How are New Shepard's tilting fins and gimbaling nozzle used together (or separately) to control the rocket?

Question

In the beginning of the video Blue Origin New Shepard self-landing rocket launch with 38 research payloads (5/2/2019) the announcer mentions that both the tilting fins and the BE-3 engine nozzle gimbal are used to control the direction of the rocket.

How are these two very different methods use? Is one used at low speeds or high atmospheric pressure and the other used at high speed or low pressure? Or do they work in combination, on different timescales, or with one serving as a "trim" to the other?

Answer 1

According to the Blue Origin publicity web site https://www.blueorigin.com/new-shepard/ , the aft fin hydraulics are effective up to mach 4 (altitude isn't specified, but actual max is [remember it's sub-orbital] mach 3), and those fins are also used as steering canards during descent.

If you are interested in re-entry control, then you should also check out the Ring and Wedge fins, and the Drag brakes, all at the top of the fuselage. These aren't control devices, but they do shift the center-of-pressure. The Ring is an annular fin, and the Wedge fins deploy through it. The Drag brakes open when descent velocity is down to mach 1, and reduce that speed "by half".

Thrust vectoring would be needed off the pad (and when re-lit for controlled descent), and neither thrust vectoring or fins would be effective during the ballistic coast phase prior to payload release.

Answer 2

It's worth noting this is rather unique as its requried to be aerodynamically stable when going forwards and backwards. This is tricky as the centre-of-lift/pressure has to be 'behind' the centre of mass in both directions.

The anular-fin being covered when the capsule is on, and open after release (which correlates to going 'up' and 'down'), helps with this but its still a tricky problem. Having controlled surfaces helps.

They don't remove the need for a gimballed engine as landing requires relatively high torque at near zero air speed. However, neither does a gimballed engine remove the need for control surfaces. This is because the engine is not always lit when traveling through potentially unstable atmospheric conditions.