Tips on the most efficient, fuel wise, Munar landing.

[Void Eternal]

If tl;dr, you can skip to the third paragraph because the stuff before it isn't too important to be read, or if you just refuse to read, just tell me the most efficient way to get a mun landing.


The training on this first has you go to an equatorial orbit, then the second part is dedicated on landing, so I thought maybe that wouldn't be as efficient. I am not worried about riskiness b/c I can retry bad burn timing and♥♥♥♥♥♥

What I typically do is go to kerbin orbit via getting Ap to a little over 70 km, then prograde burn at Ap 'till Pe is 70 km at minimum, I do this mainly b/c tourists wanting kerbin orbit, but also so that I don't have to worry about what position the moon is in during my leaving kerbin.

What I want improvement on is after kerbin orbit. Typically what I go for is getting from a single burn, starting in the most fuel efficient part of my orbit for doing this, a mun fly-by that has a periapsis of ~N/A-30 km. After I reach somewhere between 10 km and 40 km in fly-by 'orbit' of the Mun, I retrograde burn until my speed is maybe somewhere around 50 m/s. Then start decreasing more steadily and slowly until I reach the surface.

I would like to know if either the training's method of just reaching the Mun at all then orbit then descent to ~5-20 km Pe, my method, or some middle ground inbetween is the cheapest on fuel. All of this of course in order to maybe realise I might need less fuel from the start (which would be cheaper and at the same time make every bit of fuel more valuable b/c newton's second law, F=ma).

Thank you for helping make me more efficient (at fuel usage)!

[Toastie Buns]

Best fuel way is to launch and direct ascent to the mun, but let's ignore that and go to landing

Whatcha do is set that Pe to around 4km and hope to ♥♥♥♥ the large canyon or also large mountain isn't there this time you're landing (alternatively set your Pe to 4.5km) wait until you're at Pe and burn like a ♥♥♥♥♥♥♥♥♥♥♥♥ on retrograde.

Your task now is to fight the navball, you want to keep it horizontal-ish, but be decreasing in altitude. You're still going sideways at an insane speed at this point.
Should you think "OH ♥♥♥♥ I'MMA COLLIDE" then push the retrograde vector away from the ground and vice versa.

Your overall task should be to land as sideways as possible until you've mastered this. Any, repeat ANY fuel wasted on slowing down and hovvering is not at all fuel effecient.

in closing; sideways for life

[Jupiter3927]

For getting to the Mun, the most fuel efficient way is the way you don't fight gravity.
Going straight up from the launch pad to the Mun costs more fuel than going to orbit first and doing a transfer from a circular orbit.
Most players start doing their gravity turn in the low atmosphere for the fuel savings.

For landing, I'll have to check the math on this but going to low orbit then landing should be more fuel efficient.
You aren't fighting gravity during your insertion burn but you are for landing.

For actually landing, the absolute most efficient way is to go sub-orbital and do a suicide burn.
This maneuver is near impossible to do without (even with) computer assistance because you need to fire your engines on full power at the last possible moment.
You waste fuel or hit the ground hard if you mess up.
A much safer method is your controlled descent but you waste fuel fighting gravity if you keep your vertical speed low.
Try practicing with a fast descent until you get the feel for it and you'll have more efficient landings.
Custom landing gear made from structural parts can take a huge impact (50+ m/s) and survive so they're good to practice with.


Don't fight gravity and you'll have better fuel efficiency.

[Toastie Buns]

Originally posted by Jupiter3927:

Going straight up from the launch pad to the Mun costs more fuel than going to orbit first and doing a transfer from a circular orbit.

Nope. Direct ascent will always win. Try it on an interplanetary level, then you'll see the difference. Your window is just smaller, that's all.
To the mun, there's hardly any difference, but you will save yourself time, be able to timewarp faster much quicker and generally the stage that was in charge of making that happen is now falling back to Kerbin as debris, so your debris worry is gone.

[RoofCat]

I think the direct ascent case is sort of like launching from Kerbin with OP engines. You can get below 3000m/s for LKO, but that won't be the best rocket in price, performance and range. And must be started with (engine) TWR=100+ sepatrons. The same way you can get to Mun surface with direct launch and landing with least delta v. Extreme launch and extreme landing. But not with best accuracy, lowest price or best manual comfort.

In theory direct launch doesn't require you to circulize at Kerbin, so you could have a case where Pe is still below ground and thus save delta v.

In theory. In praxis though that would require very steep climb on Kerbin. Because otherwise Pe will still rise above ground while burning for Mun (even slightly orbital shaped burns work on opposite side too) which, except done with OP TWR, would waste more on vertical ascent (hovering) than the optimal gravity turn going shallower.

So in the end in my tests the result with something inbetween required more expensive ships while gaining like <10m/s savings for Mun - not really worth anything except you go for a really explosive launch (10+G or something) with even more OP build. Which will cost even more for extra nose cones, decouplers, more powerful engines, higher launch mass SRBs (might be important early on), etc.



TL;DR your described launch is pretty much optimal for human imo.
You can reach high accuracy, low costs and high comfort.

As for myself I always go for highly accurate 71..72km LKO, make burn at optimal spot moving node around and get it down to 20..25km Pe at Mun.

