WASHINGTON, March 5 (Xinhua) -- SpaceX's Crew Dragon spacecraft is planning to send three private tourists along with a professionally trained commander to the International Space Station (ISS) in the second half of 2021.

SpaceX inked a deal with Houston-based startup Axiom Space on Thursday to enable their first fully-private human spaceflight mission to the ISS.

The travel will allow the crew to live aboard the ISS and experience at least eight days of microgravity, according to Axiom Space.

Tickets may cost around 55 million U.S. dollars, and one seat is already booked, according to The New York Times.

This is the second contract SpaceX grabbed as it reached an agreement with Space Adventures on Feb. 18 to launch private citizens on Crew Dragon spacecraft into an Earth orbit higher than ISS between late-2021 to mid-2022.

Space Adventures has previously arranged eight orbital trips to the ISS for seven wealthy customers, using Russian Soyuz space capsules.

In March 2019, SpaceX's Crew Dragon completed its end-to-end unpiloted flight test to the ISS and back to Earth. Musk, SpaceX founder, said in January 2020 that the first crewed mission for the U.S. space agency NASA is expected to take place in the second quarter of this year.

As to Axiom Space, it plans to offer professional and private astronaut flights to ISS at a rate of up to two per year.

Also, NASA selected Axiom's proposal to attach its space station modules to the ISS beginning in the second half of 2024.