How do rovers brake/decelerate?

Question

Going by known record the humans have, over the last few decades, started to look around in the Solar System. Apart from astronomy, and allied sciences - there have been space landing missions to study the various planets in-situ e.g. the Apollo Program,the Venera Program, proposed Chang'e, various Mars landers (Curiosity, Opportunity, to name a couple)

Movement on Venus at a pressure in excess of 9.2MPa is difficult; this constraint does not apply to other celestials that have seen lander missions - Luna, and Mars.

Movement however is not only about motive power, and direction. It is also about acceleration and deceleration as & when necessary. Motive power provides acceleration, and maintains velocity to these rover missions. I can't recall encountering a brake system in reading about rovers on the internet. Ergo, the brake system is friction, and gravity.

• How do rovers brake?
• Was a brake system designed for extra-terrestrial use?
• What would go into design/construction of a brake system for extra-terrestrial use?

Answer 1

Curiously enough, the venerable Lunokhod rovers also had proper brakes, same as LRV. In both cases they were of usual mechanical type (friction plates pressing against the wheel), however in Lunokhod case the brakes were operated by electromagnetic actuator, while on LRV astronauts were supposed to use muscle power (same as with simple bicycle brakes).

In the end, friction stays the same, no matter if you're on Earth or some place else. The only additional requirement for friction brakes operating in vacuum is that you may want to avoid using pneumatic/hydraulic actuators (even though they can be designed for use in vacuum), and use electromagnetic actuators instead.

Additional option is to use "true" electromagnetic brakes instead of friction ones: http://en.wikipedia.org/wiki/Eddy_current_brake

Answer 2

The rovers I know of (Sojourner, MER, MSL) brake by not driving the wheels. The wheels do not free spin -- they are connected to the motors by a high ratio gear box. If you tried to turn a rover wheel with your hands, you simply would not be able to, due to the high gear ratio and the resistance of the electric motor to motion.

When power is applied to the motor, the wheel turns. When power is removed, the wheel stops.

It is important to note that a wheel may turn without moving the rover, and it is possible for the rover to move without the wheel turning. There are many examples of the former during our rover missions, where wheels have dug in or were lifted off the ground. In the latter category is the one busted wheel on Spirit that the other five wheels dragged around.

The Apollo Lunar Roving Vehicle had actual mechanical brakes. See @user16653's answer on those.