Making glass that can survive the Mariana Trench
Four teams are diving to the deepest part of the ocean, the Mariana Trench, which lies 11km down in the west Pacific.
One of them is Triton submarines, a Florida-based company.
The centrepiece of their submarine will be a 15cm-thick glass sphere, which is being manufactured by Rayotek Scientific in San Diego.
Bill Raggio, the company's Chief Technology Officer, describes the difficulties of making glass that can cope with the enormous pressures that are found at the bottom of the ocean.