Circularisation, Transfer Orbits and Capture Burns

[NewtSoup]

I have a couple of questions about the above.

When circularising my orbit above Kerbin should I also be checking the inclination and if so what should it be at for the best transfer orbit to Mun?

Often when I burn for the Mun I find the encounter is going to kick me up at around a 30-45 degree angle.  

Going for a capture burn at periapsis then puts me in a heavily inclined orbit around Mun.  This is ok for tourists and small satellites when I have plenty of dV to spare but I'd like to do things more precisely.

May I have some tips on getting a more equatorial orbit around Mun?

Edited July 1, 2017 by NewtSoup

[Starman4308]

Launch due east, and transfer due east. The Mun's inclination is 0, and KSC is on the equator, so if you are careful not to create any inclination during ascent, an equatorial Mun transfer should be very easy to get.

[Tex_NL]

If you do enter Mun's SOI at an inclination make your corrections ASAP. At the SOI's edge inclination changes are extremely cheap. Only a few m/s can completely flip your orbit 180 degrees.
If you try to rendezvous with an object already in Mun orbit try to align your Pe with the AN/DN. Then combine your circularisation burn and plane correction into one. Combining them into one is cheaper than doing them separately.

[Human Person]

Ways to get an equatorial Mun orbit:

1. Launch into a perfect orbit that has 0 relative inclination to the Mun (btw, in the case of the Mun, that is the same as 0 absolute inclination). This is possible to do, just target the Mun before lifting off and watch your inclination markers during Ascent.

2. Correct your inclination in LKO. It's ok to do for very small inclination changes like 1 or 2 degrees, but it can be quite delta-v expensive for big changes in inclination.

3. Do a mid-course correction. Changes in inclination are less expensive when you're further out.

4. Correct your orbit after you did your Mun insertion. 

Edited July 1, 2017 by Physics Student

[WanderingKid]

4 hours ago, NewtSoup said:

When circularising my orbit above Kerbin should I also be checking the inclination and if so what should it be at for the best transfer orbit to Mun?

0 degree inclination.  Mun is an excellent 'equatorial' check for AN/DN to make sure you're equatorial around Kerbin, as well, by simply targeting it and getting your ascending/descending nodes to 0, then untargeting.
 

Quote

 

Often when I burn for the Mun I find the encounter is going to kick me up at around a 30-45 degree angle.  

Going for a capture burn at periapsis then puts me in a heavily inclined orbit around Mun.  This is ok for tourists and small satellites when I have plenty of dV to spare but I'd like to do things more precisely.

 

This is absolutely normal.  You're going from a basketball to a croquet ball.  Minmus is almost a golf ball.  Anyway, minor irregularities during your transfer burn will translate to huge differences on the far side.  Luckily, as mentioned above, it's also easily corrected.  About 30-45 minutes out from Kerbin put in a maneuver node and mess with it a little.  Up/Down (purple) to cure your Ascending/descending concerns.  Faster/slower (or radial in/out) to cure your periapsis height.

To make life easier, set your maneuver node up, then focus on Mun (double click it, or tab around until it's focused) so you can see your projected path more clearly.  In the background, re-click on your maneuver node to open it up and adjust while you're looking at Mun to figure out what your correction burn should be for where you want to go.

[NewtSoup]

2 hours ago, WanderingKid said:

0 degree inclination.  Mun is an excellent 'equatorial' check for AN/DN to make sure you're equatorial around Kerbin, as well, by simply targeting it and getting your ascending/descending nodes to 0, then untargeting.
 

This is absolutely normal.  You're going from a basketball to a croquet ball.  Minmus is almost a golf ball.  Anyway, minor irregularities during your transfer burn will translate to huge differences on the far side.  Luckily, as mentioned above, it's also easily corrected.  About 30-45 minutes out from Kerbin put in a maneuver node and mess with it a little.  Up/Down (purple) to cure your Ascending/descending concerns.  Faster/slower (or radial in/out) to cure your periapsis height.

