Hi mark!

> I was just thinking about what controls for guiding the rocket that
> would be available, and thinking about the single nozzle thing with O2
> pumps pushing O2 into the combustion chamber as a way to provide some
> vector's of control to the system.  (my first reaction is hmm, this
> doesn't sound too plausible.)

Oxidizer injection (or, liquid injection) thrust vector control is
possible, it's been done by other (even amateur) groups. But, it's not
very proven, and it'd probably take a lot of development work by us.

> Anyway after seeing a picture of a 2 engine rocket on some magazine it
> occurred to me that if we had 3 or 4 thrust controllable engines tied to
> the airframe, then we'd have a good chance of having a controlled
> flight.

Yes, this is clearly the easiest way to do thrust vector control since
it requires only 3 or 4 valves. But, you now need three combustion
chambers, three nozzles, etc.

> How realistic is designing an air frame with a 3 or 4 engine backside?
> How realistic is controlling the thrust out put of the rocket engines?

The real question is, how realistic is it for us as a group to pursue
thrust vector control? And the answer we've currently come up with is
"sure, but it'll be hard and take a lot of time". So, maybe, the
question is, is TVC the right control mechanism for this group? And
although we don't know, it seems like we're leaning towards more simple
"stone knives and bear skins" approach to control, which would be small
control surfaces for lower stages and small cold-gas reaction control
systems for upper stages.

> Defining how the vehicle thrust vector will be controlled is really a
> key design choice.  Has this been made yet?

No, and luckily we don't have to right now. What's important is that we
tackle the really hard preliminary issues first, which is the design of
the avionics system and the state space observer we'll be using. Once
we've gotten that going, launched it a few times, verified it's doing
what we think, *then* we can start to think about closing the loop and
doing control. And my guess is we'll want to start playing with control
right away when we're ready, so that might mean doing something really
simple like small control surfaces for a while. Then we can start to
switch from large passive fins to small control surfaces, and then start
to think about staging, etc etc. It'll be fun as heck to solve this
problem when we get to it!

Andrew

-- 
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Andrew Greenberg

Portland State Aerospace Society (http://psas.pdx.edu/)
[EMAIL PROTECTED]  P: 503.788.1343  C: 503.708.7711
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