Arghh, I just came across your question, and I have trying to find the name of this book for 15 years, you described it absolutely perfectly. I read it in 1999, so it was definitely written before then. All of the answers people have given to your question this far are wrong, it's none of those books. I remember the hardback cover having a picture of a child in a spacesuit, which is why I picked up the book in the first place, as a nerdy nine year old. For some reason I thought the word "egg" is in the title, but I'm starting to doubt that. If I find out, I will come back to post.