Designing a good interplanetary transport

[Ruthgar]

Been playing KSP for just a few months now, and having a blast with plain old vanilla KSP. However I seem to be having a problem with designing a reliable transport ship to get to/from other planets. My current designs have managed to get to both EVE/Duna (mostly due to luck in orbitable arrangements when I launched them.) My current design is quite inefficient 5 missions each with an asparagus staged central core to get into orbit of LARGE tanks/engines, then attach the central core to a cross frame that came up on the first mission with the command module/lander. Then usually 1-2 additional missions just to top the tanks off. Now aside from the normal issues I have such as forgetting to put on extra mono-tanks on the transport to refill the lander after it gets back into orbit, or one unfortunate mission to Ike where I had forgotten to put downward facing lights on the lander (Jebediah - hmmm, I should be seeing the dayside and my landing zone coming into view now, why haven't I seen it yet??..... as the lander smashes into a mountain/cliff that was completely blocking the sun) the issues I seem to be having are two fold. One is that I simply do not have enough delta-v right now to get anywhere other than EVE/Duna and get the transport back intact, and it's only reliable getting to EVE and back, of the 3 mission attempts to Duna I've had to eject the command module from it twice while docked to the lander and use the lander to get us back on Kerbin (one transport wound up somehow smashing into an asteroid retrieval probe that I had just put into orbit somehow *wish I had been able to take pics* before scattering debris throughout the planet, second looks like it's attempting to be the next voyager probe). Also had to abandon one otw back from EVE as I keep having cross feeding issues either from refueling the lander in between landings, and one or more of the outer rocket sets will go dry during a burn and the subsequent spin the ship goes into ripped/smashed one of the stacks off and destroyed parts of the others ( had two outer stacks left intact though only had 5-10% fuel left in them, no engines left on the inner stack, but had almost 80% fuel in the surviving tanks, and no way to transfer the fuel as I was down to vapors of mono, and central core was attached with a stack separator).

So my question for you all is this, can you help me with a new transport design, that aside from whatever trips are necessary to refuel it, and replace any lost/landed probes/landers/rovers, is intact once it gets back to kerbin SOI, even if I have to send a ship to refuel it to get it back into close kerbin orbit. Also a design or mod suggestions (more along the lines of making transfers/intercepts easier while using the vanilla KSP parts) that won't force me to rely on the brute force version of a transport ship in interplanetary transfers. Also I'm assuming that my problems with refueling issues in past transports were due to the fact that I had stack separators with no crossfeeding in the design, would this be correct?

Now I'm not looking for someone to tell me how to build it piece by piece (though I wouldn't object to such a design provided it does allow me to tweak it as much as I want to), but would prefer just some ideas/guidelines.

Edited July 5, 2014 by Ruthgar
forum lagging posted it incorrectly

[Pecan]

Chapters 7 and 8 of the tutorial in my signature.

This thread should be useful: http://forum.kerbalspaceprogram.com/threads/83368-A-reusable-transfer-stage-a-good-idea

You might also like the 'checklist' mod, which is there to remind you of all the little things you might forget to add to the ship ;-0

In general, as long as you're using LV-N engines and not trying to make too huge a vehicle it should not be too hard to build a transfer vehicle for most planets. Check the delta-V requirements carefully (chapters 4/5), practice small and, if necessary, just try doing fly-bys first, without landers or other attachments. Don't be shy of taking spacestation components, spare fuel tanks, etc. to the destination as separate missions and docking them together in orbit.

For an example of how little you need consider 'Fat Sally' in chapter 5. That is capable of a landing on Ike and return or a Duna flyby. The 'Tractor Light' in chapter 7 is quite capable of taking an orange tube of fuel and two medium landers (chapter 8) to Duna for multiple landings. It can then leave them there and come back alone.

Edited July 4, 2014 by Pecan

[Ruthgar]

Thanks Pecan, going to do my 'assigned' reading now

[LethalDose]

This line concerns me about how you're going about things:

My current designs have managed to get to both EVE/Duna (mostly due to luck in orbitable arrangements when I launched them.)

Are you not waiting for launch windows on other approaches?

Also, where else are you trying to go? Jool is the only other planet that's near the ecliptic. Dres, Moho, and Eeloo all have inclined orbits. This can take more dV, but the way you're trying to get there can also have a huge impact on the needed dV.

The point of this is: this may not be an engineering issue, it may be an issue of execution.

[Ruthgar]

This line concerns me about how you're going about things:

Are you not waiting for launch windows on other approaches?

Also, where else are you trying to go? Jool is the only other planet that's near the ecliptic. Dres, Moho, and Eeloo all have inclined orbits. This can take more dV, but the way you're trying to get there can also have a huge impact on the needed dV.

The point of this is: this may not be an engineering issue, it may be an issue of execution.

