Columbia's ultimate drama begins Tuesday morning 170 miles above the south Indian Ocean when the shuttle will fly backward for what the space people call the deorbit burn.

The astronauts John W. Young and Robert L. Crippen will race toward this bleak desert 100 miles northeast of Los Angeles.

They will cross the California coast at Monterey, traveling 4,000 miles an hour and heading toward long-lost places called Buzzard Rock, Coyote Gulch and the Dead Mountains.

"Well, we come across the coastline doing Mach 6 [six times the speed of sound] at about 120,000 feet," Young, the Columbia's commander, describes the return. "Yeah, the ground track is to come across the coastline north of Monterey Bay up there, and sort of heading south it passes Bakersfield, and, at Mach 4, you're abeam Lake Isabella."

Below them the panorama of the Big Sur will blur into the burned brown mountains of the Coast Range and then to the dazzling white sand of the Mojave Desert.

At one point they will pass over the headquarters of the Flat Earth Society which, since the embarrassment of the moon flights and all these orbits, has retreated to a small headquarters in the nearby desert town of Lancaster where the society's last holdouts now argue that the earth is a disk.

The Columbia will cruise over burned-out ghost towns named Crutts and Ragtown, over exhausted mines nammed Silver King and Waterloo, over the haunts of legendary desert denizens named Death Valley Scotty and Peg Leg Smith and zero in on a dry white lake named Rogers.

"At Mach 3 you're abeam of the runway of Mojave, really going downwind at a little better than 50,000 feet," Young continues.

At that point the Columbia is expected to make a long, banking left turn off toward Death Valley, off toward the old borax mines which did so much for the economy of both this desert and Ronald Reagan.

Ancient Egyptians used borax to mummify the dead. Americans didn't really get with it until the mines were discovered near Furnace Creek. The 20-mule teams hauled the stuff out of this forsaken land. And much later, Reagan used the mule teams and television's "Death Valley Days" to keep his career from mummifying during the transition from Hollywood to politics. The president will be watching television as the Columbia makes the big swing and, sinking like a rock now, heads for Rogers Dry Lake at the military haven of Edwards Air Force Base.

"You hit the heading alignment circle into runway 23 on the north lake bed at 32,000 feet," Young says.

The Columbia will be out of gas, a big, heavy glider now -- the Flying Brickyard, some space engineers call it -- and dropping three times as hard and fast as a commerical jet.

The mesquite and the cactus and the white dry lake will be leaping up at the astronauts as they make their final turn at 23,000 feet. For the first time in 2 1/2 days they will be in truly familiar territory. Young has flown a test shuttle, taken aloft by a 747, from the height over the desert.

"You're at final -- high final -- at 12,000 feet, doping about 275 knots in a 20 degree glide," Young goes on.

A convoy of 18 trucks will be waiting below, poised for the recovery mission; poised for trouble, too.

As many as 200,000 tourists, who have been warned by the National Aeronautics and Space Administration about the rattlesnakes and water shortages out here, will be gawking as the Columbia heads home, dropping faster than any flying machine they have ever seen.

The ship will pass over U.S. Highway 58 at 10,000 feet 76 seconds before touchdown.Up to this point the computers have been flying the craft but Young will take the stick for the landing.

The landing gear will come down 19 seconds before touchdown.

"You try to touch down at 185 knots," Young says, talking of a speed of more than 200 miles an hour.

"John does it soft every time," his copilot, Cippen, adds, with a test pilot's "right stuff" grin.