Shuttle's first `fun-and-games' flight. Friday's mission includes satellite launches and tests with simple toys

After several frustrating postponements, the shuttle Discovery is finally ready to take Mission 51-D into orbit. Sometimes called the fun-and-games flight because the astronauts will play with an assortment of toys, it also has less entertaining objectives: the launch of two communications satellites and research into the effects of spaceflight on the human body.

The principal subject for these physiological tests will be the first public official to go into orbit, Sen. Jake Garn (R) of Utah. Senator Garn is the chairman of a subcommittee that monitors NASA spending.

The five-day flight is scheduled to lift off from Kennedy Space Center during a 14-minute launch window that opens at 8:04 a.m. Eastern Standard Time tomorrow. Discovery would return to the center at 8:15 a.m. April 17.

The mission has suffered serious delays. These were due partly to late discovery of a malfunction in a Tracking and Data Relay Satellite after the satellite was in Discovery's payload bay. In addition, the payload bay doors were damaged when a 2,500 pound work platform fell from a crane. The National Aeronautics and Space Administration (NASA) has blamed sloppy management for these setbacks. Agency administrator James M. Beggs says he has put the managers responsible on notice that such sloppiness will not be tolerated.

Meanwhile, the seven-member crew, commanded by Karol J. Bobko, has kept its skills honed for the variety of tasks besides satellite launching which mission 51-D involves.

Even the games with toys such as a Slinky, a spring-powered mouse nicknamed the Rat Stuff, and a yo-yo have a serious purpose. They are designed to demonstrate elementary physics using familiar objects under weightless conditions. This is part of an education program led by Carolyn Sumners of the Houston Museum of Natural Science. Films and videotapes of the experiments will be available to schools throughout the United States.

One benefit of the mission's delay is the opportunity it offered to reschedule the commercial electrophoresis test -- a process for separating proteins from solution in zero-gravity.

A similar test last fall produced enough of the material -- a hormone -- to begin testing a potentially marketable drug on animals. But the tests were canceled when bacterial contamination was found in the sample.

Once again, Charles Walker of McDonnell Douglas -- the first industrial astronaut -- will tend the equipment. This time, extra precautions are being taken to ensure that McDonnell Douglas and its partner, Ortho Pharmaceuticals, will have samples pure enough for testing. Mr. Walker will also tend a NASA-sponsored experiment in growing protein crystals. These are expected to grow larger than is possible under Earth gravity.

Other experiments include effects of weightlessness on plants and on brain cell aging, plus physiological tests such as those involving Garn.

NASA needs a successful mission if it is to begin to meet the shuttle's biggest operational challenge, namely, fulfilling its launch commitments over the next year. That means flying once and occasionally twice a month. The European-built Spacelab, for example, is scheduled for launch on April 29 aboard Challenger, which is expected to be rolled onto the launch pad Monday.

The schedule is dominated by three major scientific missions in 1986, each with critical launch dates.

An Astro multiple telescope mission to observe Halley's Comet must be launched next March within a one-week period. Then, the International Solar Polar Mission is due for launch May 15. It is to use Jupiter's gravity to flip it into an orbit passing over the sun's north and south poles. The Galileo Jupiter mission is to follow May 21. Because the latter two flights depend on Jupiter's position, they must launch within a two-week window or face more than a year's delay.