Need help with landing on mun and back. (how to do it efficiently)

[JustaGamer]

So first, allow me to say that I have been able to land on varios places on the mun before and go back. My problem is that I have never be able to do it efficiently.

Usually it takes me an average 70k rocket for me to go to the Mun, land, and fly back. And this with minimum margin of error, a "proper" rocket that will allow me to land, do science, and fly back without sweating I gonna run out of fuel and strande somewhere easily cost 100k. Needless to say playing in career mode this's not exactly sustainable.

I think, my problem is with the landing phase. Usually by the time I make interception to when I land, I can easily burn up 1800-2000 delta-V to get into mun orbit and slow down during the touch down. Anyone have any suggestion?

[jcekstro]

son8797님이 먼저 게시:

Eh ... that's a bit over the top for me. I still try to keep the built within reasonable reality, sliding on the surface is a bit ... much lol.

I only use 2.5m part for landing mission though, you're right about the 1.25m part, I always use it for flyby or orbital mission.

Suit yourself, but remember mun is one of the cheapest delta-v places to go. If you venture outside of kerbins SOI, you will have to exponentially increase the size of your vessel, making for a VERY expensive rocket. If you are worried and want to keep costs down look into 1.25m designs.

[kesat]

Didn't play for a while now - but if iirc the most efficient way to land on the mun (or any other planetary object without an atmosphere) is about killing horizontal speed first (not the same as a retrograde burn) after you got into orbit around the mun and then wait as long as possible before you kill your vertical speed (if possible: suicide burn - but that's pretty risky).


edit: Well maybe i was wrong. I just digged out my old dusty 2.5m mun lander and landed on the mun. Getting down to the surface from a mun intercept (180km) i needed around 1400m/s DV. While I'm out of practice myself too, it's still more than i expected...

[Toastie Buns]

kesat님이 먼저 게시:

Didn't play for a while now - but if iirc the most efficient way to land on the mun (or any other planetary object without an atmosphere) is about killing horizontal speed first (not the same as a retrograde burn) after you got into orbit around the mun and then wait as long as possible before you kill your vertical speed (if possible: suicide burn - but that's pretty risky).

Yeah, you're semi-wrong. Hate to be that guy, but THE most efficient way to land on the moon is via low d/V routes. You'll notice you can get to the moon for less d/V depending on what side of the planet you're currently at. You can also loop behind for a considerable detraction in cost for your orbital burn. You can also make heavy use of the blue thing on the nodes (I don't exactly know what it's called, I call it sidegrade because it amuses me) to make your descent, rather than the ever more costly retrograde burn.

Then, as you stated, suicide burn is best burn.

EDIT: You can also make your burn directly from crater to free-return depending on the phase angle between your crater and Kerbin. This is considerably cheaper than orbiting then searching for the return.

EDIT PART II, ELABORATION BOOGALOO: To explain a little further, speed increases and decreases as you orbit a planet (or anything with gravity). This is natural due to rotation, each spin you take a little speed from the planet and give it back on the opposite side, slowing down. This can be (and is) easily exploited to create low d/v docking, low d/v landing and low d/v injection burns.

Hope this made sense.

[ghpstage]

son8797님이 먼저 게시:

Eh ... that's a bit over the top for me. I still try to keep the built within reasonable reality, sliding on the surface is a bit ... much lol.

I only use 2.5m part for landing mission though, you're right about the 1.25m part, I always use it for flyby or orbital mission.

Sliding across the surface is an extreme method, but I like building to extremes.

There are other solutions to the problem of tipping over that you could use,
Some possibilities,

• Use a larger number of smaller tanks on the landing stage to shorten and widen it.
  
• Include a small horizontal thruster (Sepratron, 48-7s) in a service bay that would point vertically when the craft tips over.
  
• Add landing gear above the centre of mass so you land with your thrust angled away from the ground.

Of course each one would have its own impacts on the characteristics of the flight, perhaps forcing other changes.

[RemoteLeg]

See this video by Scott Manley that shows you exactly how to land on the Mun safely.
Many Kerbals died until I watched Scott's tutorials.

[jcekstro]

• Include a small horizontal thruster (Sepratron, 48-7s) in a service bay that would point vertically when the craft tips over.
  
  
  Holy crap that is genious. I never even thought of something like that.

[sabe042]

Your starting weight has a lot to do with how expensive your rocket will be. Here's a design that seems to work well. It is about 45k funds - not dirt cheap, but allows some science to be performed as it contains two material bays, two goo canisters, and two thermometers (inside service module).

It has about 8847 delta-V total, which is a bit more than you need. It also has a pretty good base width and can land on a gentle slope without tipping over. In my test run I was able to fly to the mun, land, and fly back with about 1865 delta-V left over. I think I flew pretty efficiently, but it was all manual. No autopilots or anything like that.
http://steamcommunity.com/sharedfiles/filedetails/?id=523673571
http://steamcommunity.com/sharedfiles/filedetails/?id=523673646
http://steamcommunity.com/sharedfiles/filedetails/?id=523673785
http://steamcommunity.com/sharedfiles/filedetails/?id=523673986
http://steamcommunity.com/sharedfiles/filedetails/?id=523674264
http://steamcommunity.com/sharedfiles/filedetails/?id=523674355
http://steamcommunity.com/sharedfiles/filedetails/?id=523674525
http://steamcommunity.com/sharedfiles/filedetails/?id=523674749
http://steamcommunity.com/sharedfiles/filedetails/?id=523675027

[JustaGamer]

kesat님이 먼저 게시:

Didn't play for a while now - but if iirc the most efficient way to land on the mun (or any other planetary object without an atmosphere) is about killing horizontal speed first (not the same as a retrograde burn) after you got into orbit around the mun and then wait as long as possible before you kill your vertical speed (if possible: suicide burn - but that's pretty risky).

