I can't remember that title!

[naochamb]

So I read this book when I was in like sixth grade. I'm almost a junior in college now and I can't for the life of me remember the title of the book. I actually work at a book warehouse, saw it once, and unfortunately didn't buy it. I should have because now I absolutely need to read and own this book. It was like I said a children's book, but it was a chapter book. It involved two girls who were best friends and would go out at night to play on some tower that they called a rocket ship and at the end of the story one of the girls ended up dying. Very vague description, I know, but if anyone knows this story or has kids who can help I'd really appreciate it!!
Thanks