Expert: Tom Whiting - 7/21/2008

Question
If it is a vacuum in space how are rockets propelled through, or turned in space?

Answer
Hi Dan,
Actually rockets perform at their best in space as there is no
atmospheric friction to slow them down.  You may be under the opinion that rockets need "something" to push against to either
accelerate or turn, but that's false.
Newton's third law of action/reaction needs no external force
or surrounding material.
(For every action, there is an opposite but equal, reaction force).
Period.

As far as turning (changing direction of travel), one has to use small thruster rockets on the sides of the main spacecraft.  All these do is rotate the spacecraft, so that the real thrust can be applied by the main engines in the new desired direction.  Thus, a change of trajectory (direction)is not a quick and easy thing to do in the vacuum of space, like steering a car or flying airplane where there is lots of outside friction which those vehicles can take advantage of, when changing travel direction.

[We're grossly misled as we see the Starship Enterprise enter a banked position and make a rapid change of direction; this
is all false thinking and only shown for the viewer's convenience.  Actually a starship might bank (tilt),  but there is no air, so the starship under real circumstances would just continue onward straight ahead, in a tilted, banked position. There
is no surrounding air or lift, to produce a turn]. In reality,
the spaceship would have to first rotate to the desired position,
then apply new thrust from the main engines to travel in a different
direction. Another trick rocket engineers use is put the rocket
engines on swivels, so that the applied thrust direction can be changed, but usually these swivels are limited to just a few degrees of angle. So spacecraft just cannot make major, rapid changes in direction like say, in your car, or in an airplane.
Hope this helps,
Clear skies,
Tom Whiting