A good example of this is the space shuttle. Take a look at it very carefully. The shuttle not only has the main engines in the back, but near those 3 engine nozzles are smaller thrust nozzles above the main 3, and below. If you also look at the nose of the shuttle, there are 3 thruster ports. Its hard to see, but there are also thrusters on the lower portion of the nose, as well as on the sides, hard to see due to the black heat tiles. With todays technology, you have to have thrusters 180 degrees from one another in order to have control of the craft. These small thrusters provide not only directional control, but braking, acceleration, turning and attitude control. Of course on future craft as depicted in WC, these thrusters are replaced with non rocket fuel burning thrusters, but the operation is the same. For every action there is an equal and opposite reaction, so if you fire a rocket to move forward, it will move in proportion to the thrust, hence the opposite direction. To slow down or stop, you need thrust in the opposite direction of travel. If you turn to the right, there is a thruster on the left providing the thrust to turn the craft right, to stop that turn, the thruster on the right provides small thrust to stop the turn, or turn to the left. Same principle for forward motion and reverse. If all you had was a thruster in the rear, you could only move forward with no directional control nor would you be able to stop the craft. It will continue to go in the forward direction until something stops it, like the craft crashing into something or another thruster is placed on the front and fired to slow the craft down.
RFB
ps, there is NO sound propagation in space. Sound is the movement of air pressure, our ear drums vibrate to those pressure changes, and those pressure changes move the ear drum and hammer to a sensitive organ inside the ear, which turns those vibrations into electrical pulses our brains interpet as sound. Since there is no AIR in space, our ear drums wouldnt move, thus no sound! A microphone works on this principle, a coil of wire is placed over a magnet. The coil moves with air pressure and sends an electrical signal produced by the moving coil over the magnet and sends that signal thru the cable to an amplifier. A speaker works in opposite to this, a coil moves accross a magnet by applying a signal to the coil terminals, the coil is in effect an electromagnet reacting to the natural magnets fields, thus vibrating the cone of the speaker, which moves the air and changes the pressure in the surrounding air, our ears pick up this pressure change and we hear sound. Space has no air so there is no pressure to change. Thus, no sound.
RFB