Minmus basics

[MPDerksen]

I would like to think I have a 3-digit IQ, but perhaps not?  I spend dV like congress spends tax dollars.  Getting to a Mun orbit (and back) is now decently do-able.  So I've decided to take the next step and shoot for a Minmus fly-by.  

Orbit around Kerbin:  Check!
Extend Orbit to 46M klicks (or whatever):  Check!
Set a course correction burn half-way to adjust inclination:  Utter failure!

Pretty sure I may be leaving my Kerbal orbit at the wrong time, but I just can't get an intercept/encounter.  Randomly moving things around is more like luck than science, and I want to LEARN what I'm doing, not just get lucky.  At this point, I'm not trying to even land.  Just pass it to collect some science and practice setting my burns correctly.

Second:  I have 1 pilot, completely out of fuel, orbiting Mun.  Eventually I'll send out something to get close enough that he can EVA over and come home.  I have no clue how to build the appropriate rescue craft.  Additionally the game is now giving me multiple "rescue" objectives from Kerbal orbit, but I don't know how to build a ship to go get them.  Do I just build an orbiter with an empty capsule and an OKTO for control, and learn to get close?  If that's it, is there a tutorial about matching orbits?  That seems like a really fundamental skill.

Last, I still struggle with landing on Mun without hitting too hard.  Playing with the Ctrl and Shift keys to keep the touchdown around 5m/s is SO hard.  Keep practicing?

I'm currently running version 1.4.  Do I, perhaps, need an update?

I know there are several questions here, but I wasn't sure if it made sense to split everything up.  Happy to do that on request.

Cheers, 

Michael

[Lapis]

1.4 should be fine, the versions don't really matter ( the later ones at least anything newer than 0.90 is essentially the same)

Do you know how much deltaV your rocket has?

I am assuming you are using maneuver nodes, I just mess around with them until I get an encounter. it could take time until you get a knack for it but after that it gets easier.

Edited January 16, 2019 by lapis

[Gargamel]

Some pics of what you are doing exactly might help, but here's something thing to keep in mind:

Minmus is inclined 6 degrees to Kerbin's Equator.   So even if you line up your timing and altitude perfectly, you could literally fly right over minmus without getting an encounter, you'll be to far "north or south" of minmus.   So during your mid course correction, adjust your inclination also by burning normal or anti normal as needed to meet up with the moon. 

[James Kerman]

I always burn for minmus on either the ascending or descending node.  You will probably need to make your apoapsis higher than minmus and you should get an intercept.  It costs about 930 Dv.  When you are at kerbin AP correct your inclination (your velocity will be at its lowest and that is when an inclination burn is cheapest).

As for rescue missions (in career) I use a basic pod/hitchhiker/heatshield arrangement that also fulfills the 5 man station contract requirement and either use the extra seats to level up crew or I loiter in the area to collect more stranded kerbals.

My method of landing (not the most efficient) is a burn to kill most of the velocity a little earlier than a suicide burn then, at about 100m and 20-30ms,  I tap shift until speed slowly decreases or X if I slow down too fast.  I usually land under 1ms.  One thing to remember is that if you are holding retrograde the SAS resets to stability assist under 1ms.

Edited January 16, 2019 by James Kerman
Added more information.

[Aegolius13]

30 minutes ago, MPDerksen said:

Do I just build an orbiter with an empty capsule and an OKTO for control, and learn to get close?

Yeah, pretty much.  You can take whatever you would normally use to orbit the Mun, add a probe core, and add a little more fuel margin for the rendezvous maneuvers.  Just make sure you have electricity for the core, and (if enabled) Commnet access.  And don't forget to double-check you DON'T have a Kerbal stowayayy in the rescue craft when it launches.  This has happened to me more times than I can count.  

 

32 minutes ago, MPDerksen said:

is there a tutorial about matching orbits?  That seems like a really fundamental skill.

