Tim Peake has said he is feeling "fantastic" after his first three days back on Earth following six months on board the International Space Station. The British astronaut held his first press conference since landing in Kazakhstan on 18 June at the European Astronaut Centre in Cologne, Germany.

"I'm feeling a lot better than I did on Saturday lunch that's for sure," he told reporters. "It's amazing how quickly the human body adapts to a new environment. After just 24 hours was able to function on the ISS. It was a bit slower coming the other way. I'm doing rehabilitation training – cycling, cross training - even just after three days I'm feeling fantastic."

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In terms of the flight back to Earth, he said: "The descent is a really exciting ride. You've got two minds. One as professional - as test pilot - thinking about dynamics. At same time, the boy inside you enjoying this fantastic ride back from space. You're very aware of everything that's going to happen. The undocking is very uneventful. You're just waiting for de-orbit burn ... Then things get very exciting."

He recounted how three loud bangs can be heard at the point of separation, at which moment the spacecraft is "tumbling in a controlled manner". "It was great being sat next to window – you can look out, you can see sparks and flames." At this point, the gravitational forces (G-force) begin to build up and Peake said it got very hot in the capsule.

After the parachute opened, the capsule is "completely flung around" and the astronauts "have to hold on and wait for it to stop". "For a second I was concerned [the parachute hadn't opened] but Yuri [Malenchenko] so relaxed and cool. If the parachute hadn't opened he wouldn't be looking so cool."

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Tim Peake spent six months in space Shamil Zhumatov/Getty

Asked if he would return to space, he said he would "do it again in a heartbeat", but added he was currently looking forward to spending time with his family. "[Being back on Earth is] wonderful, familiar, everything I missed while in space. You do think about Earth when you're in space a lot. It's nice to be back in a familiar environment. Rain – any weather down here feels unique and special."

Furthermore, he said gravity had some benefits: "Gravity is horrible when you come back to earth, but when using the loo gravity is your friend."

Over the next six months, Peake will be closely monitored to study the effects of long-duration spaceflight on the human body. What scientists learn about his physical condition will help them plan for even longer missions in the the future – including those to Mars and the Moon.

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Tim Peake at his first press conference since landing back on Earth on 18 June Getty Images

"I was very surprised to look at myself in mirror," Peake said. "I haven't lost a lot of weight. Distribution is very different though, my frame is different ... [human experiments are a] huge part of what we're doing. There is an enormous amount to learn about human body."

And this information will be key to manned missions to Mars and beyond. Peake said we are ready to take next steps in space exploration and that if the UK is to be part of this "exciting future" it must get involved now, or risk losing out altogether.

"The ESA is so active and involved in human spaceflight programme. It's extremely important the UK is involved in all of that too. We need to give our industry a chance. We need to give scientific community a chance. If we're not involved now we will miss the boat. We have a huge space sector growing at a fast rate.

"We're making decision today that will influence what we're doing in 30 years' time. If you're not involved from the start it's hard to jump on board. If we're not on board now we will miss out, and at some point we will be too far behind."