Well, I don't know about if it's the most efficient, but it's certainly more efficient than that I have been doing. I actually learnt how to do this last night. Let just say it takes a lot less delta-V to cancel out the horizontal speed 15k off the surface comparing to cancel it at 5k.

Toastie Buns님이 먼저 게시:

Hope this made sense.

sadly, nope. Care to elaborate a bit more? I'm aware of the speed increase and decrease between the min and max point, but I don't see how it will helps on an asmophereless body since there is nothing to use as an air brake. Also what is suicide burn?

[JustaGamer]

@Sabe, that's ... definetely a radical design lol. I definitely gonna have to try that sometime, 2 material bay for under 45k is too good to pass up! I have always wanted to have a 2nd bay but it would make my land profile too tall, never thought about putting them on the side like that.Thanks for sharing!

That things is not a ♥♥♥♥♥ during take off isnt it?

And I never use auto-pilot either.

[Toastie Buns]

son8797님이 먼저 게시:

sadly, nope. Care to elaborate a bit more? I'm aware of the speed increase and decrease between the min and max point, but I don't see how it will helps on an asmophereless body since there is nothing to use as an air brake. Also what is suicide burn?

Essentially, all encounters steal or give back momentum from the parent body. This is true whether you choose to stay in orbit or not. Whether it's stolen or given back is determined by the face of the planet you encounter first. This is how you can achieve free-returns from the moon, how you use grav slings to lower your d/V flinging yourself wherever you choose, etc.

Don't worry, the planet/moon doesn't mind. Truth is, in real life we'd have to sling Venus a million times before its orbit slows down by a measly 1m/s. (Of course in Kerbal it can't deviate from its path, but the same conservation of momentum laws apply)

Try putting a craft in orbit and then looking at the different ways to get to the moon. Time warp for a while and look again when the moon is in a different position. You'll find the low d/V paths.

Another fun thing to do is retrograde orbits, which allow for really easy free returns. It's a handy exploit for messing around in Jool's playground.

Suicide burns are simply burning at the last possible moment in order to kill velocity to 0m/s (or as close to as you can) This is naturally the best method for saving fuel, since you're simply not allowing gravity the chance to speed you back up. This does take practice and is different with each lander (unless you have a rigid TWR pattern) but is the way forward in my book. Adds a nice element of danger too.

TL;DR: Let Issac Newton fly the craft and burn occasionally.

[sabe042]

son8797님이 먼저 게시:

@Sabe, that's ... definetely a radical design lol. I definitely gonna have to try that sometime, 2 material bay for under 45k is too good to pass up! I have always wanted to have a 2nd bay but it would make my land profile too tall, never thought about putting them on the side like that.Thanks for sharing!

That things is not a ♥♥♥♥♥ during take off isnt it?

And I never use auto-pilot either.

No problem! It is slightly slow on take-off, especially the second stage. Be sure to use the LV-T30's for the extra power on the sides (instead of the 45's). Also, adding four solids on the sides would help a lot as well, but will increase the cost. Being wider at the top makes it a bit unstable in the atmosphere too. The fins at the bottom are necessary to keep it from flipping around. Don't deviate too far from the surface prograde vector when doing turns in the atmosphere. It wasn't horrible during lift off, but it wasn't great either.

[ghpstage]

son8797님이 먼저 게시:

@Sabe, that's ... definetely a radical design lol. I definitely gonna have to try that sometime, 2 material bay for under 45k is too good to pass up! I have always wanted to have a 2nd bay but it would make my land profile too tall, never thought about putting them on the side like that.Thanks for sharing!

That things is not a ♥♥♥♥♥ during take off isnt it?

And I never use auto-pilot either.

Its much more cost efficient to learn to fly with a scientist than to increase the numbers of material bays (and goo) as they allow unlimited re-use.

[JustaGamer]

LOL. Sabe dude, I love this design!!

So I modified your craft a bit, make it more stable, adding more chute, also give myself a few extra safety margin since it's the first time I lauch with a rocket with a weird profile like this. Here is what I came up with:

http://images.akamai.steamusercontent.com/ugc/615096183950868725/5F78B67BF7D93800309CAAEF24AB0A4AA12303ED/

You might noticed the cost ballonned to 67k, but it's because I jammed the two modules with all the science I unlocked. Take out the 2 science modules and the cost is 45k for the rocket and landing stage.

http://images.akamai.steamusercontent.com/ugc/615096183950871186/FC4B123CE90069C86EA7D9FC94CD0AE18A935183/

I get WAY MORE bang for the buck comparing to the 80k rocket that I was using

http://images.akamai.steamusercontent.com/ugc/615096183950877469/909A4492971C24A398677521BA70AB2CC6E01709/


Basically:

- I have 200+ more science in a single trip.
- I have a HUGE safety margin, hell it's not so much as a safety margin it's just straight overkill. I made Mun intercept with almost 4k Delta-V left! LOL (and this is from what I considered a bad Muna burn). My old rocket I would barely scrap for 2k Delta-V at interception with a good burn.
- Landing is riducloulsy easy with a triple profile like this comparing to the single profile landing stage. I feel like it's almost impossible to trip over.


So either I can cut down a lot of the fat to down the cost (from what I consider already a bargain). Or keep this design, I think it has enough juice to fly and land on Minmus, do my stuff there, then take off and fly to the mun, land, do stuff before return to Kerbin - in one trip. Double bang for the buck! :D

Btw, the rocket is perfectly stable during launch, I have no problem controlling it without any fin attached.

[sabe042]

That's great to hear son8797! Looks like you made some good modifications.

[The Prophet]

practice on minimus it has less gravity, and you can you mecjeb once, just to see the optimal path it takes.