# Increase in period and semi-major axis following near head-on collision between Cerise and Ariane debris (1996)

This report describes the collision of the French satellite Cerise with a piece of Ariane rocket debris (object no. 18208) in 1996: http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1997ESASP.393..589A&defaultprint=YES&filetype=.pdf

The approach angle between the two objects was 158.9 degrees (nearly head-on).

Near the end of section 4.4, the report states: "It is astonishing to note that the period and hence the semi-major axis of object no. 18208 increased during the presumed collision whereas the two objects were going in opposite directions. The delta-V in the trajectory of debris no. 18208 is in the direction of its velocity and not in the opposite direction."

Has the increase in delta-V of the Ariane debris ever been satisfactorily explained? If not, what are some possible explanations for how a near head-on collision of two orbital bodies could increase the period and semi-major axis of one of the objects?

• +1 This is a really interesting question! A good answer will have several parts; 1) establish that this is really "astonishing" to begin with and not just counterintuitive, 2) find out if it has "ever been satisfactorily explained" and 3) include a summary of the explanation. – uhoh Jun 21 at 22:46
• – uhoh Jun 22 at 0:30
• @uhoh this redirection you showed in the link would not add deltaV to the objects. The object redirected "upside" would gain Apoapsis hight, but it would lower the periapsis. And another point is: you cannot apply elastic bumbs in orbital speeds. – CallMeTom Jun 22 at 10:37
• @CallMeTom what makes you think so? Can you demonstrate this rigorously using math? If so then that would address point 1) in my first comment. If not, then for now we'll just have to call it "counterintuitive". In the mean time, if a ping-pong ball and a bowling ball collide with equal and opposite velocities, does not the ping-pong ball recoil with a higher speed than before the collision? – uhoh Jun 22 at 10:42
• @uhoh assuming both objects (1 and 2) in the figure you showed are on a (near) circular orbit, this would mean: a horizontal line is parallel to earths surface up is zenit, down is nadir. after the collision just looking at the "new orbit" would come from a lower alt and go to a higher alt, so it would be elliptical with a periapsis lower, and a apoapsis higher than before the crash – CallMeTom Jun 22 at 10:57