Could go lower, but first grand canyon on the dark side is up to 7km at some spots iirc and also if you go <10km it's basically better to land already. Because time warp(!) is limited by altitude and you will be forced to watch really slow one if you arrive lower and want to land much further from tail side. Waste real time.

[Void Eternal]

I am getting a general census that either my or the tutorial's method is better, but is going for an orbit of the mun first better or is a straight collision course after kerbin orbit better?

Originally posted by Toastie Buns:

... generally the stage that was in charge of making that happen is now falling back to Kerbin as debris, so your debris worry is gone.

Also why would debris be a worry? You can always terminate debris, or any other vessel from the tracking center, and if you mean from your own debris destroying your ship as it falls away, in order to prevent debris doing that you can point prograde before seperation, and it will fall away parallel to your spacecraft.

[RoofCat]

Transfer burn for impact is tiny bit more expensive. Like 0.1m/s :D
So ignore that.

The lower a Pe, the more efficient burn at that Pe. But also the higher the velocity there. In general Oberth effect would mean you have to choose Pe as low as possible.

Then going that route and considering your Pe might be subsurface, you land before reaching Pe (up to Mun diameter apart, actually less, probably 2/3?) and thus on one side you have less speed to bleed yet, but on other side you are not at the most optimal spot to do that burn.

It's a mess and the difference for Mun is really tiny. Also unlike Kerbin it doesn't rotate much.

My best guess would be you can save most delta v flying on a straight line from Kerbin to Mun. But that won't be the cheapest ship! And targeting would need high timing accuracy.
If you go for a regular landing though, I would guess Pe touching the surface would be best. You are at optimal spot to reduce your kinetic potential at Pe. And it is where you land. But again, for Mun those values are so tiny you could probably save more with better suicide execution on a regular landing than digging all that math for perfection in approach.

[Toastie Buns]

Originally posted by Boruba gro-Ramak:

Also why would debris be a worry? You can always terminate debris, or any other vessel from the tracking center

Yeah, but wouldn't it be just magical if you could fly your ship or engineer it in a way that the stages fell to their death in suborbital trajectories? You don't have to visit the tracking center then.

I'll level with you; my way is advanced as ♥♥♥♥, the landing is extremely hard and all about embracing horizontal velocity, but if you learn it you'll be in good stead for high G landing, which is a very, very valuable skill. Right now your d/V and remaining fuel doesn't matter, you either made it or you didn't. Who cares? The Mun is right there, a simple drive to work.

Out there in the far reaches, you'd prefer not to call for help or make overcompensating designs.

Edit: I forgot to mention eventually your space planes will need to be landed horizontally, unless you're content with it flopping on its side, or pointing at the sky like a rocket, lol

[Toastie Buns]

Ultimately, as stated in the thread, your most efficient ways to save fuel are to burn at periapsis, burn 100% throttle and make last minute burns (suicide burns). The way I described is a suicide burn of sorts, but you're interested in being as low to the ground as possible with high horizontal velocity, the idea being that you're killing momentum as late as possible, rather than killing it, falling, killing it again, floating, coming to a rest.

[RoofCat]

sort of get down to 300m/s on a regular approach very low above ground while choosing actual spot, reduce to 200m/s shortly before, put on adult diapers and then keep those 200m/s for as long as you can (depends on engine TWR). At least avoid going less than 100m/s until the very last seconds and your landing will be good enough.

Mun gravity is just 1.67m/s². Which means your good regular landing is just 20..30m/s apart from great one. I had a case when I missed 45m/s or so. Couldn't do it no matter how many times I tried. Got down to 15m/s with extreme last second burn running out of fuel exactly at touchdown and still blew up my engines or legs.

So basically just don't go too slow. And don't worry much about Mun.
This skill really shines at Tylo. And basically only there. Because perfect suicide burn there can save hundreds of m/s. Unfortunately accuracy required for that is nearly inhuman. Due to how fast you go, how far in advance you have to start, and how ground changes below you while pulling you with high G, while also being out of full resolution range.
It's also much easier to have TWR of 4 or more on Mun. It's so much harder at Tylo for at least 2 reasons - high G and far travel to get there first so you may not have that luxury of OP engines to slow down quickly. So your Tylo slowdown takes much longer and the safety reserve is tiny.

[Toastie Buns]

Everyone forgets Dres ( ; - ;) wait ♥♥♥♥ no thats least gravity, lol my bad.

[Manwith Noname]

That's because Dres doesn't exist.

[erik_stewart]

Originally posted by Toastie Buns:

Ultimately, as stated in the thread, your most efficient ways to save fuel are to burn at periapsis, burn 100% throttle and make last minute burns (suicide burns). The way I described is a suicide burn of sorts, but you're interested in being as low to the ground as possible with high horizontal velocity, the idea being that you're killing momentum as late as possible, rather than killing it, falling, killing it again, floating, coming to a rest.

Agree. I find the suicide burn approach to be the most fuel efficient for landings on all the vacuum bodies.

[Chibbity]

Change to surface mode on your Navball, lock it on hold retro, wait till the last possible moment and suicide burn.

You want to kill your vertical and horizontal at the same time.

It's like crossing a large field diagonally instead of walking two sides.