‘Let’s do this thing!’ I say to Elsa, jumping out of bed. ‘Right after I’ve changed your stinky nappy.’

I keep busy and distracted all morning, getting Elsa ready and then going round to Grandad’s house and helping him to load up Pete’s car. (Grandad doesn’t have a car so he’s roped Pete, one of his Sussex Stargazer friends, into giving us a lift.) When we’re finally packed up and on our way to the science centre, the sickness creeps back in. I wind down the window and take deep breaths. Next to me, Elsa is screaming at the top of her lungs.

‘Remind me. Why are you bringing Elsa along?’ asks Pete.

‘Alice is away at the moment,’ says Grandad. ‘Elsa won’t be a problem.’

‘Right,’ says Pete. He doesn’t sound convinced. Elsa’s been crying solidly since we left town. Right now we’re driving down a winding county lane with David Bowie blaring out of the speakers and Elsa screaming along to ‘Heroes’.

‘Here, Elsa,’ I say, handing her a carrot puff. She stuffs it in her mouth and the screaming stops. I go back to staring queasily out of the window, the wind whipping my hair. Suddenly, I get a glimpse of the turquoise observatory domes rising out of the trees. ‘There they are!’ I say.

‘Just like spaceships,’ says Grandad, turning round and smiling at me. When I was little, Grandad told me the telescope domes really were spaceships and that all the staff at the science centre were aliens. Every time we visited, he implied that there was a good chance we could end up in space. I worked out that he was lying years ago, but I still get this thrill when I see the domes. I love this place.

‘Maggie was saying she might give you a job soon,’ says Pete.

‘Maybe,’ I say, glancing at Elsa. ‘If today goes well. Maggie is the manager and she knows how much I want to work here. I’ve got to wait until I’m sixteen, but after that it’s up to her.’

‘It’ll go well,’ says Grandad. ‘You wait until you see it, Pete. We’ve got eggs, explosions, costumes … Meg worked it all out.’

‘You thought of the costumes,’ I say.

‘You do love a good costume,’ Pete says to Grandad. ‘Remember when you dressed up as Halley’s Comet?’

‘And it caught fire?’ Grandad laughs. ‘I couldn’t get away with smoking in front of the kids these days.’

Pete turns off the road and into a bumpy car park. ‘There you are,’ he says, pointing at the noticeboard by the entrance:

Cool Cosmos, 11.30. Discover just how miraculous our universe is in our hands-on, family-friendly show. Warning: will contain nuts!

Pete laughs and slams his hand down on the steering wheel.

‘Oh, God,’ I say, taking an extra deep breath of calming air.

‘Do you like the bit about the nuts?’ asks Grandad. ‘That was my idea!’

All the workshops are run in marquees and while Grandad and I set up, Elsa plays in a cardboard box. Whenever we find something she might like we drop it in the box; a piece of bubble wrap keeps her quiet for ages and she goes crazy when Grandad bats in one of the balloons we’re blowing up.