Janet Jalil

Jonathan Head, NASA is rolling out its giant moon rocket to the launch pad for a second time ahead of a mission to send astronauts around the moon, something not attempted in more than 50 years.

The move to the Kennedy Space Center in Florida comes after a problem with the rocket's helium system forced NASA to abandon a launch attempt earlier this month.

The hope is the rocket will launch in early April.

So it's time, tentatively perhaps, to get excited again.

And here's a reminder of the extraordinary nature of this mission from one of the crew.

Our science editor, Rebecca Murrell, told us more.

This is the second time the rocket's been rolled out to the pad.

The first was back in January.

And the rocket's had a few technical problems.

First of all, hydrogen leaks.

Later, it had helium leaks.

And engineers are really confident that they have fixed this.

So the rocket is rolling back out to the launch pad today.

I mean, this thing is huge.

It's nearly 100 metres tall.

It weighs 200.

Two and a half thousand tonnes.

So it's being carried on top of a vehicle called a crawler transporter.

It's being carried vertically so it can reach top speeds of about one mile an hour while it's being carried along, much slower going uphill and round corners.

So the whole four mile journey takes about 12 hours in total.