Orbital Mechanics – Simple Examples – Vocab Terms
•Prograde Burn – A prograde burn is when you apply thrust in the direction of the forward momentum of the spacecraft and accelerating in relation to the orbiting body. This in return will raise your orbit.
•Retrograde burn – Same as prograde but the exact opposite by thrusting in reverse of the momentum and decelerating. This is how a spacecraft purposely re-enters Earth’s atmosphere as will be explained shortly.
•Apoapsis (AP) – The highest altitude of an orbit around another larger gravitational body.
•Periapsis (PE) – The lowest altitude of an orbit around another larger gravitational body.
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http://upload.wikimedia.org/wikipedia/commons/a/a4/Apogee_%28PSF%29.png
1) Apoapsis; 2) Periapsis; 3) Larger Gravational Body