added ability to fire to add velocity to a achieve eclipse orbit and select circular to achieve circular orbit by applying impulse in directions to get velocity at the correct speed and direction, perpendicular to radius. this feature helps in the learning of energies change as satellite move from one circular orbit to another circular as requested by soo kok.
author: timberlake, lookang and fu-kwun hwang
scaling IJC: https://dl.dropboxusercontent.com/u/44365627/eduLabJava2012-2013/Gravity/GravitationIJC2013.zip
screenshots of lecture integration