Franklin Chang-Diaz, a member of the space shuttle crew aboard the Columbia yesterday, dreamed of exploring space as a 7-year-old in Costa Rica, "when 'astronaut' wasn't even a word."

"I used to play this game with my friends where we'd get into cardboard boxes and count down to liftoff and then go off to explore new planets," the 35-year-old Chang-Diaz said recently.

Chang-Diaz, the first Hispanic American to go into space, grew up in Costa Rica as the grandson of a Chinese immigrant. When Chang-Diaz finished high school in San Jose, the Costa Rican capital, he left for the United States with a one-way plane ticket, $50 in his pocket and no knowledge of English.

He settled with relatives in Hartford, Conn., where he slept in a room with nine cousins. He held every odd job he could find, and never remembers eating more than two meals a day.

Chang-Diaz repeated his senior year in a Hartford high school to learn English, and learned so well that he won a scholarship to the University of Connecticut, where he majored in mechanical engineering. He worked in a cafeteria to eat for free and held a nonpaying job in the school's physics laboratory, where an electrical system he built to protect its instruments is still in use today.

"Things were not easy, especially at Christmas," Chang-Diaz said. "I often wondered why I wanted to be here instead of at home in Costa Rica."

He persevered and went on to graduate study at the Massachusetts Institute of Technology. In his spare time, he managed a community house working with chronic mental patients and counseled Hispanic drug addicts.

Chang-Diaz sent his astronaut application to Houston's Johnson Space Center in 1977 as soon as he was awarded his PhD in plasma physics from MIT. He was chosen in 1980.

He set a goal of getting into space by 1986, and would have made it last year if Columbia's flight had not been postponed seven times.

"To tell you the truth, until a couple of months ago, it still seemed far away," Chang-Diaz said before the flight. "When you go to the Cape Canaveral and you see your orbiter and it's all stacked and the solid rocket boosters are already vertically mounted and the external tank is mounted, all of a sudden it becomes very real . . . "

But his childhood wish to fly to the planets has not been abandoned.

"I did my doctorate thesis on a plasma rocket engine that might be used someday to propel a spacecraft all the way to Mars," Chang-Diaz said. "Who knows? I could get to fly to Mars in a spacecraft driven by my own rocket."