The first question, of course, was size: how big did the message need to be? My first, most ambitious thought was to make it visible with the naked eye. It turns out this is pretty difficult — the International Space Station (ISS) flies so high above the Earth (400km) that a square 150m across would appear as the barely visible speck to an unaided eye. And we didn’t want to make a speck; we wanted to write something legible.

Luckily for us, the astronauts on the ISS have cameras with very long lenses (up to a metre or more!). This allows them to take pictures with pixel resolutions down to 6m. That was a more manageable size that we could begin to work with. I was also heartened to find out that this kind of stunt had actually been done twice before — once in the spring of 2015 with cars in a desert and in the autumn of 2015 on the field of a university. So it was definitely possible.

We calculated that a 6m pixel should be visible from the ISS.

We began operating on the assumption of 10m pixels and the next job was to decide what we were going to actually write. We wanted it to be a message from the whole nation to our first astronaut on the ISS, so we decided on ‘Hi Tim’. If the letters were five pixels high and each line was one pixel thick, that meant we could write the whole message in a space about 50m by 170m.

An important connection we needed to make was with the people who tell the astronauts what to take pictures of. This is the Crew Earth Observation team from Nasa. We asked our friends at the UK Space Agency to connect us through, and pretty soon we were talking about times and locations with the keeper of the target list. The only problem was that we didn’t have either.

This is when Assistant Producer Alex Collinge got roped into the secret project we were calling ‘Operation Hi Tim’. We started brainstorming places that might have large fields we could fill with a giant message to the space station. The top two contenders were Woolsthorpe Manor (Isaac Newton’s family home) and Chichester High School for Boys (Tim Peake’s secondary school). We chose Chichester because it turns out that the ISS’s orbit is such that the further south we could go, the better chance we would have. It also had the added bonus of involving young people and having a strong connection with Tim Peake.

So Alex and I got on the phone with the school. To our great surprise, not only would they be willing to have us come down and monopolise their sports fields, but they would also recruit a team of students to help us.

The next big question was: what are we going to physically make the message with? My initial thought was plastic sheeting of some sort. But that created more problems than it solved. I then thought about pitch-marking paint. It filled the criteria of easy to apply, high-contrast, and even allowed students to use the fields after they were painted.

So Alex and I got on the phone with the school again. We asked who usually paints their fields and we were put in touch with Burleys, the company responsible for landscaping at the school. Once we explained our ambitious scheme, to write a message to space, they were on board as well. Not only had they offered to generously donate their time and equipment to help us achieve our vision, but they also got Fleet involved, the company who supply pitch-marking paint. Fleet agreed to donate all the paint we needed to get the job done.

We got back to our Nasa contact and had Chichester High School added to the crew earth observation target list. To be precise, we’d do our painting on Friday 6 November at Latitude 50.827767, Longitude -0.777465.