Launching Spacecraft with Centrifugal Force

Could centrifugal force ever be used to achieve the difficult, high-energy objective of launching a spacecraft? This idea was indeed proposed, more than a century ago.

Fig. 1  A spacecraft launching system proposed by French
engineers in the early 20th century

My initial reference for most of what follows is The Dream Machines, a Pictorial History of the Spaceship in Art, Science and Literature, by Ron Miller, Krieger Publishing Company, 1993.

The Mas and Drouet catapult

In "La Catapulte tournant de Mas et Drouet", L'Avion 1913, French engineers Andre Mas and M. Drouet proposed attaching a projectile to the rim of a spinning wheel (shown at
http://www.bdfi.info/img_forum/petitinventeurgraffigny1.jpg). When the projectile reached a high enough speed, it would be detached and launched vertically, into space.

A very similar idea was proposed two years later by H. de Graffigny.

Fig. 2  The Fezandié launching system, illustrated by Frank R. Paul

The Fezandié catapult

In his story "A Car for the Moon", Science and Invention magazine, September 1923, author Clement Fezandié again proposed a similar idea. In this case the 30 ft diameter wheel is spun by the electric motor beneath it. The radial distance of the two-passenger craft is gradually increased by feeding out the chain between it and the wheel's axis, as shown. At maximum radius and speed, the craft is released.

Obviously the Fezandié system, as drawn, requires some method of keeping the craft correctly oriented. This would include, among other things, swivel links in its chain. But assuming such details were sorted out, what velocity must the projectile/craft reach, and what acceleration must it withstand in reaching it?

Escape velocity

The velocity required to launch a projectile so that it escapes entirely from the Earth's gravitational influence is about 11.2 km/sec, ignoring the effect of the Earth's atmosphere. However, in practice we cannot ignore the atmosphere, which would cause most objects travelling at this speed (nearly Mach 34) to break apart and/or burn up.

Acceleration and "g-forces"

In the system shown in Fig. 1, with the wheel turning at 40 turns/second = 251.33 radians/sec, the projectile at 50 meters radius will experience a centripetal acceleration of ω²r = 3,158,338 m/s² (nearly 322,061g). So it and the similar Fezandié system, with its chain at any reasonable length, would both exert higher g-forces than any structural material, much less a human being, could withstand.

So, it is not practical to launch a spacecraft by the centrifugal-force method discussed, because of the serious problems arising from the very large velocity and centripetal acceleration required.

A force perpendicular to the radius

I'll end this post by pointing out that the force accelerating the circumferential speed of the projectile must be exerted perpendicular to the radial line from it to the wheel's center. This leads into the concept of inertial propulsion by Coriolis force, to be discussed next time.