What is the difference between dual-spin spacecraft and hybrid(attitude control) spacecraft?

Question

The definition from this source is "Two classes of spacecraft bring together the advantages of having momentum bias and yet provide a non-spinning base for accommodation of payload elements and torquers. These are the dual-spin spacecraft and the hybrid spacecraft. In each case momentum bias is provided by mounting a rotating body—or more than one—on the non-spinning part; it is part of the structure in the case of the dual-spin spacecraft, but consists of high-speed purpose-built wheels—momentum wheels—in the case of the hybrid spacecraft."

My interpretation for this is that for dual-spin spacecraft, its momentum basis is from a large slow rotating structure while for hybrid spacecraft, it is from a high speed momentum wheels? How does these 2 differ from pure spinner spacecraft? What is the distinguishing feature that define each of them?

Answer 1

Your interpretation is correct. Galileo (Jupiter orbiter & probe) is an example of a dual-spin spacecraft. One large part of the spacecraft (structure and all) rotated, one part didn't, with a spin bearing between, and that's the distinguishing characteristic of the dual-spin method. On Galileo, instruments that wanted a spinning platform (magnetometer, charged particle detectors, etc.) were on the spinning part, and ones that wanted a 3-axis stable platform (camera, etc.) were on the non-spinning part. (I heard JPL engineers say, "Never again!" Apparently that spin bearing was a huge headache)

It appears multiple groups have adopted "hybrid" to describe their attitude control methods. For instance, one group applies it to coupling thruster control with magnetic torque rods, some use it to describe a control algorithm for controlling momentum wheels. The momentum wheel method, which doesn't require that the spacecraft be spinning, requires a fair amount of electric power when precessing the momentum wheels, so for more rapid attitude changes they can design a thruster-based system in addition to the momentum wheels, making it a hybrid on multiple counts. The distinguishing characteristic of this type of control is that none of the spacecraft structure rotates except during attitude changes; all the rotation is within components dedicated to attitude control.

Some spacecraft, Cassini as an example, use reaction wheels instead of momentum wheels. They typically have thruster systems too, used sometimes for rapid attitude changes, sometimes for reaction wheel desaturation.