There are probably a lot of threads on here about it, but I'd recommend Scott Manley's youtube tutorials first and foremost.  He's very good at explaining clearly, and I think it really helps to have a visual.  There some alternatives you can do when you're coming into an SOI (e.g., going from Kerbin to the Mun) and want to rendezvous, but it's probably easiest to get into a parking orbit and then match.  General guide to steps:

1.  Get rescue craft in parking orbit around the Mun.  I'd start out making the rescue craft's orbit a fair amount higher than the target's.  Try to eyeball the inclination, but don't worry about getting it exact yet.

2.  Find the ascending/descending node with respect to your target.  This really just means the point where the planes of the two orbits cross.  Do a normal or anti-normal burn until the orbits are in the same plane.  

3.  Once orbits are matched, set another maneuver node and do a prograde or retrograde burn until the rescue craft's orbit becomes tangent to the target's.  

4.  Drag this orbit around in a circle until you see a point where the to ships will end up close together.  If you don't see one, you may need to wait another orbit or several for the two craft to change their relative position around the Mun (as the higher one will take longer to make a complete orbit).  Keep iterating until you get a good approach, then execute the burn. 

5.  To finish the rendezvous, once the ships get close, point the active ship to "target" mode, and burn retrograde.  This will kill relative velocity.  Hopefully this will leave your Kerbal close enough to EVA.  

41 minutes ago, MPDerksen said:

Last, I still struggle with landing on Mun without hitting too hard.

It mostly just takes practice.  Do you know what your TWR is?  You want it to be high enough that you have room to recover from timing errors, but not so high your're bouncing all over the place.  Something like 5 might be a reasonable place to start.

If you're not already, leaving SAS set on surface / retrograde is pretty useful, since then you only have to worry about managing the throttle, not steering.  Just try to avoid completely killing your downward velocity, because if you start ascending again, the retrograde SAS setting will flip you upside down. 

 

[MPDerksen]

15 minutes ago, James Kerman said:

I always burn for minmus on either the ascending or descending node. 

Please explain what you mean by this.  I've seen most of the Scott Manly videos, and think I'm putting my initial burn maneuver in roughly the right place to get out to Minmus distance, but just not getting the encounter.  Too late?  Too early?  Too much inclination?  I'm tempted to get something in orbit (anything) and just play with potential nodes to learn.  

25 minutes ago, lapis said:

Do you know how much deltaV your rocket has?

I do not know how to even figure that out (Noob!).  I modeled it after the newest Scott video.  I may try landing on Mun with it first.  

With just a single occupant, I carry a pilot.  that really limits the amount of science I can return.  Can I see a picture of a viable lander with science modules on it that can make it back home?

[HebaruSan]

24 minutes ago, Gargamel said:

So during your mid course correction, adjust your inclination also by burning normal or anti normal as needed to meet up with the moon. 

Another option is to do the plane change burn in low Kerbin orbit (target Minmus, find the AN/DN labels, burn north near DN or south near AN till they get near zero). This is a less efficient expenditure of delta V, but it can make finding the encounter much easier, since with zero relative inclination you can drag a maneuver around and have it touching Minmus's orbit at all times.

(A third option is to do the plane change while launching to orbit, but that's kind of overkill just for Minmus.)

[Lapis]

4 minutes ago, MPDerksen said:

  I may try landing on Mun with it first.

that is always a good idea, for any interplanetary mission you should take to the mun to make sure that there are no issues with it.

5 minutes ago, MPDerksen said:

I modeled it after the newest Scott video.

could we see a screenshot please?

[Gargamel]

4 minutes ago, HebaruSan said:

(A third option is to do the plane change while launching to orbit, but that's kind of overkill just for Minmus.)

That's what I usually do, but mainly because I use MJ to automate my launches.  I have done it manually, but it's a real pain to do so., 

[James Kerman]

4 minutes ago, MPDerksen said:

Please explain what you mean by this.

When you have your vessel in low Kerbin orbit, go to map view and click on Minmus and select as target.  You should see two dotted lines to minmus An (ascending node) or Dn (descending).  These are the two points in your current orbit that intersect the orbital plane of minmus.  If you burn for the moon at these points you should be able to intersect Minmus without a inclination burn.

