Jarnis Posted October 10, 2011 Share Posted October 10, 2011 So, you may have noticed that no matter which way you head when going for orbit, the orbit always goes over KSC. This is because Kerbin doesn\'t rotate and, assuming you do not change your orbital plane, your orbit will always intersect your liftoff point.But... it is possible to change your orbital plane! This is definitely more of an advanced maneuver and was very hard to do before the orbital map view was added. The trick is to do a burn 'sideways', at a specific point during your orbit. You always aim towards the horizon and towards the middle point between the two yellow markers, pointing to the direction you want to rotate the orbit around the planet. Think it like this; You are flying on orbit towards east and you burn towards north - inevitably your path will curve towards north from the point where you did a burn and... the orbital plane shifts. As you have to do the burns pretty exactly at the spot where you cross your initial orbit and the new target orbit and, after 2-3 orbits, two burns per orbit, you\'ll get where you want.For this demonstration, I\'ve started with the easy-to-explain base case where you lift off and park on orbit around the equator or Kerbin. You pass between light and dark side of the planet every orbit and pass over KSC every time. But what if... we could orbit over the poles following the terminator between dark and light sides? Such an orbit would never pass over KSC. All you need is some knowledge and fuel. LOTS of fuel.Changing inclination by 90 degrees takes a lot of deltaV. I used my basic Mun Rocket design (stock parts) but for this purpose I merged the two upper stages into one three-tank+2 RCS tank upper stage. This design gets into 100km+ circular orbit with about one third of the middle stage left and transitioning to polar orbit over the terminator took the remainder of stage 2 and over 2 tanks out of stage 3. That is a LOT of fuel.The key is to burn when you are crossing your new orbital plane - in this case, the terminator between dark and light. Initial burn pointed straight north and during the first pass over the correct spot in the orbit I got about 25% of the needed change. I was still burning with the middle stage so the rocket was heavier. Important bit is to stop the burn soon after you pass the intended spot and then wait half an orbit.After first burn the middle stage was spent so half an orbit later another burn - pointing south and bit towards the dark side (90 degrees from the new orbit) got us to 45 degree inclination. Half way there. Another half an orbit and pushing the last bits and... success. Orbital plane changed from equatorial to one that goes over the poles following the line between dark and light side. All that was left was to circularize it. Easy! Link to comment Share on other sites More sharing options...
starplayer Posted October 10, 2011 Share Posted October 10, 2011 You should point that maximum efficiency is reached when the velocity is less, so some times it\'s more efficient to move to a higher orbit and change the inclination there, and then move the the lower orbit. http://en.wikipedia.org/wiki/Orbital_inclination_change Link to comment Share on other sites More sharing options...
Jarnis Posted October 10, 2011 Author Share Posted October 10, 2011 You should point that maximum efficiency is reached when the velocity is less, so some times it\'s more efficient to move to a higher orbit and change the inclination there, and then move the the lower orbit. http://en.wikipedia.org/wiki/Orbital_inclination_changeI wished to keep the how-to simple - the point being that it doesn\'t matter what altitude you do this at. It is true that it eats less fuel at a higher altitude. Link to comment Share on other sites More sharing options...
ryacko Posted October 17, 2011 Share Posted October 17, 2011 But how much fuel is consumed by moving to a different altitude? Link to comment Share on other sites More sharing options...
HAWK_180k Posted October 17, 2011 Share Posted October 17, 2011 Nowhere near as much lol! Link to comment Share on other sites More sharing options...
Saaur Posted October 19, 2011 Share Posted October 19, 2011 Very well-written, Jarnis. Should help new folks a lot. Link to comment Share on other sites More sharing options...
plazmaXIII Posted October 20, 2011 Share Posted October 20, 2011 i done some tests on this a while back. higher altitudes are best for big plane changes. this is because your going slower and forces apply better to objects that travel slower (to my knowledge). Link to comment Share on other sites More sharing options...
