A group of young adults have been left behind on earth while their parents are on a different planet building a future society. Many other people are also on earth and the feeling is that they have been left behind with little chance of escape.
The main characters all go to school together and are a tight knit group. One day they begin to discuss how they might get to the new planet. In the group are a geeky boy called 'Ispex' (or similar), a girl called Vaughn and at least one more person, probably two.
While they are discussing their plan a girl comes in and demands to fight the biggest boy in order to be included in the escape plan. She loses but refused to yield until the boy is forced to allow her to join the group. She is an orphan and they feel sorry for her.
They trick an automated dump/scrap yard into selling them parts to build a ship with. They eventually take off, along with a charmingly malfunctioning robot, and make it into space.
While in space they end up boarding a large ship where everything at first seems normal, yet after a short time there they realise the crew are in fact all dead (may be implied rather than obvious) and there is an alien 'boss' who may be responsible.
They eventually make it to their parents' planet but realise that the girl who fought to get into the group is in fact an agent for the alien boss.
Can anyone identify this book?? It's driving me mad! It's at least 20 years old, probably more.