What's the lightest yet most efficient ship build to get to the moon?

[Sbeve]

So I'm new to KSP, and I want to create a rocket that is lightweight yet super efficient that can get to at least the mun, any ideas?

[Starman4308]

First: focus on making a rocket that can get to the Mun.

Second: lightweight and efficient are relatively synonymous. That said, if you're looking for cost efficiency over mass efficiency, the cheapest designs may be somewhat heavier than the lightest designs.

Third: I've played RO/RP-1 for so long that I'm probably at this point a terrible player of the stock game, and am a bit out-of-touch on specifics. That said, I suspect you're probably looking to stage every 3000-4000 m/s, using vacuum-optimized engines everywhere except the first stage. Nuclear engines are probably counterproductive due to high monetary cost, high mass, and the low dV requirements of Mun landings.

Fourth: when in doubt, cut extraneous payload. Remember the Tsiolkovsky rocket equation: dV = Gm*ln(mw/md)

Fifth: when in doubt, cut extraneous payload. This bears repeating, especially if you ever want to dip into the Dark Arts of RP-1.

[RizzoTheRat]

Start at the top and work down.

If you're not planning an Apollo style rendezvous in orbit you probably want the Mk1 capsule, which doesn't need a heat shield to re-enter kerbin.  To get from the Mun's surface back to Kerbin you're going to need a minimum of 850ish m/s dV, so aim for at least 1000 to give yourself some leeway depending how good your piloting skills are.  That's easily doable with one smallish fuel tank (FL-T200) and a Spark or Terrier.   The Spark's lighter but the higher TWR using a Terrier makes landing easier for a new player.

You're then going to need around 1200 to get to the Mun and at least 600 to land.  For an early game lander I do that with 3 extra tanks on radial decouplers.  This lets me add the landing gear to the decouplers for a nice wide stance for sloping ground, and I dump them as soon as I launch from the Mun.  I attach my science experiments to the radial tanks and have the pilot take the data from them before launch so I'm not carting useless weight around.  Adding a 4th drop tank or just using a bigger tank is an easy way to ensure you have plenty of spare fuel if you're still learning how to land safely.

Then you just need something to launch it. 

This approach makes for a nice stable lander, but the radial tanks mean it's a bit more awkward to built a launch stage for, so another option is an inline transfer/landing stage, but that means a narrower and taller craft so you need a flatter landing area. 

[Space Nerd]

I aim for 3500 to orbit, 800 to the mun, 300 to low orbit, 1200 to land and relaunch, 300 to return, and add a few hundred more.

But I think the lightest mun rocket is something built with ion engines and a chair.

[Guest]

16 hours ago, Sbeve said:

So I'm new to KSP, and I want to create a rocket that is lightweight yet super efficient that can get to at least the mun, any ideas?

Don't we all? 

I concur with the others ITT. Don't worry too much about efficiency to start with, just make something that works. You can always improve it later. A crewed Mun return mission is a pretty major difficulty spike when learning KSP. The good news is that once you've done that, it's quite easy to get from that to Ike and not much harder to get from Ike to Duna; after that, the Kerbolar system is your oyster.

I would advise you against trying to get too fancy for your first Mun round trip, e.g. having an Apollo-style system with a separate lander and return stage, docking in Munar orbit and so on. My basic Mun rockets look something like this:

1. Launch stage -- about 1500-2000 m/s, initial TWR about 1.4 (atmospheric)
2. Insertion stage -- about 1500-2000 m/s for a total dV of about 3500 m/s for a bit of a safety margin, initial TWR about 1.0...1.2 (vacuum)
3. Transfer stage -- about 1400 m/s, low TWR (this will get me to low Munar orbit -- about 900 m/s for an intercept, about 300 m/s to get into low orbit, the rest is safety margin)
4. Lander and return stage -- about 2000 m/s, initial TWR > 0.75 (Kerbin gravity) -- about 700 m/s for landing, 600 + 400 for take-off and ejection into a return trajectory for Kerbin with a Pe around 35 km, the rest is safety margin -- you might need to burn more fuel than anticipated for landing (although 700 m/s is fairly generous). 
5. Re-entry capsule -- this is either a Mk 1 capsule with heat shield, or a Pea from Making History, with a parachute natch. Decouple prior to re-entry. Or not, if you enjoy explosions.

