How "good" is my design ?

[BluK]

Hello,

I built yesterday a ship that successfully landed on the Mun and came back. I am not that satisfied with my design because it feels big and bulky but I'm also thinking that at some point and for some missions you can't help but build big ships to get a lot of delta v.

You can find the design here : https://www.dropbox.com/s/o0ohb6hsp8t02y4/MunLander%2001.craft?dl=0

I think it might help to tell you what I thought to get to this. I tried building it from top to bottom (and maybe changed a few things at the end but the intention was here ^^). There were three phases for me, as one of the constraints I put on myself is to leave as little debris as I can in orbit, so :

• The last stages, to properly land on the Mun, take off from it and possibly some fuel to adjust my orbit to get home faster
• The middle stages, to finalize the orbit around Kerbin (this way the bottom stages will be on a suborbital flight and will crash on Kerbin), to get on an intercept trajectory and to get on an orbit as low as possible around the Mun
• And finally the bottom stages, to get in orbit around Kerbin (or just about)

Thanks to a delta v map I found, I could estimate my deltav needs to

• 580m/s to land and about 1000m/s for the trip back
• 860m/s for the Mun intercept, 310m/s for the Mun Orbit and some margin to finish the orbit around Kerbin
• 3200 m/s . But here it seems I'm not that good at piloting yet, so I often seem to need more

Here's a picture of the beast :

http://imgur.com/73uj6yb

For the propulsion, I chose for these three phases :

• 3 LV-909 with one X200-16 Fuel Tank
• 1 RE-L10 with one X200-32 Fuel Tank
• First, some boosters (6 "Kickback"s) and then 5 X200-32 Fuel Tanks mounted in what I imagine to be asparagus and powered by a RE-M3

Like I said, this ship was succesful in its mission, but I'm afraid it will be much more complicated as soon as I try to get more payload (such as tourists or scientific equipment). Do you have any advice to improve this ?

[TheXRuler]

First off, Congratulations, the first munlanding is indeed a glorious thing, I never tire of seeing what people come up with to manage this.
Well, from an efficiency standpoint your ship looks absolutely fine, although I think you might be loosing a little dV due to the slow TWR after booster ejection.
From a looks and realism standpoint, well, that another story entirely, but I guess that's not really important for you and indeed it is not what really counts. The slighly clunky looks come from those external tanks. While they are efficient, they do make it look a little silly, especiall with those SRBs attached. To reduce the complexity I would reccomend stacking three of those X-200-32 tanks (four if you can still get TWR>1.1) and then adding two T-800fueled liquid boosters with crossfeed lines feeding the centre tank (if you really need them). If possible just drop the external tanks completely (reduction of air resistance) and use four SRB's.
When building larger rockets add heavy liquid boosters. One thing you might to try out is putting stronger, lower ISP engines on the boosters and a lower thrust higher ISP engine on the centre tank. Also, watch your TWR, going over ~1.5 at launch quickly gets inefficient due to more air resistance in the low atmosphere, going lower than ~1.2 results in bigger gravity losses.

Edited January 7, 2016 by TheXRuler
forgot sth.

[Reactordrone]

You could strip some weight out of the lander to improve its Delta v. You're carrying over a tonne of RCS fuel and you could probably get by with a single LV-909 rather than three saving another tonne. The ASAS unit is probably unnecessary, the 3 man pod had plenty of reaction wheel torque. Overall it's not too bad though, my first three man Mun vehicles were monsters by comparison.

[Plusck]

33 minutes ago, BluK said:

[...]

Thanks to a delta v map I found, I could estimate my deltav needs to

• 580m/s to land and about 1000m/s for the trip back
• 860m/s for the Mun intercept, 310m/s for the Mun Orbit and some margin to finish the orbit around Kerbin
• 3200 m/s . But here it seems I'm not that good at piloting yet, so I often seem to need more

[...]

Like I said, this ship was succesful in its mission, but I'm afraid it will be much more complicated as soon as I try to get more payload (such as tourists or scientific equipment). Do you have any advice to improve this ?

If it is successful, what more do you need?

580m/s to land on the Mun is an absolute perfect, lossless landing from an extremely low orbit. I have a station parked in a higher orbit (which has ended up being an unnecessary 40x80km elipse) to make warping possible, and it takes about 750-800m/s for an average landing while aiming for a specific landing site.

Therefore, landing a 4-ton Mk1-2 pod is to me the most obvious thing not to do on the Mun to simplify your life in future. I understand that you're aiming to reduce debris and wastage, so bringing your expensive scientific instruments back to Kerbin on your pod is better than abandoning them (especially since you know you'll get better instruments in future, so therefore a permanently orbiting Mun lander that you refuel before using is not yet an efficient option), but heatshields can be added to lander cans for return to Kerbin, cutting weight drastically.

