Noob Needs helpwith my design.

[Nervustwitch]

While I do not have a picture of the rocket I am using on my career mode I do have to say that one is a bit over kill. Mine does not use asparagus staging, but it has 4 srb and 4 outer thrusts and one center, with the center piece staying all the way to Mun with fuel left. I will get a picture of it soon as I need to finish the video of the Mun Mission, been too busy to do it right now.

Yeah I figured it was overkill.But for some reason I used almost all fuel in the big tanks to get to Minmus,the last lil bit left in them I used to slow me down as I got close to the surface then dropped them.The lander engine and fuel was only used to land and return with and I still had some left.I kinda burned a bit to much fuel trying to figure out a path to Minmus,I get to the mun easily but Minmus proved a lil challenging for me to plot a course.I do have MJ installed but mostly using it for info and to learn with to see how it is doing some node manuevers.I try to do all burns and such myself,MJ kinda feels cheap to use.

[SRV Ron]

Yeah I figured it was overkill.But for some reason I used almost all fuel in the big tanks to get to Minmus,the last lil bit left in them I used to slow me down as I got close to the surface then dropped them.The lander engine and fuel was only used to land and return with and I still had some left.I kinda burned a bit to much fuel trying to figure out a path to Minmus,I get to the mun easily but Minmus proved a lil challenging for me to plot a course.I do have MJ installed but mostly using it for info and to learn with to see how it is doing some node manuevers.I try to do all burns and such myself,MJ kinda feels cheap to use.

That flight profile is what you want. Enough fuel to orbit and start landing so you save all of the lander fuel for landing and return.

Try a few more flights to see if you can do the mission more efficiently as you learn how to do the gravity turn and the insertion burn.

[Nervustwitch]

I have the gravity turn down pretty well on launch and setting course and orbit for Mun,Minmus makes me work that encounter.As for lifting off from other planets i need some work there,not really sure what I need to do to be efficient at taking off.

Well it did work for the Mun also.I was able to land but I was about 12sec short of my final burn to return to kerbin on lander fuel.But I made a couple mistakes that I assume caused that.

1.I kept lifting back up while trying to land,lost fuel there.

2.While messing around int VAB,I forgot that I put on 2 of those mini radial liquid engines on the lander which I know it did not need,I was just messing around and forgot to remove.

3.And the last mistake that when I landed the lander tipped over on its side.I tried to use RCS to tilt it up but just wasnt strong enough.I jettisoned the goo containers and applied very small amount of throttle and skid it accross the the surface until I went over the crest of hill then applied more throttle and got back into somewhat of an orbit....lol.

I think Im gonna design a much more stable lander and build it outwards a bit.

Just to be sure I really only need the enigine with 50 thrust to land on the moon,correct? And if my landers get bigger do I need more to land them or is gravity so little that it doesnt affect it much?

Thx again its been fun and frustrating so far.

[Pecan]

Better to get there with an overengineered solution than fail with an optimised one :-) Congratulations, it seems like you've "got it" now, so you'll just get better every time you practice - and so will your rockets.

[Taki117]

Yeah I dont a tall lander.Im trying to picture the fuel and engine design you suggest but I cant really get what is meant.You add tanks and engines to the side of the junior,the fuel line is throwing me off by what you mean.

Thx for help.

Exactly what I said you quite literally attach a fuel line going from the tanks (If you placed them with symmetry keep it on) to the engine.

Pics to illustrate (This is an oversimplified lander)

[Nervustwitch]

Ahh gotcha,I was picturing multiple engines for some reason.I actually have a similar type design in the works right now.

As for landing on the Mun,I think Im gonna build a probe lander and orbit the Mun and do a quick save in orbit and just practice landing many times to get it down ,and take offs of course.I know I could practice it at the launch pad but the difference in gravity throws me off.

Now I just gotta figure out how many biomes minmus and mun have and land there for science.

Also does the bigger lab that allows for less transmission loss really do much for landing.I cant se it being that much help seeing as most of the experiments are one time use or am I missing something.

[Taki117]

Ahh gotcha,I was picturing multiple engines for some reason.I actually have a similar type design in the works right now.

As for landing on the Mun,I think Im gonna build a probe lander and orbit the Mun and do a quick save in orbit and just practice landing many times to get it down ,and take offs of course.I know I could practice it at the launch pad but the difference in gravity throws me off.

Now I just gotta figure out how many biomes minmus and mun have and land there for science.