Yeah, those approaches/returns were calculated with just the old calibrated mark 1 eyeball, and what looked to be the best time to leave. Having now looked up the exact delta-v's and approximate windows that I should have used and recalculated my old trips I was actually wasting between 20-40% of my fuel onboard making up the differences. That's what I get for being impatient, also figured that I was losing at least another 10% due to it be overengineered on the brute force method of planetary transfers.

ps. This game is the first time I've actually had to use what I was taught about orbital mechanics outside of purely paper problem solving, even though I've spent the last 20 years working on and around ACTUAL SRBs, liquid fueled orbitable transfer stages, and reentry systems. Pulled out my old study materials on the stuff, and turns out I had messed up the equations slightly (was forgetting a number or two on the right side of the decimal points) Not so big a problem getting into orbit, but the error in my calculations was actually increasing exponentially the farther out I planned on going.

Edited July 5, 2014 by Ruthgar

[Ruthgar]

btw, how do you change the thread status to answered?

[GoSlash27]

I know it's already been answered, but I have some additional pointers to help you along...

If you can lift 5 tons to orbit then you can do just about anything in this game. Your transfer ship will need at least 1 LV-N engine, so that's 2 1/4 tons, leaving you 2 3/4 tons for empty tanks. You also don't need your orbital insertion stage with all it's attendant extras (RCS, guidance, solar panels, engine, etc) since your transport already has all of that stuff. So that means you can put it right on top of your booster/ transstage and use the leftover payload for even more tankage. Just be sure to leave enough fuel in it to attain and stabilize LKO. You don't need more than that at launch, since everything else you launch will be rendezvousing with it. Then you can fuel it up, bring up a payload, and you're all set.

If done properly, you can build a transport that will move 5 tons of cargo anywhere in the system without having to lift any more than 5 tons at a time.

This is the transport I'm using based on the 5 ton limit:

Best,

-Slashy

[Cerberus738]

This thing got me into laythe orbit and has 2 landers along with it. sadly after doing a few landing missions on jool's moons i don't have enough fuel to bring the guys home. fuel ship is now en route. good thing they packed plenty of snacks!!!!

[AlexinTokyo]

btw, how do you change the thread status to answered?

Edit the first post, select 'Go Advanced', and you can change the 'Prefix' pulldown from [unanswered] to [Answered]

[Ruthgar]

Edit the first post, select 'Go Advanced', and you can change the 'Prefix' pulldown from [unanswered] to [Answered]

Thanks AlexinTokyo, and thank you to everyone else for your help. Yeah, it turns out my main issues were an over-engineered design with design flaws (more engines than needed, decoupler stacks when I didn't need them, not enough RCS jets in the right places or not enough reaction wheels to turn the thing (took about 5 mins to do a 180)), or just plain forgetting to put alternate docking ports on (first one was 90% assembled when I noticed I had included no extra docking ports for the lander to refuel. Other main issue was making simple mistakes in orbital mechanics which is funny considering I've worked on/around SRBs for the last 20 years. So installed some of the informational mods MJ, kerbal engineer, etc.... along with the ScanSat and interstellar mods, and started a new career. Built a ship with about the third the science and that has litterally 1/2 the D-V of what I originally used to go to Minimus and just orbit in my old career. This ship managed to send a lander down to Minimus, get it back to Kerbin orbit, then successfully landed back on Kerbin, lander section fully intact. Had to use Bill to do it though, Jeb was injured during the initial prototype test flight.

Damn thing barely made it out of kerbin orbit, without asparagus staging I pitched it over too early and then burned up a lot of the lander fuel just getting into a stable kerbin orbit. Didn't think I would actually make it that flight, but I did.

Thanks again everyone for your help, I'm gonna go design some more over engineered ships, though with the information you've all given me, along with using those informational mods (that KES mod with the actual distance to surface, got me onto Minimus on the first try, without any bouncing, excess thrust to send me back up a few hundred meters, etc... there was however one moment of panic when the lander did pitch to a 45 degree angle and I thought I would have to retry, but actually settled down no problem.) ( and yeah I know I can only use that lander you see on the low grav worlds, but it's actually a lot of fun to use)

[Pecan]

Congratulations :-)

However you want to play it, of course, but that lander and, particularly, the Kerbin return, is huge!

ETA: Oh, and I LOL'd at the flag text :-)

[LethalDose]

Yeah, those approaches/returns were calculated with just the old calibrated mark 1 eyeball, and what looked to be the best time to leave. Having now looked up the exact delta-v's and approximate windows that I should have used and recalculated my old trips I was actually wasting between 20-40% of my fuel onboard making up the differences. That's what I get for being impatient, also figured that I was losing at least another 10% due to it be overengineered on the brute force method of planetary transfers.

ps. This game is the first time I've actually had to use what I was taught about orbital mechanics outside of purely paper problem solving, even though I've spent the last 20 years working on and around ACTUAL SRBs, liquid fueled orbitable transfer stages, and reentry systems. Pulled out my old study materials on the stuff, and turns out I had messed up the equations slightly (was forgetting a number or two on the right side of the decimal points) Not so big a problem getting into orbit, but the error in my calculations was actually increasing exponentially the farther out I planned on going.

Well, welcome to the party. It'll be interesting to see what an actual rocket engineer can come with in this game.

If you haven't gotten them already, some other mods you may want to consider are Kerbal Alarm Clock and Protractor. I use the former, but not the latter (though I hear good things about it).

Best of luck!