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

Geert Sassen geert at navtools.nl
Fri Apr 25 10:12:27 EDT 2008

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.



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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