Rocket Improvements for a Moonshot?

[sardia]

This is a the rocket I built for a 4 man rescue attempt + moon landing. Can I make this any cheaper or more efficient? There's up to 4 kerbals I can rescue, all orbiting kerbal and the moon. In addition, I have a moon landing contract as well. I did the trick where I used a decoupler main stage as a cheap radial first stage. I don't suppose I should just strap on another stage of boosters?

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Edited November 1, 2015 by sardia
fix photo

[Phil deCube]

I can't see your picture.

[Snark]

I can't see your picture.

Yah, me neither.

Could you try using imgur.com? Works well, is super simple to use, doesn't require signing in with username/password.

[celem]

Oh wait i've not seen this trick. Your SRB first stage is welded onto that decoupler on the bottom of the main stack? thats neat...

I cant tell what all the engines are, there are a few odd choices however and Im not sure you can easily orbit that. As soon as your SRBs go you are on what? a skipper? with 0.87 atmo TWR its really gonna struggle, even given that you'll be up around 10km. Then it looks like a poodle above that, which is a good munar transfer engine, and produces much more dV than in the atmospheric screenshot, but due to the low dV of the rocket at this point you will end up circularising on it, which wont go well.

The top stage with the radials is probably thrusty enough for your mun launch, though those have heinous efficiency they would work well to assist your weaker launch stages.

It probably all adds up for a mun landing on paper if you hop between vac and atmospheric dV display, but you dont have thrust in the right places and im not confident this will orbit kerbin. That skipper or whatever it is under the bottom decoupler is definately gonna need a friend at anyrate, and you will need more dV if you plan to have the 'guessing poodle' as a transfer and not have to double as circulariser(it really wont do that well, its gonna suck).

Some tweaks I would make off the top of my head. Halve the fuel on the poodle or whatever that third stage is, give what you removed to the skipper. give the skipper four of those radial buggers, you want at least 1.0 sea level TWR to have any hope of making the climb from where the SRBs deposit you. Ideally it needs another stage, that poodle is awful in any kind of atmosphere. In a perfect world you shorten the skipper stages fuel very slightly, call it the topstage and stick a mainail below with gas for days.

The lander is quite top-heavy looking, but you dont appear to have radial decouplers yet. Its tricky to lift 4 guys out in a hitchhiker like that, you are on a narrow base. You can fake radial attachments by using the little girders, but since you probably dont have fuel lines you then move all the gas to the radials, engines under them and put the legs out there too for more stable landings.

edit: just went away and had a fiddle in the VAB, using what I read to be your tech. I cant come up with a solution to be honest, not without busting weight caps. You capped at 140? More boosters pushes really hard off the pad but doesnt help you massively longrun since they get pretty bad pretty quick as you climb. Also its gonna start getting very hard to steer.

Edited October 28, 2015 by celem

[Streetwind]

My big recommendation:

Purpose-build your rockets. Don't try to do everything all at once. If you try to use the same craft to rendezvous with multiple targets in low Kerbin orbit, then transfer to the Mun, then rendezvours with multiple targets in munar orbit, then land on the Mun, then take off again, then transfer to Kerbin and land... that won't work in any efficient manner. Rather, build a craft that collects all your stranded Kerbals, and then design a different craft that lands on the Mun.

To improve your current design to that end:

- Use a mk1 pod instead of a mk1 inline cockpit. You can still attach all your parachutes, and even add anoter chute instead of nosecone. The rocket will be pointier and smaller, and the radial parachutes will be better protected from reentry heat.

- Speaking of reentry heat, you do have a heatshield below the Hitchhiker, right...? Just asking because I know you can mount the decoupler so that it is invisible.

- Since you're not landing on the Mun, get rid of the thumpers, the landing legs, and any science gear you might have brought. Also get rid of the fuel tank between the Hitchhiker and the adapter. Losing all that weight will greatly improve the performance of your other stages too, without you having to do anything about them.

However, your screenshot confuses me. If I read that right, you have a Poodle stage with an X32 tank giving you only 629 m/s worth of dV? That makes no sense. It should be three times that much or more. The Poodle is the most efficient chemical engine in the game, and the payload above it isn't large enough to dominate the x32 tank to that extent. So either something is screwy with the way you built, or with your staging order (though it looks fine from here), or with the way that KER calculates your dV. For example, if you built at least partially bottom-up, that may result in KER not understanding the craft structure correctly. Always try to build top-down, meaning: never put extra propulsive stages above your root part.

