Susan Okie, a former Washington Post reporter who is now a practicing physician, has been a friend of astronaut Sally Ride since they were teen-agers. She explains:

Several months before her scheduled lift-off, Sally Ride invited me, her best friend during high school, to write about her background and training. Although she placed no limitations on my journalistic freedom, I had reservations, knowing Sally's reticence and fearing conflict between the dual roles of reporter and friend.

I lacked the detachment of a stranger, but I was able to draw on 17 years of observations and memories. I chose to write these articles hoping to share not only a historic voyage, but my understanding of a remarkable woman.

Sally and I met when she entered my sophomore class at Westlake School, a girls' prep school in Beverly Hills known for its academic excellence, its Hollywood connections and its tennis team. Although the schedule of field trips included a visit to a department store to study china patterns, the school had sent its best students to Eastern colleges or to Stanford. But before Sally came along, its most famous alumnae were movie stars: Shirley Temple and Candice Bergen.

Sally was a fleet-footed 14-year-old with keen blue eyes, a self-confident grin, and long, straight hair that perpetually flopped forward over her face. I was six feet tall, stoop-shouldered and myopic, a success in the classroom but a disaster on the playing field.

We were academic rivals, both on scholarships, and carpooled together from a remote and unfashionable region of the San Fernando Valley. We felt out of place among the actors' daughters and Bel Air belles. Our friendship was instantaneous.

But even with close friends, Sally always seemed to enjoy being an enigma. Her favorite songs in high school were Simon and Garfunkel's ballads about personal isolation, and her favorite poem was "Richard Cory" by Edwin Arlington Robinson, the story of a rich young man who was the envy of everyone in town until he unexpectedly blew his brains out. The quotation she chose to head her senior writeup in the Westlake yearbook was, "I do not think, therefore I am a moustache," Jean-Paul Sartre's parody of Descartes' "I think, therefore I am."

In all the hours we spent on the telephone during high school, she never discussed boys or romance. Later, during college and graduate school, I had to interrogate her to find out what was happening in her personal life.

During a recent week in Houston to accompany her during training for next month's space shuttle flight, I found that, despite her eagerness to share her enthusiasm about it, she was as protective of her emotions as ever.

She said her reluctance to reflect too deeply on her motives for going into space was partly a deliberate decision to avoid distraction during her training. But it is also partly the characteristic psychic camouflage that has always made her an elusive character.

"'Closeness,' " said her sister, the Rev. Karen Scott, "is not a word that is often used to describe relationships in our family."

Sally discovered science in ninth grade. A teacher at her junior high school introduced her to some of the elements of physics and to the brain teasers in Scientific American. Scott recalls the arrival of that magazine in her sister's life as a major event.

Sally had endless patience for challenging math problems, scientific puzzles and the acrostics she found in the Saturday Review. She regarded science as mental gymnastics, sheer fun.

But in our junior year of high school, she met a teacher who believed it was also the unifying principle of life.

Dr. Elizabeth Mommaerts was a sprightly, middle-aged Hungarian woman with a doctorate in human physiology. A few years earlier, she left a research position at the University of California at Los Angeles, because of what she perceived as job discrimination, and became a teacher at Westlake, where her daughter was a student.

In her year-long course at Westlake on the workings of the body, Dr. Mommaerts radiated enthusiasm for the intellectual purity of research and offered a view of human nature that seemed to blend chemistry and poetry. When we reached the chapter on reproduction, she departed from the text and delivered a series of almost mystical lectures on love, marriage, work and emotional fulfillment.

For her favorite students, Dr. Mommaerts had dinner parties at her house, where she introduced us to French food and wine and told stories about her youth in Europe. Never hesitating to deliver verdicts on her students' potential, she marked Sally early for a research career.

Sally was captivated. Although she maintained her deliberately cultivated image as an underachiever, refusing to study for physiology tests except in the car on the way to school, she cared very much what Dr. Mommaerts thought of her.

On the day of the final examination in June, Sally and I presented Dr. Mommaerts with the most difficult brain teaser we could find--the 1960s equivalent of Rubik's Cube--to occupy her time while we took the test. She had solved it before we finished the first question.

Six years after we finished high school, Dr. Mommaerts committed suicide after a succession of personal crises in which she repudiated teaching, marriage and finally even science. Before her death, she worked for a time as a real estate agent.

Each renouncement was a new beginning for her, undertaken with all the enthusiasm she had bestowed on her physiology course, but each ended in disappointment. For Sally, then a graduate student in physics at Stanford, Dr. Mommaerts' denial of science was almost as grave a blow as her death. Neither of us found it easy to relinquish our cherished image of Dr. Mommaerts as a fulfilled woman, and to accept her reality as a struggling, human one. Our anger did little to ease the pain.

Sally still finds it difficult to talk about Elizabeth Mommaerts. But she sometimes tries, calling, late at night, when she comes across a book or letter that reminds her.

At times of triumph, she said, she forgets for a moment that Elizabeth is dead. It happened when she was chosen as an astronaut.

"She's the one person in the world I wanted most to call--even more than my parents," Sally told me. "And I can't."