Two dozen chicken eggs and a bunch of baker's yeast are on the manifests of two shuttle flights scheduled for 1986, one sponsored by Kentucky Fried Chicken and the other by the Lawrence Berkeley Laboratory at the University of California (Berkeley).

The eggs will be flown into orbit to determine whether chicken embryos can survive the rigors of weightlessness, while the yeast will help measure the effects of weightlessness on cell division. Both experiments were planned by students, a sophomore at Purdue University and a senior at San Francisco's Lowell High School.

"I got the idea for flying baker's yeast from the first Spacelab mission where bread mold was grown in orbit," said Greg Delory, 16. "The mold was supposed to produce spores every 22 hours but in space it lost its circadian rhythm and produced spores all the time." Delory won a competition to design a shuttle experiment while attending the U.S. Space Camp in Huntsville, Ala., under the auspices of the Marshall Space Flight Center there.

John Vellinger, 20, who won a competition to design a NASA experiment, said, "We hope this will give us some data about the feasibility of raising chickens as a food source in space."

SALVAGE CREW . . . The crew of the space shuttle Discovery will try to revive a Navy communications satellite as part of its eight-day mission beginning Aug. 24.

The satellite, called Leasat, has orbited lifelessly for the past four months. But shuttle managers say the chances are only 50-50 that the crew will be able to repair it.

Before the rescue attempt, the crew will deploy communications satellites for the American Satellite Co. and the Australian government and another Navy satellite that is almost a duplicate of one the crew will try to rescue.

The salvage attempt will be made by astronauts William F. Fisher, 39, a physician whose nickname is "Fish," and James D.A. van Hoften, 41, whose nickname is "Ox." At 6 feet 4 and 210 pounds, van Hoften is the biggest of the 103-member astronaut corps; he also helped restore the "Solar Max" satellite to service last year.

The two astronauts face what most shuttle managers believe is the toughest task ever faced by a spacecraft crew. Not only is the drum-shaped satellite loaded with more than 10,000 pounds of flammable rocket fuel, but it has been in the cold, black seas of space for so long that some of its fuel lines may have frozen, swollen or even burst. The fuel in those lines is hydrazine, a fuel so toxic that it can eat through the spacesuits Fish and Ox will be wearing.

Even if the two astronauts succeed in "hot wiring" the satellite so that it can receive commands from the ground, they will have to wait to find out if they succeeded. Their last task is to put the nozzle of the satellite's Minuteman motor in a thermal cover that will trap solar heat to warm the motor before it is fired, a wait that will last anywhere from two weeks to two months.

THE OTHER COMET . . . Halley's comet is getting all the attention this year, but on Sept. 11, an obscure comet named Giacobini-Zinner will have the news to itself.

That's the day an equally obscure spacecraft called the International Cometary Explorer will fly through Giacobini-Zinner's 310,000-mile-long tail when the comet is 44 million miles from Earth. Even if the Explorer doesn't survive the trip, it will be the first spacecraft to intercept a comet.

The historic encounter will happen about 6,200 miles behind the comet's head, where the tail is split in two by what scientists call an "electric current sheet" that puts a different magnetic charge on each side of the tail. Because there are no cameras on this spacecraft, the only measurements its instruments will make are the kinds dear to the hearts of physicists exploring the "particles and fields" of outer space.