TL;DR: your rocket should have way more dV than it shows, but you still shouldn't try to do four rescues and a Mun landing and return in the same flight.

[NathanKell]

10km is only .1763 sea level pressure, so very nearly vacuum thrust already. 636 out of 650 kN.

[TheXRuler]

Soo I didn't feel much like describing everything seperately so instead I whipped up something in the VAB quickly which is almost the same, costs 2000 funds more, wheigs a little less and has the same exact amount of parts.

First off, that trick for geting radial decoupling weas new to me as well and at ~1000h ingame time there aren't many things I haven't seen so thanks for that

I just played around, minmaxing the stages a little. You see, on the first two or three stages the additional couple hundred kg from the cockpit won't make a huge difference, however, on the final stage it's really well worth using the lander can, since that has a lower mass and it will actually be carried the entire way. Basically make you stinginess with added weight directly proportinall to how long you will be carrying that stage with you, the further the stingier. Also I made the lander design two stage which has two main advantages, more dV due to dropping unnecessary weight and more stability because the center of mass is lower down and you have a wider base.

The rest of the rocket is mainly unchanged apart from the fact that I use two skipper engines instead of just one as that allows you to carry quite a bit more fuel to orbit at little additional cost. I also slightly increased the length of the first liquid fueled stage since otherwise you would be wasting precious lifting capacity. One thing I did, then reverted because I don't know what you have unlocked was stick some winglets (preferrably with control) at the base of the first LFO stage, this will give you control early on, since the SRB's are ungimballed and the radial lander design shifts the CoL far forwards.

As you can see from the screenshots, this setup will give you around 4000m/s of dV once in orbit, which should be way more than you need for going to and from the mun.

Here is the craft file in case you wish to muck around with my design/take a closer look. (Edit: Turns out dropbox is a little messed up atm and I can't upload the file there, if you still want it PM me and I'll send it to you via hamachi/teamspeak/skype/facebook/email/whatever)

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[TheXRuler]

Street Is right though, it would be a lot easier to build a dedicated lander craft and a seperate craft to rendevousz in orbit. Assuming you have the tech I think the best way to do things would be to stick a small, automated lander on the top to recover the single kerbal from the surface, then land only that. Also go to the mun first for two reasons, if you postpone the landing that means you are essentially lugging a whole load of dead weight around the whole time. Also, you will not get stranded in munar orbit since you will be taking all the fuel you wanted for the kerbin rendevousz. Then, if you start running low in munar orbit already you can go straight back to kerbin and not have to worry so much about leaving people stuck in orbit around another body, requiring a seperate (and expensive) rescue missin. Remember you can very carefully aerobrake yourself back into a circular orbit without spending another ~850m/s to slow down. Just aim for around 30km (at least that worked well in .90) although to be more precise I reccomend getting the Trajectories Mod or whatever it's called now which will display your orbit after aerobraking. Also very usefull for pecise landings on atmospheric bodies.

Edit: However I think I "slightly" overbuilt the lander/transfer stage so it should still be easily doable with my craft. Say you use up 400 m/s for rendevous in orbit around Kerbin + 850m/s to get to the mun and 1000 m/s for each landing and takeoff that would still leav you with ~1300 m/s for rendevous in mun orbit and return to kerbin which should be waaay more than you need.

Edited October 28, 2015 by TheXRuler

[mabarry3]

@TheXRuler: Any chance you can pm me the craft file for that mun lander? Interested to look at it a bit, it's cheaper than my current lander (probably because i overbuild wayyyy too much, smh) and that seems usable enough for tourist missions too.

[sardia]

I think I can cheap out a bit more here, replace the command module with a probe core, that should lighten the top stage. Indeed, I neglected to put a heat shield. I don't believe the hitch hiker is known for its heat tolerance, so I'll add that. Normally I just turn my engine stage as the shield but that's not the case here.

The throttled srb stage lifts me high enough that the second stage has a twr of 1.1. There's 3900 delta v in the first two stages, minus the atmospheric inefficiencies. Note how ker engineer is set to atmospheric delta v, while mech jeb is not.

