On turning

I spend quite a lot of my time reading, and occasionally commenting on, other writers’ SF. One thing that I have noticed only too often, and tried hard to avoid in my own writing, is a spaceship that thinks it is an aeroplane.

Of course spaceships do have to get down to the ground, and up to orbit again, and to do that they have to get through the atmosphere. The problem comes when a spaceship is in vacuum. the pilot pulls back on the stick and the machine executes a screaming high rate turn.

Er, no. You can’t do that.

Aeroplanes turn because moving the controls moves the elevators, ailerons and rudder. These push against the airflow and around she goes. My eighty-footers have control surfaces for use in atmosphere, have a close look at the top right hand corner of the cover picture of Run From The Stars and you’ll see one. But once the ship is in vacuum they do exactly nothing.

Changing direction in vacuum means ejecting reaction mass, in other words firing some sort of rocket engine. That means using up mass that you have taken on board and can’t replace.

And that leads to a whole set of new problems.