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 Soviet Design Appears In Debt to U.S. Shuttle

LEAD: American experts believe there are no fundamental differences in design, capability and function between the American space shuttle and the Soviet version that made its first test flight yesterday.

American experts believe there are no fundamental differences in design, capability and function between the American space shuttle and the Soviet version that made its first test flight yesterday.

Official photographs of the Soviet shuttle, first released in September, and drawings prepared earlier by United States intelligence analysts show a craft that is virtually identical in shape and size with the American re-usable orbiters. The similarities extend from the delta wings and vertical tail structures to cargo bays with roughly the same payload capacities. Even the paint job, white with black trim, is much the same.

The strong resemblance has raised questions about whether Soviet engineers came up with their design for a shuttle orbiter independently or copied American plans.

In a report last year on Soviet military power, the Defense Department said: "Soviet orbiter development has been heavily dependent on U.S. orbiter propulsion, computer, materials and airframe design technology. By using U.S. technology and designs, the Soviets were able to produce an orbiter years earlier, and at far less cost, than if they had depended on their own technology." Similar Functions Cited

Soviet space officials, acknowledging the similiarities, contend that they are inevitable because both shuttles were designed to serve much the same function, ferrying people and cargos into low earth orbit, then returning to a runway landing.

But American specialists in the Soviet space program question this explanation. They point out that American engineers considered several quite distinct designs, including those with marketly different wing and fuselage configurations, before settling on the one adopted in the early 1970's.

"The fact that the Soviets picked a design identical to ours can't be coincidental," said Nicholas L. Johnson, a specialist on Soviet space technology on the staff of Brown Teledyne Engineering Corporation in Colorado Springs, Colo. "There's no doubt they took advantage of a vast amount of engineering development that went into ours."

Mr. Johnson declined to comment on whether any stolen designs or equipment might have figured in the Soviet shuttle program.

"I don't think stealing was necessary," he said. "A lot of the information was unclassified and open, if you knew where to look." Differences in Boosters

One major difference between the American and Soviet shuttles lies in the booster rockets. The Soviet orbiter has no large rocket engines of its own but does have small maneuvering rockets that also help in reaching orbit. Almost all the propulsion is provided by the giant Energiya rocket, which can hoist at least 220,000 pounds into low earth orbit.

The American shuttle has three main permanent hydrogen-fueled engines. They provide the final thrust toward orbit, after two solid-fuel booster rockets are jettisoned.

The Energiya rocket, which was designed to launch both shuttles and unmanned cargo craft, has four main engines fueled by liquid hydrogen and oxygen and four strap-on rockets that burn kerosene and liquid oxygen. Only the strap-on rockets are re-usable.

"From a capability standpoint, this doesn't make any real difference," Mr. Johnson said. "The Soviets made the decision to throw the engines away. Still, having them on the Energiya rather than on the orbiter doesn't seem to give them any advantage in boost capability. They can put 100 metric tons in low earth orbit. Our shuttle can boost 100 to 110 metric tons." Problem in First Test

The launching of the Soviet shuttle, named Buran, Russian for snowstorm or blizzard, is the second test of an Energiya rocket. When the rocket was first tested, in May 1987, its dummy payload failed to reach its planned orbit. The trouble lay in the payload's propulsion, not in the Energiya.

Speculation about a possible Soviet shuttle began a decade ago. But not until last spring did Soviet officials acknowledge that such a craft would be tested "in the nearest future." It was once thought that the Russians were racing to launch theirs before the redesigned American shuttle returned to service. But the Discovery flew in late September in the first American shuttle mission since the Challenger explosion in January 1986, which killed seven astronauts.

Problems with the automated landing system may have been one reason the Soviet shuttle was not tested sooner, some American experts said. By last spring, Mr. Johnson said, the Russians had conducted at least 20 landing tests, and they "may not have been completely successful."

Engineers familiar with the American shuttle said that an automated landing is an extremely difficult technical problem. Although computers handle most of an American shuttle's operations, astronauts take control in the final approach to landing. Sign of Advanced Computers

"If the Russians pull off a successful automated landing, my hat's off to them," Bill McInnis, an engineer who formerly worked for the National Aeronautincs and Space Administration, said before yesterday's flight. "The first conclusion I would draw is that their technology is a lot more sophisticated than we have been led to believe. It means they have a much more extensive on-board computation capability than they've demonstrated in the past."

While the Buran was designed for fully automated flight, at least one Soviet astronaut, Igor Volk, is known to be preparing to fly the shuttle on future missions and has participated in some landing tests.

By contrast, the American shuttles carried crews from the start, partly to speed up testing of the much-delayed program. Flying without astronauts would have required extensive alterations in the computer software to respond to radio beacons along the route.

Some earlier descriptions of the Soviet shuttle, based on fragmentary reports, indicated that the vehicle had jet engines that allowed greater maneuverability on landing. Early designs of the American shuttle included such engines, but they were eliminated to save weight and reduce the cost. Engines Used for Tests

But like the United States' shuttle, American experts have concluded, the Soviet craft must glide back without power. If it ever completed its re-entry without enough energy to reach the runway or was swept off-course by crosswinds, it would have no engines to correct the course or to fly around and try again.

The reports about engines originated because the Soviets had to use engines to perform some tests. Mr. Johnson said the Soviet Union has no aircraft capable of carrying the shuttle to an altitude high enough for the tests, for which the United States used a 747 jumbo jet.

A Soviet shuttle that was seen in some pictures mounted to a Bison bomber was probably not a fully equipped vehicle.

Experts say they have seen photographic evidence of four Soviet shuttles. It is not clear how they will be used, though eventually they will probably haul people and cargo to an orbiting space station being planned for the 1990's, the Soviets have indicated. The current Mir station will probably continue to rely on the expendable Soyuz spacecraft for its ferry service.

Soviet newspapers report that each shuttle could carry 6 to 10 people. At 120 feet, the Soviet craft is three feet shorter than its American counterpart. Smaller Vehicle Developed

The Pentagon has said that the Russians are also developing a class of smaller, two-person re-usable space planes for swift access to orbit. At least five small models have been tested in orbit and the full craft is expected to make its first test flight in two or three years.

As designed now, American engineers said, the Buran does not have a docking module to link with a space station. But such a connecting unit could probably be installed in a cargo bay at the aft of the crew compartment. This is where future American shuttles will be modified for docking with a space station that is being planned for the mid-1990s.

In view of the generally conservative testing philosophy of the Soviet space program, the first manned flight of Buran may not come for at least a year, experts said. Another unmanned test might come first.

In a recent article in Aerospace America, a publication of the non-Government American Institute of Aeronautics and Astronautics, James E. Oberg, an authority on the Soviet space program at the Johnson Space Center in Houston, wrote that "the appearance of a few cosmonauts in orbit" aboard a shuttle "does not mean that such vehicles will quickly supplant the tried-and-true current stable of manned hardware."

By JOHN NOBLE WILFORD