## About

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.

## Applets

### Julian Date Converter

#### First Published: 5/23/2002

### About

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

### About

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

### About

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

**BPlane**: Gives flyby parameters given the incoming and outgoing velocity vectors.**ConvertFromJD**: Converts from a Julian date to the year, month, day, hour, minute and second.**ConvertToJD**: Opposite of the last function.**FindC2C3**: Support for other orbital mechanics functions.**LambertUV**: Gives the two velocity vectors given two position vectors and the time between them.**M2E**: Converts the Mean Anomoly to the Eccentric Anomoly.**OE2RV**: Converts orbital elements to position and velocity vectors.**Rot1, Rot2, Rot3**: Rotates a vecotor about the x, y, z axis.**RV2OE**: Converts position and velocity vectors to orbital elements.**cross**: Gives the cross product of two vectors.**dot**: Gives the dot product of two vectors.**sinh, cosh**: Gives the hyperbolic sine and hyperbolic cosine.

## Future Work

- Switch the applet projects to the Netbeans IDE.
- Write documentation for the functions.
- Create Flyby applet - Trajectory calculator using a flyby of planet to reach its target.
- Add graphics to the Direct Traj applet.
- Fix minor bug in Julian Date converter that in newer versions of Java, causing the month to be unreal on start up.

Updated: 30/20/2021