Full details can be found on the ESA website.
Send your proposal by 10:00 GMT (11:00 BST/12:00 CEST) on 4 April 2014.
In May of last year, Tim Peake was selected to conduct a six-month mission aboard the International Space Station (ISS) and will fly as part of Expedition 46/47 in November 2015. He will become Britain’s first “official” astronaut.
Follow Tim on Twitter @astro_timpeake.