In 2001: A Space Odyssey, there is a scene with a shuttle craft from Earth carrying an international crew approaching an orbiting space station. Strauss's Blue Danube waltz is playing in the background.
"Here I was doing something very similar to what I saw in that movie 20 or 30 years ago, so I felt like the world was unfolding as it should and also that I was very fortunate to be doing this," Thirsk recalled recently.
Thirsk, the first Canadian to take part in a long space mission, was looking back at his own experience in anticipation of Canadian astronaut Chris Hadfield's launch for the ISS today.
"It's a once-in-lifetime opportunity to fly up to the station," Thirsk says. "Not very many Canadians have the chance to do that. I felt very grateful."
It is a pretty select club — those who have lived aboard the 12-year-old ISS, in its orbit roughly 400 kilometres above the Earth. Hadfield, in fact, will become its first Canadian commander in March.
Thirsk remembers every moment of his "wonderful experience" with pride.
When he floated through the hatch to enter the station, other crew members were waiting, their cameras flashing.
"It felt like I was entering inside a Salvador Dali painting because the station was just so surreal compared to the spacecraft simulators that I'd trained in for the previous two and a half years."
Simulators are orderly and clean. The space station less so.
"It looks like a working lab," says Thirsk. "There are hoses going all over the place and cables all over the place, all kinds of computers that are located about.
"Stowage is a big issue on the station so there's stowage all over the walls but also the floor and the ceiling, and I as floated in I thought 'Oh-oh, what have I got myself into?' "
Thirsk was aboard the space station for more than 180 days, a fairly standard tour of duty, and he says it took him a couple of weeks before he felt fully acclimatized.
"You sort of figure out by asking questions and by observing and looking around why hardware is deployed the way it is, and it all begins to make a whole lot of sense. After two weeks I felt like I was born there."
The emotional connection
Cruising around the globe in a high-tech, $150-billion lab with more living space than a five-bedroom house is daunting enough.
But Thirsk remembers a more significant challenge during his six months in space: the importance of keeping an emotional connection with those he cared about on Earth.
"I enjoyed every minute that I was aboard the space station but I'd say the biggest distraction for me though was my family, concern about my family.
"I missed a lot of birthdays and anniversaries. I missed other family events, school concerts, Boy Scout events, and after a period of time that begins to get to you.
"When there are troubles with the family at home, it's not as easy for me to function as husband or as father from 400 kilometres above the Earth's surface."
Throughout his time, there was a daily connection with his family through email and internet phone, and weekly video conferences.
"Those kinds of things are helpful," he says. "But it's of course not the same as being physically there with your family and friends and nature."
A toll on the body
An engineer and physician, Thirsk resigned as an astronaut earlier this year after nearly 29 years with the Canadian Space Agency. He is currently vice-president of public, government and institute affairs for the Canadian Institutes of Health Research in Ottawa.
But he still holds the Canadian record for the longest time — 205 days over two missions — in space, which is always something researchers are interested in.
As much as six months in space affects an astronaut mentally and emotionally, it can play havoc with the body, too. Internal organs are affected by space flight in different ways.
"There are some organ systems that are more affected such as the cardiovascular system where the heart becomes weaker, the heart muscle atrophies a little bit, you lose about a half litre of blood volume as well," says Thirsk.
"The anti-gravity muscles, those muscles that you need to stand up on Earth, begin to atrophy away and get weak and flabby."
So astronauts work out two hours a day and take nutritional supplements. Thirsk took a medication prescribed to postmenopausal women for osteoporosis to minimize bone loss.
When Thirsk returned to Earth, it took about a year for his bone calcium to return to its pre-flight level. Other body systems readjusted more quickly.
"It took me maybe a day before I felt comfortable enough to walk alone without anyone supporting my elbow," he says.
"It took me two weeks to be steady enough for my flight surgeon to return my car keys.
"As soon as we get back we get into a very intensive rehab program to help return the mass and the strength of our muscles. I'd say within six weeks my muscles were back to their pre-flight status."
Best night's sleep
Thirsk talks easily and proudly of his time on the station. He remembers the hectic pace of daily activities, and, perhaps surprisingly to the rest of us who have never been in space, the ease with which he fell asleep each night.
"What was kind of cool was that every night I was asleep within five or 10 minutes," he says, noting that he'd hop in his sleeping bag, put in earplugs sometimes to counter the sound from the fans and motors running constantly and put on an eyeshade to counter the light coming in every 45 minutes as the ISS circled the Earth every 90 minutes.
There were two reasons for that ease: "One is the state of exhaustion. We all work pretty hard every day and the second is weightlessness.
"It is absolutely the best waterbed in the world, or off the planet," he says. "Weightlessness is just so comfortable. There's no pressure anywhere on your back, your side, your front."
Thirsk says the biggest surprise for him from his time aboard the ISS was "how well I worked as a teammate with my other crew members and with the ground team."
"Prior to the start of training we met with the mission managers who described all of the mission objectives they had planned for us for our six months in space.
"I didn't say anything but I sort of thought in my mind good luck with that — it's just too ambitious of a mission. But you know, we accomplished every single one of those mission objectives."
Thirsk says he'd return to the space station "in a heartbeat," but he feels no wistfulness at Hadfield's opportunity, "just pride."
"Chris was my backup and Chris is an astronaut's astronaut and he is up to the task."