What is a Screw Rocket and how can I use it to move an asteroid?

I ran across this recent paper on the use of screw-rockets for asteroid deflection. Screw rockets seem similar to nuclear powered mass deflection, which is a concept that SEI has examined, notably of multiple mass drivers. Interesting that it was submitted for the Chinese Journal of Astronomy and Astrophysics. Note: The SEI MADMEN concept is not referenced in the paper.

Reference:
Asteroid Deflection: How, where and when?
Authors: D. Fargion
(Submitted on 12 May 2007 (v1), last revised 3 Sep 2007 (this version, v3))
Chin. J. Astron. Astrophys. Vol. 0, No. 0, (200x) 000–000
Chinese Journal of Astronomy and Astrophysics

Abstract:
To deflect impact-trajectory of massive km^3 and spinning asteroid by a few terrestrial radius one need a large momentum exchange. The dragging of huge spinning bodies in space by external engine seems difficult or impossible. Our solution is based on the landing of multi screw-rockets, powered by mini-nuclear engines, on the body, that dig a small fraction of the soil surface, to use as an exhaust propeller, ejecting it vertically in phase among themselves. Such a mass ejection increases the momentum exchange, their number redundancy guarantees the stability of the system. The slow landing (below 40 cm s^-1) of each engine-unity at those lowest gravity field, may be achieved by save rolling and bouncing along the surface. The engine array tuned activity, overcomes the asteroid angular velocity. Coherent turning of the jet heads increases the deflection efficiency. A procession along its surface may compensate at best the asteroid spin. A small skin-mass (about 2 10^4 tons) may be ejected by mini nuclear engines. Such prototypes may also build first save galleries for humans on the Moon. Conclusive deflecting tests might be performed on remote asteroids. The incoming asteroid 99942 Apophis (just 2% of km^3) may be deflected safely a few Earth radius. How to tag its trajectory is described. Its encounter maybe not just a hazard but an opportunity, learning how to land, dig, build and also to nest save human station inside. Asteroids amplified deflections by gravity swing maybe driven into longest planetary journeys.

Link: Abstract

Link: PDF of Paper

Link: SpaceWorks Engineering, Inc. (SEI) paper on multiple mass drivers for asteroid deflection (from the 2007 Planetary Defense Conference)

Link: SpaceWorks Engineering, Inc. (SEI) presentation on multiple mass drivers for asteroid deflection (from the 2007 Planetary Defense Conference)