NASA and its private launch service provider SpaceX are preparing to send four astronauts to the International Space Station (ISS).
The crew will travel into orbit in a dragon capsule atop a Falcon-9 rocket.
It will be only the second time that this launch system has been used to transport people.
A successful demonstration flight conducted in May follows, marking the resumption of astronaut missions from US soil after a nine-year hiatus.
The Falcon-Dragon combo is expected to leave the Kennedy Space Center in Florida at 19:27 local time (00:27 GMT, Monday).
It’s an “instant launch window,” which means the mission must release the button if it is to take the station as it circles the Earth above.
Much depends on the weather, of course. Unacceptable winds on the space coast have already forced a 24-hour delay.
Should there be a further postponement for any reason, the next attempt would be made on Wednesday.
The crew consists of three astronauts from the US space agency (NASA) – Commander Michael Hopkins, Victor Glover and Shannon Walker – and highly experienced astronaut from the Japanese space agency (Jaxa) Soichi Noguchi.
They called their dragon ship “Resilience”.
The group will spend approximately six months on the station, increasing its complement to seven.
Kate Rubins of NASA and cosmonauts of the Russian space agency (Roscosmos) Sergey Ryzhikov and Sergey Kud-Sverchkov are already on board the 410 km high platform. Having a team of seven on the ISS will triple the amount of microgravity science that can be conducted on the platform.
Victor Glover will become the first African American astronaut to undertake a long-duration mission on the station. In the 20 years that humans have permanently occupied the orbiting facility, black astronauts have only visited it for short periods.
NASA says this launch means it has fully entered the new era of purchasing crew transportation services from private contractors, rather than owning and using its own vehicles, as is the case with the now retired space shuttles.
SpaceX is in charge on launch day, albeit with NASA looking over its shoulder. They are the people of the company who will conduct the show from Kennedy’s “fire room” and the SpaceX onboard operations center in Hawthorne, California.
It is also the SpaceX staff that conducts the activities close to the pad, tying the NASA crew to the seats of the Dragon and closing the hatch.
Everyone involved in the launch had a chance to practice their roles on Thursday during a dress rehearsal. This saw the astronauts don their white spacesuits and take the steps they will actually take on Sunday.
The controllers are watching the weather closely. While conditions in Florida seem favorable, they must also be acceptable along the entire flight path to orbit.
If something goes wrong during the ascent and the Dragon Pod has to abort the mission and return to Earth for an emergency crash, it will want to avoid strong winds and rough seas. The controllers are then monitoring the time at around 50 points along a route that stretches along the east coast of the United States and across the Atlantic to the west coast of Ireland.
But it is not only important for the return of a capsule. SpaceX wants to go back and retrieve the Falcon’s first stage so it can be reused. This involves landing the booster on a drone ship and this becomes more challenging the higher the waves.
SpaceX has signed contracts with NASA worth more than $ 3 billion to develop, test and fly an astronaut taxi service. As part of this report, the company conducted a demonstration mission in May in which astronauts Doug Hurley and Bob Behnken were taken to the station and then safely returned to Earth.
The contractual agreements also provide for six “operational” or routine missions: this flight is the first.
NASA has a similar deal with aerospace company Boeing, although its service is a good year behind SpaceX.
The agency says its new procurement model for transportation to low Earth orbit has saved it billions of dollars in procurement costs. It intends to use these economies to finance its ambitions on the Moon and Mars.
NASA is close to testing the giant new rocket it commissioned to bring astronauts back to the lunar surface, a goal it hopes to achieve in 2024.