Introduction to Orbital Mechanics

Explore what orbits are, how ellipses describe paths around a larger body, and Kepler’s first law with orbital velocity, period, inclination, and center-of-mass motion.

Explore conic sections and orbital shapes, from circles to ellipses, by examining focus points, major and minor axes, and the points of closest and farthest approach in an orbit.

Earth's oblate shape and 23.5-degree tilt create seasons and varying sunlight, while its elliptical orbit features perihelion in January, aphelion farther away, and March, September equinoxes.

Treat Earth as a point mass so all orbits are elliptical with the mass at a focus; atmospheric drag and two impulses are required to reach and circularize an orbit.

Relate orbital velocity to orbit altitude and semi-major axis for circular orbits and to apogee, perigee, and eccentricity for noncircular ones, including gravity, atmosphere, and escape velocity.

Define the orbital period as the time to complete an orbit, from 90 minutes in low-Earth orbit to 24 hours in geosynchronous and geostationary orbits.

Explore orbital inclination and orbital plane, learn how 0° aligns with the equator and 90° with the poles, how sun-synchronous orbits provide fixed local times for imaging.

Define orbital elements as parameters that describe an orbit's shape and position relative to the equatorial plane. List eccentricity, semi-major axis, inclination, longitude of ascending node, and true anomaly.

Explore elliptical orbits described by semi-major axis and eccentricity, where velocity and energy vary with altitude, and orbital period enables low-earth, geosynchronous, and fixed-orbit designs via orbital elements.