Minimus Orbit

[[email protected]]

I've been trying to fly by or get into an orbit around  Minimus. I follow all the directions from Utube videos, use the nav ball, adjust inclination at half way, arrive at the Minimus orbit, with the planet close by, but no capture? It sails right on by. I've gone to the Mun several times and landed, but I did that by eyeballing it. I'm obviously missing something.

[Val]

Moved from Tech Support as it seems like a Gameplay question.

[Geonovast]

2 hours ago, [email protected] said:

I've been trying to fly by or get into an orbit around  Minimus. I follow all the directions from Utube videos, use the nav ball, adjust inclination at half way, arrive at the Minimus orbit, with the planet close by, but no capture? It sails right on by. I've gone to the Mun several times and landed, but I did that by eyeballing it. I'm obviously missing something.

You won't just magically get captured by Minmus.  You need to set up the counter, then burn retrograde at your encounter's PE to actually get into orbit.

Unless the encounter itself is what you're having a problem with.  Why are you changing inclination halfway?  It's much easier to do that in LKO.   Minmus' SOI is also much smaller than the Mun's, so you may just not be close enough for the encounter.

Can you get some map view screenshots?  Will help quite a bit.

[bewing]

4 hours ago, Geonovast said:

Why are you changing inclination halfway?

Because it requires a lot less fuel/deltaV, because you are going a lot slower.

And actually, the SOI sizes are about the same. A bit over 2000 km for both.

Edited December 17, 2018 by bewing

[Plusck]

5 hours ago, Geonovast said:

Why are you changing inclination halfway?  It's much easier to do that in LKO.

What? No! Really?

Changing inclination halfway costs at most dozens of dV, and even if it results in a steeply-angled burn in LMiO to capture into an equatorial orbit, will cost far less than trying to alter an LKO orbit to suit Minmus.

Your posts are usually spot-on and correct. What happened here?

5 hours ago, Geonovast said:

You won't just magically get captured by Minmus.  You need to set up the counter, then burn retrograde at your encounter's PE to actually get into orbit.

Yes, definitely. :up:

5 hours ago, Geonovast said:

Can you get some map view screenshots?  Will help quite a bit.

Yes, definitely again :up:

Edited December 17, 2018 by Plusck

[Geonovast]

8 minutes ago, Plusck said:

Your posts are usually spot-on and correct. What happened here?

I said it was easier, I didn't say it was cheaper.

[Plusck]

44 minutes ago, Geonovast said:

I said it was easier, I didn't say it was cheaper.

Ah, OK.

Still, I can't agree. Getting into any kind of destination-oriented orbit is not simple. I've never really tried for Minmus since it didn't seem worth the effort. On the other hand, I regularly do Moho-oriented orbits because the end result can make a huge difference to the dV budget (a hundred at least and maybe several hundred m/s overall).
I've never found it "easy" to get exactly right...

[bewing]

And I find the midcourse correction thing to be very easy. Look at your target orbit crossing, and ask "am I early or late, or too far North, South, East, or West?" Then make a tiny burn in the opposite direction by hand, until they line up.

[Gargamel]

I actually prefer to launch into the same plane as minmus.... that way I don't have to muck around with inclination changes at all.    But then again, I do rely on MJ for this, but I have done it by hand a number of times just to do it by hand. 

[[email protected]]

The problem is the capture. I have a 95% capture rate for mum, and thats eyeballing it.  The problem is I'm right on with the suggested orbit, but no capture.  I have no problem getting an orbit, if I can just get the capture.  Should I make my orbit exactly on or exceed it. I haven't figured out what the 2 grey markers on the Minimus orbit are. Are they the best capture point the closer together they are?

[ElWanderer]

12 hours ago, [email protected] said:

The problem is the capture. I have a 95% capture rate for mum, and thats eyeballing it.  The problem is I'm right on with the suggested orbit, but no capture.  I have no problem getting an orbit, if I can just get the capture.  Should I make my orbit exactly on or exceed it. I haven't figured out what the 2 grey markers on the Minimus orbit are. Are they the best capture point the closer together they are?

Sounds like you are missing the sphere of influence altogether. You can't capture if you don't get close enough.

The two grey markers indicate closest approach. You want to plot a manoeuvre and tweak it in all directions until you find which way (or ways) causes the markers to get closer and closer together. If you change your trajectory such that you will go into the planet's sphere of influence, the display will change to show a periapsis at the target. You can keep tweaking until this periapsis is nice and low, then burn the manoeuvre.

[Scarecrow]

Those grey markers need to be on top of each other for an intercept.

[Zhetaan]

14 hours ago, [email protected] said:

The problem is the capture. I have a 95% capture rate for mum, and thats eyeballing it.  The problem is I'm right on with the suggested orbit, but no capture.  I have no problem getting an orbit, if I can just get the capture.  Should I make my orbit exactly on or exceed it. I haven't figured out what the 2 grey markers on the Minimus orbit are. Are they the best capture point the closer together they are?

In the interests of clarity, capture means something different in KSP.  What you call capture, we generally call an encounter.  Normally, that wouldn't be an issue, except that capture also has a meaning:  it means to go from a fly-by encounter to a stable orbit around the target body.

Since the issue appears to be the encounter, I'll give the standard advice:  you need to move the closest approach markers together.  I'm not certain of how close you're getting to begin with, but the fact that you are seeing the markers is a good indication that you're in the right neighbourhood, at least.  When you set up a manoeuvre node, the intercept markers will change to reflect your future orbit after the burn.  You can play with the node controls to see what you need to do to get the encounter well in advance of the actual burn, and thus plan the encounter without wasting fuel.

As far as making your orbit exactly on or exceeding Minmus's orbit, it is most efficient to have your transfer orbit be exactly tangent to Minmus's orbit at the point of encounter (well, technically, you want it to be slightly under-powered so that your encounter has a low-periapsis flyby rather than an impact that you then have to undo, but that correction is usually only one or two metres per second).  It's okay to exceed a bit if you need to get an encounter, but then every extra metre per second that you spend to get to Minmus over the minimum is a metre per second that you have to cancel once you arrive.  Again, this is expected in normal manoeuvring, but it's something to plan for in advance.

[Superfluous J]

I prefer to make my maneuver node to burn at the An or Dn to Minmus, and just burn up extra to meet Minmus on the way up or down. It's a tiny bit more m/s in your initial burn to avoid the mid course correction later and I never did the math but don't even notice the difference when slowing down at the Minmus encounter.

Of course you can't care too much what angle you come in. I fix that after I've achieved orbit by making sure I encounter Minmus such that my Pe is on its equator, or touches the orbit of the thing I want to rendezvous with, then burn into an elliptical Minmus orbit. Then I go out to Ap (which is also the An or Dn) and fix it there for like 1m/s. Then I slow down again at Pe to encounter or whatever.