Astrodynamics Java Project


A orbital mechanics project originally created while I was in Aerospace Engineering graduate school. Orbit tools is a Java class which has functions that are useful in creating astrodynamic Java programs. It was used in a program I created while working at the Space Environment Center. A separate class, planetary elements, calculates the orbital elements for a planet at a given time. These three applets based on these two classes are on this site the Julian Date Converter, Planetary Elements Applets and Direct Trajectory Calculator.


Julian Date Converter

First Published: 5/23/2002

Orbit Tools: Julian Date Converter. Requires Java to run.


Simple applet to convert from a Julian Date to normal time and normal time to Julian Date. Julian Dates are commonly used in orbital mechanics. Note: normal time is Greenwhich Mean Time (GMT)

Pop-out Version

Planetary Elements

First Published: 5/24/2002

Orbit Tools: Planetary Elements Applet. Requires Java to run.


Gets the orbital elements at the Julian Date inputed. It also converts the orbital elements into position and velocity vectors relative to the sun. (Coordinate system is mean ecliptic of J2000)

Direct Trajectory

First Published: 6/6/2002

Orbit Tools: Interplanteary Trajectory Applet. Requires Java to run.


You put in the planets you want to travel between, how long you want to take and what dates to look at and it gives which day is best to leave. It also gives position and & velocity vectors for leaving the departure planet and arriving at the target planet and the heliocentric orbital elements of the transfer orbit when leaving the departure planet. This information can be input into mission design programs as the starting point. It is based on what is commonly called the zero-patched-conic method (aiming from the center of one planet to the other ignoring everything except the Sun's gravity). HEV is the hyperbolic excess velocity (aka V infinity).

OrbitTools Functions

Future Work

Updated: 30/20/2021