SpaceX plans to send four members of the public to space – if they can afford it.

The company will allow civilians to buy placed onboard the Crew Dragon spacecraft, which was built to take US astronauts to the International Space Station.

It is still not clear exactly how much the mission will cost. A single seat is likely to be worth many tens of millions of dollars.

It is also not confirmed when the tourists will be able to set off on their mission. But it should be before the end of 2021 and will last five days, according to Space Adventures, the booking agent that has partnered with SpaceX to sell the trips.

“This historic mission will forge a path to making spaceflight possible for all people who dream of it, and we are pleased to work with the Space Adventures’ team on the mission,” said SpaceX president Gwynne Shotwell in a statement.

Nasa's groundbreaking decade of space exploration: In pictures Show all 10 1 /10 Nasa's groundbreaking decade of space exploration: In pictures Nasa's groundbreaking decade of space exploration: In pictures Mystic Mountain, a pillar of gas and dust standing at three-light-years tall, bursting with jets of gas from fledgling stars buried within, was captured by Nasa's Hubble Space Telescope in February 2010 Nasa/ESA/STScI Nasa's groundbreaking decade of space exploration: In pictures The first ever selfie taken on an alien planet, captured by Nasa's Curiosity Rover in the early days of its mission to explore Mars in 2012 Nasa/JPL-Caltech/MSSS Nasa's groundbreaking decade of space exploration: In pictures Death of a star: This image from Nasa's Chandra X-ray telescope shows the supernova of Tycho, a star in our Milky Way galaxy Nasa Nasa's groundbreaking decade of space exploration: In pictures Arrokoth, the most distant object ever explored, pictured here on 1 January 2019 by a camera on Nasa's New Horizons spaceraft at a distance of 4.1 billion miles from Earth Getty Nasa's groundbreaking decade of space exploration: In pictures An image of the Large Magellanic Cloud galaxy seen in infrared light by the Herschel Space Observatory in January 2012. Regions of space such as this are where new stars are born from a mixture of elements and cosmic dust Nasa Nasa's groundbreaking decade of space exploration: In pictures The first ever image of a black hole, captured by the Event Horizon telescope, as part of a global collaboration involving Nasa, and released on 10 April 2019. The image reveals the black hole at the centre of Messier 87, a massive galaxy in the nearby Virgo galaxy cluster. This black hole resides about 54 million light-years from Earth Getty Nasa's groundbreaking decade of space exploration: In pictures Pluto, as pictured by Nasa's New Horizons spacecraft as it flew over the dwarf planet for the first time ever in July 2015 Nasa/APL/SwRI Nasa's groundbreaking decade of space exploration: In pictures A coronal mass ejection as seen by the Chandra Observatory in 2019. This is the first time that Chandra has detected this phenomenon from a star other than the Sun Nasa Nasa's groundbreaking decade of space exploration: In pictures Dark, narrow, 100 meter-long streaks running downhill on the surface Mars were believed to be evidence of contemporary flowing water. It has since been suggested that they may instead be formed by flowing sand Nasa/JPL/University of Arizona Nasa's groundbreaking decade of space exploration: In pictures Morning Aurora: Nasa astronaut Scott Kelly captured this photograph of the green lights of the aurora from the International Space Station in October 2015 Nasa/Scott Kelly

The travellers will not get to visit the International Space Station or anywhere else on their trip. Instead, they will fly up in the Crew Dragon craft blasted off using SpaceX's Falcon 9 rocket, enjoy some time in orbit, and then drop back down to Earth.

If the mission is successful, that will allow the tourists to be at the highest altitude ever achieved for a private citizen. That will also mean they will have a view of Earth that has not been offered in decades, since astronauts have in recent times set off only to the relatively nearby orbit of the space station.

"Honoring our combined histories, this Dragon mission will be a special experience and a once in a lifetime opportunity — capable of reaching twice the altitude of any prior civilian astronaut mission or space station visitor," Eric Anderson, chairman of Space Adventures, said in the same statement.