The problem of disorientation in a rotating spacecraft is treated as an example of the general case of habituation to an unusual motion environment using all sensors and active movements. The dynamic response of the sensors is stressed. Several avenues for work on combating disorientation are mentioned

Young, L. R.

English

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15. Human Disorientation in a Rotating Spacecraft* 
LAURENCE R. YOUNG 
Massachusetts Institute o f  Technology 
The problem of disorientation in a rotating spacecraft is treated as an example of the general 
case of habituation to an unusual motion environment using all sensors and active movements. 
The dynamic response of the sensors is stressed. Several avenues for work on combatting 
disorientation are mentioned. 
INTRODUCTION 
Before the first manned space flight launches, 
there were numerous predictions, many of them 
quite dire, about the deleterious vestibular reac- 
tions to be expected in weightlessness. Fortu- 
nately, a t  least in the early days of space flight, 
vestibular problems were minimal. We should 
not be led into a state of overconfidence regarding 
the possible seriousness of disorientation or mo- 
tion sickness in future space programs. Although 
the concern about motion sickness prior to the 
first manned space flight proved to be unfounded, 
the Soviet cosmonauts did report several in- 
stances of stomach awareness. The problem was 
raised again during the Apollo program, when 
the astronauts had a high incidence of vestibular 
related problems. Berry (ref. 1) reports five of 
the six crewmen on Apollo 8 and 9 reported 
symptoms of motion sickness, and one on Apollo 
10. In all cases, adaptation took place. Berry 
(in ref. 1) summarized his views of this problem 
in 1969: 
It appears that the opportunity to move about more 
freely in the Apollo cabin than in previous spacecraft is 
a factor producing the motion sickness problem. Sensory 
inputs from the semicircular canals to the central nervous 
system during head movements in space are thought to 
be enhanced due to altered activity of the otolith organs 
in the weightless state. This is a significant problem 
which must receive continued attention in the space pro- 
gram, for it can markedly affect astronaut performance. 
* Supported by NASA grants NGR-22-009-025 and 
NGR-22-009-156. 
Later Apollo flights (through 14) were appar- 
ently not subject to the motion sickness symp- 
toms. Astronaut Ed Mitchell (ref. 2) has 
commented on the recognition of a requirement 
for some pre-flight “vestibular training.” The 
Apollo 14 crew did considerable active flying in 
jets prior to their mission, and experienced no 
symptoms of motion sickness. The situation in 
regard to possible disorientation and motion 
sickness symptoms for non-astronauts in a space 
vehicle rotating to achieve artificial gravity is 
even less clear. 
The pending development of a space station 
to be used not only by pilot astronauts, but also 
by scientists for experiments and observation 
further points out the need to try to under- 
stand the expected orientation responses, both 
in weightlessness, and in a rotating spacecraft 
with its attendant problems of bizarre stimula- 
tion. The only direct experimental evidence 
which relates to this problem is from the Pensa- 
cola rotating room work which, although quite 
valuable in itself, is of course limited by the ever 
present 1 g from the earth’s gravitational field. 
One approach to research on possible disorienta- 
tion in a rotating spacecraft is through the 
extension of modelling of the vestibular system 
to make predictions as to the expected system 
response for different types of head and body 
motions in a rotating spacecraft. The physical 
forces, centrifugal and Coriolis, can be well pre- 
dicted and, we feel, can be used to make accurate 
predictions of vestibular outputs not only from 
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126 SEVENTH CONFERENCE ON MANUAL CONTROL 
semicircular canals and otoliths individually, but 
