Long Term Stable Hill Sphere: 744,820 kilometers from surface of Terra (748,000 km from center).Ultra-Cautious Hill Sphere: 496,540 kilometers from surface of Terra (498,670 km from center).Lunar Orbit: Luna's orbit around Terra has a pericenter of 363,300 kilometers and a apocenter of 405,500 kilometers.If the perigee is less than 2,000 km it is called a " highly elliptical orbit." High Earth Orbit (HEO): anything with an apogee higher than 35,786 kilometers.This orbit is affected by the outer Van Allen radiation belt. It is jam-packed with communication satellites like sardines in a can. One revolution takes one sidereal day, coinciding with the rotational period of Terra. Geosynchronous Orbit (GEO): exactly 35,786 kilometers from surface of Terra (42,164 km from center of Terra).The most common altitude is 20,200 km which gives an orbital period of 12 hours. Also known as "intermediate circular orbit." Commonly used by satellites that are for navigation (such as Global Positioning System aka GPS), communication, and geodetic/space environment science. Medium Earth Orbit (MEO): 2,000 kilometers to 35,786 kilometers.
Affected by inner Van Allen radiation belt. At 160 km one revolution takes about 90 minutes and circular orbital speed is 8 km/s.
Ellipses have two focal points instead of one center, and one is parked on the barycenter of the primary-secondary system.
The center of the secondary object's orbit is the center of the primary object, but this too is wrong. Pretty much all natural orbits are ellipses, though many look like circles to the naked eye (that was Kepler's valuable contribution to rocket flight). Orbits are the sine qua non of space stations and communication satellites. You will be in a wonderful state of free-fall…until you hit the ground.Īn orbit is a clever way to constantly fall towards a planet but never hit the ground. If you jump out a window of a skyscraper, or out of an aircraft at high altitude, you will fall down. What is an orbit? That elliptical path traced by a secondary object ( i.e., Luna) as it moves around a primary object ( i.e., Terra). Using orbits is critical for flying your spacecraft from planet A to planet B. What is relevant to our interests is this class includes spacecraft, space stations, satellites, moons, and planets. Pretty much everything in space that is not a beam of electromagnetic radiation or a torchship moves in an orbit.