[MPDerksen]

2 hours ago, James Kerman said:

When you have your vessel in low Kerbin orbit, go to map view and click on Minmus and select as target.  You should see two dotted lines to minmus An (ascending node) or Dn (descending).  These are the two points in your current orbit that intersect the orbital plane of minmus.  If you burn for the moon at these points you should be able to intersect Minmus without a inclination burn.

makes sense.  HOWEVER!  don't I need to time it so that when I've crossed that distance, Minmus will be there?  I'm not clear on this part.

[Superfluous J]

10 minutes ago, MPDerksen said:

makes sense.  HOWEVER!  don't I need to time it so that when I've crossed that distance, Minmus will be there?  I'm not clear on this part.

Yes you do. But by adding prograde to your burn to extend your apoapsis out past Minmus' orbit, you DO change the time you cross the An/Dn marker. Dramatically so, in fact. You can easily double the amount of time to get to Minmus, giving you a large leeway.

To start, extend your orbit until your apoapsis is near the other An/Dn marker from where you started (what you normally would do to go to Mun, only at Minmus' An/Dn markers instead of the "correct" location based on where Minmus is), and you should get encounter markers (light blue) on Minmus' and your orbits. Then keep extending your Ap by adding prograde to the maneuver node, and the markers should get closer. Eventually, they'll be so close they'll turn into an actual encounter.

You may also need to drag the maneuver node itself around your orbit a little bit to make the encounter better.

[James Kerman]

17 minutes ago, MPDerksen said:

don't I need to time it so that when I've crossed that distance, Minmus will be there?

Just to expand on @5thHorseman's advice - The higher altitude your Ap, the slower you are going so your vessel will linger for quite a while in relatively the same spot, behind Minmus, making an encounter easier. 

I like to enter the sphere of influence of minmus after Kerbin apoapsis (on the way back down to kerbin) so that I can course correct at Ap.  A little trick I use when performing a course correction here is to lower my engine thrust (right click on engine, reduce bar on the thrust limiter).  This is a useful method whenever you want to make fine corrections.

[bewing]

2 hours ago, MPDerksen said:

makes sense.  HOWEVER!  don't I need to time it so that when I've crossed that distance, Minmus will be there?  I'm not clear on this part.

You need to lead Minmus in its orbit by about 60 degrees. Anything down to about 45 degrees works. When it comes to the midcourse correction, it's a lot easier to do it by eye, rather than using a maneuver node. You look at the orbit of your craft, and the orbit of Minmus (move the camera around so you can see the intersection point very closely). Ask yourself, "is my orbit below Minmus', or above?" If it's below, burn north on the navball's horizon line. If it's above, burn south. Do it gently, and watch your orbit change. When it just exactly touches Minmus' orbit, stop.

And a rescue ship is any ship with an extra empty seat and a hatch. You get within 2.2km, and then your rescuee gets to fly his jetpack over to your craft on EVA. Sometimes you need to use the "transfer crew" feature to make a seat available in the pod that you are attempting to board.

You might also want to try Shift and X for throttle during landing -- that's what I use. Using the thrust limiter on your engine also can increase your level of control a lot.

Edited January 16, 2019 by bewing

[Draalo]

For your first trys i recommend a HECS for rendevouz and rescueing. Because it can hold pro-/retrograde by itsself.

If you dont have the HECS yet use a MK! pod and a lander can below. Leave the lander can empty and put a pilot into the pod.

 

If you have to burn only a tiny amount of dV (like 5m/s) just rightclick your engine in space and set thrust to 1-10%.

Or use RCS, H and N are the keys you can use for fine adjustments.

(If you dont use RCS empty the monopropellant in all Capsules to reduce weight)

[Orc]

Greetings all.

MPDerksen, I'm not exactly a newbie, but I'm no expert either BUT I have landed on Minmus enough times to think that I have a clue about what I'm doing.

