Hermann Oberth's tired eyes were glued to a huge TV screen at the Goddard Space Flight Center in Greenbelt yesterday as he sat watching the space shuttle Challenger land after a week orbiting the Earth.

Then, having seen the spaceship safely down, his lids drooped and the 91-year-old man fell asleep, content to know that the dream he had nurtured as a boy in pre-World War I Germany was still alive.

Oberth, a legend to the more historically minded enthusiasts of space travel, is the last scientist survivor of the era early in this century that transformed the literary fantasies of Jules Verne into the routines of modern space exploration.

Konstantin E. Tsiolkovsky, the Russian who worked out some of the early theory of rocket propulsion, died in 1935. Robert H. Goddard, the American who experimented with early rockets and for whom NASA's Greenbelt facility is named, died in 1945. But Oberth, who made the most complete analyses of the problems and prospects of human space travel, has lived to see it happen.

"Events," the Romania-born West German citizen said through a translator, "have proven me right. One has to be an optimist."

In 1923 Oberth wrote a book in which he not only showed mathematically that it was possible to escape Earth's gravity but anticipated a host of other aspects of spaceflight not seriously approached for another 30 years.

Oberth not only worked out the spaceship's propulsion system and architectural form -- even down to the rocket engine's nozzles -- he designed spacesuits and methods of eating in weightlessness, conceived of astronauts performing spacewalks, proposed space stations in Earth orbit as jumping-off points for interplanetary travel, considered the problems of weightlessness and motion sickness (a problem astronauts still face), proposed that the stations spin slowly to create an artificial gravity and suggested the use of flying shuttles that could take off like a rocket, visit the space station and land back on Earth like an airplane.

Oberth worked out the physics of joining two spacecraft in orbit, something NASA calls rendezvousing and docking. He anticipated that photographs of the Earth from space would be useful for studying the ground and forecasting weather. He foresaw that telescopes in Earth orbit could gather far better astronomical data than those that must peer from the ground through the atmosphere.

Oberth also said that astronauts traveling around the moon could learn about its far side, which is always turned away from Earth. He even claimed that practical uses for space travel would someday make it a profitable enterprise, something the shuttle is intended to achieve.

All of this Hermann Julius Oberth wrote as an amateur physicist and mathematician in the early 1920s, as a soldier in the Austro-Hungarian army in World War I, working entirely unaware of Tsiolkovsky or Goddard. Oberth's commanding officer was impressed enough to send the young man's paper to the War Ministry. The generals rejected it as obvious fantasy.

After the war Oberth entered the University of Heidelberg and submitted as his dissertation a longer version of the paper, complete with elaborate mathematical formulas proving the truth of his ideas. Again it was rejected.

Eventually Oberth paid to have the paper published on his own. "The Rocket Into Interplanetary Space" soon gained a wide and enthusiastic following. "The foregoing," Oberth concluded in the book, "demonstrates that it is possible, with present day science and technology, to construct vehicles which could attain cosmic speed and that it is probably possible for men to ride in these vehicles."

Oberth's unbounded optimism was, however, tempered. He said in the book that it could take more than a decade to realize his dreams.

"It has proven to be much more complicated than I thought," Oberth said yesterday.

As fame came to Oberth, so did a young rocketry enthusiast named Wernher von Braun. Von Braun, who would eventually lead the American effort to put a satellite into space, started as Oberth's assistant and then left to join the German government's military rocket research program at Peenemu nde. Von Braun rose quickly and brought his old mentor to Peenemu nde, where he worked on the V2 rocket, the first major weapon of war based on Oberth's ideas.

After World War II, von Braun and much of his staff were brought to the United States to develop the Redstone rocket and, eventually, the Saturn V that sent spaceships to the moon. In the 1950s Oberth joined von Braun for three years but then retired to West Germany in 1958.

Since then Oberth has lived quietly and in relative obscurity, forgotten by many newcomers to space exploration. Oberth visited Cape Canaveral, then known as Cape Kennedy, in 1969 for the launch of Apollo 11, which made the first lunar landing, and he returned a week ago to witness the liftoff of Challenger. Since the launch he has been touring NASA facilities, where his role in the history of space travel has required some explaining.

"You know," said Anna Roth-Oberth, a daughter who is accompanying him on this trip, "Professor Oberth is the father of spaceflight. Yet it was not until last year that he first could hold in his hands a piece of the moon. There were tears. He cried."