objects. In so doing, no attempt is made to approximate the masses and other inertial properties of simulated weightless objects and, as a result, astronauts usually do not get an accurate feel for handling the objects in zero gravitation.

The WETFITS concept eliminates the need for lead weights and polystyrene foam. Instead, one would use a volume of water to approximate an object with a specified mass and make it close to neutrally buoyant. A sphere was chosen for the shape of the volume to minimize the drag force created by moving the object through the water in any direction. The sum of (a) the mass of the water in the sphere and (b) the extra apparent mass from boundary-layer generation would approximate the mass of the simulated object. A WETFITS would include internal baffles to enable some simulation of rotational inertia.

This work was done by Kathryn M. Miller, Michael J. Stagnaro, Christophis Lovchik, Dominic DelRosso, and Pierre Thuot of Johnson Space Center. No further documentation is available. MSC-22501

NASA Tech Briefs Magazine

This article first appeared in the January, 1998 issue of NASA Tech Briefs Magazine.

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