(Slightly old mail, left over from the pre-Space-Access pileup...)
On Mon, 19 Apr 2004, Alex Fraser wrote:
> I had thought that bandwidth was the universal term used to
> describe a control system, but couldn't quite figure out how to put the
> parts together to get a number. Would the control system term
> "bandwidth" be the same as an information system's "bandwidth"?
Bandwidth, properly speaking, is the range of frequencies that can pass
through a system. Information systems have this only in a loose sense.
> Do the various methods of rocket control have different amounts of
> minimum bandwidth to achieve the same fineness of control?
Yes and no. The bandwidth requirement is not a function of the type of
actuator (e.g. RCS jets), although different actuator types may have more
or less trouble *achieving* high-frequency response.
On the other hand, greater cleverness in the control-system design *can*
substitute for bandwidth to some extent. For example, a disturbance that
is too big and too quick for the control system to catch without a
noticeable lurch can be dealt with much more cleanly if its size is
well-known and there's a bit of advance warning, so you can feed in the
correction in advance. E.g., during the Voyager Jupiter encounters, the
spacecraft would twitch a bit every time the tape recorder started or
stopped, because the torque on the tape reels started the spacecraft
rotating until the ACS system caught it, while on later planet encounters,
the software had been smartened up, and recorder start/stop operations
automatically commanded an ACS jet firing to cancel the torque. (A rocket
example: on a multi-engine rocket, if you shut down an engine in flight,
the control system should be told about this as the shutdown command goes
out, so it can crank in the proper compensation as the engine shuts down,
rather than waiting to notice an attitude departure and then scrambling to
correct it.)
Henry Spencer
[EMAIL PROTECTED]
_______________________________________________
ERPS-list mailing list
[EMAIL PROTECTED]
http://lists.erps.org/mailman/listinfo/erps-list
