The Earth - Moon Neighborhood Once we leave the Earths atmosphere we are in space. However, the Earth - Moon Neighborhood is actually very crowded with A variety of man made objects, (satellites) and a lot of natural phenomenon like the Van Allen Radiation Belt, Near Earth Asteroids (NEA’s), also known as Near Earth Objects (NEO’s). There are hundreds of satellites orbiting the Earth at a variety of orbital altitudes and inclinations. Some times there are satellite crashes, creating a lot of orbital debris. There are thousands of Near Earth Asteroids, of various sizes, some of which actually pass between the Earth and the Moon. Some enter the Earth’s atmosphere, and some actually impact the Earth (that might be why we care about them – see the Tunguska Event). In addition there are special locations of interest where large space structures can be in a stable orbit in the Earth - Moon Neighborhood. These locations are called Lagrange Libration Points (a good place for a large space structure or a colony). S. Akerley 2011

The Earth - Moon Neighborhood L4 L5 L1L2 Earth Lagrange Libration Point L5 Geo-Synchronous Earth Orbit (GEO Approx. 22,500 miles Altitude) Lagrange Libration Point L4 Space Station Orbit (LOE) (Approx. 150 miles Altitude) (Atmosphere ends at 65 miles Altitude) (Hubble Telescope approx miles Altitude) NEAs Near Earth Asteroids Over the last 18 Years, More than 90 NEAs have been identified or have passed between the Earth and Moon Orbits. An Average of 5 per year. It is estimated that there are about 5000 NEAs of various sizes. Some have or will enter the Earths Atmosphere, and some will impact the Earth.. N1 N2 N3 N4 N79 N89 Note: Lagrange Libration Point L4 and L5 Are equidistant from Earth and Moon At the Moons orbital distance Moon (238,900 miles) Van Allen Radiation Belt (30,000 to 40,000 miles) S. Akerley 2011

400 Meter Diameter S. Akerley 2011

Close Encounters Different types of NEA Near Earth Asteroid “Fly By” Encounters

Earth’s Gravity Well art work courtesy of NASA S. Akerley 2011 Gravity Wells Earth L5 MoonNear Earth Asteroids (NEA)

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