The Poynting-Robertson Effect and Secular Changes of Orbital Elements
  The Poynting-Robertson (P-R) effect has been applied to meteoroids for several decades. It is well known that the P-R effect produces only changes in the orbital plane of the particle. The differential equations governing the secular changes in both eccentricity and semi-major axis are known since the time of Robertson, provided the initial orbits are not near circular. A disadvantage of this type of osculating orbital elements is that it cannot be applied to motion of arbitrarily shaped particles. Relevant type of osculating orbital elements is discussed. It's application to the P-R effect is presented and simple analytical formulae for secular changes in both eccentricity and semi-major axis are derived. 
Jozef Klacka