SpaceX has launched its third crew to the International Space Station this morning, reusing a rocket and crew capsule in a human mission for the first time.

The Crew-2 mission blasted off from pad 39A at the Kennedy Space Center in Florida at 10.49am Irish time, after being delayed a day by adverse weather along the flight path.

French astronaut Thomas Pesquet becomes the first European to fly on a SpaceX Crew Dragon.

There will be 11 astronauts in total on the ISS, as the Crew-2 team overlaps for a few days with Crew-1 astronauts, in addition to three Russian cosmonauts.

Mr Pesquet will be accompanied by Americans Shane Kimbrough and Megan McArthur, and Japan's Akihiko Hoshide.

Crew-1 is set to splash down off the Florida coast on 28 April.

It is the third time SpaceX will send humans to the ISS as part of its multi-billion dollar contract with NASA under the Commercial Crew programme.

The first mission, a test flight called Demo-2, took place last year and ended nine years of American reliance on Russian rockets for rides to the ISS following the end of the Space Shuttle programme.

The Crew-2 mission will reuse the capsule from Demo-2 and the Falcon 9 booster previously deployed for the uncrewed Demo-1 mission, a key cost-saving goal of NASA's partnerships with private industry.

Thomas Pesquet, Megan McArthur, Shane Kimbrough and Akihiko Hoshide before launch

Ahead of the launch, European Space Agency (ESA) astronaut Andreas Mogensen of Denmark said the mission was also a major step forward for Europe, which has dubbed it "Alpha" after its own naming convention.

"On the one hand, it means a lot of course to have an astronaut going to the International Space Station, but at the same time it's also the next mission in a long line of missions."

Germany's Matthias Maurer will be the next European on a SpaceX mission this autumn, followed by Italy's Samantha Cristoforetti next spring.

ESA will also be a key partner to the US in the Artemis programme to return to the Moon, providing the power and propulsion component for the Orion spacecraft, and critical elements of a planned lunar orbital station called Gateway.

Mr Mogensen predicted that in the hours leading up to the launch, Mr Pesquet, who is a close friend of his, would be feeling a "sense of relief" to finally start the mission after years of planning.

"You're very focused on what's going to happen, on your tasks at hand," he said.

"Thomas and his crewmates have spent hours in a simulator training for this, they've gone through the launch procedures, they've gone through the docking procedures... there's not a whole lot of time for nervousness."

The Crew-2 team has around 100 experiments in the diary during their six-month mission. These include research into what are known as "tissue chips".

They are small models of human organs that are made up of different types of cells and used to study things like aging in the immune system, kidney function and muscle loss.

Another important element of the mission is upgrading the station's solar power system by installing new compact panels that roll open like a huge yoga mat.

After launch, the Falcon 9 rocket will return to Earth for an upright vertical landing on a drone ship, and the Crew Dragon capsule is scheduled to dock with the ISS at 5.10am (10.10am Irish time) tomorrow, with hatch opening two hours later.

Mission will carry Irish schoolgirl's experiment

This morning's launch carried with it a computer experiment by two Irish schoolgirls.

The 17-year-old girls are the first Irish students to have had their computer experiment for the International Space Station (ISS) accepted.

Niamh Staines and Kitty Joyce are 5th year computer science students at the Mount Temple comprehensive school on Dublin’s northside.

Mr Pesquet brought the girls’ computer code with him when he took off this morning, and will run the Dublin teenagers’ experiment during his stay on the space station.

The experiment is to investigate the effects of weather patterns on the temperature of Earth’s surface.

The successful experiment was described by the Niamh and Kitty.

"We can measure the heat exposure of the surface of the Earth using an infrared camera, known as Izzy, to take photos of the regions that the ISS passes over. We will analyse these to compare the temperature of certain regions of the Earth’s surface with the cloud coverage passing over them at that time."

David Frew, the Computer Science teacher at Mount Temple, said that Niamh and Kitty were "very excited" to have their experiment accepted for the International Space Station.

"Niamh and Kitty have shown self-directed independent learning, which is a key concept in a subject such as computer science. This achievement is entirely down to their hard work and diligence," he said.

"Remote learning has been difficult for everyone during the last year and a half but these two girls have pulled together and demonstrated a high level of dedication and application."

"That shows we can overcome anything in the face of uncertainty when you have passion and commitment for what you are studying," he added.

The experiment is one of those submitted by 214 teams from Europe and Canada that have been awarded "flight status" this year. The teams represent 21 countries and 862 young people.