Astronauts Test Jet Pack in Untethered Spacewalks

Two jet-propelled astronauts unhooked their lifelines from the space shuttle Discovery on Friday and flew free 150 miles above Earth in the first untethered spacewalks in 10 years.

Mark Lee and Carl Meade had only one jet pack between them and took turns flying with the one-of-a-kind, $7-million unit. The jet pack is meant to be a life preserver for space station crews of the future.

“This thing works like a champ,” Lee said as he hovered over Discovery’s cargo bay, firing tiny jets to guide his way.

He was only the seventh person to fly free in space. Meade was No. 8.

The next step was even more dramatic: With a brilliant blue Earth as a backdrop, Lee and Meade stood at the end of Discovery’s 50-foot mechanical arm. Meade, his feet secured to the crane, shoved Lee into a head-over-heels tumble of the sort a spacewalker might experience in an emergency.

Meade apparently didn’t realize his own strength, and Lee somersaulted again and again. Lee asked him to be more gentle. Meade obliged, and this time Lee did a slow-motion pirouette.

When it became Lee’s turn, he joked: “There’s no baseball going on, Carl, so I guess I’ll have to catch you, huh?”

The trickiest exercise of the seven-hour spacewalk had each spacewalker propel himself along the length of the shuttle arm, which was bent at a sharp angle. They scooted from the shoulder to the elbow, around the bend, up to the end and then back down again--never using their hands.

Until Friday, only six astronauts had walked in space without a lifeline to the mother ship, all in 1984. The first was NASA’s Bruce McCandless.

Each of the first six human satellites used NASA’s massive manned maneuvering units, which were mothballed because of their size and expense.

The new jet pack, called SAFER--for Simplified Aid for Extravehicular Activity Rescue--weighs just 83 pounds on Earth but, like everything else, nothing in space. It is not nearly as thick or cumbersome as the old one. There are 24 tiny nitrogen gas jets, and the spacewalker guides himself with a joystick.

The rules for the spacewalk were simple: No flying more than 25 feet from Discovery and no speeding. And only one spacewalker untethered at a time.

The average speed of each jet-propelled spacewalker was just one-half foot per second, or a measly one-third m.p.h. The maximum speed of the jet pack is 7 m.p.h.