[FPSPACE] How tightly are the Soyuz modules bolted together?

[Mgr. Antonín Vítek, CSc.]

>
> Thanks, Geert...
>
> My understanding of the 'role of the roll' on the Soyuz DM is that it
> nulls
> out the lift and helps focus the likely descent path into a predictable
> area. The roll is not necessary for stabilization, which is achieved
> through
> the center-of-mass distribution on the DM and would occur even without a
> roll. In that case, however, the lift vector could be in almost any
> direction, and linger there if the cabin did not attain a significant roll
> rate. This could throw it over a much wider area, making the ground search
> much more difficult. Does this interpretation coincide or contradict the
> impressions others have?
>

I agree, but this comment:

Yes, the angle between symmetry axis of DM and the velocity vector (angle
of attack) is mantained automaticaly as the rotation moment generated by
aerodynamic force and inertia force is naturally zeroed, leading  to the
nonzero angle of attack. Nonzero angle of attack generates some "lifting
force" (rather say "transverse force" - TF). Vector TF (its direction) is
mantained by roll control. During the normal descent, the TF is at least
in early stages of re-entry oriented "upwards" and this leads to slower
descent rate --> smaller deceleration. Also heating rate is somewhat
smaller (but total heat amount might be higher).

If ballistic descent is chosen, TF vector makes 360 deg turns, effectively
zeroing the TF.

But, if orientation is lost (meaning roll command), in the worst case TF
vector may be oriented "downwards" --> steeper descent --> very high
deceleration (too high Gs) and extreme heat flux --> all is dangerous.

BTW, stable orientations due to CG offset are two: one with lower heat
shield in the correct orientation and the second in the opposite sense.
Terrible!


Mgr. Antonin Vitek, CSc.

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