Two astronauts are on course to make history today as they prepare to launch into space.
The joint effort by Nasa and SpaceX to send astronauts into space from the US was planned to happen on Wednesday, May 27, but it was cancelled because of bad weather conditions.
Today, Robert Behnken and Douglas Hurley are on course to travel to the International Space Station (ISS) on a rocket built by billionaire entrepreneur Elon Musk’s firm.
If all goes as planned, the mission, named Demo-2, will see SpaceX become the first private company to send astronauts into space.
It has been postponed once because of the weather conditions and it is touch and go whether it will happen this evening for the same reason.
It will also be the first time in nine years astronauts will have launched into space from US soil.
Lifting off from Launch Pad 39A atop a specially instrumented Falcon 9 rocket, Crew Dragon will accelerate its two passengers to approximately 17,000 mph and put it on an intercept course with the International Space Station.
Once in orbit, the crew and SpaceX mission control will verify the spacecraft is performing as intended by testing the environmental control system, the displays and control system and the maneuvering thrusters, among other things.
In about 24 hours, Crew Dragon will be in position to rendezvous and dock with the space station. The spacecraft is designed to do this autonomously but astronauts aboard the spacecraft and the station will be diligently monitoring approach and docking and can take control of the spacecraft if necessary.
What time is lift-off?
It is scheduled to take place from the Kennedy Space Center in Florida at 3.22pm EDT, which is 8.22pm UK time.
How can I watch it?
Nasa is streaming the launch live on Nasa TV, which is available to watch on YouTube. Coverage will start before the launch, so you can get a glimpse of last minute preparations, interviews and more in the lead up to the big moment.
Can I see it in the sky?
As long as the weather remains clear and the launch stays on time, it should be possible to see the spacecraft from the UK.
If it all goes to plan, skywatchers in the UK could see the rocket flying over the UK 15 minutes after lift-off at around 8.37pm, Manchester Evening News suggest.
However, because of the earlier schedule, it will likely be too light to see the capsule coming overhead at that time.
There is hope as it passes the UK for a second time at around 10.15pm, which will make for a better viewing with darker sky conditions, but the vehicle will be very low on the horizon in the southwest.
For help keeping track of the ISS, the European Space Agency (ESA) has a useful live spotting feature online and you can put your postcode into the Spot the Station website.
The ISS is the third brightest object in the sky and is visible to the naked eye. It looks like a fast-moving plane only much higher and travelling thousands of miles an hour faster.
Why is this mission so important?
The mission, known as Demo-2, will allow the US to once again send humans into space rather than relying on paying Russia for a lift on their spacecraft as they have done for the past nine years.
According to Nasa, this is a demonstration mission to show SpaceX’s ability to ferry astronauts to the space station and back safely.
It is the final major step required by SpaceX’s astronaut carrier, the Crew Dragon, to get certified by Nasa’s Commercial Crew Programme for more long-term manned missions to space.
Who are Robert Behnken and Douglas Hurley?
Mr Behnken, 48, and Mr Hurley, 53, are experienced Nasa astronauts who have been involved in testing of the Crew Dragon capsule.
Mr Hurley, who was a fighter pilot in the US Marine Corps, was on the final flight of the space shuttle Atlantis in 2011 before it was discontinued.
Mr Behnken was a flight test engineer with the US Air Force before joining Nasa, and has spent just over 29 days in space, which includes 37 hours of spacewalking time.
He will serve as the mission’s joint operations commander and take responsibility for the rendezvous, docking and undocking of the Dragon capsule, while Mr Hurley will be in charge of the launch, landing and recovery of the vehicle in his role as the Crew Dragon spacecraft commander.
The two men will be wearing spacesuits designed by SpaceX with help from Hollywood costume designer Jose Fernandez.
Mr Behnken and Mr Hurley will test the Crew Dragon’s environmental control system, the displays and controls, and the manoeuvring thrusters.
They will also monitor the autonomous docking system during the approach to the space station, according to Nasa.
The duo will become members of the Expedition 63 crew and perform further tests on the Crew Dragon along with other tasks related to the space station.
But the pair’s main mission is to conclude the validation process that is required by Nasa to ensure the spacecraft designed to carry astronauts can operate safely.