alexmun

Here's the method I use to get the orbital inclination I want upon insertion around a new body: Do your insertion burn at periapsis as usual, but stop as soon as you have an apoapsis inside the SOI (you need to be quick on the engine cut-off because the apoapsis will be moving FAST when it first appears). Wait until you're back at apoapsis, then do a normal inclination change. Your orbital velocity should be nearly zero so the inclination change will be almost free. Go back to periapsis and circularize as usual. This typically only takes a few delta-v more than a normal orbital insertion and you can get whatever inclination you want. The only disadvantage is it takes one extra orbit.

I've made a couple of updates to the calculator. The main one is that it can now calculate transfers consisting of an in-plane ejection followed by a mid-course inclination change burn (suggested by tavert). The plane change burn is done at 90 degrees to intercept for optimum efficiency. The two methods have slightly different launch windows but largely similar delta-vs as long as the inclination between origin and destination is not great (as one would expect). If there is a significant inclination difference, the plane change method can be significantly cheaper when transferring to a higher orbit (for example, the first launch window to Dres is about 500m/s cheaper with the plane change method). The ballistic method seems to be consistently cheaper when transferring to a lower orbit. You can also have the calculator select the optimal transfer type at each point on the plot which tends to increase the size of your possible launch windows.

Thanks, alterbaron! I like coffeescript a lot, it makes javascript programming much more pleasant IMHO.

That sounds great!

What I do is guesstimate based on my orbital velocity and the delta-v of the burn. For example, if my orbital velocity is 2000 m/s and my delta-v is also 2000 m/s and the ejection inclination is 2.8 degrees, I would burn about 5.6 degrees north of prograde on the navball. If the delta-v is more than your starting velocity, burn closer to the desired angle, if it's less burn proportionally farther north or south of prograde. Then after the main burn is complete I check my inclination with Kerbal Engineer and make fine adjustments north or south as necessary. It's not perfect but it seems to work pretty well. Also, keep in mind you'll probably need to start your burn before you get to the actual ejection angle since your engines don't have unlimited thrust. I try to split the difference so I'm halfway through the burn when I hit the ejection angle.

That's a good idea. I'm out of town this weekend, but I might work on that after I get home. Don't feel stupid, this stuff is not easy. I'm still figuring a lot of it out myself. What the chart shows you is how much delta-v (change in velocity) it takes to get from point A at a specific time and arrive at point B at a specific time. So the blue areas of the chart represent the most efficient times to leave and arrive. Also have a look at olex's calculator (http://ksp.olex.biz) which does a better job of walking you through the mechanics of doing a transfer.

Yes, that's exactly right. The transfers try to hit the center of the planet which becomes pathological at 180 degrees if there is any inclination at all between the orbits. The Hohmann transfer works for Duna even though it is inclined because the inclination is low enough that its sphere of influence always intersects the ecliptic. I find it interesting that the lambert problem finds a solution of 1046 m/s delta-v at a transfer angle of 165 degrees vs the Hohmann transfer's delta-v of 1043 m/s with a small mid-course inclination correction required, so I think they end up being very close in delta-v required. The Hohmann transfer may require less delta-v for the insertion burn, because the orbits will intersect at a smaller angle.

Yes, this is definitely a problem. I usually calculate how long the burn is going to be then start my burn half that time before I hit my ejection angle. It's not perfect but it tends to get me close enough that a few small adjustments give me an encounter. For inclination changes, making the correction midway through your transfer is a very reasonable approach (you don't even need to do it at the ascending or descending node, you just need to incline your orbit so it intersects the target orbit at the right point). However, there are a couple of advantages to doing the inclination change as part of your ejection maneuver. First, combining two maneuvers into one requires less delta-v in the same way that traveling diagonally is a shorter path than traveling horizontally then vertically to get to the same point. Second, the closer you are to a planet when you perform a maneuver the more you benefit from the Oberth effect. The hard part is figuring out how much inclination you need on your ejection maneuver in order to hit your target. That's one reason I made my launch window calculator.

One thing to note is that Kerbal Alarm Clock's timing is based on Hohmann transfers, which is awesome for coplanar, circular orbits. Unfortunately, Moho's orbit is neither circular nor coplanar with Kerbin's. I got frustrated enough trying to hit Moho without wasting a ton of fuel to put together a calculator to visualize the actual optimal launch windows. You can try it here: http://alexmoon.github.io/ksp

Yes, my whole motivation for making this was to calculate transfers to Moho. As Mr Shifty said, it calculates transfer orbits that hit specific points in space at specific times so it works for any eccentricity and inclination of orbits.

