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.