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

[Jim Oberg]

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?



----- Original Message ----- 
From: "Geert Sassen" <geert at navtools.nl>
To: "Jim Oberg" <jeoberg at comcast.net>
Cc: <fpspace at friends-partners.org>
Sent: Friday, April 25, 2008 9:12 AM
Subject: Re: [FPSPACE] How tightly are the Soyuz modules bolted together?


> Good day Jim,
>
> When the SAS system fires, the PO is left behind attached to the last 
> rocketstage, only the BO and DM are lifted clear (f.i. ref 'Challenge to 
> Apollo' page 574), the SAS is attached to the BO, so the DM is lifted up 
> by its connecting bolds to the BO, and when these are severed it drops out 
> of the shroud for emergency landing.
>
> With regards to the Soyuz 11 tragedie it was noted that 12 explosive bolts 
> fire to separate the Soyuz into its three compartments (ref 'Challenge to 
> Apollo', page 783), however this probably includes the bolds attaching BO 
> and DM. In 'Soyuz' from Hall/Shayler it is mentioned that 6 explosive 
> bolts and 6 pyrocharges are used for the separation of BO and DM, and 6 
> pyrocharges for the separation of PM and DM, while 8 pyrocharges are used 
> to separate cables from the PM to the BO,  4 for separating the coolant 
> lines, 11 for separating backup control lines, and 2 are used for 
> separating the periscope of the DM ("Soyuz", ISBN 1-85233-657-9, page 46), 
> however this might relate to the original Soyuz version and might have 
> changed with the various versions.
>
> I could not find any reference to a redesign of the BO/DM separation after 
> Soyuz 5, although the narative of Volynov sure sounds even worse then the 
> reports from the last two missions. I noted the remark that on the latest 
> landing the units separated at the start of re-entry 'as they are designed 
> to do', while the Volynov report describes a quite heavy explosion 
> (probably of the PO fuel tanks) which separates the compartments, so this 
> sounds a bit like the apparent re-design includes a back-up system which 
> kicks in as soon as re-entry heat or decelleration is measured, but I 
> can't find any info on this.
>
> Also I have not yet found a clear description of the way the system is 
> switching to 'ballistic descent'. This includes (requires) a constant roll 
> of the DM, however in the case of Soyuz 5 it is noted that all the DM fuel 
> was exhausted very early in the re-entry, when the system was trying (and 
> failing) to stabilise the DM in its correct attitude, so if all fuel was 
> already exhausted, how was this constant roll achieved?
> To me it sounds a bit like the whole combination is placed in a constant 
> roll prior or shortly after retrofire, using the PM thrusters. If 
> everything works correctly, this roll is stopped by the DM thrusters where 
> after the normal re-entry guidance kicks in, however if this doesn't work 
> then the DM is already rolling so in a worst case scenario no further 
> action is required for a ballistic re-entry (CG location will take care 
> that it rightens itself in the correct attitude). This explains how Soyuz 
> 5 could make a ballistic descent with all fuel depleted, but it's only my 
> guesswork, can't find any clear description of this. I also seem to 
> remember reading somewhere (with regards to Soyuz stock-life, which is 
> basically defined by the degration of H2O2 fuel of the DM thrusters) that 
> in a worst-case scenario the DM can make a safe (ballistic) landing 
> without using the thrusters, which once again seems to imply that the 
> required roll is achieved by some other means.
>
> Regards,
>
> Geert.
>
>
> Jim Oberg wrote:
>> If the Soyuz modules (DM and PO) did not separate cleanly when commanded 
>> to last Saturday, how much force was required to complete the separation, 
>> and where did that force come from?
>>
>> Since the 1969 very-near-disaster (and I talked with Volynov for an hour 
>> about that in 2005, getting some corrections to my own 2002 narrative of 
>> the incident, mainly how he survived post-landing), apparently the force 
>> required to pull away has been designed to be much gentler. No unyielding 
>> cables or bolts, just nested slip-joints and plugs held in place during 
>> launch (and orbital maneuvers) by thrust vectors and minimal tightness, 
>> but ready to slip free with far less force than required in the 1960s.
>>
>> Still, doesn't the SAS (escape tower) firing sequence still show the 
>> entire spacecraft, PO (equipment section) included, pulling free at tower 
>> firing, and then the PO being separated and falling out of the aero 
>> shroud before the DM (descent module) does? That implies VERY strong bolt 
>> connectors. Or is the fully fuelled PO left atop the third stage from the 
>> moment of initiation of the escape system? This requires only strong 
>> BO/DM bolts.
>>
>>
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