| A | B |
|---|
| Brute Force Method | Impractical means of traveling in a short, straight line to another planet |
| Hohmann Transfer Orbit | Most efficient means of interplanetary travel utilizing Kepler's Three Laws of Planetary Motion |
| aphelion | point in the orbit farthest from the Sun |
| perihelion | point in the orbit closest to the Sun |
| Focus of an ellipse | one of two points defining the ellipse |
| ellipse | A plane curve defined by the locus of points for which the sum of the distances from each point to two fixed points is equal |
| major axis | line passing through both foci of an ellipse |
| minor axis | line passing through the center of the ellipse and perpendicular to the major axis |
| launch opportunity | an angular relationship of the destination planet, the Sun, and the base planet when a launch would result in a successful Hohmann transfer orbit |
| launch window | time of day when blast off from base planet would result in successful Hohmann transfer orbit |
| Kepler's First Law | Law of Ellipses - the shape of an orbit is an ellipse |
| Kepler's Second Law | Law of Equal Areas - an orbiting body sweeps out equal areas in equal time periods |
| Kepler's Thrid Law | Harmonic Law - the square of a planet's orbital period is proportional to the cube of the semi-major axis of its orbit |
| gravity | the force "driving" planets and all orbiting bodies |
| Half an ellipse | ideal shape of a Hohmann Transfer Orbit |
| Superior Planet | a planet with an orbit outside that of Earth's |
| Inferior Planet | a planet with an orbit inside Earth's orbit |
| apolapsis | generic term for the point in any orbit farthest from the gravitational focus |
| peripolapsis | generic term for the point in any orbit closest to the gravitational focus |
| Astronomical Unit | distance unit used by astronomers equal to the average distance of the Earth from the Sun, about 150,000,000 Km or 93,000,000 miles |
| gravity assist | utilizing the gravitational force of another celestial body to accelerate a spacecraft |
| perturbation | A small change such as a variation in a planet's orbit resulting from the gravitational influence of other celestial bodies |
