The space shuttle Challenger dropped silently out of coal-black desert skies early this morning to land within 300 feet of its target, bringing to an almost perfect ending the most successful shuttle mission so far.

During a six-day flight that began with a spectacular night launching, the eighth shuttle mission launched a communications satellite for the government of India, linked up with the once errant Tracking and Data Relay Satellite communications satellite and exercised its robot arm with the heaviest payload so far.

"This was a fabulous mission, the cleanest mission we've had yet," said Air Force Lt. Gen. James A. Abrahamson, associate administrator of the National Aeronautics and Space Administration. "The crew looks good and the spacecraft looks its very best. We think it was a superb mission."

With no onboard lights or power to help them, astronauts Richard H. Truly, Daniel C. Brandenstein, Dale A. Gardner, Guion Stewart Bluford II and Dr. William E. Thornton swooped out of the darkness today onto a brilliantly lit concrete runway at 3:40.40 a.m. EDT.

"That was a very black sky we had out here tonight, no help from the moon at all," said Abrahamson. But the world's most powerful searchlights, putting out beams of 4.8 billion candlepower that could be seen almost 100 miles in every direction, provided the beacon that the astronauts needed as they glided their huge spacecraft to a perfect landing in the desert.

"Dick Truly commander of the flight touched down only 300 feet from his aiming point," Abrahamson said. "That's as good as we see in the daytime."

"Based on what we've seen here tonight, I think night landings will become routine," Truly said at a welcoming ceremony. "The people who developed this lighting system made it all possible."

The astronauts were welcomed back by the largest and most enthusiastic group of invited guests ever gathered here at the end of a shuttle flight. Because Bluford was the first black American astronaut to fly in space, NASA invited hundreds of officials of the NAACP and the Urban League, who turned out in the hundreds and rose in a standing ovation to welcome Bluford and his four crewmates back.

Almost embarrassed by it all, Bluford nevertheless seemed delighted by the reception. "I'm really humbled tonight to see so many people out here at 4 o'clock in the morning to welcome us back," Bluford said. "I feel very proud to be a member of this team, and I think we have a tremendous future with the space shuttle, I mean all of us."

The second standing ovation was for Thornton, 54, the astronaut affectionately known as "Dr. Bill" who became the oldest person to fly in space. Visibly moved by the welcome, Thornton looked out over the audience, paused, wiped his eye and said:

"Once in a while life treats us even better than we think we deserve. I know of no point in my life that will ever reach this, to come home to a welcome like this and to work in space with a crew like this."

Abrahamson said that there were only 18 "anomalies"--space parlance for the little things that go wrong during a space flight without slowing down or impairing the mission. That is the lowest number of "anomalies" any of the eight shuttle flights has experienced.

Even the six rats the crew took with them into orbit came back robust, healthy and feisty. The rats were carried into space to test something called the Animal Housing Module, which will be used on occasional future flights to carry laboratory animals into space for testing purposes.

So smoothly did the night landing go that Abrahamson already was looking ahead to the next flight, scheduled for Oct. 28. On that flight, the Challenger's sister shuttle Columbia will launch the $1 billion Spacelab built by the European Space Agency.

"We all feel pretty good about going into the ninth mission," Abrahamson said. "Our biggest unknowns were running our communications through the TDRS satellite and while there were some bugs in the early part of this flight, we came out of it pretty well."

Abrahamson said that the space agency's next milestone will be a landing at the Kennedy Space Center in Florida, where only liftoffs have taken place so far. Abrahamson said there is a strong possibility that the first landing at Kennedy will be made at the end of the 10th flight, planned for early next year.

It was a highly successful week for the space shuttle program. In welcoming back the five-man crew, NASA Administrator James M. Beggs had this to say: "It was an old Russian scientist who said the Earth is the cradle of mankind, but mankind can't stay in the cradle forever, and we've been proving that out here again and again and again."