The Hohmann transfer is ideal as long as the orbits are coplanar. When the orbits are not coplanar 180 degrees is actually bad because it takes a lot of delta-v to rotate your apoapsis around to hit your target. If you compare a Kerbin-Duna plot to a Kerbin-Moho plot you can see the difference. The Kerbin-Duna plot (which has very little relative inclination) is mostly one large window with a very narrow line at transfers very close to 180 degrees that are slightly more expensive. The Kerbin-Moho plot (which has significant relative inclination), on the other hand shows two distinct lobes, one for transfers of less than 180 degrees and one for transfers of more than 180 degrees with a large "ridge" separating them. Kerbin and Duna are close enough to coplanar that you can pretty much ignore the problem, especially since you don't actually want to hit the planet, although you can theoretically save a few delta-v by doing a few degrees off of 180. Kerbin and Moho are far enough apart in inclination that it would be very expensive to try to do a 180 degree transfer.

As long as you download all the scripts, stylesheets and images it should work fine offline. All the calculations are performed in the browser.

Sure, just click on the GitHub ribbon in the upper right corner. It all runs in JavaScript in your browser so you can also look at it that way. Most of the math I got from: http://www.braeunig.us/space

I've put together a web app that generates porkchop plots for ksp: http://alexmoon.github.io/ksp

Yeah, getting to Moho is hard. You can get there and achieve orbit with about 5000m/s of delta-v, but the launch window is small and very different from what the Hohmann transfer calculators would suggest since Moho's orbit is eccentric and inclined. In fact, my troubles getting to Moho are what got me to put together a tool to calculate proper launch windows for inclined/eccentric orbits. You can try it out here: http://alexmoon.github.io/ksp.

What is it? After one too many failed attempts to make it to Moho with a minimal delta-v vehicle using the standard Hohmann transfer calculations I decided I needed a tool that would let me calculate transfers to and from eccentric and inclined orbits quickly and easily. Not finding such a tool already out there I decided I'd have to just make it myself. What does it do? Just give it basic information about the transfer you wish to perform and it will create a porkchop plot showing you the delta-v required to execute the transfer depending on the time of departure and time of arrival. Once you have picked a departure and arrival time you can click on that point of the chart to get a detailed look at the maneuvers needed to perform the transfer. What does it look like? Like this: Looks awesome! How do I use it? Just go to http://alexmoon.github.io/ksp and follow the instructions. To get the most use out of it, you'll probably want a few mods such as Kerbal Alarm Clock to keep track of the current time and Kerbal Engineer Redux or MechJeb to monitor your orbital characteristics. Please note that there is a bug in the current version (6.0.3) of Kerbal Engineer: when performing a transfer to a body with a smaller orbit, the "Angle to Retrograde" displayed is actually your angle from retrograde, so you'll need to subtract it from 360 degrees to get your actual angle to retrograde. I also calculate the phase angle slightly differently from how Kerbal Engineer does so it may be off by a few degrees for inclined orbits. Finally, I don't personally use MechJeb so while I assume it gives you enough information to set up the ejection maneuver correctly, I haven't actually tried it. I look forward to getting lots of great feedback from the community. Please let me know if you run into any bugs or errors or if there is other data you would like to see. Changes 2014-04-06 Added support for Kerbin time. Changed the color map to use a logarithmic scale. 2014-03-02 Added support for multiple-revolution ballistic transfers. 2014-01-26 Added ability to edit orbits and add new bodies. Improved UI. 2013-07-06 Changed the y-axis of the plot to be time of flight instead of arrival date. This makes the whole area of the plot meaningful and makes the periodic nature of the launch windows more clear. Added advanced settings to optionally control the scale of the x and y axes to let you zoom in or out on an area of the plot you are interested in. 2013-07-04 Implemented an all-new lambert solver. More robust and much faster than the old one. Added a tooltip to the ejection delta-v parameter giving the prograde and normal components of the maneuver. Added UT tooltips to dates in the transfer details. Fixed a minor bug in the ejection angle calculation. 2013-06-04 Another new transfer type! The optimal plane change transfer searches for the best possible angle at which to perform the plane change maneuver. This is fairly slow, so I've also kept the previous mid-course plane change transfer type which uses 90 degrees to intercept as a reasonable guess. The optimum transfer type now chooses between the ballistic and optimal plane change transfer types instead of using the mid-course plane change transfer type. That does mean it is now as slow to calculate as the optimal plane change transfer type. Internet Explorer 10 is now supported. 2013-06-03 New transfer types! You can now compare ballistic transfers (a single ejection burn to create an intersecting orbit) to transfers with a mid-course plane change, or select optimal to automatically pick the lowest delta-v transfer type. Crosshairs on the chart show your selected transfer The minimum delta-v transfer is now selected automatically after plot generation 2013-05-30 Initial release

Coincidentally, I've just finished up a tool specifically designed to show you how big your launch window is. You can give it a shot at http://alexmoon.github.io/ksp. It creates what's known as a porkchop plot which shows how the delta-v required to execute a transfer varies with your departure date and time of flight.