# Down to Earth: Folding satellites and maps

06 March 2018

## Interview with

Dr Stuart Higgins

## PIA18655_hires.jpg

In this episode of Down to Earth, Stuart Higgins looks into how satellites have helped us fold our maps...

Stuart - Keeping spacecraft powered up during missions is a challenging task. The bigger and heavier something is, the more expensive it is to launch meaning giant batteries are out of the question. Solar panels were a favourite for use in space because they offer a relatively good power to weight ratio, but they also require a large area to operate.

To save space during the launch, solar panels were often folded away inside the spacecraft, slowly unfolding up in orbit. Getting the unfurling right can be one of the more nerve wracking parts of the mission because if the panel gets stuck, the spacecrafts batteries would soon run out of power and its mission over.

In the 1970s and 80s, astrophysicist, Koryo Miura, was working on how to fold solar panels and other structures for space. He mathematically determined an optimal folding method that critically allowed the solar panel to be unfolded with a single pulling movement. This meant that not only did the folding offer the benefit of saving space, it also minimised the number of motors needed to unfold the solar panel.

Miura also took care to minimise how the folds caused tensile stress in the material. If you told a piece of paper in half and the half again, the outside fold has to bend around multiple thicknesses of paper applying greater strain. In his calculations, he tried to minimise the risk of the fold tearing. As well as being useful for deploying solar panels in space, the Miura fold has also been used to make subway maps that can be easily unfolded, presumably by confused tourists struggling to find their way.

And the usefulness of the Miura fold doesn't end there: researchers at Cornell University are excited about how different kinds of Miura fold can be used to create metamaterials. A metamaterial is where a small repeating pattern gives a material new or unusual properties so, in the case of the Miura fold, the repeated parallelogram style folds turn a floppy sheet of paper into something with greater structural strength. The researchers were interested in what would happen if they could apply the same folding patterns but on a much smaller scale to material such as graphene to see how their properties would change.

As for space applications, research into origami related structures is continuing with an even more elaborate folding method being developed that allows solar panels to be deployed in a circle using the rotational force of the spacecraft alone. So that’s how solving the problem of folding solar panels for spacecraft led to easy to unfold maps and has helped inspire research into new ways of working with materials.