12 November 2015 Last updated at 07:08 GMT
He blasts off for his six-month mission on 15 December.
But what exactly is the International Space Station and what will Tim be doing on it? Hayley's been finding out.

American Woods, who last competed in August last year, planned to play in this week's Safeway Open, but withdrew saying his game was "too vulnerable".
The 14-time major winner had back surgery in September and October 2015.
"It's going to be a hard grind to come back and compete against the best in the world," said Briton Faldo, 59.
Faldo was "not surprised" when the world number 786 withdrew from the PGA Tour opener on Monday.
The 40-year-old has not won on the Tour since 2013 and sits on 79 victories, three behind the all-time record held by fellow American Sam Snead.
Faldo told BBC Sport: "Golf is a wicked game, it dangles a carrot.
"Ten years ago, I'd hit balls and think, 'I can still play, I can still hit it'. Then you'd go to the course and can't make a score. Everything is stacking up against him now. Physically, mentally and obviously competing."
Woods was a vice-captain for the United States as they beat Europe to win the Ryder Cup earlier this month, but Faldo thought he looked like he was "struggling just getting in and out of the golf buggie".
The Englishman added: "Watching him walk, he just doesn't look supple to me.
"I know the stamina needed to play 72 holes. He may be able to hit balls on a range, but there's a rhythm to that.
"On a course, you get a five-minute gap between two shots. I think maybe he is starting to hit the ball better, but it's the stamina to play."
Woods will also miss the Turkish Airlines Open in November but said he may be ready for his foundation's event, the Hero World Challenge, in December.

The five Katyusha rockets came from part of Syria controlled by Islamic State (IS) militants, the Kilis governor's office said.
Turkish artillery fired back at IS positions across the border, Turkey's Hurriyet news daily reported.
Kilis has a Syrian refugee camp and shells have landed from Syria before.
Four of the rockets hit residential areas of Kilis - a town where an estimated 120,000 Syrian refugees outnumber local Turks.
A Turkish citizen and five other Syrians were also wounded in the rocket fire.
Cross-border artillery fire has hit Kilis almost daily recently. Twelve people were wounded there on 11 April, then the following day two people were killed and six wounded in a similar strike, Hurriyet reported.
In a few weeks' time, British astronaut Tim Peake will be making himself at home aboard the International Space Station.
[NEXT_CONCEPT]
Six-time major winner Sir Nick Faldo says "everything is stacking up against" Tiger Woods in his attempt to return to golf following injury.
[NEXT_CONCEPT]
Rockets fired from northern Syria have killed four Syrians, three of them children, in the Turkish border town of Kilis, local officials say.