Getting from Mum polar orbit to minimus

[TanDeeJay]

I have 2 contracts, 1 to increase the capacity of my mun orbit space station by 5 and a 2nd to build a base on minimus to hold at least 5 kerbals with 2 scientists.

I was thinking I might be able to combine these 2 missions and stop off at the mun station to drop off the mun expansion module, and then to fly on to minimus with my base.

Now, technically, I could complete the mun mission just by docking my minimus base to the mun station for 10 seconds, but that would leave the mun station with a capacity of 16 rather than the contracted 21. Would this cause a problem later in the game?

But my real question is how hard is it to get a direct flight from mun to minimus, given that my mun station is in a polar orbit? And what is going to be my most effecient way to make that transfer? My "minimus base" stage has about 1200dv.

[Superfluous J]

1st question, it won't cause any problems with contracts. Once you complete the contract they don't care.

2nd question, you want to leave Mun when your orbit is parallel to mun's orbit, and burn prograde as you're going the same direction as Mun. use maneuver nodes to make sure you burn in the right place. It doesn't take very much to reach Minmus from Mun. you may have a harder time keeping your resultant transfer orbit from going too high.

That's for the timing of your ejection based on where you are on Mun, but the timing for when Mun and Minmus are in the right location relative to each other is a bit trickier. I personally would just eject when it was convenient and fiddle with my Kerbin orbit to reach Minmus later. Takes a bit more dV but it's more seat-of-your-pants which is my style.

[bewing]

Important info: If you fly to the Mun and directly dock your minmus station to your mun station, then undock -- then your minmus station will no longer be "new", and your minmus contract will fail.

You can do the minmus contract first, then fly the whole contraption to the mun and do the docking and that will cover both contracts perfectly.

But if you go to the Mun first, then you have to be very very careful not to ever dock your whole minmus station to the mun station. You would have to decouple a hab section from the main craft without docking, then dock the hab section to the Mun station while it is in free flight -- and it would just get complicated and annoying.

But yes, as 5th horseman basically said, to get from the Mun to Minmus takes very little deltaV but you have to time it right. You would want to go when your orbit is parallel to the Mun's velocity vector, and that vector leads the position of minmus by about 90 degrees, as I recall. And the trip takes about 15 days.

[BeanThruster]

4 hours ago, TanDeeJay said:

But my real question is how hard is it to get a direct flight from mun to minimus, given that my mun station is in a polar orbit? And what is going to be my most effecient way to make that transfer? My "minimus base" stage has about 1200dv.

I would say, you have enough dv (1200 m/s) to get a transfer from Mun to Minmus. If I remember correctly, you need maybe 600-700 m/s to get an equatorial orbit, and then a 200 m/s for the ejection burn and a 100 m/s for Minmus insertion. You end up with 200 m/s spare dv, for final maneuvers and rendez vous.

You may find useful the online transfer planner at https://alexmoon.github.io/ksp/

OR, you may take the difficult way and directly eject from the munar polar orbit. Quite difficult, but not completely impossible. The problem here is that you have a very small tolerance in getting an encounter and you could end up wasting a lot of time orbiting around Kerbin, but if you complete the transfer, you will have something to tell your grandchildren when you get old.

Granpa TanDeeJay: Did I ever tell you about that time I transfer from a polar orbit...

grandchildren (hysterically crying): naaa, not again

[TanDeeJay]

6 hours ago, bewing said:

Important info: If you fly to the Mun and directly dock your minmus station to your mun station, then undock -- then your minmus station will no longer be "new", and your minmus contract will fail.

You can do the minmus contract first, then fly the whole contraption to the mun and do the docking and that will cover both contracts perfectly.

But if you go to the Mun first, then you have to be very very careful not to ever dock your whole minmus station to the mun station. You would have to decouple a hab section from the main craft without docking, then dock the hab section to the Mun station while it is in free flight -- and it would just get complicated and annoying.

But yes, as 5th horseman basically said, to get from the Mun to Minmus takes very little deltaV but you have to time it right. You would want to go when your orbit is parallel to the Mun's velocity vector, and that vector leads the position of minmus by about 90 degrees, as I recall. And the trip takes about 15 days.

So to do mun 1st, I would need to carry a separate mun habitat module and not just rely on the minimus base to temporarily provide the necessary increase in supported number of kerbals? I started designing my craft with 2 separate modules, but wondered if it would be possible to do it with just 1. Separating a module and docking it is not that difficult. I've built a multi module habitat ring in my sandbox where i had lots of practice doing exactly that. DPAI mod helps a lot there.

I was actually thinking of using some of that 1200 dv to do the kerbin to mun transfer and then refueling at the mun station, but if that makes the ship not "new" I guess that means I can't do it that way? Or would it only become not new if the ship docks and completes the contract, so that if I used a ship already docked to the mun station to transfer fuel, then the minimus base would remain "new"? 

[TanDeeJay]

7 hours ago, 5thHorseman said:

 you want to leave Mun when your orbit is parallel to mun's orbit, and burn prograde as you're going the same direction as Mun. use maneuver nodes to make sure you burn in the right place.

Does this also apply when transferimg from a mun polar orbit back to kerbin? The few times I've had to do that I had enough trouble getting to kerbins atmosphere that I considered moving my station back to a prograde orbit.

[bewing]

2 hours ago, TanDeeJay said:

So to do mun 1st, I would need to carry a separate mun habitat module and not just rely on the minimus base to temporarily provide the necessary increase in supported number of kerbals?

Correct.

2 hours ago, TanDeeJay said:

Does this also apply when transferimg from a mun polar orbit back to kerbin?

Pretty much, but to get back to kerbin you want to be going retrograde along the Mun's orbit, rather than prograde. But yeah, if you are in a polar orbit then you can really only leave twice during a Munar month.

[TanDeeJay]

1 hour ago, bewing said:

to get back to kerbin you want to be going retrograde along the Mun's orbit, rather than prograde. But yeah, if you are in a polar orbit then you can really only leave twice during a Munar month.

Wow! Highly useful information! No wonder I had so much trouble getting back to kerbin. It also explains why the maneuver  node for my mun returns from a mun prograde orbit always end up where they do. It never occured to me it was because that was retrograde to kerbin.  And also why its always so much cheaper retuning to kerbin than getting to the Mun.  Makes sense though.  So how many days/hours either side of that mun polar orbit to kerbin transfer window is it still relatively cheap?

Edited November 30, 2019 by TanDeeJay

[paul23]

So we're all just going to ignore the typo "mum" and all kind of yo momma jokes?

[Superfluous J]

2 hours ago, TanDeeJay said:

So how many days/hours either side of that mun polar orbit to kerbin transfer window is it still relatively cheap?

It's pretty forgiving, really. Just test it with several maneuver nodes to get a feel for it. At a rough guess I'd say 15-30 degrees on either side would not incur losses so big as to make me personally wait, so long as I had the dV available.

[bewing]

5 hours ago, paul23 said:

So we're all just going to ignore the typo "mum" and all kind of yo momma jokes?

No, it's more like Roger Rabbit. We're just seeing whose willpower breaks first. Shave and a haircut, ....

[TanDeeJay]

5 hours ago, paul23 said:

So we're all just going to ignore the typo "mum" and all kind of yo momma jokes?

Its the autocorrect on my phone that keeps converting mun to mum.

2 minutes ago, TanDeeJay said:

Its the autocorrect on my phone that keeps converting mun to mum.

Ahhahaha I corrected all the autocorrected spellings in the text but missed the title