Propellant Leak Is Testing U.S.-Russian Cooperation Sides Negotiating How Close Discovery Should Get To Mir

Russian space officials Saturday balked at the idea of letting a leaky U.S. space shuttle get near their space station Mir, as flight planners in Kaliningrad and Houston experienced their first taste of joint decision-making in the fledgling partnership.

The shuttle Discovery is scheduled to close to within 38 feet of Mir Monday afternoon and then circle it, in preparation for later missions during which an American spaceplane will dock with it.

But the Russians Saturday expressed concern that propellant leaking from three of 44 maneuvering jets aboard the U.S. orbiter might contaminate delicate optical and other surfaces on Mir. They proposed that the approach be limited to no less than 1,000 feet if the leaks persist.

One of the two leaky thrusters is part of a set of three on the orbiter’s nose that, by previous agreement with the Russians, are required to be working during the close approach to Mir. That set is part of an indirect, less efficient method of braking in which the jets are fired slightly off to the side rather than in the direction of motion in order to protect Mir from the direct blast of a firing jet.

Having one of the three jets shut because of a leak would not prevent Discovery from navigating in close, but robs it of backup capability in case the other jets in the trio fail. This could force the shuttle to fire other jets directly at Mir.

Similarly, the second leaky jet, located on the orbiter’s tail, is on the same propellant line with other jets required for close operations. Shutting the line would further reduce backup capability.

NASA officials argued that the leaks do not yet constitute a serious problem and counseled patience. However, said NASA spokesman Steve Nesbitt, “The Russians are doing the same kind of analysis we would be doing if the roles were reversed.”

Leaks in the shuttle thrusters are fairly common occurrences during flights, Nesbitt noted. “That’s why we have so many.”

There are 38 primary thrusters (14 in the nose and 12 on the tail) and six so-called vernier thrusters (two in the nose and four aft). They use nitrogen tetroxide oxidizer and hydrazine fuel.

Two jets started leaking oxidizer soon after Discovery’s Friday morning liftoff and a third leak appeared late Saturday, officials said. Only two of the three could have any possible effect on close operations during the rendezvous.

Flight official Randy Stone said that in 50 percent of cases, the leaks fix themselves. In one of the leaks that developed early, he said, the leak rate has already cut itself from one pound an hour to half that. If the leaks do not abate, however, he mentioned the possibility of closing to a compromise distance of 400 feet from Mir.

The specifications for the rendezvous have been negotiated in detail by the two space agencies, with the Russians consistently expressing concern about minimizing damage that might be caused to Mir as the two spacecraft converge. Both are orbiting Earth at 17,500 mph.

The two sides agreed that the shuttle would not approach to less than 1,000 feet if it did not have backup jets to use in case the primary braking jets failed, Discovery commander James D. Wetherbee said in an earlier interview.

Meanwhile, Discovery continued to raise its orbit gradually to match that of Mir. By late Saturday, it was closing at a rate of 190 nautical miles in altitude with each revolution of Earth.

Before they went to sleep at midday, Discovery’s six crew members successfully completed scheduled activities, including a study of radiation from a phenomenon known as “shuttle glow,” and deployment of a series of small spheres and rods to aid ground trackers to study debris orbiting Earth.

Today’s schedule includes checking of the 43-pound robot Charlotte. Her job is to reduce the crew’s workload by tending experiments while they sleep.