There was also awkwardness when he and his backup, Thirsk, arrived in Houston to begin training. Because the shuttle's robot arm had performed so well, NASA offered Canada a chance to fly some of its citizens. The first Canadian in orbit, however, would only be a payload specialist, NASA-speak for someone considered a guest passenger.
Aside from the experiments he would tend, Garneau was taught little about the shuttle's systems other than how to cook his food, prepare his sleeping berth, use the toilet and escape the spacecraft in an emergency.
That minimal training enabled him to go within months of his selection. At the time, however, some American astronauts had been waiting as long as 17 years. Garneau said later he felt "eyes burning through my back" when he walked down the halls.
"I felt I should keep a low profile because some of these people are probably resentful of the fact that, having been selected less than a year before, I flew 10 months later. That was viewed as parachuting by the professional astronauts."
He was the second non-American to lift off on a NASA aircraft before it became common to have French, Italian, Japanese or Russian crew members aboard the shuttle.
Garneau's first mission, which lifted off Oct. 5, 1984, was, from a technical or scientific point of view, uneventful, one of five launched that year.
Each day, Garneau was supposed to use his brief communications with the grounds to send results from 10 on-board Canadian experiments. Canadian reporters on the ground, however, wanted more pizzazz.
"They wanted to have a half-hour with Marc Garneau in space every day of the mission. Marc, what are you doing? What have you been eating? Have you gone to the bathroom? They wanted that, close and personal. And yet I had been told I would have a few minutes per day, mainly to send down experiment results."
He came across as such a guarded, cautious man that one press wag, alluding to The Right Stuff, Tom Wolfe's book about astronauts, dubbed Garneau The Right Stiff.
On the ground, the spotlight on his family shone just as intensely. It felt, Garneau says, as if every day of that year a media crew was at their home, setting up television lights, microphones and reflectors.
The public attention meant he posed for magazine covers dressed in clothes he would never wear and was asked whether he vomited in space. (For the record, he was often seasick as a sailor, got sick during his training flights, but did not suffer in orbit.)
No incursion into his private life was greater than in 1987, when his first wife, Jacqueline Brown, from whom he had separated, committed suicide. For a while, the Canadian astronauts boycotted The Ottawa Citizen, the newspaper that first reported the news.
It was a soul-searching time for Garneau, as he wondered whether his public life had affected his ex-wife, whether he should continue his grinding, high-pressure career.
For five years, he was a single father who juggled parenthood with the workaholic life of an astronaut. "That was a tough one. The twins were 11 years old now so that was easier than if they were 4 or 5. But it was tough."
He eked by, with the help of his parents, and the arrival of his second wife, Pamela Soame, whom he met in 1988 and married in 1992. Still, Garneau did at one point wonder if he should quit the space program. "I did think about it. But it was never to the point where I went over the top and said, 'No, I'm not going to do this any more.' "
Professionally, those years were also marked by uncertainty. Challenger, the orbiter that carried him into space, blew up in 1986, killing all seven on board.
Garneau thought flights would resume within a year and stuck around to help prepare the scheduled shuttle missions of fellow Canadians Roberta Bondar and Steve MacLean. In fact, it would be 1992 before those two went into space.