From: Gary Hoffman (ghoffman@spacetech.com)
Date: Sat Jul 27 2002 - 08:54:21 PDT
No Mark,
Braking is not easier than propulsion. Thermodynamics says that the
effects have to be equal and opposite.
We - on Earth - discovered brakes early, as you say - Friction brakes.
They take kinetic energy, and by the use of friction, convert it to thermal
energy, which is then convected to the surroundings.
In a spacecraft, there is no earth under us, nor is there air around us. We
can't effectivily use friction braking, and there is no practical way of
rejecting the vast amounts of thermal energy.
Thats why spacecraft have thrusters and retro-rockets. The thrusters point
in all directions for steering...and the retro-rockets point backwards for
braking. And then, during renetry, we use Friction. Ever see how hot that
gets ??
Regards,
Gary, AA2IZ
Aerospace Engineer
Specialty- Thermodynamics and Propulsion.
>
> not reaaly... thermodynamics says that braking is much easier than
> propulsion - just check the history: we had brakes long before we
> had motors!
>
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