The father of hard sci-fi remembered.

As he sat in a back room at 2002's PhilCon (Philadelphia's annual science-fiction convention), Hal Clement looked less like a superstar and more like somebody's confused grandfather. But neither the half-eaten jelly donut in his hand?constantly on the verge of divulging its strawberry-flavored guts everywhere?nor his forest-green blazer, khaki pants and robin's-egg-blue v-neck sweater ("doddering chic"?) could change the fact that, more than 60 years go, Clement revolutionized the field of science fiction, becoming in the process one of the genre's most important and beloved authors. Like the books they pen, you can't judge a writer by his cover.

Clement, who died in his sleep on October 29, 2003, at the age of 81, effectively created what is now known as "hard sf," a combination of accurate science and rousing, idea-based storytelling. From his first published short story, 1942's "Proof," to his final novel, 2003's Noise (Tor Books), Clement strove to balance the worlds of fact and fiction, fastidiously working out his tales from the ground up?designing whole planets and then populating them with strange creatures and intrepid Earth-born explorers.

"I got into writing in the first place because, by my middle teens, I was beginning to realize that there were serious flaws in many of the stories as far as scientific accuracy was concerned," Clement said that day at PhilCon. "And with the typical teenage arrogance, I was quite certain that I could write a story that didn't have such errors."

Noted science fiction historian and author James Gunn says that Clement "saw what the imagination could do if disciplined by scientific reality. After Hal showed what was possible, a new hard sf writer was likely to be called 'a new Hal Clement.'"

And there were many of them: John Taine, Gregory Benford, Larry Niven, Stephen Baxter?each adding another block to Clement's literary foundation. Clement's innovations helped the genre to gain acceptance by mainstream critics and readers. Suddenly science fiction presented bigger ideas than rampaging aliens and interstellar sex queens; gone was the schlock, the dubious technology, the questionable bending of nature's rules. In their place was honest exploration of modern notions as writers attempted to grapple with emerging theories and technological discoveries, at the same time pushing these notions to their very limits. Clement liked to say that every time he heard the words "of course," he tried to see what would happen if that "of course" was proven wrong.

Clement recognized that science fiction was the fiction of ideas. According to Philip Klass, who's been writing sf since the 1940s under the name William Tenn, Clement's ideas were often the main characters. But, says Klass, "Hal never forgot that the story was key. Without it, even the best ideas would become boring and fail to capture the reader's attention. Hal always wrote good stories."

And none were better than Mission of Gravity. First published as a four-part serial in Astounding Science Fiction's April through June 1953 issues (under the name "Heavy Planet"), the novel takes place on the planet Mesklin, where a day lasts 18 minutes and gravity transitions from three times our own at the poles to a whopping 700 times Earth-normal at the equator. It's here that visiting humans enlist Mesklin's inhabitants?intelligent centipede-like creatures with technology comparable to our own in the 15th century?to help them retrieve a downed spacecraft.

Clement took pains to work out as many details as possible for his story in order to satisfy even the most discerning reader. Only then would he decide on a plot. "I'd try to figure out the planet, figure out the creatures on it," he explained. "I'd work out the planet's temperature, atmosphere, rotation period and all the other things. Then I'd figure out what sort of trouble the natives or explorers or both were likely to run into."

Still, there were certain topics that just never came up during the course of the story. "I never did work out how they reproduced," Clement admitted. "During a lecture once, I told the crowd that there are many instances of Earth-born creatures with similar makeups that might provide some clues as to how the Mesklinites do it. For instance, there's an aquatic worm that crawls along the bottom of the ocean. When it encounters a solid structure, like a rock, it grasps it with its hind legs but keeps crawling with its front. Eventually, it rips itself in two! Now, apply that to the Mesklinites. And then ask yourself?what might they consider pornography?

"Later," he continued, "two girls came up to me and blurted out, 'Rubber bands!' I thought that was just great."

Hal Clement was the professional name of Harry Clement Stubbs. Born in Somerville, MA, on May 30, 1922, he grew up in Boston. His love of science fiction began at the age of seven when he saw a Buck Rogers comic strip. "In one of the panels, a character remarked that someone was heading for Mars, 47 million miles away, and it would take him about 20 days to get there, even at 100,000 miles an hour," recalled Clement. "I had never heard of Mars at the time, and the distances and speeds seemed rather startling to me as well. And not quite right."

His father, unable to provide sufficient answers to his son's queries, sent Clement to the library. He came back with "Jules Verne's Trip to the Moon under one arm, and an astronomy book under another," he remembered. "And that focused me on a pattern, near as I can make out."

Clement's interest in science never waned. He earned his B.S. in astronomy from Harvard in 1943, after which he entered the Army Air Corps Reserve. He flew 35 combat missions in WWII. After the war, he earned his M. Ed. from Boston University on the G.I. Bill. Returning to school in 1963, he got an M.S. in chemistry from Simmons College. Harry Clement Stubbs became Hal Clement when the author decided that his professors might not approve of his writing science fiction. It was only later that Clement discovered one of his professors was also writing for the field. But by then, the new moniker carried such notoriety that dropping it would be impossible.

Besides working as an author, Clement taught chemistry for 40 years, 38 of them at Milton Academy in Milton, MA, before retiring in 1987. It was this love of education that drove him to attend endless science fiction conventions, both as a panelist and guest, says Anthony Lewis, coordinator of the New England Science Fiction Association's NESFA Press, which published a three-volume career retrospective of Clement in 2000. "He loved to talk to people, and on any range of subjects. That was just the kind of person Hal was?friendly to everyone, and always looking to exchange ideas."

Clement published dozens of stories and 15 novels over the years. He was guest of honor at the 1991 World Science Fiction Convention, won a retroactive Hugo award in 1996 for his 1945 short story "Uncommon Sense," was inducted into the Science Fiction and Fantasy Hall of Fame in 1998 and voted a Grand Master by the Science Fiction Writer's Association in 1999.

While one of Clement's goals was to improve the scientific accuracy of modern science fiction, he freely admitted his failures. The author liked to tell a story about MIT's Science Fiction Society who, after getting some computer time, worked out the exact shape of the planet Mesklin. "It turns out I got it wrong," said Clement. "They took great pleasure in telling me. My only response to them was, 'I wrote the story to give them fun, and I hadn't really thought of that form of fun.'

"But," he said, smiling, "I still accomplished my goal."