[FPSPACE] Soyuz DM roll during ballistic entry profile

[Geert Sassen]

Regarding your questions:

a) 'eyeballs out' G's will have been minimal (almost zero). In all 
separation-related accidents (including several Vostok/Voschod missions 
and Soyuz 5) the service module separated very early in the re-entry and 
the cabine neatly came back to its stable 'heatshield forward' mode 
prior to pulling any G's. Remember on initial re-entry the hatch was 
exposed to the most heating, it is not made for this and it can not 
survive the 'real' full heating of re-entry, only the very first signs 
of re-entry load, so the service module must have separated very early 
in the re-entry and the cabine returned to its stable position probably 
long before the crew started to feel any G-force, in any other situation 
they wouldn't have survived...
b) Already answered by Anatoly.
c) I do not think there is any connection between the ballistic re-entry 
and the apparently very rough touch-down. Only remark on this is that 
during Soyuz-5 the DM seemingly was still rolling after main parachute 
deployment, causing the parachute lines to twist, and this caused a very 
rough landing. This might have been due to the fact that on Soyuz-5 all 
fuel of the attitude control system was exhausted prior re-entry. The 
main chute will first deploy in one suspension mode, the DM is then 
hanging under something like 50-60 degrees of vertikal and this should 
stop any remaining roll. Later, shortly prior to release of the 
heatshield, the main chute is switched to dual suspension mode, where 
after the DM is hanging vertikal in order to make max. use of the 
softlanding rockets. As far as I know there is no mention anywhere that 
the DM on 19 april was also still rolling after main chute deployment 
(aka Soyuz 5), if it was the crew definitely should have noticed it. For 
complete description of soyuz parachute descent, see f.i. ref 'Soyuz' by 
Hall/Shayler, ISBN 1-85233-657-9, page 68, or http://www.astronautix.com .

Soyuz landings are always rough, although this basically can be said 
about ANY parachute descent, for Gemini a descent speed of 32 fps (10.8 
m/sec) is noted under main parachute (ref 'Gemini' by David Shayler, 
page 317), for Apollo this was 30 fps (9.1 m/sec) (ref 
http://www.astronautix.com/craft/csmchute.htm ), while for Soyuz a 
descent speed under main parachute of 9.85 m/sec is stated (ref 'Soyuz' 
by Hall/Shayler), so basically the descent speed under main parachute is 
almost identical for all manned craft. Note on Soyuz the soft-landing 
braking rockets should fire aprox.1.5 mtr above the ground and reduce 
the actual touch-down speed to 2-3 m/sec, while offcourse the 
Gemini/Apollo missons didn't have these braking-rockets and actually hid 
the water with 9-10 m/sec. Splashing down in water, as opposed to 
touching down on land, will slightly reduce the shock-load, but this 
should not be over estimated: water can be very 'hard' as well.

Basically, just looking at the figures, I think it is incorrect to state 
a Soyuz landing is more rough then a Mercury/Gemini/Apollo parachute 
landing, those craft ALSO touched down very rough, only a lot of years 
have passed since then and in those days it was probably more easily 
taken for granted that touch-down was rough...

Slight differences in admospheric conditions can influence the parachute 
descent speed, and most of all the actual horizontal windspeed at the 
landing location is of great importance: if there is a strong horizontal 
windspeed on touch-down the DM will not only have to cope with a 
vertical speed (reduced by the soft-landing rockets), but also a 
horizontal speed (which is NOT reduced by rockets).  This horizontal 
speed can quickly  build up quite high: a  force 4 Bf wind (just an 
'average' wind) is already 8.2 m/sec, causing the cabine to go almost as 
fast 'sideways' as it is going 'down'.  Quite apart from the matter 
whether the soft landing rockets fired or not, a 'slight' wind at the 
landing location can already easily cause a 'rough' landing including a 
'bounce' an/or causing the cabine to be dragged along by the chute.

This also demonstrates that there is no 'easy' solution by increasing 
thrust of the soft-landing rockets or increasing parachute diameter. 
Quite apart from a 'winged' design, only solution would be a doppler 
radar (able to measure not only vertikal, but also horizontal speed) 
together with a far more advanced guidance system and variable thrust 
rockets, which should be able to make a complete 'powered descent' for 
the final 10-15 meters, reducing both vertical and horizontal speed to 
zero on touch-down. However, to make this possible we are talking about 
a complicated and expensive design which would have almost nothing in 
common with the present soyuz and would in itself be prone to a lot more 
possible failure-modes...

Regards,

Geert.





palladium at aol.com wrote:
> Avete, amici!
> Following the Soyuz near-disaster (which was, by the way, almost exactly duplicated the Soyuz reentry snafu recounted in my novel, Red Moon, which itself was based on the Soyuz 5 anomaly), a couple of questions came to mind:
> (a) How much time did the crew spend pulling high Gs in "eyeballs out" mode? Did any of them show physical signs of such stress-- i.e. redenned eyes or skin?
> (b) Is the orbital module jettisoned before or after retrofire?
> (c) Could the steeper descent and higher re-entry speed translate into a higher landing (or "impact") speed as well, accounting for the big "dent" observed in the tundra? Or would this be effectively nulled out once the parachute opens?
> D.S. Michaels
> -----Original Message-----From: Javier Casado <fjcasadop at yahoo.es>To: Geert Sassen <geert at navtools.nl>Cc: fpspace at friends-partners.org; "Mgr.Antonín Vítek,    CSc." <avitek at lib.cas.cz>Sent: Mon, 5 May 2008 9:35 amSubject: Re: [FPSPACE] Soyuz DM roll during ballistic entry profile
> Absolutely clear now, thanks to both, Geert and Antonin.
> In fact, as I see, the complication is not in the maneuver to get thisprecession movement, but in the capsule design. What they indirectly achievewith that CG offset is (in addition to the proper "natural" attitude forreentry) to get a main inertia axis for the vehicle that is not coincidentwith its simmetry axis. This way, a simple firing of the "roll" thrustersproduces a precession movement instead of pure roll. Ingenious.
> It is amazing to me how those old designers did so much with so little.Today, virtually no designer could calculate an inertia axis without CAD!
> Regards,
> Javier