SPIN RATE & GEOMETRY DESIGN
The total artificial gravity acceleration inside a rotating space habitat can be expressed as the vector sum of the centripetal acceleration, the relative acceleration and the Coriolis acceleration.
The magnitude of the nominal artificial gravity sensation in a rotating space station can be expressed by its centripetal acceleration where the artificial gravity force is equal to the centripetal force. Centripetal acceleration depends only of the angular velocity of the rotating object and its radial distance from the rotation axis, becoming larger for greater speed and smaller radius. Less radius means less total weight and implies less launching and material costs. Effects of the centripetal force could be accepted as artificial or simulated gravity and the whole system can be accepted as artificial gravity generator.
Rotation can cause important problems including the Coriolis forces provoked by any movement unparallel to the rotation axis. If a head is moved into a plane different then the plane of rotation, the inner-ear fluid movement keeps in the previous plane giving a disorienting and nauseating sense of rotation in the new plane. This sensation becomes worse with higher rotation rates and shorter radius of rotation. To obtain healthiest gravity it is needed to reduce the Coriolis forces to acceptable levels corresponded to the spin rate between 1 and 2 rpm and to increase the habitat’s tangential velocity. Taking in account the effects of the Coriolis forces. to produce the Earth normal gravity sensation (1g) with 2 rpm rate of spin, the radius of rotation have to be at least 735 feet with the tangential velocity of about 105 miles/hour. It is too ambitious in the short-term. Anyway, some steps could be made in the years to come making a smaller and cost-effective artificial gravity generators. The centripetal acceleration must have some minimum value to guarantee practical advantages of the artificial gravity. How much of artificial gravity is needed for long and healthy stays in space? Which is the optimal gravity? Inferior levels of gravity sensation could be also acceptable being more cost-effective to achieve them. Higher rotation rates then 2 rpm will reduce the ideal 735 feet radius still producing acceptable levels of the Coriolis forces.
A variety of experiments performed on people shown the following results:
- Min. radius: 39.4 feet.
- Maximum rotation rate: 3 - 6 rpm.
- Comfortable centripetal acceleration: 0,3•g - 1,0•g.
- Min. tangential velocity: 32.8 feet/second or 22.4 miles/hour.
As the artificial gravity acceleration equal to one third of the Earth gravity (approximately twice Moon gravity) is considered acceptable gravity level from medicine standpoint, a simplified, cost-effective and achievable EDGG could be designed in accordance with the following values of the four determining parameters:
ga = artificial gravity acceleration = g/3 = 10.62 feet/s2
r = radial distance from the center of the rotation = 62 feet
n = rotation rate = 3.95 rpm
v = tangential velocity of the rotating habitat = 25.66 feet/s = 17.49 miles/h