Second salvage try set for satellite.

Second salvage try set for satellite

The Leasat 3 communications satellite, deployed from the space shuttle on April 13, was left stranded when the rocket motor that was to have raised it to a higher orbit failed to fire. Four days later, an attempt during the same shuttle mission to snag what appeared to be an incompletely thrown switch on the satellite went just as planned, but still the rocket did not ignite (SN: 4/27/85, p. 261). Now NASA has announced plans to try a second salvage operation--the third attempt, in other words, to get Leasat 3 into position.

It is scheduled for shuttle mission 51-I, due to take off on Aug, 24 or later, a flight that will also deploy three other satellites including Leasat 3's successor, Leasat 4. Shuttle astronauts have already performed one piece of successful satellite surgery-- when they refurbished the Solar Maximum Mission satellite 14 months ago--but Solar Max carried no fully fueled rocket.

The problem with Leasat 3 was at first thought to be the failure of a timer, or "sequencer,' that was to have ignited the rocket 45 minutes after deployment. Now the thought is that the sequencer may have been somehow disconnected from the electrical system completely, but the first steps of the salvage mission will be to ensure that the rocket does not ignite on its own.

After the shuttlecraft has matched positions with the satellite, astronaut James van Hoften will ride out on a platform attached to the shuttle's remote maneuvering arm, attach a grab bar to the slowly spinning satellite and use his space-suited "bare hands' to bring the spin to a halt. Then he will reposition the satellite toward fellow astronaut William Fisher, in the open cargo bay, who will lock down the original activating switch, install some "shorting plugs' to make sure the sequencer stays out of action and, just to be on the triply-safe side, insert "safing pins' so that the rocket would not fire even if it got the signal.

With the satellite rendered as inert as it can be, the astronauts --still outside the shuttle--will set about readying it for its next launch attempt. Van Hoften will remove the handle he had previously installed, replacing it with a stronger one that will allow Leasat 3 to be held in position by the manipulator arm itself. Next, Fisher will connect wires from a "remote power unit' (being developed by Hughes Aircraft Co., the satellite's builder) whose signals will be used to reposition a number of switches so that commands can get to the satellite's decoder without going through the now-silenced sequencer.

The final step will be to install an additional unit so that Leasat 3 can receive its commands from the ground. And even then, safety reigns: Lest some mishap on the ground send the rocketfiring order too soon--such as while the shuttle is still in the vicinity--the new unit, says David S. Grissom of the NASA Johnson Space Center in Houston, will not accept its first command for eight hours.

At last, van Hoften will start the satellite spinning again-- again by hand--at about two revolutions per minute for stability; the arm will release its grip on the handle, and the crew will reenter the shuttle cabin, as much as six hours after they left.

Then it is back to the original question, already asked twice before: Will the rocket fire? In a dormant state since April, notes NASA, the satellite has been existing at temperatures "well below the design and test limits of the liquid and solid propellant systems, electronic units, batteries and all other components. This factor, when combined with the complexity of the modifications to be made . . . appreciably limits the chances of success.'

Grissom himself is more optimistic, noting that the details of the salvage operation are relatively straightforward and have been confirmed in repeated ground tests. Meanwhile, Hughes Communications, Inc., the corporate division that is leasing Leasat 3 and three others to the U.S. Navy, expects the operation to cost it about $10 million to $20 million. Leasat 3 is insured for about $80 million, but collecting on it could have significant effects on premiums for future satellites.