And he'll be running into all sorts of creepy crawlies during a mission which will isolate him from the rest of the world.
No, it's not a trip to some strange unexplored planet.
Where is this dangerous, hostile environment? In Italy. More precisely in the picturesque island of Sardinia, best known for its turquoise waters, ruby-coloured wines and timeless fishing villages.
But Saint-Jacques won't be visiting the conventional way.
He and five other international astronauts are living and working underground for six days in the island's caves, off the west coast of Italy.
The 42-year-old rookie is the first Canadian astronaut to take part in the European Space Agency's CAVES program. CAVES is the acronym for Cooperative Adventure for Valuing and Exercising human behaviour and performance Skills.
Saint-Jacques says the underground experience is a lot like life aboard the International Space Station.
He and his colleagues have to work in confined spaces, with minimal privacy. They will face technological challenges and will have limited supplies for hygiene and comfort — just like in space.
"It's an exercise in teamwork, in a foreign, exotic and essentially dangerous environment," he said in an interview just hours before he headed underground.
"Six of us, a Canadian, two Americans, a Dane, a Russian and a Japanese astronaut, are spending six days in an unexplored, unmapped cave here in Sardinia."
The aim of the CAVES program is to prepare astronauts to work effectively and safely as a team — one that comprises members from different cultures, who must co-operate with each other to solve problems in uncharted areas.
Saint-Jacques says he and his team will be doing scientific exploration as well as mapping, and taking geological and biological samples.
He has already completed his basic astronaut training in Houston, learning to fly aircraft, how to use the Canadian robotic arm and how to work in heavy space suits.
But that's all been technical training.
He says learning to work and survive in a cave, as part of a multicultural group, is not something you can get in a classroom.
"We are as isolated as much as astronauts in orbit," the Quebec City-born Saint-Jacques said.
"Every day, you have one tag up with ground control and you can have emergency conversations if you want. But you have a mission to accomplish."
Saint-Jacques, who's married and has one child, is no stranger when it comes to spending time in confined spaces.
In October 2011, he and five crewmates took part in NEEMO-15, a mission in an underwater facility off the coast of Florida.
They lived in "Aquarius," a subaquatic laboratory and habitat, 19 metres below the surface for six days. It was supposed to be a 13-day mission, but was cut short by an approaching hurricane.
NEEMO stands for NASA Extreme Environment Mission Operations.
As for the future, Saint-Jacques admits a mission off the planet is still several years away. Any decision involving a space assignment is out of his hands.
"I have no idea. I know it will be years and, you know, that's not a bad thing because there's still a lot of preparation before I'm ready," he said.
"These decisions are taken way above my pay scale."