While sipping coffee this morning and modeling rocket behavior with a pen, it occurred to me that you surly could steer the rocket with the various methods, but you could not accurately position the vehicle. If you are trying to land on the X mark (or fly through a small fixed donut) and it is important to really hit that mark you will find you move the machine sideways by altering the thrust line (vanes, gimbels or what ever). I'm sure this is no great discovery and has been considered for years, I just haven't seen it discussed here.

Donald Qualls wrote:

Alex Fraser wrote:

The choices are?

- Change the thrust direction, gimble mount for engine or bell.
- Alter the stream of gases, vanes or diverters.
- Fins, aerodynamic forces
- Multiple engine thrust control
- Separate attitude thrusters
- and dimly in my memory from this list, a discussion of altering the plume by injecting fuel off center


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.

Fluid injection amounts to non-solid jet paddles; same class as the Jetavator (a ring around the nozzle that can be impinged on the exhaust stream to divert it) and paddles that do the same thing with a non-continuous actuator -- no roll control.

Theoretically, CG shift could be used to provide pitch/yaw control, but not roll (well, in a vehicle that looks like a collection of strap-on boosters, with some flexibility in the couplers, perhaps, but I wouldn't want to fly in it).

While in atmosphere, fluid (gas) injection at the nose can be used to steer in much smaller flows and velocities than attitude jets by altering the stagnation point, though it has little effect at low (i.e. subsonic and low supersonic) speeds on vehicle shapes suitable for high supersonic flight.

Similarly, boundary layer control by surface suction could be used to create body lift differentially for pitch/yaw steering, and depending on shape possibly also roll; mostly good at subsonic speed.

A steerable shock wave probe in the nose (like the probes used on some sub-launched missiles to give a better aerodynamic profile to a missile that had to fit maximum volume in a fixed diameter tube) could give pitch/yaw at supersonic speeds.



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