also on the basis of combined canal and otolith 
stimulation. 
The physical force field resulting from transla- 
tion or rotation inside a rotating spacecraft has 
been described in reference 3. In  vector form, the 
linear and angular acceleration stimulating the 
vestibular system are 
where the subscripts 
h-I indicate head, with respect to inertial 
space, 
h-B indicate head, with respect to the rotat- 
ing base, measured from the hub, 
W, is the angular velocity of the space sta- 
tion with respect to inertial space, 
F is the vector from the hub of the space- 
craft to the subject’s head. 
In  each of these equations, the acceleration 
sensed visually, with respect to the rotating 
spacecraft, is only the first term on the right-hand 
side. 
The term 2 (&X?h-B)  represents the Coriolis 
acceleration associated with linear velocity not 
parallel to the axis. It results in variations in 
radial force, which is higher when walking in the 
direction of spacecraft rotation, and lower when 
walking away. It also produces tangential accel- 
eration when moving radially, toward or away 
from the center. 
The term 6, X 6 h - B  represents the cross-coupled 
angular accelerations which stimulate the semi- 
circular canals about an axis normal to the head 
rotation and the spacecraft axis of rotation. 
To apply the vestibular models which have 
been developed for predicting human dynamic 
spatial orientation, the total acceleration must 
be used as stimulus, as seen in figure 1. (See also 
ref. 4.) 
MODELLING DISORIENTATION 
I N  UNUSUAL ENVIRONMENTS 
Jones (ref. 5 )  has pointed out the need to 
consider the dynamic characteristics of the vse- 
FIGURE 1.-Vestibular model applied to 
sensation in a rotating spacecraft. 
tibular sensors as well as the “bizarre stimulation” 
in predicting spatial orientation in a rotating 
environment, and refers to analog simulation 
using models such as shown in figure 1 as perhaps 
the best approach to the problem. At the present 
time, however, these models are still in their 
infancy and serve a true predictive role only in 
the most elementary case of dynamic space 
orientation : when the stimulus is pure rotation 
about an ‘(earth vertical” axis or vertical linear 
acceleration. The dynamic interaction between 
vestibular pathways and among different orienta- 
tion sensors is being investigated for active and 
passive motion in normal and unusual motion 
environments (ref. 6). 
A useful starting point is a taxonomy of dy- 
namic orientation situations, as follows: 
Case l.-Passive motion, no visual cues, pure 
rotation or translation. Examples : post rotation 
sensation; oculogravic illusion. 
Case 2.-Passive motion, no visual cues, con- 
sistent combined vestibular stimulus. Example: 
head motion in pitch or roll. 
Case 3.-Passive motion, all sensors, normal 
environment. Example : automobile passenger. 
Case 4.-Passive motion, all sensors, conflict 
between sensors. Examples : simulator sickness, 
airplane turning illusions. 
Case 5.-Active motion, all sensors, not 
habituated to unusual environment. Example : 
first hours aboard ship. 
Case 6.-Active motion, all sensors, habitua- 
tion to  specific motion pattern. Example: skater’s 
habituation to spins. 
Case 7.-Active motion, all sensors, habitua- 
tion to general motion in unusual environment. 
Example: ‘(sea legs.” 
Clearly, the situation of free motion in a 
HUMAN DISORIENTATION I N  ROTATING SPACECRAFT 127 
the radial is 
I 
EXAMPLE 'SEALEGS" 
SLOW ROTATlNG ROOM 
ROTATING SPACECRAFI 
FIGURE 2.-Case 7: active motion, all sensors, habitua- 
tion to general motion in unusual environment. 
rotating spacecraft belongs to case 7, which is 
shown schematically in figure 2. 
SOME APPROACHES TO 
REDUCING DISORIENTATION 
Consideration of practical solutions to the 
problem of reducing to a minimum the discomfort 
and performance decrement in a rotating space- 
craft leads to several avenues to be explored (refs. 
7 through 9). Many of these have been mentioned 
by others and some of them appear highly im- 
practical at this point. Nevertheless, the sugges- 
tions for investigation are 
