[FPSPACE] Soyuz DM roll during ballistic entry profile

Thu May 8 19:55:27 EDT 2008

Not sure about A and C, but orbital module is certainly jettisoned after braking maneuver, as shown in these animations:

http://www.russianspaceweb.com/soyuz_flight.html

This was the lesson of a 1988 incident, when the Soyuz was stranded in orbit without the habitation module and critical life-support facilities it contains:

http://www.russianspaceweb.com/mir_close_calls.html

Anatoly Zak

----- Original Message -----
From: palladium at aol.com
Date: Thursday, May 8, 2008 6:36 pm
Subject: Re: [FPSPACE] Soyuz DM roll during ballistic entry profile
To: fjcasadop at yahoo.es, geert at navtools.nl
Cc: fpspace at friends-partners.org, avitek at lib.cas.cz

> 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 am
> Subject: 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 this
> precession movement, but in the capsule design. What they 
> indirectly 
> achieve
> with that CG offset is (in addition to the proper "natural" 
> attitude for
> reentry) to get a main inertia axis for the vehicle that is not 
> coincident
> with its simmetry axis. This way, a simple firing of the "roll" 
> thrusters
> produces 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
> 
> 2008/5/5 Geert Sassen <geert at navtools.nl>:
> 
> > The shape of the soyuz cabine is such that with aerodynamic 
> forces 
> acting
> > on it, it will automatically seek a stable attitude in which the 
> vector
> > connecting centre of volume and centre of gravity is pointing 
> exactly 
> in the
> > direction of movement. However, as the centre of gravity is 
> offset in
> > regards to the 'vertikal' axis of the DM, this attitude will 
> generate 
> an
> > angle of attack of less then 90 degrees, which again will result 
> in a 
> 'lift'
> > vector (TF) perpendicular on the vertikal axis.
> >
> > Now, when you roll the DM a certain angle, the line connecting 
> centre 
> of
> > volume and centre of gravity will no longer be pointing in the 
> flight> direction, and in order to seek a new aerodynamically 
> stable 
> position, the
> > aerodynamic forces will cause a certan pitch and/or yaw of the 
> DM. 
> This in
> > turn results in a change of the angle of attack, which then in 
> turn 
> results
> > in a change of the direction of the lift (TF). So basically, by 
> only 
> using
> > your roll thrusters, you will cause a change in pitch and yaw and 
> this will
> > cause a change of angle of attack and thus of generated lift.
> >
> > Using this system you will not need to use the pitch and yaw 
> thrusters> during descent, the only thrusters used in this part of 
> the descent 
> are the
> > roll thrusters, by controlling the roll angle you automatically 
> control
> > pitch and yaw due to the offset CG and the shape of the DM. To 
> say 
> the DM is
> > 3-axis stabilised during a normal 'lifting' descent is a bit 
> misleading, in
> > fact you are only controlling the roll angle and the aerodynamic 
> forces do
> > the rest.
> >
> > Using this system it is extremely important that you know the exact
> > location of the CG (this is why the soyuz has moving 
> counterweights 
> near the
> > chairs which have to be set in a certain position), any error in the
> > location of your CG will result in an targeting error in your 
> landing> location.
> >
> > During a ballistic descent you need to 'null' the lift force or 
> else 
> you
> > might get into a situation where the lift-vector is accidently 
> making 
> your
> > trajectory steeper instead of more shallow. The only method to 
> 'null' 
> the
> > lift is by introducing a constant, slow, roll of the DM. Once 
> again, 
> due to
> > the offset CG and the shape of the cabine, this will result in a 
> pitch and
> > yaw movement (precession), in fact you introduce a 'corkscrew' 
> motion 
> to the
> > DM during descent, however as the TF ('lift') vector is now 
> turning 
> 360