For Minmus fly by take the ship that you used to fly by the Mun. Add a little extra fuel (usually 1 FT 800 should be plenty). You will probably need to upgrade your launch pad to make room for the mass requirements. Add solar panels. You will definitely not be able to get there and back on the MK1 Capsule's batteries. If you are using SRBs to get the thing moving upgrade them. If you need to upgrade them passed Thumpers then you are doing something either very wrong or very different. My last Minmus fly by went up on three Thumpers almost all the way to orbit, two burning at 75% thuster limiter on a core burning at 50%. 

 

Launch and achieve orbit at your preferred altitude. I like anywhere between 80k and 95k. Go to the Map View. Select Minmus as your target. You should now see Ascending and Descending nodes on your orbit. Minmus is typically 7degrees or so out of alignment with you. Time warp till your ship is almost at one of the nodes and turn to Normal or anti-normal (depending on the node, I think its Normal at Descending, and Anti-Normal at Ascending). Burn slowly until your orbit lines with Minmus's orbit. It doesn't have to be exact within a degree or so is fine.

 

Now do your burn to intercept Minmus, just like as if you were going to the Mun, or intercepting an object in LKO. Keep in mind that if you are doing a fly by the gravity of Minmus will twist up the return part of your trajectory. You need to keep your wits about you when you exit the flyby. If you prefer to orbit Kerbin before re-entry, then make sure you have enough propellant. If you like letting your kerbals live dangerously then reduce your Periapsis to around 45K and enjoy the bumpy, hot ride.

 

Have fun. Minmus is just the beginning.... Oh and watch out for Minmus's terrain on your first landings there. That little green jewel can be a real meanie.

 

Regards

Orc

[MPDerksen]

39 minutes ago, Orc said:

Greetings all.

MPDerksen, I'm not exactly a newbie, but I'm no expert either BUT I have landed on Minmus enough times to think that I have a clue about what I'm doing.

For Minmus fly by take the ship that you used to fly by the Mun. Add a little extra fuel (usually 1 FT 800 should be plenty). You will probably need to upgrade your launch pad to make room for the mass requirements. Add solar panels. You will definitely not be able to get there and back on the MK1 Capsule's batteries. If you are using SRBs to get the thing moving upgrade them. If you need to upgrade them passed Thumpers then you are doing something either very wrong or very different. My last Minmus fly by went up on three Thumpers almost all the way to orbit, two burning at 75% thuster limiter on a core burning at 50%. 

 

Launch and achieve orbit at your preferred altitude. I like anywhere between 80k and 95k. Go to the Map View. Select Minmus as your target. You should now see Ascending and Descending nodes on your orbit. Minmus is typically 7degrees or so out of alignment with you. Time warp till your ship is almost at one of the nodes and turn to Normal or anti-normal (depending on the node, I think its Normal at Descending, and Anti-Normal at Ascending). Burn slowly until your orbit lines with Minmus's orbit. It doesn't have to be exact within a degree or so is fine.

 

Now do your burn to intercept Minmus, just like as if you were going to the Mun, or intercepting an object in LKO. Keep in mind that if you are doing a fly by the gravity of Minmus will twist up the return part of your trajectory. You need to keep your wits about you when you exit the flyby. If you prefer to orbit Kerbin before re-entry, then make sure you have enough propellant. If you like letting your kerbals live dangerously then reduce your Periapsis to around 45K and enjoy the bumpy, hot ride.

 

Have fun. Minmus is just the beginning.... Oh and watch out for Minmus's terrain on your first landings there. That little green jewel can be a real meanie.

 

Regards

Orc

This is very helpful.  But a clarification:  I thought that inclination changes were most effective when you were halfway to the target.  Or am I thinking of something different?

[Orc]

Hi MPDerksen

You wrote: This is very helpful.  But a clarification:  I thought that inclination changes were most effective when you were halfway to the target.  Or am I thinking of something different?

 

AFAIK any change in DeltaV (which is what a inclination change is) are most effective at either the Apiapsis or Periapsis. Since your As and Ds nodes are not at your Apiapsis or Periapsis you need to pick the pick the one closest to your current position. 

