Averaging of equations of cometary orbital motion with allowance for nongravitational effects

A study was made of a Keplerian elliptical cometary orbit experiencing some nongravitational perturbing acceleration with the components S, T, W in an orbital coordinate system. After writing the equations for perturbed motion, the equations are averaged (this requires stipulation of the law of changes of perturbing nongravitational acceleration as a function of heliocentric distance r). A simplified law of continuous change in the components of reactive acceleration is selected and the rates of secular changes in the elements of the cometary orbit under the influence of nongravitational reactive acceleration are determined. Formulas are derived which can be used in predicting cometary orbits. It is shown that the components of relative velocity of gas escape can attain several kilometers per second. The estimates made by the proposed method are consistent with the high velocities of axial rotation of the nucleus of Halley's comet. With rapid rotation of the nucleus the radial gas jet initially directed toward the Sun as a result of thermal inertia continues to rotate together with the escape sector.