Michelle Issel was pulling Cs in her chemistry class at Mark T. Sheehan High School in Wallingford, Conn. A 17-year-old honors student and president of the school's Key Club at the time, Issel says she didn't like science and still doesn't. The only reason she took the course, she says, was to meet college requirements.

Hardly the prototype of a budding scientist, Issel nevertheless is the brains behind one of three student-originated scientific experiments astronauts are scheduled to perform aboard next month's flight of the space shuttle Columbia.

Issel was one of 1,500 students who submitted ideas for the experiments in a national contest two years ago sponsored by the National Aeronautics and Space Administration and the National Science Teachers Associations. Hers and nine others were selected for various shuttle flights.

"I wasn't getting particularly good grades," said Issel, now a freshman at American University. "I more or less entered to bring my grade up and get on the good side of my teacher."

Issel, who says she was "the least likely person to win a contest like this," proposed growing triglycine sulphate crystals in weightless space. The crystals, made from a liquid solution, are used to detect infrared rays emanating from the earth during satellite studies of the earth's surface.

Crystals grown on earth are flawed because gravity pulls heavier particles to the bottom of the solution, while lighter ones rise to the top. The shuttle experiment could show whether crystals with fewer imperfections can be grown in space.

Besides Issel's crystal experiment, the Nov. 11 flight is scheduled to carry another testing surface tension in liquids and a third examining how near-weightlessness affects the way sponges form.

"I don't think any of our students are going to end up winning Nobel prizes for their work," said NASA spokesman Alan Ladwig, who insists the experiments are not necessarily meant to be practical, or commercially valuable.

"We're trying to get the kids interested in science," he said. "It has meant a lot of hard work for them and a lot of pressure. You know, we don't just throw these things on board."

Issel started growing salt crystals in class at Sheehan High School and conducting research at the public library after school. Once her experiment was chosen, NASA, which holds the right to patent Issel's crystal growing procedure, assigned her to a corporate sponsor for the project, Hamilton Standard, a Connecticut-based firm that manufactures the space suits used aboard the shuttle.

The company paid for engineering and materials to turn Issel's concept into hardware for the space flight. Issel worked with Hamilton engineers to get the project ready.

"It's basically her baby and we're supporting her," said Hamilton engineer Vick Fetter. "She has to know what's going on. She probably knows more about crystals than I do."

Since her experiment was chosen, Hamilton Standard has flown Issel several times to NASA's space flight centers in Houston and Cape Kennedy to explain her experiment to reporters, and to brief the flight's four astronauts, whom she described as "real down-to-earth people."

She also plans to be on hand for the launch, and at the shuttle's landing at Edwards Air Force Base in California, where she will retrieve the 21-pound box containing the experiment, analyze the results and issue a final report to NASA.

Tom Cigas, Issel's high school chemistry teacher, concedes that Issel's work earned her "a little extra credit" in his class. He gave her a B.

At American University, she is enrolled in a course in earth sciences, but says the NASA experiment "hasn't helped at all. The professors seem intrigued, but they never fail to remind me that my job is to pass their course."

Nor, she says, has her success with crystals dissuaded her from a career in international relations.

"I don't have a head for math," she said. "I want to make money."