Silicon014 Posted August 12, 2012 Share Posted August 12, 2012 I recently gained an interest in gravitational slingshots. I attempted one by using the Mun to reach Kerbol orbit, and it worked. I have no clue how to see how efficient the maneuver was compared to a Hoffman out of the system, so could someone please do the math for me? I'd also be much obliged if you were to show and explain your work so I can learn. Below are some facts about the trip and rocket.Starting Orbit: 130km around Kerbin, circularFuel expended for the TMI: 2222.9Munar Periapse: ~10km(Unfortunately, I don't know the Specific Impulse for the rocket I used, as it uses the old Burn Rate stat)Rocket Thrust: 1100Burn Rate: 66Kerbol Apoapse: 13,810,000 kmKerbol Periapse: 13,190,000 kmIf you need any other information AT ALL, I can get it for you easily. Please just leave a reply asking for a specific stat(s) Link to comment Share on other sites More sharing options...
Kosmo-not Posted August 12, 2012 Share Posted August 12, 2012 Spell check is evil. Hohmann is the way to spell it.Also, it's not a Hohmann transfer that you would be using. It's an escape trajectory.Doing an escape trajectory from Kerbin orbit is more efficient than a slingshot around the Mun due to the Oberth effect. Link to comment Share on other sites More sharing options...
Silicon014 Posted August 12, 2012 Author Share Posted August 12, 2012 Are you sure? It cost me 828 delta-v's to get my TMI, but would it not cost a couple hundred more to reach escape velocity by doing a straight burn to escape velocity? Link to comment Share on other sites More sharing options...
Kosmo-not Posted August 12, 2012 Share Posted August 12, 2012 It would have cost you only 82 more delta-v to escape Kerbin. Link to comment Share on other sites More sharing options...
Silicon014 Posted August 12, 2012 Author Share Posted August 12, 2012 Thats still a higher efficency escape > Link to comment Share on other sites More sharing options...
Rainbow Dash Posted August 12, 2012 Share Posted August 12, 2012 so its cheaper to go from Kerbin orbit to the suns SOI than to slingshot around the Mun? Link to comment Share on other sites More sharing options...
Kosmo-not Posted August 12, 2012 Share Posted August 12, 2012 (edited) It's a more efficient escape from Kerbin, but as far as getting to another planet, it's probably not.*edit*Okay, I did some rough calculations. In the best case scenario for a Mun slingshot, the break even point is around 1200m/s of needed velocity when exiting Kerbin's SOI. This is about 300m/s delta-v. I used 100km as parking orbit around Kerbin, and 3km periapsis for the Mun slingshot. Past expending 300 delta-v, it would be more efficient to do the escape trajectory directly from Kerbin orbit. This is also assuming you transfer to the mun such that your periapsis is on the back retrograde sector of the Mun. Edited August 12, 2012 by Kosmo-not Link to comment Share on other sites More sharing options...
Silicon014 Posted August 12, 2012 Author Share Posted August 12, 2012 Well then my hopes are dashed . I was gonna do something cool instead of just a boring escape burn, but NO NO NO NO. Maths have dun proven me wrong againz Link to comment Share on other sites More sharing options...
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