eder@ssc-vax.UUCP (Dani Eder) (03/21/85)
> > Any engine can do a plane change if it is pointed out of plane. > I've seen the transfer orbit elements for a few PAM missions and they > do reduce the inclination by about 3 degrees. I'm not sure why because > it is more efficient to let the apogee motor take it out instead; perhaps > it allows finer balance between the two stages without having to shave > out propellant. > > Phil When you are in orbit you have a velocity vector. To go to a transfer orbit you make that vector longer (increase velocity). To change orbit inclination you make the vector point in a different direction. The velocity your rocket has to provide is the difference between your initial and final velocity vectors. If you are already planning to add velocity, you can add a few degrees of plane change for almost nothing. This reduces the large plane change at GEO when you circularize. The circularization burn is at lower velocities. Since the vector you are reorienting is smaller, plane change is less expensive at GEO. But at large angles, the cost is non-trivial. The angles are split so as to maximize the payload delivered by minimizing the total velocity required. The typical split is 2.5 degrees at perigee and 26 degrees at apogee. This is much clearer graphically (sigh, no graphics terminal.) Dani Eder/ Advanced Space Transportation, Boeing Company/ ssc-vax!eder/