PSY 873 (Dr. Albery)  

 

Problem Paper  #7

 

31 May 1995

 

Kaz Shimada, M.D.

 


1          Problem #7

 

On L+5 day a space shuttle orbiter began rotation around its y-axis at 12 rpm for an hour.  Commander is at 22 feet forward of the y-axis.

 

2          At 10 sec into rotation, what is CMDRÕs symptoms?  Nystagmus or turning sensation?

 

Because threshold for oculogyral illusion for humans is 0.11û/s2, even if CMDR had no visual cues, he/she will recognize during acceleration phase from 0 to 12 rpm that there is a rotation of the vehicle, that it is not a linear acceleration along its x-axis.

 

Turning sensation - yes.  When angular acceleration is stopped suddenly (shuttle turning at constant velocity), turning sensation persists because time constant for onset of low-frequency cupula response in humans is about 10 seconds.  Steady state for cupula deflection is not yet returned to neutral position 10 seconds after the cessation of angular acceleration.  It takes about 30 seconds for steady-state.  Because of zero angular acceleration, cupula response is diminishing at 10 seconds into constant angular velocity turning.

 

Nystagmus - yes.  CMDR is supposed to have vertical nystagmus whose quick phase direction is the same as direction of the turn of the vehicle, and which is diminishing in amplitude.

 

Because of conflict in senses, CMDR might have some uneasy feeling or motion sickness symptoms.  Otolith sensing linear acceleration, and semicircular canals sensing rotation. 

 

3          What is difference if eyes are open or closed?

 

Eyes open - visual cue will be stationary when window view is unavailable; it will conflict with otolith and semicircular canal information.  If outside view is available, it still might conflict with otolith cue.  More, it is possible that when window is filled with ground image, autorotational sensation would be felt because of vection illusion.

 

Eyes closed - there will be conflict between otolith and semicircular canal information.

 

These sense will be declined after 30 seconds into constant speed rotation of the vehicle.

 


4          What G force is acting?

 

Assuming this is a simple (not a coupled) solid body rotation around a fixed axis, centrifugal force vector at CMDR position is approximately pure +Gx (eye-ball out).  Here some cephalic deviation of the vector is neglected (cockpit is in the upper deck).  Length of the +Gx vector is:

 

    

 

Thus there is no substantial negative effect in terms of control operations.  This is statically equivalent to pilot restrained in a seat and facing to the ground on earth.  If CMDR is reaching to instrument panel, Gx at hand will be 1.2 G (at 24 feet).  There is no large G gradient for body motor functions.

 

5          What symptoms occur when CMDR move his head at 5 minutes after the rotation commences?

 

Five minutes after the rotation of the vehicle stabilized (constant angular velocity rotation), semicircular endolymph dynamics will be stationary, and no rotational sensation is felt when CMDR head is stable.  His/her otolith is sensing 1.1 Gx.  This is equivalent to shuttle nose pointed to the ground in atmosphere.

 

When CMDRÕs head is moved, cross-coupling acceleration will be exerted on semicircular canals.  One plane of rotation is orbiter rotation about its y-axis.  The other is head motion pivoted around cervical spine.  The amount of resultant cross coupling is Iωxθ˙.  When planes of two rotations are parallel, there is no cross coupling (when CMDR move head in sagittal plane.)  In this case, movement of head in coronal plane produces cross coupling acceleration to semicircular canals, which induces Coriolis stimulation effect.

 

There is an temporary proposal for the magnitude of cross coupling aboard artificial gravity spacecraft, which is 2 rad×sec- 2.  A range of rapid head motions possible for man is from 2.5 to 3.5 rad/sec.  When vehicular rotation is at 12 rpm and head angular movement is at 2 rad/sec, resultant cross coupling is approximately 2 rad×sec- 2, which is the limit for Coriolis effect.

 

Thus there is a good chance for CMDR to have Coriolis illusion if head is moved.  How this is modified by 5-day microgravity exposure is uncertain.

 

Since the direction of centrifugal acceleration  is along body x-axis, cardiovascular collapse from hydrostatic body fluid dynamics is unlikely.

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