Slashy noted earlier that a rocket doesn't need steering fins, just gimbal and SAS. So I ditched them to save cost. Not sure if the last stage can escape the moon and go home. I might just send a proper rescue craft once it gets to lko.

[sardia]

I made some adjustments to improve my second stage allowing me to conserve my 3rd stage for rescuing kerbals as far as minmus.

1. No more mun lander.

2. Poodle + fuel tank as improvised heatshield.

3. Replaced command module and added an extra chute.

4. Put tail cones onto SRBs. The cost seems questionable, given the performance gains. I think its worthwhile to put a cone on top, but not anything expensive. Maybe replace them with parachutes and go install stage recovery mod, but that's more trouble than it's worth.

5. KIS wrench for orbital unpacking of cargo bay. (RCS, solar panels)

6. Six SRBs added, more boosters, but with a lower burn rate to get me higher. This allows Skipper to fire at 1.1 TWR. I stay vertical longer, but it's more stable given I cheaped out on tail fins.

7. Lowered the SRB attachment point so it collides with main stack less often.

My previous rocket went dead when it ran out of juice behind the moon, so I had to revise it into the below pic. Now there's 3 guys to be rescued, and two failed rescue rockets all orbiting the mun.

[Snark]

Have you considered an asparagus arrangement for the bottom stage booster? You could pack eight 1.25m liquid boosters around it. Efficient, stable, lots of dV, and you can attach SRBs below them.

I see that you've been doing some clever design gymnastics to work around not having radial decouplers... but if you have the tech for fuel ducts, radial decouplers can't be far behind. Can you squeeze out just a few science points somewhere so you can get them? Will really make life easier.

Here's another trick that can help give your SRBs some legs. Works with radial decouplers, but you could easily adapt it to your stack decoupler trick. It's a sort of poor man's asparagus. Let's say you have a rocket where you work out that you need six SRBs running at 85% thrust. Instead of attaching them as one set of six, all at the same thrust and jettisoned together, add them as two sets of three. Set A is at 100% thrust. Set B is at 70%. All six are activated at launch. The takeoff thrust is the same as before, but set A will burn out first and can then be jettisoned while set B continues.

Edited October 30, 2015 by Snark

[TheXRuler]

Dude for real, just make your currently third stage a two stage vehicle, instantly more dV. One of the most important things I have learned in KSP is this: If you wan't more dV, edit one of the top stages, then make the booster stages big enough to handle that. You could add sixteen SRB's for probably about the same dV gain as you would get from adding a single flt-400 + LV909 to the topmost stage, it's just the way rockets work.

[sardia]

As a rescue ship, my biggest consideration is cost. Sure I could make a super efficient 2 stage rocket to rescue a single kerbal, but the profit margins there are slim. Sending a rocket that cost 10-20k more but rescues 2-3 kerbals improves my profit margin tremendously. This especially helps now that the kerbals are spawning around the mun or minmus now. For my munshot/rescue from surface, I'll do either

tiny 1 man rescue lander + probe using this rocket as a base,

or

make an actual rockets with expensive parts that I took out to save $$$, like adding radial liquid boosters, fins, and SAS. Then I can asparagus stage the crap out of it while maintaining good control. Oh, and research docking ports.

Question, is it possible to have a lander with a poodle engine on the moon? It looks much cleaner though I suspect I need radial engines or bigger landing legs.

[ForScience6686]

Srb are cheap and made to be disposable, so stick with those to get through the thick atmosphere. Poodle is a good engine choice, and you are correct in the larger legs. But if you are using a tiny lander you'll be better off with the 909 I think. Less weight, and you don't need the power of the poodle. I use it more for a transfer stage. Always build as light as possible.

[sardia]

Success, I managed to not only make it to the moon and take off, I also managed to land within 2.2 km of the stranded kerbal. That was pretty good thing considering I didn't actually bring a kerbal with me. That's right, I used the rescue kerbal to plant the flag on the mun to complete them both. Did you know that this rocket is strong enough to tip over without breaking into pieces? I was quite surprised when that happened. I had to tip it back up, and then fire the rockets to take off.

There's some strange behavior with heat and the lander legs. It looks like the legs overheat quickly when retracted, but cool off when extended. Maybe a bug with how the game draws their cubes?

asds