To make life easier, set your maneuver node up, then focus on Mun (double click it, or tab around until it's focused) so you can see your projected path more clearly.  In the background, re-click on your maneuver node to open it up and adjust while you're looking at Mun to figure out what your correction burn should be for where you want to go.

Thank you kindly.  I'm doing pretty much everything correctly then.  I'd discovered the ability to view my path close to Mun by double clicking on Mun  came in handy when a company wanted a satellite on a retrograde orbit around Mun.  Captured into Mun by choosing to encounter on other side to normal and let Mun do most of the dV work for me.

[NewtSoup]

Big thanks for all the tips.  Making the fine adjustments seems to improve the efficiency of the overall mission.  This is my best Munar Orbit so far for the tourists and I have plenty of dV to return.  In fact I'll have about 200m/s left over which I'll use to slow down in the upper atmosphere.  I'm still using the 6 Kerbal Tourist ship design that WanderingKid gave me :).  Thanks loads, I've learned a lot from it about dV to orbit, to mun, to mun orbit and back.

[Spricigo]

1 hour ago, NewtSoup said:

 In fact I'll have about 200m/s left over... 

Something that would be obvious,  when you think more about:

If you consistently have 200m/s left over (as in never need to use that remaining XYZ amount of fuel )  the ideal is to remove it.  

If instead is 200m/s needed to slow down in atmosphere,  consider if a pair of stub wings (e.g. 2x Delta Deluxe Winglet)  can be a cheaper option than that extra fuel. 

In any case try to be alert to possible improvement to your frequently used vessels.  Improved designs make piloting easy and good piloting allow for simpler design,  is really a win-win situation. 

[WanderingKid]

20 hours ago, Spricigo said:

If you consistently have 200m/s left over (as in never need to use that remaining XYZ amount of fuel )  the ideal is to remove it.  

The particular ship in question is meant to be rendezvous friendly with plenty of extra dV, it's just not being used for that yet, but it's also newbie friendly in terms of extra fuel for adjustments and learning the efficient methods.  That said, you're absolutely right in general.  The iteration of removing unnecessary parts and getting better with the equipment allowing you to remove yet more... makes things more efficient in the long run. 

However, 200 dV extra is basically the 20% engineer's overkill when you're talking a Mun orbit, which runs ~1,500 dV all told with no mistakes from LKO 75km. 

22 hours ago, NewtSoup said:

Big thanks for all the tips.  Making the fine adjustments seems to improve the efficiency of the overall mission.  This is my best Munar Orbit so far for the tourists and I have plenty of dV to return.  In fact I'll have about 200m/s left over which I'll use to slow down in the upper atmosphere.  I'm still using the 6 Kerbal Tourist ship design that WanderingKid gave me :).  Thanks loads, I've learned a lot from it about dV to orbit, to mun, to mun orbit and back.

Wonderful news.  Something you might want to look into, specifically for tourist orbits on Mun, is free return trajectories.  Basically you shoot your apoapsis up to ~14.5Mm from Kerbin, do a high altitude retrograde flyby, and you're already on your way home.  While you're at the periapsis of that particular flyby, you can slow down, barely get an orbit, trigger the 'orbit the Mun' condition, then speed up again and head home.

[Spricigo]

 

22 minutes ago, WanderingKid said:

However, 200 dV extra is basically the 20% engineer's overkill when

 

Sure. The keywords in my advice are consistently and never need. If that may be not the case, well... Its called safety margin for a reason.

Also good to keep in mind the 80-20 principle: 80% of the result is because 20% of the work.

and the two rules of optimization:

1. Don't optimize.
2. (for experts only) Still don't

Explanation: Not only optimization is doing the remaining 80% work for the last 20% of the possible result (often a even more screwed work/result ratio) but, specially if you are trying to optimise your own work, you probably will be limited by the same factors that prevented you to get things correct to be begin with. You are probably better engaging in a new task than pursuing a trifle of improvement of one that is already satisfactory. So 'If I change X it will still give enough performance' is nice while 'I need to find a way change Y for it to work better' is bad.