PhysicalEnvironment in Space and its effects on Biological Systems
Theuniversal law of gravitation states that the force of attractionbetween two objects is directly proportional to the product of theirmasses and inversely proportional to the square of the distancebetween them. That is Fg= Gu
Where:Fgisthe force of gravity,
Guisgravitational constant (6.67384×10-11m3/kg.s2),
m1and m2 arethe masses of the two object,
risthe distance between the two objects.
Forcereduces at a constant of 0.25 its previous value as the distancebetween two object doubles. Therefore, to create a microgravity(10-6G)environment, a distance of 6.37 x 106km is required. The lower orbit of the earth is approximately threehundred kilometers from the surface of the earth. Therefore,microgravity in orbit does not mean absence of gravity.
Forceis equal to mass times acceleration. Therefore, acceleration (a)can be equated as a= Gu.Acceleration of any object at the earth’s surface is approximately9.8 m/sec2.This is called gravitational acceleration. On the other end,gravitational acceleration at the space station is 8.69 m/s2.Therefore, space shuttle in the orbit of the earth experiencesearth’s gravitational acceleration of 8.69 m/s2.However, this gravitational acceleration is counterbalanced by thecentrifugal acceleration produced by the space shuttle to create freefall around the earth.
Biologicalsystems in living things are adapted to functioning at earth’sgravitational acceleration. Therefore, change in gravity has profoundeffects on the functioning of human biological systems.Weightlessnessin space causes deterioration of weight bearing bones and muscles,fluid shifting, loss of blood plasma, and also affects the sensorymotor, neurovascular, the cardiac and the immune systems.Sedimentation of particles in fluids, which occurs in low gravity,reduces the effective movement of gas-filled volumes and vesicles dueto reduced buoyancy. This eventually causes flocculation of particlesin spherical shapes and autocoagulation. Humans are also exposed tohigh doses of radiations in space that ionizes cellular atomsresulting to mutations and rupture of chromosomes. Also, temperaturevariations, low gas molecular activity and lack of pressure in spaceaffects human biological systems.