 

Veterans and Those with the Know-how of the Math are welcome to correct me.

 

Regards

Ork

 

[bewing]

9 minutes ago, MPDerksen said:

This is very helpful.  But a clarification:  I thought that inclination changes were most effective when you were halfway to the target.  Or am I thinking of something different?

You get the most inclination change per unit of fuel if you wait until you are halfway, yes. But it leaves you shooting blind a bit -- if you do your inclination change while you are still in orbit, then the manuever node tool will tell you when you have an intercept -- while you are still in orbit. If you wait until later to do your inclination change then you won't know for absolute certainty that you have an intercept until you do the inclination change.

Edited January 16, 2019 by bewing

[Rauko]

3 hours ago, bewing said:

You get the most inclination change per unit of fuel if you wait until you are halfway, yes. But it leaves you shooting blind a bit -- if you do your inclination change while you are still in orbit, then the manuever node tool will tell you when you have an intercept -- while you are still in orbit. If you wait until later to do your inclination change then you won't know for absolute certainty that you have an intercept until you do the inclination change.

You can get the best of both. You can set your prograde maneuver node in orbit, and set a midcourse inclination maneuver node BEFORE burning the first (perhaps you may have to change the number of patched conics in the game menu,so that you can see your current orbit,the one after initial burn,the one after correction burn, and the minmus orbit, I dont know the default value)

That way you set effficient burns, but have plenty of time to fiddle with your nodes to grant intercept. (Provide you can burn VERY accurately your nodes)

[Kryxal]

8 hours ago, bewing said:

You get the most inclination change per unit of fuel if you wait until you are halfway, yes. But it leaves you shooting blind a bit -- if you do your inclination change while you are still in orbit, then the manuever node tool will tell you when you have an intercept -- while you are still in orbit. If you wait until later to do your inclination change then you won't know for absolute certainty that you have an intercept until you do the inclination change.

I tend to use a second maneuver node to find out where Minmus is going to be when I get up there, it's not hard to drop it on the AN/DN.  It at least gets you close enough to get target markers, then you redo it once you make the actual first burn.

[MPDerksen]

\

Sorry about the watermark...

Maybe we take a step back?  How do I determine how much dV this thing has?  How much is a reasonable range to get into LKO of about 85K?  I'm sure many of you will consider the grossly over built for a LKO rescue, but can we just start here, have some success and then refine it?  I can get to about 70K before I have to dump off the 4 externals.  Then, I'm left with the middle stage to circularize.  My hope from there is that I have MORE than enough to learn to meet up with the stranded Kerbal in orbit, get her on board, then land.  I've already tested everything (landed fine) without worrying about the interception part.  

Here is my map of what's going on:

my rescue craft is at 3:00, behind the 3 individually stranded 'nauts.  I've set the one closest to me as target, and this is now what I see.  Next, I'll read up on matching orbits etc. but those orange handles seem VERY far apart, and I've NO idea how to close the distance.  

(Indeed, I have no idea about many things, but I will say I'm having quite a bit of fun with this....)

[HebaruSan]

Rendezvous will be easier if you're ahead of your target: pick a spot, drop a maneuver node, and boost the prograde vector until the close approach distance gets near zero. To catch up, you need to lower your orbit, which is going to be tough in the above pictured situation.

[Kerbalstar]

For rendezvous you first need to make sure that your orbit is higher or lower than the target significantly, then use maneuver nodes to get an encounter. Pinging @Snark, because I'm tired and he can explain in great detail.

[MPDerksen]

Right, making progress.  I raised my Ap a bit, time warping, and my intersection is getting closer each round and my target catches up.  Stay tuned.  (may wish I had added some RAS thrusters on this yet)

My orbit remains a bit bigger than that of the target.  Do they have to be exact?  I'm actually not even sure how close I need to be to the lost derelict to "collect" him.  Maybe I'm supposed to EVA over to claim it?

Edited January 16, 2019 by MPDerksen