Jarnis Posted October 20, 2011 Author Share Posted October 20, 2011 i done some tests on this a while back. higher altitudes are best for big plane changes. this is because your going slower and forces apply better to objects that travel slower (to my knowledge).Correct. It is optimal to spend some fuel to raise the orbit higher before doing a major plane change (fuel spent doing that will be less than you would spend for the plane change at a lower orbit). If you want to end up back at the lower orbit after the change, then the answer to 'does it save fuel to raise the orbit first?' becomes 'it depends', mostly on how much you plan on changing the inclination.But assuming you have the fuel, it can be done at any altitude. Link to comment Share on other sites More sharing options...
Rickenbacker Posted October 25, 2011 Share Posted October 25, 2011 Just had to try this, and yes: att extremely high altitudes (not sure HOW high, but my speed was down to 50m/s) it takes almost no power to change the inclination about 80-85% degrees. The last few degrees seem to take a lot more, however... And you\'ll raise your periapsis a LOT pushing further . Link to comment Share on other sites More sharing options...
Peewee Posted October 25, 2011 Share Posted October 25, 2011 Just had to try this, and yes: att extremely high altitudes (not sure HOW high, but my speed was down to 50m/s) it takes almost no power to change the inclination about 80-85% degrees. The last few degrees seem to take a lot more, however... And you\'ll raise your periapsis a LOT pushing further .If you rotate your craft to keep it pointed at the orbit normal, this doesn\'t happen. Link to comment Share on other sites More sharing options...
Ivan Ivanovich Posted October 25, 2011 Share Posted October 25, 2011 Also, to save power when lowering your orbit back to circular, dip the perigee to about 65,000 meters. You\'ll notice that you will get slowed down a little by the atmosphere and hence lose a little of your perigee, but at the same time your apogee gets lowered considerably. Usually, the power to push the perigee back up to 65,000 meters, which is done when you\'re at apogee again, is less than trying to do a retro burn to lower your apogee 'manually'. When your apogee is back to an agreeable level, push the perigee back up when you\'re at apogee and you\'re set.The fuel consumption is lowered considerably that way. Link to comment Share on other sites More sharing options...
Rickenbacker Posted October 26, 2011 Share Posted October 26, 2011 If you rotate your craft to keep it pointed at the orbit normal, this doesn\'t happen.<slaps forehead> Of course! Why didn\'t I think of that? Damn, I feel stupid now . Trying to push the ship sideways with the engine facing back... Link to comment Share on other sites More sharing options...
Jarnis Posted October 26, 2011 Author Share Posted October 26, 2011 <slaps forehead> Of course! Why didn\'t I think of that? Damn, I feel stupid now . Trying to push the ship sideways with the engine facing back...I believe that this is what the experts call 'L2Pilot Issue' Link to comment Share on other sites More sharing options...
Rickenbacker Posted October 27, 2011 Share Posted October 27, 2011 Yeah, what IT guys refer to as a 1d10t problem... Link to comment Share on other sites More sharing options...
Saaur Posted October 31, 2011 Share Posted October 31, 2011 Yeah, what IT guys refer to as a 1d10t problem...That\'s id10t, not 1d10t. Geez, PEBKAC much?};-)> Link to comment Share on other sites More sharing options...
Phoxtane Posted October 31, 2011 Share Posted October 31, 2011 That\'s id10t, not 1d10t. Geez, PEBKAC much?};-)>If my history teacher hadn\'t explained what PEBKAC is, I\'d have no clue what you were talking about. Link to comment Share on other sites More sharing options...
Hypocee Posted November 1, 2011 Share Posted November 1, 2011 PICNIC\'s always been my favorite.(Problem In Chair Not In Computer) Link to comment Share on other sites More sharing options...
TheCardinal Posted May 4, 2012 Share Posted May 4, 2012 Not to revive an old thread, merely a well meant THANK YOU! for the explanation hoe to change the inclination of a trajectory. I still had not figured it out myself. Link to comment Share on other sites More sharing options...
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