Also does the bigger lab that allows for less transmission loss really do much for landing.I cant se it being that much help seeing as most of the experiments are one time use or am I missing something.

The mobile processing lab allows you to reuse the Goo can and Science Junior as well as increasing the transmission value for most experiments. Minmus has 11 I believe, and the mun has about the same. EAch Crater on the mun is it's own biome, as well as the highlands, lowlands, poles, and polar lowlands. Minmus biomes are the flat lakes (Each one is seperate), the slopes, the midlands, lowlands, poles and slopes.

[Kerba Fett]

Congratulations on your Minmus landing. It feels great the first time you set down off of Kerbin. I can't believe you landed on a hillside though. lol. There's those gigantic plains that you can see from orbit that are prefectly flat.

A question about your lander, Was the RCS system was intended to stand you back up if you fell over or were you going to keep your capsule mostly vertical and use those to control your horizontal speed?

I recently managed my first career landing on Minmus as well. This is the lander I used. To make it less tippy I put the legs on decouplers and angled the legs out a bit. This gives it a nice wide stance. Originally I was using girders but noticed that these are much lighter. As a bonus you can put stuff on the ship hull under them but not with girders. I used 3 legs to keep the weight down and 2 way symmetry on the goo containers for the same reason. I left off the science jr since I thought it would raise the COM too high and I didn't want the extra mass of an RCS system.

Once I landed I took a surface sample and did an EVA report. Put them back in the pod then used the EVA pack to jet over to 2 nearby biomes for another surface sample and eva report. Of course you can only carry one of each and have to take it back to the lander before going on to the next. You get some nice range from the EVA pack on Minmus.

For my next version of the lander I'm thinking of getting rid of the goo containers to save the weight. I then make little disposable probes that I launch from the same transfer vehicle that brought the lander. If I can get one in each biome I try bring down the lander within range of the EVA pack and go collect the probe data and take a surface sample and EVA report. By taking the data I get the return bonus without using dV on the lander.

I was looking at the science returns on this as well. A goo report from Minmus paid 50 science while a surface sample and EVA report from the same location was worth 190. It's great if you can get both, but less goo equals more dV for more landings.

I notice you use mechjeb. As you can see I prefer to use the translatron to manage my descent rate. Have you played with making custom windows with it? There's some amazingly helpful info in there that you don't normally see. Notice my hover time in the fuel window. I had to chuckle when I noticed that.

If you like to fly with a manual throttle you can Display local gravity and current accelleration in a window. When they're the same you're at hover thrust.

[Nervustwitch]

Yeah Im not good enough yet to judge where I want to land,but the landing was easier than I thought it would be on the hill side.

as for the RCS I put them on there to help control it a bit,figured it would help me since it was gonna be my first landing ever,wasnt really thinking about tipping over until I landed on the Mun and fell over.But the RCS wasnt strong enough to put me upright.I had to slide slowly across the surface until I launched off the hillside the hit full throttle and it saved me....lol.

As for MJ,I havent messed with the custom windows yet,may need to look into that.I mostly just use MJ for the info.When I was trying to figure out how the nodes worked I would use it to look at what it was doing then hit save game load and try to do the same,worked really well for me that way...easier for me to learn that way.

I have reworked my lander to be more stable.

Here is my current one,I havent used this revised version yet but were the center tank is with the engine I had a Fl-t200 tank but I cut it kinda close to the Mun landing and back,it was doable but wasnt much room for mistakes.So Im gonna try it with the T400,I think its overkill but I need the extra breathing room until I get better.It landed really easy.I have decouplers on the goo and the t200 tanks with the legs.But the added weight from the revised lander has thrown off my launch staging,so I''ll tweak it a bit.

I know I dont need the ladders but I m not that good at the jetpack yet so I use them for now.

EDIT:I think I will move the tanks with the legs on them up a bit to take some of the top heavy out after looking at the pic

screenshot windows 8

Edited February 5, 2014 by Nervustwitch

[Kerba Fett]

Looking at the picture of your revised lander, 2 things come to mind. You've got plenty of room under your radial mounted tanks. You could mount your rcs tanks there and lower your COM quite a bit. The small radial mount tanks or even the small stack mount ones would work and still leave plenty of ground clearance.

Also, if you made your center tank shorter than the radial mount ones you could nestle the science Jr between the fuel tanks and the capsule would sit lower.

