[AR] Re: Flight Computer
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Sat, 26 Dec 2015 22:41:18 -0500 (EST)
On Sat, 26 Dec 2015, David Weinshenker wrote:
For small vehicles the moments of inertia are small and sensor delays
that would be unnoticeable on a Saturn 5 will make an 8 ft rocket
uncontrollable.
Which might be an argument for some sort of hardware control loop
at the hardware-facing end, with at least (for example) basic
rate-stabilizing feedback handled "down in the op-amp level",
rather than going through the "digitize and calculate" of the
software system (which could handle higher-level lower-frequency
tasks like mode switching and loop lock/unlock commands if required.)
And this was, indeed, how things worked on the Saturn V, with that
remarkably sluggish computer -- the computer's job was *guidance*, not
control. There was a separate "flight control computer" -- a boxful of
analog electronics -- charged with making sure the vehicle pointed the way
the guidance computer said it was supposed to be pointing. The control
computer got inputs from the digital computer, a set of rate gyros, an
accelerometer, and some odds and ends. It ran those through filters,
shaping networks, amplifiers with programmable gains, etc. -- this wasn't
a trivial piece of hardware -- to drive the engine actuators and (on the
third stage) the RCS thrusters.
Henry
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