GCSE is 'General Certificate of Secondary Education', the exams you take at 16 in the UK (they replaced the old 'O Level' and 'CSE' exams, and many would say they are easier now - including me!). Presumably he's built something as a project, and it's gone missing?.
I don't quite see why he's mentioning it here though?, he already seems to be aware that his only hope is to build another!.