By the way, you have tried putting it on the launch pad and making sure a Kerbal can get up the ladders with those struts there right? Those helmets of theirs are pretty big and space looks limited from this angle.

As for your launch stage, you might want to consider a modification of this design.

My launch stage consists of 2 jet engines mounted on a bicoupler. (you need to rotate them a bit) I then put 2 of these on another bicoupler for 4 jets. I haven't unlocked quad couplers yet and these are quick to reconfigure. I use a single jet fuel tank with 12 intakes using 6 way symmetry. On top of that is a structural fusalage. This provides a grab point for the launch clamps. I'm not sure the fins are needed but I had a rotation issue in an earlier payload.

This setup provides 600 kn at launch and burns a negligable ammount of fuel going up to 20 km where you fire the rockets on the next stage.

The advantage here is that you're not using rocket engines in the lower atmosphere where they're less effective.

While this ship got my transfer vehicle into orbit, I did have to transfer some fuel from the lander to do it. I was already planning on an orbital refueling so it wasn't that big a deal, but next time I'll probably radial mount a pair of dual jet booster for a bit more kick.

I've radial mounted the dual jet versions to larger rockets using 6 way symmetry, but it really starts to eat your framerate with that many parts. Did get a 120 ton station to 350m/s and 20km though.

These things have become the workhorse of my launch system. The only thing you need to do different is to stage the engines before the launch clamps and wait till the engines come up to full power before releasing the clamps.

[Taki117]

SNIP

EDIT:I think I will move the tanks with the legs on them up a bit to take some of the top heavy out after looking at the pic

PIC SNIP

You have tons of room under those landing legs, and drawing fuel from the outer to center tank, it doesn't need to be that big. It also looks like you are trying to do way too much with your lander. Keep it simple, also, you could slide those radial tanks up and not only would this help to lower the CoM but it would also help with stability. In either case, I wish you the best of luck.

[Nervustwitch]

Thx again.

Yeah I only have 1 ladder on it and the kerbal can fit just fine.I raised the outer tanks and it has much lower COM.If i put my RCS tanks under the outter ones wouldnt that just be adding more weight?I hardly use that much RCS fuel.I added the struts until I get landings down a bit more so that it can withstand some abuse.I hit the mun surface pretty hard tonight and bounced up and did a flip and kicked in rcs to get it back under control to land in the east crater.

Using jet engines is cool idea,wouldnt have thought of that really.I have my launch and orbit transfer stage down fairly good,for me.its getting me to the mun several times now,I think I have 5 flags now and a couple on Minmus.

Taki77 I had the smaller tank there but kinda cut it close on fuel so I put that there until I get more control and alot less fuel waste landing on the mun.When I take off from mun all radial tanks are empty and ket jettisoned after take off along with the goo cans.Yeah the struts and ladder isnt needed Im sure,but doing to much with it?i just have the experiments for the most part on it.

[nala2624]

I had a similar problem at a fairly early part of the career. Not enough thrust to get to the Mun. As Dave pointed out, over half the dV is just getting off the ground and into orbit. Therefore, most of your power should be in the early stages. I uses a semi-onion-staging rocket. Onion-stage rockets "shed" layers of propulsion systems over time. In this case, tanks and engines. Most of the thrust is in the early stages to maximize dV early in the launch and the empty tanks and engines weight is shed over time add up to less weight you have to haul into orbit.

Parachutes on all 4 tanks on final stage with one top-mounted and 2 radial chutes on the command module. Tanks and engines are all modded but the concept works with stock parts. This design is one is used to get into a Munar orbit. Still designing and testing a lander model. I don't have access to fuel lines yet so asparagus-staging isn't an option for me yet.

Side note. I am a big fan of asparagus-staging but I still believe that onion-staging has it's uses.

[Pecan]

If you don't have fuel lines yet then you aren't doing onion staging either.

Unstaged (artillery) - whatever can go bang, goes bang and makes the ship go up (or bang). When the bang stops the up stops.

Stack staged (classic) - lowest engines go bang, higher ones can't because lower are in the way. When a stage stops banging it's dropped and the beat goes on with the next one.

Radial staged - outer engines go bang as long as they can then are dropped and the (next) inner 'ring' starts banging. Much like stack staged but allows you to easily have more engines in the earlier (outer) rings.

Parallel staged (which you're probably doing) - since all radial staged engines can go bang at the same time they do, but the inner ones have bigger fuel drums and keep banging longer.

