Astro is a project originally created while I was in graduate school. Orbit tools is a java class which has functions that are useful in creating astrodynamic java applications and applets. 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. 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

Simple applet to convert from a Julian Date to normal time and normal time to Julian Date. Note: normal time is Greenwhich Mean Time (GMT)

### Planetary Location

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

### Direct Trajectory

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 & velcoty 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 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

Updated: 10/1/2010