80 m/s for Eve elliptical orbit. How? Also general transfer maneuver question.

[Ayreos]

Using the Kerbin DeltaV map from the wiki i noticed the "Eve Elliptical Orbit" requirement is listed at 80 m/s. It requires me easily ten to twenty times that amount to achieve that step. The (literally) shaky mission planner makes it impossible to figure out when or how i should be trying to correct my orbit to achieve that result (especially the inclination). I do use the angles from the "Transfer Calculator" to achieve a capture cheaply and i do try to adjust the inclination during the Kerbin escape burn, but ultimately i'm nowhere close to the 80 m/s to achieve Eve orbit. What's worse, i have the same issue with Duna.

Is it all about adjusting orbital inclination mid transfer? And if so, when should i do the normal/antinormal burn during the said transfer, since there is no indication of ascent/descent points in the transfer orbit?

And for the next question i would like to know whether i can achieve the "c" transfer illustrated in the following picture: http://upload.wikimedia.org/wikipedia/en/7/7c/Trans-Mars_injection.png. Does it require multiple burns during the transit? I don't seem to be able to achieve something like that with a single ejection burn. I'd love to be able to perform interplanetary transfers regardless of optimal windows at times, even if they require considerably more fuel. Another example: https://directory.eoportal.org/image/image_gallery?img_id=177350&t=1338287802176.

Thanks in advance.

Edited May 15, 2015 by Ayreos

[Jaeleth]

I'm not sure I understood the first question but once the prograde burn is complete, try to plan the normal/ anti-normal manuever close to kerbin and check it's effects by shifting focus to eve. Note that the normal/anti normal will shift your trajectory up or down but to get the correct eve insertion at a specific orbital inclination, if that's what you want, you shall, probably have to burn a little radial or anti-radial resulting, in practical terms, in an advance or falling back of your trajectory relatively to eve's path, resulting in larger or smaller inclination angle. So, to try to answer your first question: to get an insertion with elliptical orbit and a certain inclination, even polar, you have to burn normal or anti normal close to kerbin and radial or anti-radial enroute, not too far, because it will be less controllable, and not too close, because you will need lots of dV.

second question i think it is possible to do that with a single burn, never tried that one; what happens, sometimes, is that the traveled distance is so big that the slightest speed variation in the first burn might get you off the SOI of the target.

as a bottom line, for long flights, i never do it in a single burn, always do a middle burn for optimal insertion point, but then again, those enroute burns, if at an adequate distance, are so tiny that, many times, can be performed with a gentle blow of the RCS thusters and, therefore, are no factor to fuel consumption, I approached Duna, this way.

[KSK]

Using the Kerbin DeltaV map from the wiki i noticed the "Eve Elliptical Orbit" requirement is listed at 80 m/s. It requires me easily ten to twenty times that amount to achieve that step. The (literally) shaky mission planner makes it impossible to figure out when or how i should be trying to correct my orbit to achieve that result (especially the inclination). I do use the angles from the "Transfer Calculator" to achieve a capture cheaply and i do try to adjust the inclination during the Kerbin escape burn, but ultimately i'm nowhere close to the 80 m/s to achieve Eve orbit. What's worse, i have the same issue with Duna.

Is it all about adjusting orbital inclination mid transfer? And if so, when should i do the normal/antinormal burn during the said transfer, since there is no indication of ascent/descent points in the transfer orbit?

Thanks in advance.

Not sure if this helps but it looks like the 80m/s figure is only for the capture burn into Eve orbit and is the absolute minimum required for capture. Note the apses for that elliptical orbit - 107km by 85,000 km! To get into a 107km circular orbit requires another 1300 m/s of delta-V which would be more like the amount you're seeing.

For interplanetary missions in general, I find Alexmoon's calculator to be invaluable, since it gives you the transfer windows in days, rather than asking you to muck about with phase angles. It's been a while, but for going interplanetary, I normally aim to get an encounter of any sort when setting up my initial transfer burn and then - as you say - doing a mid-course correction. Exact timing isn't critical if I remember rightly and sometimes I found it useful to actually do a slightly larger correction burn later in the journey rather than fiddle around trying to do .1 m/s adjustments.

A very useful trick (if you're not already using it) is to use Focus View on your destination when setting up your course correction. Makes it much easier to fine tune the approach when you can see your orbit relative to your target.

[Superfluous J]

I think I can answer the first one. Your periapsis is too high. That "80m/s to capture" assumes you're coming in with a periapsis down around 100km over Eve's surface (not far off the atmosphere). Down there, you get the full benefit of the Oberth Effect and each m/s of dV in your thrust really packs a punch on your apoapsis.

Edited May 15, 2015 by 5thHorseman
typo

[Cebi]

I thought that 80m/s in DeltaV map is minimal transfer dV between two SOI boundaries. Was i wrong?

[Ayreos]

Not sure if this helps but it looks like the 80m/s figure is only for the capture burn into Eve orbit and is the absolute minimum required for capture. Note the apses for that elliptical orbit - 107km by 85,000 km! To get into a 107km circular orbit requires another 1300 m/s of delta-V which would be more like the amount you're seeing.

That's exactly my issue. I need thousands of m/s to get a capture and stop the escape from occurring. So i burn most of the fuel intended for getting in low orbit, plus the fuel intended for the return journey during this process. From other answers i can deduce i should focus on performing a proper correction burn. I just remember trying and failing to change the end result.

I think I can answer the first one. Your periapsis is too high. That "80m/s to capture) assumes you're coming in with a periapsis down around 100km over Eve's surface (not far off the atmosphere). Down there, you get the full benefit of the Oberth Effect and each m/s of dV in your thrust really packs a punch on your apoapsis.

This sounds like the solution. I didn't think you could do that. I tried dozens of times and never got such a close pass... It also explains why there is an "aerobraking possible" sign at the 80 m/s figure as well. I just have to enter the EVE SOI on a trajectory that skims its atmosphere.... exciting!

EDIT: I got it. My mistake was trying to use the mission planner while focusing on the destination body. The shaky planner made it impossible to see any changes in the entry orbit. I just had to scratch the planner and actually modify my orbit in real time, while focusing on the destination. At first try i got a 60Km aerobrake on Eve, which got me into a 3.6Mm to 59Km Eve orbit for peanuts, coming very close to the 80 m/s estimate on the chart.

Thanks again to all who answered! KSP is suddenly as exciting as the first day i played it!

Celebratory picture: http://oi58.tinypic.com/51apsi.jpg

Edited May 15, 2015 by Ayreos
Question 1 fully resolved