There has been a continuous presence of humans in space since 2000, when the International Space Station became operational.
Now, as the floating laboratory gets closer to its inevitable retirement, there are questions around what would replace it.
Private companies are looking to commercialise low Earth orbit, with space stations that would welcome tourists, researchers and astronauts.
Meanwhile, government space agencies have increased their focus on the Moon, with Nasa, China and Russia looking to build a lunar base.
The National highlights some of the space stations that were announced by private companies and governments.
In October, Jeff Bezos’ Blue Origin announced plans to build a private space station in Earth orbit, called Orbital Reef.
The space tourism company hopes to build a “mixed-use business park” and is promising access to media, tourists, astronauts and researchers.
It is going to be a commercially developed, owned and operated low-Earth orbit station, built in partnership with Boeing, Redwire Space, Sierra Space, Genesis Engineering Solutions and Arizona State University.
“For over sixty years, Nasa and other space agencies have developed orbital space flight and space habitation, setting us up for commercial business to take off in this decade,” Brent Sherwood from Blue Origin said at the time of the announcement.
“We will expand access, lower the cost, and provide all the services and amenities needed to normalise space flight. A vibrant business ecosystem will grow in low Earth orbit, generating new discoveries, new products, new entertainments, and global awareness.”
The plan is to begin operations within this decade, after launching a power system, core module, life habitat and a science module. This would enable the station to host up to 10 people, initially.
Genesis Engineering Solution, an aerospace and technology provider, would supply single-person spacecraft on the station, allowing those on board to go on spacewalks.
Less than a week before the Orbital Reef announcement, Nanoracks had unveiled plans of a commercial space station that would aid efforts in scientific research and tourism.
Founded in 2009, Nanoracks is a commercial space company that has sent more than 1,300 research payloads and small satellites to the ISS.
Now, it has gone into partnership with Voyager Space, a company into space exploration, and aerospace firm Lockheed Martin to build its first free-flying space station, called Starlab.
It would include a large inflatable habitat, designed and built by Lockheed Martin, a metallic docking node, a power and propulsion element, a robotic arm for servicing cargo and payloads, a laboratory to host research, science and manufacturing capabilities.
Up to four astronauts would be able to occupy the station. The company hopes to begin operations by 2027.
Space infrastructure company Axiom is planning to launch a commercial module to the ISS that would become its own independent station once the ISS retires.
The station will offer access to researchers, astronauts and tourists. By 2028, the Axiom modules would be ready to detach from the ISS, allowing microgravity research, manufacturing and life support testing.
The first two modules that will be launched would each have four crew quarters.
Axiom also plans to launch the first paying crew to the ISS next year.
Nasa has ambitious plans to build a station in the Moon’s orbit.
Called the Lunar Gateway, the station would host astronauts before they land on the lunar surface, using a human landing system.
It is part of the space agency’s deep space exploration plans, which includes building a sustainable human presence on the Moon under the Artemis programme, and sending astronauts to Mars from there in future.
Plans for the Gateway includes a Habitation and Logistic Outpost, an initial crew cabin that would offer astronauts basic life support and space to prepare for their trip to the lunar surface.
Nasa chose SpaceX to deliver cargo and other supplies to the station.
China-Russia lunar station
Earlier this year, China and Russia unveiled plans to build the International Lunar Research Station.
The proposal involves sending several Chinese and Russian missions to the Moon over a 15-year period.
Five facilities and nine modules are planned for the station, intended to support long and short missions to the Moon's surface and orbit.
The plan includes a facility that would support round-trip transfer between Earth and the Moon, lunar orbiting, soft landing, take-off on lunar surface and re-entry to Earth.
A long-term support facility on the surface will include a command centre, energy and supply modules, and thermal management.
Designs also include a “hopping robot” and smart mini-rovers that would move around the surface of the Moon.
The plan is to launch six missions by 2025 during phase one of the station’s construction.
It was reported that China is also working on a lander for human Moon missions.
China has astronauts in low Earth orbit who live on Tianhe, the core cabin module of its Tiangong space station.