Can’t get out of Mun escape!

[Oscrat1000]

Hello All! Lately I have been trying to land on the Mun but every time I get into Munar orbit I can’t change my trajectory and fly right to Mun escape and it seem impossible to alter my trajectory no matter which way I boost. Any tips or ideas are much appreciated. Thanks!

[Gargamel]

Moved to gameplay questions. 

[CFYL]

There are a bunch of Tutorials on the wiki. https://wiki.kerbalspaceprogram.com/wiki/Tutorials#Mun

I can't speak as clearly as those. Maybe you can read them, and post your questions here if you still can't complete your mission.

[Zhetaan]

2 hours ago, Oscrat1000 said:

Hello All! Lately I have been trying to land on the Mun but every time I get into Munar orbit I can’t change my trajectory and fly right to Mun escape and it seem impossible to alter my trajectory no matter which way I boost. Any tips or ideas are much appreciated. Thanks!

You can boost, though, right?  If that's the case then it's a matter of one of two most likely causes:  pilot error and rocket design.

Pilot error is the easiest thing to correct, but it assumes that you are completely new to KSP and need help learning to fly.  That's not a bad thing (we were all new at this once), but if you can get a rocket into orbit and fly to the Mun, then it suggests that rocket design is the most likely issue.

Just the same, if you are completely new and need help learning to fly, then some basic instructions are in the spoiler.

Spoiler

I'm going to assume that when you speak of getting to Munar orbit, you mean a hyperbolic orbit or flyby.  Mathematically, there are a few solutions to go from a flyby to capture into a closed orbit, but there's only one 'best' solution.  It's a combination of two things:  you have to boost at the right location, and you have the boost in the right direction.

The right location is the periapsis, or the point on your flyby that is closest to the Mun's surface.  I'm going to guess that your problem is not that you're crashing into the Mun's surface (though trying to avoid that and overcorrecting is a possible reason why you keep escaping).  Generally, if you're trying to land, then the closer you can orbit the body that you're trying to land on, the better.  You need to avoid the atmosphere (easy for the Mun, since it doesn't have one), and you need to avoid crashing into tall mountains, so there is a minimum 'safe' altitude that avoids terrain and gives a good margin for error and for orbital operations, which for the Mun is about 15 km.  Since you're having trouble achieving orbit, let's say that any periapsis altitude between 15 km and 50 km will be good--we can fine-tune later.  It's less efficient to capture at a higher altitude, but it turns out that so is escaping when you want to capture.

If you need help finding the periapsis, it's the little downward-pointing arrow on the orbit with a Pe inside it.  The forum doesn't include such a marker in its icon suite, but here's an image of one from the wiki (it's the one on the right):

 

There may be a couple of such flags in different colours:  that only means that you have a periapsis for Kerbin orbit as well as Mun orbit.  In that case, you want the Mun one.  If you're currently orbiting Kerbin, then the Pe marker that you want will be orange.  If you're currently flying by the Mun, then the Pe marker that you want will be blue.

The right direction is to boost retrograde.  That is the direction indicated by this marker on the navball:  

Figuring out the timing of the burn and the burn duration is a science in itself, but the nice thing about KSP is that it includes two tools to help you in this.  One is the manoeuvre planner, which is the ability to click on your orbit and create a manoeuvre node to see how a planned burn will affect your trajectory.  The second is map view, which lets you see how your burn is affecting your orbit in real time.  Either or both of these will help you ensure that you reduce your orbit to something vaguely circular rather than escaping to points unknown.

On the other hand, let me ask:  are you simulating an Apollo-style mission?  Do you have a separable lander of any configuration?  Your problem may be that, assuming that they are docked nose-to-nose, your upside-down vessel is the control point for the whole assembly, and every time you orient retrograde to burn for capture, you're actually burning prograde to escape.  If that's the case, then right-click on the pod correctly oriented, select 'Control from Here', and try again.