Onion staged (symmetry 3+) - parallel, but fuel lines feed all engines 'inside' as well as the engine they're directly attached to. Means the outer fuel drums are used up really quickly but inner rings still have full drums when the outer ones are dropped (earlier).

Asparagus staged (symmetry 2) - Onion, but dropping pairs of drums/engines at a time instead of waiting for 3 or more to empty. 2 being the minimum you need to maintain symmetry this is the fastest/most efficient way to use-up and jettison empties.

The general point is that with Onion/Asparagus you get the benefit of as many engines firing at the same time as possible (as with parallel) but you don't need to give inner engines bigger drums to keep them banging longer (because they initially take their fuel from outer drums).

Slack tanks - Sometimes you find that you only need a few powerful and efficient engines to give you the thrust you need but that each engine needs big fuel tanks to keep banging long enough. It may then be worth moving some of this fuel into an outer 'slack' stage (one without engines). The fuel in these will be used first and the tanks jettisoned, leaving the rest of the vehicle with all the engines but less dry-tank mass to push.

The trick is to balance exactly when you drop slack tanks and excess engines so that whatever's left has just the thrust and fuel left that you need. You need a lot of thrust to get moving from launch and - ideally - reach terminal velocity as soon as possible. Then you want lower-but-increasing thrust to follow the terminal velocity curve until it gets so high in the upper atmosphere you throw in everything your rocket can give in order to get to orbit. Finally, you need very little thrust (to mass) in order to circularise your orbit. That profile suggests - small(ish) engine on core stage (last to be jettisoned) that is mainly there to circularise*, big-as-possible engines on inner stage (penultimate jettison) for the upper-atmosphere rush to space, slack tanks for intermediate stages (no more thrust but added endurance for the inner engines) and as-big-as-you-need engines on the outer, launch, stage to help get you up to terminal velocity. Easy.

Actually doing it is a different matter, of course ^^.

[*I favour a light core stage but temstar recommends a heavy one with more fuel than I do. His designs (eg; forum.kerbalspaceprogram.com/threads/33381-0-20-2-Zenith-rocket-family-(modernised-for-0-20-x-with-perfect-subassembly)) assume that last stage will be doing the 'rush to space' that I assign to the penultimate 'inner stage'. Blizzy's engine cluster calculator defaults to 20-25% thrust from the central stack (core stage) for the same reason].

Apologies in advance for all the mistakes I've probably made in typing this off the top of my head.

Edited February 6, 2014 by Pecan
Link to Blizzy's calculator

[Nervustwitch]

Some very useful info Pecan.

I have been using Asparagus to get into orbit and its made my life easier with building the stages.My only problem is that I use trial and error to figure out how big of a launch stage I need to get a certain weight payload to say the Mun.

Ex:If I have an 8ton lander then how do I know before I try for the Mun how much lifting power do I need to get into Kerbin orbit.Then how much do I need in the next stage to finish all my maneuvers to save my lander fuel for only landing and return.

What should be say the ideal ALT. for your boosters to get you to?Mine dont get me that far,around 7500m and I could be losing fuel from dropping SRB's to soon.

Guess I need to do some more reading since I really dont even really know what Delta-V is.Is there a mod that will give me info to tell me that I can make or at least should?I know MJ has some useful info,especially in the custom windows.

[Pecan]

The favourite mod for designing rockets is Kerbal Engineer Redux (KER). If you have MJ already then it has a delta-V window but KER can tell you the stats for different bodies apart from Kerbin - handy when you want to know if your mun lander can, actually, land on the mun and get back to orbit ;-0 Apart from MJ and/or KER the most important thing is a delta-V map (haven't got a link handy but a forum or internet search will find you plenty).

DeltaV maps tell you how much delta-V (acceleration) is required to go places, such as a) get into orbit from Kerbin's surface (4,500m/s), get to the mun and orbit there (1,090), c) land on the mun (580), d) come back (1,670). With a pretty comfortable margin for error you need 7,600m/s deltaV at launch for a round trip. To put it simply - you increase your deltaV by adding fuel; the more you've got the more the engines can do ...