As for the heatshield - you're carrying at least 600 Kg more than you need in ablator for a Mun or Minmus return, and you can reduce this with a right-click in the VAB.

Finally, nosecones. I've gone through phases of adding them to everything, and not adding them at all. On balance, I think it is always preferable to add them if feasible.

[BluK]

You've all given me a lot to work with

3 hours ago, TheXRuler said:

. Also, watch your TWR, going over ~1.5 at launch quickly gets inefficient due to more air resistance in the low atmosphere, going lower than ~1.2 results in bigger gravity losses.

It seemed to me that around 1.5 wasn't too bad to avoid the drag around 10.000m but I do tend to put just a bit more. That's probably me wanting the lauch to be quicker ^^ That data will surely be useful

 

3 hours ago, Reactordrone said:

You could probably get by with a single LV-909 rather than three saving another tonne

Yes so the reason I went with three is rather silly I think. The diameter of the engine is smaller than the tank, which feels weird to me. It also feels like it's not drag efficient so I thought to put the engine on the side, and for symmetry reason, I decided to put more than one. Also by putting engines on the side, I thought I'd have more room below the lander for the struts. I don't know if it's a real issue though...

 

3 hours ago, Reactordrone said:

The ASAS unit is probably unnecessary, the 3 man pod had plenty of reaction wheel torque.

That's something I should have realised by myself I just went from the Mk1 to the next pod without checking its real abilities (except for the crew capacity)...

3 hours ago, Plusck said:

580m/s to land on the Mun is an absolute perfect, lossless landing from an extremely low orbit.

The margin I had (I won't say I did it on purpose ^^) allowed me to get to a quite low orbit around the Mun without using the fuel from the lander. I even managed to start deccelerating with the RE-L10 so hopefully, the fuel I had on the last phase was enough to land and get back But that's good to know. Also I should pay more attention to how much dv I really use.

For now, I'll keep landing on the Mun as long as I don't have space stations. I feel like it's a good exercise for when I'll land on other planets or moons. But it'll be quite fun to have space stations ^^ can't wait

3 hours ago, Plusck said:

As for the heatshield - you're carrying at least 600 Kg more than you need in ablator for a Mun or Minmus return, and you can reduce this with a right-click in the VAB.

Finally, nosecones. I've gone through phases of adding them to everything, and not adding them at all. On balance, I think it is always preferable to add them if feasible.

I never really paid attention to how heavy the ablator was. Like you said, I had plenty left when I got back, I'll work on it. As for the nosecones, I don't know if there are larger ones (for the fuel tanks) but I haven't unlocked them yet.

[Plusck]

57 minutes ago, BluK said:

For now, I'll keep landing on the Mun as long as I don't have space stations. I feel like it's a good exercise for when I'll land on other planets or moons. But it'll be quite fun to have space stations ^^ can't wait

For this part, I think I must have been unclear. I wasn't suggesting not landing on the Mun (which is essential, as you say, and much less forgiving than Minmus), but rather not using the Mk1-2 pod to do it if you want to travel light. The Mk1-2 command pod (with monoprop) weighs 1.37 tons per occupant. Although it does have a lot of things going for it (space for docking port, decent torque, stability on re-entry, etc.) it is the heaviest option when it comes to landing crew. Mind you, the Mk2 lander can is (inexplicably) not much better.

[Vegetal]

That's actually pretty good for a beginner. Nose cones are badly needed on those side tanks, and I see you have no docking ports, so there is no point in having an RCS system. Ditch that and drain all monoprop from the capsule itself.

And I can understand your reasoning for the side mounted engines, but try using two instead. Keep in mind though, the less TWR you have on the Mun, the harder the landing will be.

Oh and the heat shield. Take all the ablator off, you can do a direct reentry from Mun or Minmus with no ablator, relying only on the shield's thermal resistance.

You seem to have a good margin there in terms of delta V. That's good for a start. When you optimize your final stage and get more comfortable with the game, you will be able to work with reduced margins, and that means your lifter stages will be *way* smaller, so don't worry too much about size now, you will get better.

[radonek]

My 0.02:

Bottom sidetanks should be attached to top ones via decoupler, not to central tanks. Better aerodynamics. And of course, nosecones, when you have them. If you are unsure about aerodynamic profile, just launch the thing straight up and see how high it gets. Also, if you put some engines under side boosters, you will see when they run out of fuel. If you don't need TWR, just slap on Ants.

As for lander - good lander is squat - low and wide, in case you have to land on slope.  Having lander engines in side gondolas is good idea, it pushes down CoM and gives you better stability, so make full use of it: instead of empty structure make them into fuel tanks and have smaller and lower central tank. Spread your fuel weight wide, not high. Also, move landing legs onto gondolas, this will further widen your base. Ladder steps on command pod are unnecessary. And solar panels can be blocked by big tank, put some on it too.
 

[radonek]

I took liberty to have a take on your design: http://imgur.com/a/WYFdl