Don't forget to tell us whether that worked (and if not, then please provide a screenshot of your rocket, preferably in flight, so we can try to diagnose the problem).

Good luck!

 

 

[Snark]

3 hours ago, Oscrat1000 said:

Hello All! Lately I have been trying to land on the Mun but every time I get into Munar orbit I can’t change my trajectory and fly right to Mun escape and it seem impossible to alter my trajectory no matter which way I boost. Any tips or ideas are much appreciated. Thanks!

The short answer is:

1. wait until you are at your closest approach to the Mun (where the "Pe" marker is)
2. point your ship so that is centered on the navball crosshairs
3. thrust until you're captured to orbit.

That glosses over a lot of useful details, for which I'd suggest reading @Zhetaan's excellent, detailed post just above. 

But the simple version boils down to this.

[king of nowhere]

if you apparently can't change your orbit no matter which way you boost, i suspect you are not boosting after all.

does your orbit actually change? maybe you run out of fuel, or maybe you are using an unmanned probe and you have no control. or maybe you have no reaction wheels, so you can't control your direction.

pictures would help

[Oscrat1000]

@Zhetaan Which stage do you want a photo of? (I’m playing sandbox btw)
I’ll make a list below:

Ascent stage (1 mammoth and 4 twin boars)

Intermediate stage 1 (1 mainsail)

Intermediate stage 2 (again, another mainsail)

The payload is a permanent one part Munar base with a poodle and 8 baguette tanks for descent control.

(I also have a quicksave at a Mun encounter with this craft.)

Edited May 20, 2022 by Oscrat1000
Edit- Added quicksave and fixed a few grammatical errors

[CFYL]

6 hours ago, Oscrat1000 said:

Ascent stage (1 mammoth and 4 twin boars)

Intermediate stage 1 (1 mainsail)

Intermediate stage 2 (again, another mainsail)

The payload is a permanent one part Munar base with a poodle and 8 baguette tanks for descent control.

One problem with a large ship is that, it is hard to turn it to the correct direction. You may need to add reaction wheels or RCS thrusters+RCS tanks to your ship. As mentioned above by @Zhetaan, burning retrograde at pe will get your craft into an closed orbit around the Mun.

A screenshot of your craft at this quicksave, showing its major parts, would be helpful.

6 hours ago, Oscrat1000 said:

(I also have a quicksave at a Mun encounter with this craft.)

 

[Oscrat1000]

Thanks so much everyone! I got into Munar orbit! 
It’s asymmetric and with a perapsis of 629,823m and an apoapsis of 1,138,875m.

(I don’t really know how to paste photos since I’m on mobile so that’s why I wrote down the stats) 

I also quicksaved and should I try to close my orbit or go in for landing? 

Thanks again for all the help, Oscrat1000.

Edit- I still have intermediate stages 1 and 2 but 1 has barely any fuel.

Edited May 21, 2022 by Oscrat1000

[king of nowhere]

1 hour ago, Oscrat1000 said:

Thanks so much everyone! I got into Munar orbit! 
It’s asymmetric and with a perapsis of 629,823m and an apoapsis of 1,138,875m.

(I don’t really know how to paste photos since I’m on mobile so that’s why I wrote down the stats) 

I also quicksaved and should I try to close my orbit or go in for landing?

how much deltaV do you have left? how much thrust to weight?

there are many things you can improve with your manuevering. You have a very high periapsis, which is a reason why you had so much trouble closing the orbit; you should plan your manuever node to enter with a low periapsis.

 

[jimmymcgoochie]

That rocket is massively overbuilt for going to the Mun- you don't need two Mainsail-powered stages to get there unless your base is absolutely huge, plus the Mainsail is pretty inefficient in space and heavy to boot. Without seeing any pictures of the craft in question it's hard to give concrete advice, but I'm pretty sure that you don't need a Poodle to land your base on the Mun, and you definitely don't need two Mainsail-powered upper stages to get there.

