I have an idea for that book, whilst they're on the planet, there could be a few of them in space stations orbiting the planet. And 'Gravity' style, the station could get attacked or have a malfunction or something, and one of the secondary main characters gets lost shooting in space with no way of returning! Dark maybe, but it would be great for those of older age, e.g. our age. Saying as though we are now in Key Stage 4 D:
'Gravity' Link: http://www.imdb.com/title/tt1454468/