New! What's the most fuel efficient way to brake during landing on Mun??

[uboats]

I tried many ways landing on Mun, straightly down, ascending orbit landing.

But for both I was always suffering less fuel.

For kerbal X which can land on Mun with about 15% fuel left.

While I tried several times that straightly down does not need circularize orbit and can save some dV.

Even in this case, I spent all fuel but still several hundreds meters above the surface.

I'm not sure when to start braking and should braking be turned on till touching the surface or need to be turned off midway?

I always turned the engine burning at max during landing for kerbal x which is very fuel consuming.

So is there any guide on how to efficiently landing on Mun manually? And can be extended for other planets?

Edited November 9, 2013 by uboats

[Geschosskopf]

As I hear it, the most fuel-efficient way to land on an airless world is where the deorbit burn puts you into like a 30-40^ downward arc. You then follow this down ballistically and only burn at the last moment possible.

However, I never do this at Mun because you don't have all that much control over the slope you land on, due to starting from high enough to arc down like this. Unless you're aiming at something already on the ground in a known flattish area, you have no real idea what the ground looks like until it's too late to do much about it. This can cause landers to tip over.

So, what I do instead is the straight-down method. But I do this from no higher than 10km (and no lower than 7-8km). This way, I can pick my spot with great accuracy and don't fall vertically far enough to need to burn that much on the way down.

[Tw1]

What you want to do, is come in mostly horizontal, then once you are slow enough, hover about for a bit before piking a final spot to land.

I typically do a burn about 1/2 to 1/4 of an orbit before I pass over the landing spot, putting my ship on a suborbital trajectory which ends a bit further than the intended landing area. Then, a second, much larger burn is made to kill the horizontal velocity, before vertical touch down.

This video (not mine) demonstrates efficient low TWR landing on the Mun. Note that this is an older edition of Mun, and you probably should be careful to orbit higher than the ridges.

[Daishi]

It all really depends on the capabilities of your lander. If it has a higher thrust, its generally safer when you come down vertically because you can slow down faster (but uses more fuel because high-thrust engines are less fuel efficient than low thrust ones).

However, for a low-thrust lander, you need to be able to get into a low orbit first so you have a shallow arc in your trajectory you can use for a longer braking burn. Engines like the LV 909, Poodle or LV N are ideal for this, and are the most efficient in the game.

However i think your main problem stems with the Kerbal X itself - it simply doesn't have enough fuel for a safe landing. It uses a Poodle, so its efficient, but because the lander doesn't have enough fuel no matter what you try, you'll have a hard time reserving enough for a return trip. I just tested it out and i'm on the Mun with 6 units of fuel left (no idea how you got 15% left in the tank). The main problem with the X is that you're carting down an engine heavier than you need, a heavy command capsule, parachutes, and a big decoupler.

Most of that in an ideal world (ala Apollo) would be left in orbit around the moon, to save weight and fuel, and connected up with later during a docking. So you descend with a lighter landing capsule, a dedicated fuel reserve and smaller engine, on a shallow trajectory so you have plenty of time for a braking burn for that little engine.

Theres a good tutorial with a two stage lander in "To the Mun" under Training - this should give you an idea of what an efficient Munar descent craft should look like. The Kerbal X isn't it

[Tidus Klein]

How I save D/V on mun landing, get the lowest orbit possible, for me its a seat clenching 5500 to 7000, witch by the way is low enough to see your CM fly by:cool:. at that low of an orbit you should be going some where around 500 M/S burn all that off and fall straight down. now place a maneuver node in the map view as seamlessly to the ground as possible(better to be above the ground) you will now have a rough guess in time till you hit the ground, turn your lights on if you have any and start looking for your shadow(if not on dark side) the moment you reach your maneuver node you should be in the range of 1000-500,m off the ground burn till your downward speed is about 20 M/S. and you should be able to see your shadow, watch that, but don,t trust it completely it will warp with the terrain, watch your lights to as soon as you see them start to light up the ground burn to 10 m/s and fall

now wait till your lights have almost completely light up the ground and your shadow is coming at you relatively quick. burn to 5 m/s and try to keep M/s under 10m/s as you start to fall again once once your shadow is right on top of you you should be able to guesstimate your self how far the ground is and land, never land faster then 5 m/s any higher then that and your in the danger zone of breaking something.

It normally takes me around 550 D/v to land on mun, and around 450 if I really try to be efficient.

PS always try and use the RCS to aim your ship at the bottom of a crater there normally the safest most none tillty place to land.

[toomuchbrew]

Break our brake? Either way, it is pretty efficient to use the ground to brake your decent, but it still break your lander. I end up with around 400 too 700 Dv ratio chew through before I get to where I want

Edited November 8, 2013 by toomuchbrew

[voneiden]

now place a maneuver node in the map view as seamlessly to the ground as possible(better to be above the ground) you will now have a rough guess in time till you hit the ground

Alternatively, use the cockpit view which features a nifty radar altimeter (and vertical speed meter and of course the navball).

[ttnarg]

With out testing it I cant say for sure but if you passing throw Mun SOI (as if your on a fly by path or free return orbit) then I think:

In theory aiming your craft at the middle Mun and pulling off a prefact suicide burn with 0 hover time would use the the least fuel.

But in practices timing those is hard I would aim my periapsis to almost touch the surface then do a hard burn to 0 my surface speed as I'm reaching my periapsis than should put me at the hight of my Periapsis with out the need for split second timing and should be almost be as good as a theoretical prefect suicide burn.

[TimMartland]

Technically, the MOST efficient way to land is by lithobraking at 900m/s, but i suspect thats not what you wanted

[numerobis]

In theory aiming your craft at the middle Mun and pulling off a prefact suicide burn with 0 hover time would use the the least fuel.

This theory is false; if it were true, the ideal ascent would be straight up, which is not at all the case.

You burn less by setting periapsis to just skim the surface, then when you get close to landing, burn at full throttle, adjusting your pitch so as to maintain constant vertical velocity (whatever your landing struts can manage). I don't think we have a proof that this is optimal, but it's far better than plummeting.

ttnarg is correct in that ideally you set the periapsis just right from as far out as possible -- from LKO if that's where you're starting from.

Another place to save fuel is in how to get to Mun in the first place: first your launch, of course. That's most of your trip; save a couple percent there and you get lots of leeway on the rest.

You can save a tiny bit (~30 m/s iirc) using a bielliptic transfer from very low Kerbin orbit. Launch to 70km LKO, then burn until the edge of Kerbin's SOI, and when you're there, raise periapsis to the Mun's orbit. That takes more burning than getting to the Mun, but you more than make up the difference because you'll be going slower when you land. You can shave the cost down yet more by doing a gravity assist off the Mun to get to the edge of Kerbin SOI.

[Frederf]

Separate the approach phase and landing phase.

Approach at minimum safe Pe over landing site. Retrograde burn initially until vertical speed reaches some safe maximum (-10m/s perhaps) and angle as necessary to maintain this vertical speed while reducing lateral. Once lateral speed is down to approximately your descent rate (within 45 degree of vertical), convert to landing phase.

[700NitroXpress]

Check out my video mission where I went to the moon and back to Kerban, I explain everything I'm doing in the orbital maneuvers and braking for landings. Mun landing is 20 minutes in.