Re: Steering

On Mon, 3 May 2004, Donald Qualls wrote:
> > Are these the only ways? Have I missed any? Gyros?
> 
> Reaction wheels, as used to point the Hubble Space Telescope, sometimes 
> incorrectly referred to as gyros.

There are several variations on that theme.  Reaction wheels are spun up
or spun down to induce torque.  Momentum wheels spin at a roughly constant
speed to provide gyroscopic stiffness.  Control-moment gyros, aka
gyrodynes, spin at a constant speed and you rotate them on another axis
for torque (loosely speaking, pushing against their gyroscopic stiffness). 

Trouble is, getting substantial torque out of any of these requires a lot
of wheel mass and a lot of power.  They're all in use on *spacecraft*, but
the only use I'm aware of in a rocket is one or two antitank rockets that
use a single momentum wheel to keep them going straight. 

> Theoretically, CG shift could be used to provide pitch/yaw control...

The "rocket belts" and similar devices make some use of this, I believe.
I'm not aware of any use in a larger vehicle.

                                                          Henry Spencer
                                                       [email protected]