Cometary Tails
Comets have two tails. The type 1 tail points directly away from the Sun. Observations have been made of a part of this tail disconnecting, and accelerating away in the direction of the tail. This feature is consistent with the ideas on Dynamic Gravitational Fields.

A requirement is that the Comet should be ROTATING, and at a rate sufficient to create it's own Dynamic Gravitational Field, although it is possible that this field could also be the result of the comets enormous velocity as it accelerates towards the Sun, and composed of suitable materials, probably of a magnetic nature.  This field would indeed point away from the Sun, exactly as our Planet's Field does.

 If the portion of the tail directly behind the head, which tends to accelerate away at times, were to be in the form of an Electric Field similar to that found in the Earth's atmosphere, but perhaps swept to the rear, then it would indeed accelerate away from the head if it became physically disconnected, or ejected, from the head. It would be attempting to find the center of gravity of the comets D G Field. Also of interest is the fact that comets appear to create their own light source,  indicating not only rotation and an electric field, but  perhaps also an atmosphere.
Anywhere that we find acceleration away from a rotating body, we have another indication that the ideas relating to building a machine to mimic these effects may not be too absurd.
                                          Asteroid or Comet  Heating and Light Emissions