UM graduate student's project goes aloft with Glenn Space socket wrench to
Frank D. Roylance
Published on Friday, October 30, 1998
A University of Maryland graduate student has put a wrench in the works of John Glenn's space ship.
It's a ratchetless space wrench, and the $4,000 prototype is scheduled for six days of automated tests in the shuttle Discovery's cargo bay.
The wrench mechanism was invented at the Goddard Space Flight Center in Greenbelt. But it was adapted for space by Brian Roberts, an aerospace engineering student at College Park.
"I'll be holding my breath and following it over the course of the mission, hoping it lands safely and we get our data back," said Roberts, 28. A masters candidate at UM's Space Systems Laboratory, he flew to Florida to see his wrench hurled into orbit.
Socket wrenches in most homeowners' toolboxes have toothed ratchets in their hubs. To apply pressure to a bolt, you have to back the handle up a few degrees until the next tooth clicks down and engages the socket.
That can be a problem in space. "If you don't have a lot of teeth [in your wrench], you have to move the handle back before you can tighten again," Roberts said.
Astronauts fixing a space telescope or building a space station in a bulky space suit may not have room to maneuver the wrench. Or, "the distance they have to move may be longer than the range of the suit," Roberts said.
The UM space wrench is a "3-D sprag" wrench. Its hub mechanism was designed by Goddard inventor John Vranish and was named one of the seven best electro-mechanical designs of 1997.
Instead of a ratchet, it uses four tiny metal "sprags." The vaguely rectangular bits of metal allow the wrench handle to turn in one direction but wedge themselves into grooves in the hub to prevent movement in the other direction.
Designed as brakes for the joints of robotic arms, sprags were adapted for socket wrenches by Goddard machinist Mike Wade.
"I thought they would be great to use in space," Roberts said.
Old-style sprag wrenches have jammed or had their lubricants evaporate in space and must be repaired on Earth. The stainless steel, titanium-coated 3-D sprag mechanisms don't need lubrication.
Roberts added space-proven aluminum handles to the new sprag mechanism.
Discovery astronauts will flip a switch and the wrench mechanism will be spun by a motor, then reversed and "locked" once every two hours. Its performance will be recorded by computer.
Pub Date: 10/30/98
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