> > degree circles, the average effect will be a zero-lift ballistic 
> trajectory.
> >
> >
> >
> > Mgr.Antonín Vítek, CSc. wrote:
> >
> > The "roll" is rather slow - 17 deg/sec and exyactly it is not 
> simple 
> roll,
> > but precession o symmetry axis aroun velocity vector. Due to the 
> fact,> that CG has som offset from the symmetry axis of DM. 
> ThereforeDuring 
> the
> > precession rotation the TF actually makes 360 deg turns with the 
> above> said (17 deg/sec) angular velocity. As a result, the 
> trajectory is
> > "ballistic" i.e. without any lateral force. As a resut, the 
> descent it
> > steeper, landing spot in nearer to the point orf EI and the 
> landind 
> time
> > is aearlier than in normal (i.e. aerodynamically controlled) descent
> >
> >
> >
> > Sorry for coming so late with comments about this matter (I had 
> lots 
> of
> > unread mails), but I disagree with the role of the roll that has 
> been> proposed here for the Soyuz ballistic descent.
> >
> >
> > As Antonin said:
> >
> >
> >  "the angle between symmetry axis of DM and the velocity vector 
> (angle of
> > attack) is maintained automatically 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)."
> >
> >
> > Ok, I agree with that. However, rolling the capsule doesn't mean 
> you'll
> > roll
> > the TF vector: since the DM is a revolution body, its roll does 
> not 
> affect
> > its aerodynamic properties (except for a very small Magnus effect 
> that may
> > appear; this would create a small lateral velocity vector, in 
> addition to
> > the lift called TF by Antonin). In other words: if the angle 
> between 
> the
> > capsule's velocity vector and its symmetry axis (that is, the 
> angle of
> > attack) does not change, then the lift direction does not change, it
> > doesn't
> > matter if the capsule rolls or not. So, rolling the capsule does 
> not 
> mean
> > to
> > roll the lift vector, thus "neutralizing" it; the lift keeps 
> pointing 
> the
> > same direction, independently of the roll.
> >
> > What is the purpose of the roll, then? In my opinion, it is 
> simply for
> > stabilization. Jim said that "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", but this is not exactly true. I 
> mean,
> > yes,
> > the required attitude is naturally attained by means of the 
> center-of-mass
> > distribution, but without some kind of added stabilization (that 
> supplied
> > by
> > the roll), this attitude would be much prone to perturbations,
> > oscillations,
> > etc. The capsule is spin-stabilized during descent to maintain 
> "stable"
> > the
> > natural attitude attained by its center-of-mass position.
> >
> >
> > In a "normal" descent, however, the capsule is not spin-
> stabilized, 
> but it
> > has a 3-axis stabilization achieved by its ACS thrusters. I 
> suppose 
> that
> > this is changed to spin-stabilization in the case of ballistic 
> descent> simply for safety (no dependence on the ACS).
> >
> >
> > Regards,
> >
> >
> > Javier Casadohttp://es.geocities.com/fjcasadop
> > <fpspace at friends-partners.org> <fpspace at friends-partners.org>
> > _______________________________________________
> > FPSPACE mailing 
> listFPSPACE at friends-partners.orghttp://www.friends-
> partners.org/mailman/listinfo/fpspace
> >
> >
> >     Mgr. Antonin Vitek, CSc.
> >
> > Office: Main Library, Academy of Sciences of the Czech Republic
> >   Narodni 3, CZ-11522 Praha 1 - Phone: +420/221 403 255, fax 
> +420/224 
> 240 611
> > Home: Kytin 127, CZ-25210 Mnisek p. B., Czech Republic
> > Phone: +420/318 592 865, cell +420/603 148 201 - Coord.: 14.2178 
> deg 
> E,
> > 49.8485 deg N, 442 m ASL
> > My satellite home page: 
> http://www.lib.cas.cz/www/space.40/index.html> Home e-mail: 
> avitek at seznam.cz>
> >
> > _______________________________________________
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> >
> >
> >
> >
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Anatoly Zak
http://www.russianspaceweb.com