The Human Eye in Space

Human visual hardware is a result of a billion years

of evolution within the earths atmosphere where

light is scattered by molecules of air, moisture,

particular matter etc. However as we ascend into

our atmosphere with decrease density, light

distribution is changed resulting in our visual

hardware receiving visual data in different format.

Some Aspects to Consider: 1. Visual acuity is the

degree to which the details and contours of

objects are perceived. Visual acuity is usually

defined in terms of minimum separable.Large

variety of factors influence this complex

phenomenon which includes : # Optical factors-

state of the image forming mechanisms of the eye.

# Retinal factors such as the state of the cones. #

Stimulus factors such as illumination, brightness of

the stimulus, contrast between the stimulus and

background, length of time exposed to the

stimulus. * Minimum separable: shortest distance

by which two lines can be separated and still be

perceived as two lines. "During the day, the earth

has a predominantly bluish cast..... I could detect

individual houses and streets in the low humidity

and cloudless areas such as the Himalaya

mountain area.... I saw a steam locomotive by

seeing the smoke first..... I also saw the wake of a

boat on a large river in the Burma-India area...

and a bright orange light from the British oil

refinery to the south of the city (Perth,Australia.)"

The above observation was made by Gordon

Cooper in Faith 7 [1963] and which generated

much skepticism in the light of the thesis by

Muckler and Narvan "Visual Surveillance and

Reconnaissance from space vehicles" in which

they determined that a visual angle of ten minutes

was the operational minimum, and that the

minimum resolvable object length [M.R.O.L] at an

altitude of 113 miles would be 1730 ft. This

limitation of acuity was revised the next year to 0.5

seconds of arc for an extended contrasting line

and 15 seconds of arc for minimum separation of

two points sharply contrasting with the

background. Orbiting at 237 miles in the skylab it

was possible to see the entire east coast [Canada

to Florida Keys] and resolve details of a 500 feet

long bridge based on inference. Of Interest is the

fact that even though the mechanical eye [camera

systems] can resolve objects greater than fifty

times better than the human eye, without the

human ability to infer, interpretation of the data is

meaningless. Conclusion: Visual acuity in space

exceeds that of earth norm when objects with

linear extension such as roads, airfields, wake of

ships etc. 2. Stereoscopic vision: the perception of

two images as one by means of fusing the

impressions on both retinas. In space one has to

deal with a poverty of reference points. For

hardware evolved in a reference oriented

paradigm, this possess a grave