Rewriting book and Science Snippets

I've pulled a science fiction book out that I completed a number of weeks ago after about six rewrites. I believe that a person's writing gets better with age--age of the book being written and not necessarily the age of the person writing it. I've had time to write a number of other things and have returned to the book with a fresh mind and hopefully it won't require too much work. I've completed the first three chapters and it's not too bad yet. The dialogue needed some help but the book seems flow along as it should. I've started on my drawings for the third book in the Adventures of Curtis, Connie, and Cosmic Cat also. I'm trying to hold the length of this book oriented towards young readers down to around a hundred and fifty pages, but may have a difficult time, unless I let some of it spill over as part of second book. We'll see how it goes.

The new Science Snippet follows:

When an astronaut is launched into space it is during a window—what is meant by this?

A launch window is determined by the relative velocity and position of the object in space that the astronaut is attempting to reach. Most space launches are limited in their ability to reach a desired target. This is because of the limitation of thrust and fuel carrying ability. A rocket must be launched within a certain time or it won’t have enough fuel to reach the place in space it is trying to get to. This is sort of like when an athlete is running a relay race. The athlete must start out, at the correct time, and get to the other racer at the correct time with the correct velocity or the baton won’t be passed correctly.