Technical Overview
Software
Physical Model
- Earth's gravity is modeled as a spherical-harmonic
gravitational
model using
the coefficients from the Joint
NASA GSFC and NIMA Geopotential Model: EGM96.
- Earth's atmosphere is modeled as a composite of three
atmospheric models: U.S. Standard Atmosphere (1976) from 0 km to 25 km
altitude,
CIRA-72 for 25-500 km altitude, and CIRA-82 with Tinf=1000
K for 500-1000 km altitude.
- Earth's orientation is measured relative to the J2000 frame
by
calculating the Greenwich sidereal-time (precession, nutation, and
polar motion will be implemented in the future).
Orbital Maneuvering
- The employed orbital maneuvers are continuous-thrust
maneuvers derived from Gauss' form of the [orbital element] variational
equations and agree with classical
impulsive-thrust
maneuvers if massive instantaneous thrusts were to be used aboard each
spacecraft.
- The terminal rendezvous autopilot employs a steady-state,
Linear-Quadratic-Controller applied to the linearized equations of
motion for a "docking" spacecraft
in the vicinity of a "station" spacecraft in a circular orbit
(Clohessy-Wiltshire equations of motion).
Numerics
- The numerical integration of the equations of motion are
calculated using the Runge-Kutta-Fehlberg adaptive step-size algorithm.
- The Linear-Quadratic-Controller is calculated using a
customized linear
algebra library for Java.
