How to design rocket to mun flight?
I have been trying for couple of days to build launcher to my mun ship. I have Apollo inspired design. I have launched couple of different combinations. Below you see best attempt I can get and now I want some suggestions to design mun rocket that will actually go to mun. These flights have never exited atmosphere. I have already flown unmanned probe and unmanned rover to Mun so transfer burn will not be problem, only design.
Craft file if screenshot doesn't tell enough, 0.20 all stock
Last edited by Katve; 24th May 2013 at 13:23.
A suggestion; less is more. I can get to the moon with just 10 FL-T800 tanks. (Not counting the lander itself.)
Originally Posted by allmappedout
Senior Rocket Scientist
It starts with knowing how much delta-V (change in velocity) is required for each phase of the mission. For an apollo-style mission, I design the lander first, followed by the CSM and the stages to get it to orbit and to the mun.
Here is a link to a very recent apollo-esque design of mine: http://forum.kerbalspaceprogram.com/...-Kerpollo-Mini
Don't go too tall perhaps? Distribute the weight from the internal tank to the external tanks.
Here are some things to improve:
- Replace the Mainsail on your orbital stage with some side-mounted LV-Ns, the difference in ΔV (available change in velocity) should be quite amazing.
- The amount fuel is absolutely overkill, a good pilot using efficient engines can land on the mun from orbit and return to Kerbin with maybe 1000 units of fuel (just a guessed number, haven't done any actual testing).
- Try putting everything on more symmetrical, having wings off-center doesn't really help.
- The RCS of each stage should be top/middle/bottom not middle/middle/middle.
- Really only a cosmetical thing, but turn symmetry off when placing ladders.
- Also replace the lander's egine with two side-mounted LV-Ns, some people say that this isn't very efficient, but I seem to get way more ΔV when doing it that way.
- Edit: Use the AV-R8 winglets, the Delta-Deluxe winglets don't give you as much control (but more lift for compensation).
Hope this helped a bit.
Last edited by Ben Kerman; 24th May 2013 at 09:47.
Junior Rocket Scientist
if you're using Kerbal Engineer, you should aim for a total delta-v in the 7100-7500 m/s range.
less than that if you feel like taking a risk
for example, here's a 3-seat rocket that can go to the Mun and back no problemo:
Sr. Spacecraft Engineer
Two things that come to mind when I look at your ship:
1) The transfer/command module part looks a bit big and you're using a rockomax diameter engine (so either a poodle, skipper or mainsail).
2) Liquid fuel boosters are rather small in comparison to the payload. Also no SRBs.
So basically you can either make the payload smaller or the first stages bigger, the former is a bit trickier while the latter is fairly simple (also I figure you are more interested in that). For one I think you could cut the rockomax-16 tank and just leave the rockomax-32 on the command module stage. If you're using a mainsail (I don't think you are) swap it for a poodle or skipper. You don't need a lot of thrust on the transfer stage, although granted nobody likes sitting 6 minutes doing a transfer burn (like I did recently with my single NERVA setup). Either way the mainsail is rather heavy and mostly dead weight for a transfer stage, it's ISP is also meh (but it's good for the heavy lifter that it is if you need thrust).
Either way I split up my tips into two sections for both shedding mass and making a better carrier rocket.
Shedding mass on the payload:
The lander, now I'm unsure what I see there (don't have KSP on this PC to check the .craft). Is that a rockomax-32 tank or a hitchhiker storage pod+rockomax-16 below (well above since it's upside down) the lander can? A rockomax-32 tank would probably be overkill, to get a 2-man lander can into munar orbit for a return rendezvous (20 km altitude is what I use) from the surface you need less than two FL-T200 tanks worth of fuel (or just one FL-T400) and a single LV-909 engine.
The problem though is landing there in the first place, but a rockomax-16 tank and a poodle should be enough for that. Still you want to get back and minimize mass you're taking back into LMO to rendezvous with the command module. You can do what apollo did and have the rockomax-16+poodle as a descent stage and a single or double lv-909 attached to the minimum amount of fuel for the return/ascent stage. Or you can experiment with external detachable fuel tanks. Landing on the Mun is far harder than getting back from its surface when it comes to fuel.
As for the command module if it has a mainsail swap it like I mentioned. If not you can experiment with the LV-N as its efficiency greatly reduces the fuel you need for a transfer burn but you don't need to if you don't want to. Also you would probably need two LV-N atomic engines to have decent transfer burn time, possibly more (if you dislike long burns). Side-mounting them is recommended as bi/tricouplers+fairings have a few issues (inner fairings crash into your engines) with the stack decoupler attached to the bottom of the fuel tank they're feeding from.
Double orange rockomax-64 jumbo+mainsail is the way to go for liquid stages for those very heavy payloads. If they're still too heavy to lift that (having less than 1.0 TWR for 5-10 seconds while avoiding overheating is usually worth it, but longer is questionable). Do proper asparagus staging. You have 4 liquid fuel boosters all connected to the central rocket (unless I'm blind and can't see how it really is), you should split them into 2 pairs for decoupling while retaining symmetry (you just need to drag individual decouplers into new stages so it doesn't matter you placed them in 4-fold symmetry and they got grouped automatically). Then connect the first pair to get jettisoned to the pair that goes second and the second pair to the main stage. So you stage and drop 2-2-1 and not 4-1. It's more efficient but you lose on some thrust (which is usually irrelevant but may cause problems if you're really on the edge of 1.0 TWR).
SRBs are your friends, strap as many as you can to the sides of your 4 outer liquid stages, symmetrically of course. Naturally have them all fire alongside your other lifting engines at launch, just throttle the thrust so you don't burn too much or accelerate too fast in the thicker lower parts of the atmosphere. I recommend putting a strut on the top of every SRB and attach it to the tank they're mounted on so that they're stable (assuming the rest of your rocket isn't too wobbly).
If that's still not enough then add more rocket (also struts, space tape is very important). For my biggest payloads I launched them with 8 double jumbo+mainsail side-rockets (with SRBs) around the main one. All staging in pairs for maximum efficiency.
Senior Rocket Scientist
For a 1 kerbal Mun lander, that is severe overkill.
Originally Posted by RawChicken
Also, reaching orbit is not all about power; It's mostly about efficiency. Learn to fly an efficient flight path for your rocket.