# Perigee Drag

### What is the velocity and radius versus time for an elliptical orbit?

Given apogee r_a and perigee r_p and \mu_e = 3.986e14 m3/s2 and angle from perigee, true anomaly: \Large \theta

 eccentricity: \large e = ( r_a - r_p ) / ( r_a + r_p ) semimajor axis: \large s = ( r_a + r_p ) / 2 characteristic velocity: \large v_0 = \LARGE\sqrt{{\mu \over 2}\left({1 \over r_a}+{1 \over r_p}\right)} eccentric anomaly (ellipse center angle): \large E=\arccos\Large\left({{e+\cos(\theta)}\over{1+e\cos(\theta)}}\right) mean anomaly: \large M = E - e \sin( E ) time from perigee: \large t = M / \omega radius: \large r=s\Large{{1-e^2}\over{1+e\cos(\theta)}} perigee radius: \large r_p =( 1-e ) s perpendicular velocity: \large v_{\perp}= v_0 ( 1+e \cos( \theta )) perigee velocity: \large v_p =(1+e)v_0 total velocity, tangent to orbit: \Large v=\LARGE \sqrt{{{2\mu}\over{r}}-{{\mu}\over{s}}} angular momentum: \large L =\LARGE \sqrt{ { 2 \mu ~ r_a ~ r_p } \over { r_a + r_p } }

( note: a is more commonly used for the semimajor axis. I use s to avoid confusion with apogee )

PerigeeDrag (last edited 2016-09-18 19:27:12 by KeithLofstrom)