Kathy,
demonstrating the rocket mouse is such an essential part of inquiry learning. Having viewed the rocket mouse in action, the children will be able to apply their own understanding as they work in small groups to make their own and to improve on its launch and landing.
You can choose (or better yet, let the children choose) to look at vertical distance, or horizontal landing distance. Children can use non-standard measures, perhaps holding their hand to the height and then moving to a wall and placing a post it note to mark the height.
At Blackrock Castle, in our workshops, we start on the table, and as the children become more confident and the rocket mice go higher, we ask “I wonder where we could launch from that would give us a bit more space?” This encourages the children to move the launch to the floor, and fewer mice then hit the ceiling.