Reasons for difficulty controlling a vessel are usually one of:

• No power. This will not only disable the reaction wheels, but also disables probe cores and can result in a complete loss of control on an uncrewed vessel. Add power sources (solar panels, RTGs, fuel cells) and/or storage (batteries) to mitigate against this.
• No usable control point. Aside from a lack of power, probe cores will also stop working properly if they're in hibernation mode. Crew pods will only provide control when there's a Kerbal inside them to operate the controls. Make sure your probe cores aren't set to hibernation mode (hibernate in warp is fine and is a good idea to save power) and if crew are aboard, that at least one of them is in a command pod rather than a Hitchhiker or lab module.
• No signal to Kerbin, which prevents most manual controls with probes- SAS and full/zero throttle will still work unless you have 'require signal for control' switched on in the difficulty settings. Add more/larger antennae to mitigate against this (all antennae can co-operate to boost the total communications range on a vessel, apart from the Communotron 16S which doesn't), establish relay networks to cover blind spots when a direct signal to Kerbin is unavailable. If you're playing with CommNet switched off, you can ignore this point.
• Insufficient control authority, often because you're using a small reaction wheel (e.g. built into a probe core) to try and turn a large, heavy rocket. Add reaction wheels to improve control authority, RCS is an option but uses finite propellant whereas reaction wheels use electricity which can be generated for free, firing the engine at low throttle may also help thanks to engine gimbal but will also use fuel and alter your trajectory in a potentially undesirable way.
• No SAS, either because you're using the Stayputnik probe core that doesn't have it or because your crew aren't pilots, who are the only Kerbals who can use SAS. A scientist or engineer can still operate the controls, but it's a lot easier to fly with a pilot. Use a probe core with SAS built in to counter both problems (a probe core with SAS will still provide SAS when a non-pilot Kerbal is at the controls) and/or make sure a pilot is flying.

[Oscrat1000]

@jimmymcgoochieThanks for the tips! I was missing a big enough reaction wheel and power. Just as a quick question, what engine should I use on the intermediate stage/stages instead?

Also,  what should I replace the poodle with?

Thanks again, Oscrat1000

Edit- Do you burn on the retrograde to close orbit?

Edited May 22, 2022 by Oscrat1000

[king of nowhere]

9 hours ago, Oscrat1000 said:

@jimmymcgoochieThanks for the tips! I was missing a big enough reaction wheel and power. Just as a quick question, what engine should I use on the intermediate stage/stages instead?

Also,  what should I replace the poodle with?

that depends entirely on how big your payload is. if it has to drop a whole mun base, it may actually need big engines. you should look at the TWR - thrust to weight - value. you can see it in the VAB.

for the first stage, you want a TWR around 1.5 (sea level). for subsequent stages to reach orbit, you want a TWR around 1 to 1.5 (vacuum), though you can get by with a bit less. for stages in orbit, you want a TWR around 0.5, less power to save mass on the engine. that's also enough to land on Mun, though more thrust makes things easier.

 

 

Quote

Edit- Do you burn on the retrograde to close orbit?

yes, always. the point is that you are too fast for the planet gravity to hold you, and so you slow down until that's no longer the case. how else did you manage to get captured in the past?

to get to Mun, you burn prograde from low kerbin orbit until your apoapsis reaches Mun, it should take around 850 m/s of burn. You want to have a low Mun periapsis - around 10 km is best - because it will make injection cheaper. then you reach Mun, and when you are at periapsis you burn retrograde; if you do it well, it should take roughly 100 m/s to get captured in an elliptic orbit, and another 200 m/s to circularize the orbit.

if you are spending more, it means you can improve

Edited May 22, 2022 by king of nowhere

[Oscrat1000]

Thanks everyone! I’ve landed in the Mun Highlands! 
 

Thanks Again, Oscrat1000