Current concepts on medical problems of space flight are outlined. A critical discussion of several aspects and a few original items are contributed. The following points are given special consideration:

1. Biorhythmics.

The space flight situation will inevitably lack the normal diurnal periodicity. The physical and chemical determinants of this periodicity are not yet fully understood as to their physiological repercussions. Illumination, electric potentials, ionisation, humidity, temperature etc. will probably have to be artificially controlled in a rhythmic fluctuation.

2. Body perception during weightlessness.

According to the literature this function would be lost. Arms and legs would be floating in a virtually unknown and consequently uncontrolled manner; attached to the body they would no longer be its functional members. Whereas it is true that gravity-induced traction and pressure are no longer existing within the body it should however not be concluded that consequently these forces are totally lacking. They stem as well from the interplay between flexors and extensors giving rise to an influx of proprioceptive information. The situation of weightlessness is in this regard not unlike that of floating in water.

3. Motoric and, more specifically, locomotoric activities during weightlessness.

a. The activities require great wariness and adroitness. In order to minimize accidentally incurred collisions, walls and objects within the space ship should be smooth with rounded corners and resilient surfaces.

b. Muscular atrophy is without doubt in the long run a feared consequence of weightlessness. However there is no reason to expect complete muscular inactivity.

4. The introduction of an artificially created, centrifugal, weight in a manned satellite (space station) poses several problems.

a. "Free-falling" objects will - relative to an inertial system outside the satellite - pursue a straight path, determined by the tangential velocity at the moment of free-falling. Viewed by an observer within the satellite the path will not coincide with the vertical.

b. An inmate of the satellite will experience weight changes when moving to and fro. Following the satellite's direction the weight will increase; conversely, walking in the opposite direction the weight will decrease.

c. Walking within the satellite the satellist will experience progressive changes in body position, in this experience the visual - graviceptive - and semicircular sensory information are mutually conflicting.

d. Rotations of the head occurring around an axis not parallel with the axis of the satellite will provoke "false" impulses in the semicircular canals. This will lead to tilting sensations and tilting reactions. A mathematic analysis of these effects is given in chapter 5 with a note on the possible untoward general repercussions. For these latter the descriptive term of satellite-sickness was chosen as a special variant of motion-sickness or kinetose.

5. Motion-sickness as a clinical entity.

The pro's and con's of a strictly vestibular theory are weighed against the virtues and shortcomings of a broader concept in which due attention is also given to psychic, neurovegetative and other factors. The preselection tests to determine individual susceptibility will, according to the theory adhered to, be essentially differently designed. A follow-up study of candidate pilots is given; the results seem to lend support to the broader concept of motion-sickness.

6. The confinement in a small space ship may well prove to be a heavy burden on the psychic endurance of the occupants.

Existential and phenomenologic concepts are adduced to visualize the picture of which, as yet, our knowledge can only he based on data from more or less similar situations. The "break-off" phenomenon is discussed. In order to facilitate the exchange of thought in a general medical idiom the word "ecplexia" is proposed as a synonym of "break-off".

7. The physiologie accommodation in an empty visual field.

Whereas a stimulus free field (= empty visual field) may occur at high altitudes in the atmosphere this state of affair does no longer prevail when the outer boundaries of the atmosphere are reached and crossed. In space there is always a star-laden sky visible since the atmospheric light-dispersion is no longer present to veil the starlight. The conclusion seems warranted that conditional myopia from optic emptiness is no problem of space medicine.

The envisaged accelerations for rocket propulsions and emergency-capsule ejections require protective devises. As such is proposed a free swinging self directing capsule in which the man is always in an optimal position whatever the direction of the resulting accelerations is. Within this capsule the man could be placed in a tub. In this state of immersion the principle of Archimedes might materially boost the g-tolerance and even lend substantial protection against crash injuries. A further asset of this principle is the freedom it furnishes to arms and legs to execute any (fine) movement.

9. Telecommunication.

In interplanetary flight all efforts should be made to establish optimal radio contact. To counteract the distance-attenuation of the signal, a directed beam - very short wavelength - will have to be used.

10. Artificial weight in space ships.

Just as in the instance of the manned satellite - the space station - an artificially created weight should be introduced in the much smaller ships designed for interplanetary flights. To this end a proper solution seems to be feasible by building a two-cabin ship. The cabins are interlinked by cable or tube and are made to rotate around their combined centre of gravity.