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Unformatted text preview: Orbit Change Orbital Element Orbit Insertion Rockets cannot always put you in desired orbit ! orbit trasnfer want Get Need orbit transfer!! Types of orbital maneuver Changes in shape/altitude of orbit Changes in orbit plane Changing Altitude Perigee Change in Velocity at Apogee Orbital Transfer Impulse Thrust Assumptions
! Orbit change requires change in velocity " Requires thrust ‘force’ (rockets, etc.) " Conserved energy and angular momentum in twobody problem changes ! Thrust is assumed to be instantaneous " Acceleration happens instantly ! For rockets : good assumption " For electric propulsion : bad assumption Types of orbital maneuver Changing Altitude Hohmann Transfer Hohmann Transfer Orbit Transfer Introduction
15 ! One of first problem faced by spacemission designers
" How to go from one orbit to another? In 1960s, NASA engineers and astronauts developed orbit change procedures Figured out complex Lunar mission architecture Initial and final orbits are in same plane Often used to go from initial parking orbit to final orbit ! Refining orbit transfer process: Gemini mission
" " ! For our study, assume:
" " ! Fuel is critical for all orbit maneuvers ! use most fuel efficient maneuver: Hohmann Transfer Introduction of Hohmann Transfer
16 ! 1925, German engineer, Walter Hohmann theorized fuelefficient way to transfer between orbits
" Amazing because there were no satellites!! Hohmann Transfer
17 ! Using tangent ‘on/offramps’ " Tangent to initial and final orbit ! As little energy as possible " Minimum fuel ! Assumptions " Coplanar " Major axis aligned " Instantaneous velocity change ! Tangential means change in magnitude only, no change in direction of velocity 18 Hohmann Transfer: required velocity change #VA " V p ! Vcs #VB " Vcs ! Va Plane Change Near Equator = Better! Prograde vs. Retrograde US vs. Russian Launch Vehicle
! Florida launch
" 28.59° Lat ! Russian launch
" All above 45° Lat ! Much energy wasted being far from equator! Outofplane Change in orbital plane (inclination) V ! V "V #V " 2V sin $
2 ...
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 Spring '11
 jinkang

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