Sun – Earth System Understanding Orbits Earth’s rotation axis Equator Sun’s rays Orbiting Spacecraft Eclipse Equator Spacecraft orbit SSE-120

Earth System Understanding Orbits q r h Orbit plane Orbit inclination Earth radius h Orbit altitude SSE-120

Earth’s rotation around the sun Understanding Orbits Earth’s rotation around the sun Equinox Winter Summer Equinox SSE-120

Launching a spacecraft Understanding Orbits Launching a spacecraft SSE-120

All orbits go thru the center of the earth Understanding Orbits All orbits go thru the center of the earth SSE-120

Launching a spacecraft into a terminator orbit Understanding Orbits Launching a spacecraft into a terminator orbit SSE-120

Launching a spacecraft into a terminator orbit Understanding Orbits Launching a spacecraft into a terminator orbit SSE-120

Launching a spacecraft into a terminator orbit Understanding Orbits Launching a spacecraft into a terminator orbit SSE-120

Spacecraft enters eclipse Understanding Orbits Spacecraft enters eclipse Launching at noon or midnight Spacecraft leaves eclipse SSE-120

f = Q - 180 Understanding Orbits Calculating eclipse time for a noon-midnight orbit d h r r + h q f q Solution d = [(r + h)2 – r2]1/2 Q = cos-1 [r/(r+h)] f = Q - 180 Eclipse time = [(2* f)/360] * orbit time SSE-120