The main way to screw efficiency up completely is to either be much too greedy about your payload (forget a Science Jr or multiple crew members, for example), or to use way too powerful (=heavy) engines. If you keep the payload reasonably small and stay within these dV/TWR numbers you ought to be fine. Another way to screw it up is with bad aerodynamics: if your lander/return stage isn't streamlined you need to put it in a fairing, otherwise your rocket will want to flip and/or burn much more fuel than you expected in the early part of the launch. 

Note that these numbers are fairly high and assume that you're not an expert hotshot pilot/orbital mechanic. Once you get better you can shave off a fair few hundred m/s off each stage. Don't forget the batteries and check your staging. And have fun!

Edited January 27, 2020 by Guest

[XLjedi]

What does "Get to the Mun" mean?

I believe the first mission in early career related to the Mun is just a Fly-By mission... 

So I tend to view a Mun Mission in terms of at least 4 different mission objectives:

1. Fly-By
2. Orbit
3. Land on
4. Land on and return

In which case, I view items 1 & 2 as maybe the most likely what you were looking for?  In which case, I'm typically more interested in fewest/lowest tech nodes required vs. size/weight/efficiency.

 

[fulgur]

I feel it's a tiny little ionic SSTO, perhaps with a Terrier. Not sure whether a nuke could do it, the TWR might be a little low.

[Kergarin]

the ant is the enige you want to have on your lander, its light weight makes it more efficinet than all the engines with higher isp

Edited January 27, 2020 by Kergarin

[RizzoTheRat]

13 hours ago, XLjedi said:

What does "Get to the Mun" mean?

I believe the first mission in early career related to the Mun is just a Fly-By mission... 

So I tend to view a Mun Mission in terms of at least 4 different mission objectives:

1. Fly-By

Good point.  For an initial flypast you can save a bit of dV with a free return trajectory.  If you pass in front of the Mun rather than behind it the Muns gravity will slow you rather than accelerate you, so you can use this to get an intercept with Kerbin without needing another burn.  The Early Apollo missions did exactly this so that if there was a failure they would still get back to earth.

When you get the initial intercept with the Mun, focus the camera on the Mun and burn gently prograde until the Pe comes out the other side of the Mun, then focus back on Kerbin and get the Pe there to about 40km, but check the Mun Pe is above about 10km so you don't crash.

13 hours ago, Kergarin said:

the ant is the enige you want to have on your lander, its light weight makes it more efficinet than all the engines with higher isp

But the low TWR can make landing a lot trickier for a new player.  Landing a lander with a 5:1 TWR is a lot easier than one with 1.5 TWR.

[Lt_Duckweed]

On 1/27/2020 at 12:53 PM, fulgur said:

I feel it's a tiny little ionic SSTO, perhaps with a Terrier. Not sure whether a nuke could do it, the TWR might be a little low.

A nuke as tons of twr for the Mun.  Actually you can use nukes to land on/take off from all airless bodies in the game, and a combination of nukes, breaking ground props, and wings on all atmospheric bodies other than Eve.

Edited January 29, 2020 by Lt_Duckweed

[KerikBalm]

10 hours ago, Lt_Duckweed said:

Actually you can use nukes to land on/take off from all airless bodies in the game, and a combination of nukes, breaking ground props, and wings on all atmospheric bodies other than Eve.

While a nuke does have greater than 2:1 TWR on Tylo, I wouldn't recommend using them to land there.

Also, in addition to Eve, you should mention Jool too.

[Lt_Duckweed]

Just now, KerikBalm said:

While a nuke does have greater than 2:1 TWR on Tylo, I wouldn't recommend using them to land there.