... Which means apart from fuel tanks it's generally useful to have some engines. The higher their ISP the more efficient they are and the more thrust they'll deliver from a certain amount of fuel. How much acceleration - deltaV - that thrust actually translates into depends on how heavy the whole vehicle has become now it's payload + fuel + engines = the higher the mass the less the engines will be able to push it all. That's where the TWR (Thrust to Weight Ratio - although it should really be 'mass', not 'weight') comes in. MJ or KER will also tell you your rocket's TWR at each stage but it's simply thust divided by mass - if you have less thrust than mass (TWR < 1) gravity will always win and you aren't going anywhere. With TWR = 1 your rocket will 'hover' but not accelerate away from the surface. TWR between about 1.6 and 2.0 at launch is recommended to accelerate quickly. Once in space you don't need much TWR but the more you have the shorter time you'll have to spend on each maneuver 'burn'. For landings/ascents you'll again need to make sure you have sufficient TWR for whatever you're landing on or taking-off from.

So - you now know what TWR and deltaV are (more or less) and how much of them you need (roughly). You also know that your payload is 8 tonnes. Even a poorly-designed launch rocket should provide a "payload ratio" (what it can lift to orbit versus the mass of the fuel + engines) of 10% so you can quickly estimate that the total thing will mass 80 tonnes - most of which will be fuel.

Method 1: 1) do the maths, 2) build the rocket

Method 2: 1) stick a decoupler and a fuel tank under your payload and add your favourite engine, 2) adjust the size of the fuel tank until the TWR (that MJ or KER tell you) is between 1.6 and 2, 3) if the deltaV isn't enough yet add an asparagus-stage, 4) adjust the fuel tanks on this stage so the TWR is still between 1.6 and 2 (if it's over 2 consider using smaller engines on this stage), 5) go to step 3.

You should be able to get 15% or more payload ratio with a bit of messing around but don't sweat that too much - make something that works before trying to make it efficient.

Launch vehicle - needs ~4,500m/s deltaV and TWR 1.6 - 2 across all stages to get you into orbit.

Transfer vehicle - needs ~1,090m/s deltaV and only TWR 1ish to get you from Kerbin to the mun and into orbit there (Minmus is harder to reach but easier to land on = an easier mission)

Lander/return vehicle - needs ~1,670m/s and (Kerbin) TWR 0.2ish to take off and return from the mun (it's gravity is only 0.16 of Kerbin's). If you're using KER just make sure the mun TWR is > 1.

(With a good margin for error on all but the launch stage - it's no bad thing to have the transfer stage finish the circularisation burn as it means no debris left in Kerbin orbit)

And that's the vehicle. Now you need to fly the thing.

Most important there is the 'ascent profile' for your launch from Kerbin - if you can work-out and fly an optimal path there you're doing a lot better than me! mhoram (?) and others have been having a long discussion about working all that out. Again, you'll have to do a forum or internet search, I don't have the link handy.

Vehicle design is as much an art as a science, beyond the basics. Really efficient rockets tend to be pig-ugly and don't have much margin for error (because margins aren't efficient). How you want to do things - and how much time you want to spend building versus flying - is up to you and practice to find out. Have fun :-)

Edited February 6, 2014 by Pecan
typos

[PPR]

The thing that seems to trip up a lot of new Kerbonauts in terms of rocket design is the notion that more is not always better.

1) Start with the top stage: Less is more. Every kg of mass at the top requires 45-50kg rocket/fuel to get it to the Mun and back. All that extra mass creates complexity and structural stress, so more can go wrong. Try stripping unneeded parts off the top and see what it does to your delta-v. For example, removing one radial parachute can increase your delta-v by 130. A photovoltaic cell can increase it by 10. Sometimes even choosing between two parts that serve similar functions can make a difference. For example, the TR-18A stack decoupler is 25kg lighter than the TR-18D Stack separator, but they do basically the same thing. Even something as innocent as a strut connector (50kg each) can make a difference. Put 10 of those on your ship and you need 22 tons more of fuel. It all adds up.

2) More thrust can be wasteful. On the launch stage you need a thrust-to-weight ratio of more than 1.00 to get off the ground, but more than 1.5 tends to get wasted because the faster you go the more work you have to do pushing through the thick atmosphere at sea level. Also, more powerful engines tend to be heavier (see point 1). Experiment with your engines and you'll see what I mean.

3) Staging can make a huge difference. On your design for example, you have 13 rockets firing on stage 6 with TWR of 3.65. If instead you fired all of solid rocket by themselves, it should be enough to get you off the ground. The next stage you could fire four of the liquid fuel boosters, which should be enough to keep you accelerating. Then the last two boosters. Lastly the central rocket. By splitting that one overpowered stage into 4 moderately-powered stages, you could make huge difference in your delta-v.