US space agency Nasa has "scrubbed" the launch of its Artemis 1 Moon mission on Monday after encountering an engine problem.
Lift-off was put on hold because of a temperature issue with one of the four engines on the 101-metre Space Launch System (SLS) rocket, Nasa said.
September 2 and 5 have been penciled in as alternative flight dates.
What is Artemis 1?
The Space Launch System, the world’s most powerful rocket, is on the launch pad at the Kennedy Space Centre in Florida, ready to take the Orion spacecraft to space, which will then start its solo journey to the Moon.
Artemis 1 is an uncrewed test flight that will test the rocket and spacecraft’s performance. If successful, it will pave the way for Nasa’s Artemis programme, which seeks to return humans to the lunar surface after the Apollo missions ended 50 years ago.
Jim Free, associate administrator for exploration systems development at Nasa, said space flights are a risk and the latest one was a “calculated risk” that is needed in the programme's long-term mission.
“As ready as we are to fly, it’s important to stress Artemis 1 is a flight test,” he said.
“We’ve engineers with rigour, but even the best models and tests aren’t full proof.
“As part of our review today, we discussed managing expectations, recognising things may not go to plan.
“However, our team is agile, and they are prepared for what space may throw at them as it pushes our vehicle to its limits.”
This will be the rocket’s maiden flight. It will lift off with 3,991 tonnes of thrust, soaring at speeds of 40,233 kilometres per hour in about eight minutes to reach space.
The Orion spacecraft will spend about six days in the Moon’s orbit collecting data, so mission control can assess its performance.
How to watch the Artemis 1 launch
Florida’s space coast is expected to host more than 100,000 visitors who want to witness the launch.
Earlier, local media reported that most hotels were already fully booked and tickets that offered great launch views were already sold out.
Launch day will be a star-studded event, with many celebrity performances lined up.
A live broadcast of the launch will include celebrity appearances by actors Jack Black, Chris Evans, and Keke Palmer, as well as a special performance of The Star-Spangled Banner by Josh Groban and Herbie Hancock.
It will also feature a performance of America the Beautiful by The Philadelphia Orchestra and cellist Yo-Yo Ma, conducted by Yannick Nezet-Seguin.
The launch will be streamed live on Nasa’s official website, the Nasa app and Kennedy Space Centre’s YouTube channel.
Pre-launch events started on August 22, while the launch countdown began on August 27, at 6.23pm UAE time.
Apart from the plan to launch on Monday, there are also back-up dates of September 2 and 5.
How to track the Artemis 1 mission after launch
The public will be able to track the Orion spacecraft on its journey to the Moon in real time.
Nasa launched the Artemis Real-Time Orbit Website, or Arow, website on August 28.
“During Artemis I, Orion will travel to 40,000 miles [64,373 kilometres] beyond the Moon in the first integrated flight test with the Space Launch System rocket,” the space agency said.
“Using Arow, almost anyone with internet access can pinpoint where Orion is and track its distance from the Earth, distance from the Moon, mission duration, and more.
“Arow will be available beginning August 28 on Nasa’s website and on the @NASA_Orion Twitter account.”
The website visualises data collected by sensors on Orion and sent to the Mission Control Centre at Nasa’s Johnson Space Centre in Houston during its flight.
It will provide periodic real-time data beginning about one minute after liftoff through separation of the SLS rocket’s Interim Cryogenic Propulsion Stage, approximately two hours into the flight.
Once Orion is flying on its own, Arow will provide constant real-time information.