Also, in addition to Eve, you should mention Jool too.

Jool can be SSTO'd with props and nukes tho.

[fulgur]

The size of a SSTO which can carry a nuke into orbit may or may not be too big to have a TWR of more than one, certainly when fully fuelled. Must have a go at building myself a Mun-capable craft without refuelling...

[KerikBalm]

2 hours ago, Lt_Duckweed said:

Jool can be SSTO'd with props and nukes tho.

I'd like to see that, got a link?

[Lt_Duckweed]

22 minutes ago, KerikBalm said:

I'd like to see that, got a link?

 

[RizzoTheRat]

3 hours ago, fulgur said:

The size of a SSTO which can carry a nuke into orbit may or may not be too big to have a TWR of more than one, certainly when fully fuelled. Must have a go at building myself a Mun-capable craft without refuelling...

Bear in mind an SSTO doesn't mean single stage to another body.  A nuke powered craft capable of getting from LKO to the Mun and back which fits inside the cargo bay of an SSTO is a lot more efficient than lugging a load of useless wings and jet engines to the Mun.

[KerikBalm]

2 hours ago, Lt_Duckweed said:

 

Interesting, similar to what I expected, a lot of part cliping to make everything fit inside something to shield from drag... I remember one version where there was a bug and you could make things dragless with a fairing (but that's not the case here)

[Lt_Duckweed]

4 hours ago, KerikBalm said:

Interesting, similar to what I expected, a lot of part cliping to make everything fit inside something to shield from drag... I remember one version where there was a bug and you could make things dragless with a fairing (but that's not the case here)

Yeah there is a ton part clipping.  I've learned a lot about the dynamics of Jool Flight since then, so my next goal is to do it without fairing abuse, which I think is achievable.

[fulgur]

6 hours ago, RizzoTheRat said:

Bear in mind an SSTO doesn't mean single stage to another body.  A nuke powered craft capable of getting from LKO to the Mun and back which fits inside the cargo bay of an SSTO is a lot more efficient than lugging a load of useless wings and jet engines to the Mun.

That's as may be, but it would not be the lightest. And it would not be eligible for the K-Prize.

[KerikBalm]

What if it came back from mun and redocked with the carrier SSTO, then would it be eligible? (I'm not 100% sure what the k prize is)

[Lt_Duckweed]

Mun vtol ssto's aren't too difficult once you get in the swing of it, I actually made one with rotating nerv pods before breaking ground was even a thing.

They can get, off the top of my head, about 35% payload fraction delivered to the Munar surface.

Edited January 30, 2020 by Lt_Duckweed

[RizzoTheRat]

20 hours ago, fulgur said:

That's as may be, but it would not be the lightest. And it would not be eligible for the K-Prize.

The lander would be way lighter than anything that can single stage it from Kerbin, and potentially the whole thing could be lighter as it doesn't need anywhere near as much fuel, but yeah it wouldn't be eligible for the K-Prize as that's about single stage to wherever space planes, which is a subset of fully reusable vehicles and excludes the most efficient way of doing the job

Edited January 31, 2020 by RizzoTheRat

[kerbiloid]

Spoiler

Did somebody try a Breaking Ground pogo stick to start from the Mun surface before ignition to save some fuel?

 

[moar ssto]

I haven't tried low mass Munar, missions, though I have done a low mass(maybe not very low) Lunar crewed land and return mission with a less than 90t stock part rocket, there is also a slightly heavier version of it that can land on both Ceres and the Moon. 

Edited April 20, 2020 by moar ssto

[HansonKerman]

On 1/27/2020 at 7:56 AM, Space Nerd said:

I aim for 3500 to orbit, 800 to the mun, 300 to low orbit, 1200 to land and relaunch, 300 to return, and add a few hundred more.

But I think the lightest mun rocket is something built with ion engines and a chair.

pfff lol idk but one orbital stage, some sepatrons, and an ion powered space chair might do it