Defensetech's Noah Shachtman says,
All space projects get into orbit pretty much the same way – by burning lots of rocket fuel, a spaceship powers itself past the sky. NASA and the Army Research Lab have another idea: "Slingatron," a giant, hypervelocity, rapid-fire slingshot. The machine would spin a projectile faster and faster through a spiral-shaped tube, building up increasing amounts of centripetal force along the way – just like a discus-thrower, spinning himself around before a toss, or like a latter-day King David, winding up his weapon before he whacks Goliath.
Reader comment: Dr. Paul J. Camp, in the Physics department of Spelman College in Atlanta, GA says,
The explanation on this item says: "The machine would spin a projectile faster and faster through a spiral-shaped tube, building up increasing amounts of centripetal force along the way."
A. The centripetal force vector points toward the center of the path. It can only change the direction of the velocity but has no effect on the speed of the projectile. For that, you need a force with a component parallel to the velocity (a tangential force).
B. Forces don't "build up." A force cannot be accumulated over time, to be used at a later date. Forces result from interactions between particles and are fixed in size by the nature of the interaction. For example, the electric force depends only on the amount of charge on each particle and the distance between them. Allowing two charges to interact for a week will produce no more or less force than allowing them to interact for a nanosecond.
This device is nothing but a cyclotron for macroscopic particles (see the Wikipedia article on same).