By Chris Skeldon 
The launch was halted on Monday because a sensor reported that one of the rocket’s four central stage engines had not cooled sufficiently, in preparation for pre-ignition.
John Honeycutt, the program manager supervising development of the Space Launch System rocket, said temperatures of three of the engines approached the target below 420 degrees Fahrenheit, while the temperature of the fourth appeared to be about 40 degrees higher. If the engine is too hot, it may shut down during takeoff.
At a news conference Thursday, mission officials said that analysis of other data had convinced them that the temperature sensor was faulty and that the engine was, in fact, cold enough.
What is Space Launch System and Orion?
In order for astronauts to reach the moon, they would need a large rocket. The Space Launch System is that rocket — the most powerful rocket since the Saturn 5 took NASA astronauts to the Moon in the 1960s and 1970s. The plane, scheduled to launch on Monday, is 322 feet high and will weigh 5.5 million pounds when refueled.
The rocket, known as the SLS, has some visual similarities to the retired space shuttle. That’s by design: To simplify the development of its new lunar rocket, NASA reused much of the space shuttle technology in the 1970s.
Monday’s SLS payload is Orion, a capsule designed for multi-week flights from low Earth orbit. There will be no crew on board this flight, but it can carry up to four astronauts. If this flight is successful, a quartet of astronauts will travel on the next mission, Artemis II.