(1) Devise active movement training sched- 
ules for habituation. Regulate schedule by mea- 
suring disorientation so as to minimize habituation 
time and symptoms of disorientation. 
(2) Design the visual surround to have no 
outside view which cannot be shut out, no strong 
visual verticals or horizontals, distinctive colors 
for all walls having the same orientation with 
respect to  the spacecraft motion. 
(3) Orient cabins and work stations so that 
most walking is parallel to the axis of rotation; 
and head movements are nodding motions about 
that axis (ref. 8). 
(4) Construct radial stairs or ladders to curve 
(against the direction of spacecraft rotation for 
ascending and in the direction of rotation for 
descending) so that the direction of the apparent 
vertical does not change relative to the subject 
ascending or descending at a constant rate. (Of 
course, this condition does not apply to the limbs 
because of their reciprocating motion.) The 
transcendental equation for angle 0 away from 
cot e = (To,, - 2v sin e)/v cos e 
where r is the radius and v is the man's relative 
velocity. 
As an example, for w,=O.5  rad/sec (4.8 rpm) 
at a radius of 6.1 m (20 ft) and relative velocity 
of 0.58 m/sec (1.9 ft/sec), the passageway should 
be tilted by ten degrees. Of course, a simpler 
solution is to provide two-sided radial ladders in 
which one ascends by facing into the direction 
of spacecraft rotation and descends facing away 
from this direction, so that Coriolis forces always 
push the subject toward the ladder. 
(5)  Finally, variable individually controlled 
visual surrounds could be further investigated. 
We have had initial success in reducing disorien- 
tation in single axis rotations by displaying a 
pattern of moving stripes which is driven in 
agreement with the semicircular canal model 
prediction of this sensation of rotation. We are 
currently experimenting with a three axis system 
using a diffuse large field Moire pattern. 
One could imagine a device utilizing a head 
mounted CRT and head position monitor to 
display a "combatible scene" during head move- 
ments. This visual pattern could be arranged to 
approach the actual spacecraft visual surround 
as the subject habituated to the effects of active 
head movements in a rotating environment. 
1. 
2. 
3. 
4. 
5. 
6. 
REFERENCES 
BERRY, C. A.: Summary of Medical Experience in the 
Apollo 7-11 Manned Spaceflights. Recent Advances in 
Aerospace Medicine, Douglas E. Busby, ed., Dor- 
drecht, Holland. D. Reidel Publishing Co., 1970, pp. 
MITCHELL, E. : Personal communication. Cambridge, 
Mass., Apr. 1971. 
STONE, R. W., JR. ; AND LETKO, W.: Some Observa- 
tions on the Stimulation of the Vestibular System of 
Man in a Rotating Environment. The Role of the 
Vestibular Organs in the Exploration of Space. NASA 
YOUNG, L. R.: The Current Status of Vestibular 
System Models. Automatica, vol. 5, 1969, pp. 369-383. 
MELVILL JONES, G.: Dynamic Cross-Coupling in the 
Semicircular Canals. Recent Advances in Aerospace 
Medicine, Douglas E. Busby, ed., Dordrecht, Holland. 
D. Reidel Publishing Co., 1970, pp. 235-248. 
GUEDRY, F. E., JR.: Conflicting Sensory Orientation 
3-41. 
SP-77, 1965. 
128 SEVENTH CONFERENCE ON MANUAL CONTROL 
Cues as a Factor in Motion Sickness. Fourth Sym- 
posium on the Role of the Vestibular Organs in Space 
Exploration. NASA SP-187. 
7. GRAYSIEL, ASHTON; THOMPSON, ALLEN B.; DEANE, 
ROBERT; FREGLY, ALFRED R.; COLEHOUR, JAMES K.; 
AND RICKS, EDWARD L., JR.: Transfer of Habituation 
of Motion Sickness on Change in Body Position 
Between Vertical and Horizontal in a Rotating 
Environment. Aerospace Medicine, vol. 39, no. 9, 
Sept. 1968, pp. 950-962. 
8. LORET, B. J.: Optimization of Space Vehicle Design 
with Respect to Artificial Gravity. Aerospace Medi- 
cine, vol. 34, no. 5, May 1963, pp. 430-441. 
9. HELD, RICHARD; AND FREEMAN, SANFORD J.: Plas- 
ticity in Human Sensorimotor Control. Science, vol. 
142, no. 3591, Oct. 25, 1963, pp. 455-462. 


Human disorientation in a rotating spacecraft

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