I need smart people

[Conarr]

I was wondering if some of you smart people could help me with my Interplanetary Drive Core. Here are some pics:

and

I have more if you need.

Here is the craft file. The one requires mechjeb and KSPX mods.

Here is the stock version

I'm looking to make it more powerful without giving up too much in the way of efficiency or adding a bunch of weight. If I could get it to around 9k delta V, 1000 kN and no more than 180 tons, that would be perfect. I could actually give up quite a bit of delta V come to think of it since I use the Kethane mod and carry a Kethane drop tank attached to one of the docking ports.

ps, I am adding a couple RCS blocks to it now to make it a bit easier to handle on orbit and solar panels so it won't die of electrical asphyxiation.

Edited June 15, 2013 by Conarr
To add stock craft file

[falofonos]

9 tons of drop tank on the side stages for more deltaV

or lose the large nuclear engines for 10 tons more fuel

or both for 20 tons more fuel.

alternatively, swap the side tanks for 4x rockomax X200-32 with large nuclear engines on each, increases weight by 2x large nukes but provides the extra thrust you seek.

Not sure what the fuel pipes are doing. running a loop like that may cause odd mass imbalances.

Edited June 14, 2013 by falofonos

[strongest_2hu]

Easy mode: remove three of those four huge RCS tanks. 10 tons gone. How could you ever hope to use that much RCS fuel in normal orbital docking operations?

Harder mode: are those the stock tailcone things holding those engines on, and if so, remove them because that is 2.4 tons of dead weight. Hold the engines on with cubic octagonal struts or something.

Beyond that the only way to get more power is to use more engines or more powerful (less efficient) ones, either of which will reduce your delta-V. The only way to get more delta-V is to carry more fuel, use more efficient engines, or reduce non-fuel weight. These are decisions that only you can make based on what you need or want.

[Conarr]

The RCS tanks are for extended operations on orbit around various planets. Think it's overkill?

[falofonos]

At 3.4 tons each, the RCS fuel isn't a great burden but unless you plan to carry craft docked to all 4 ports you could probably lose 2 of the ports and rcs tanks entirely saving 7.4 tons

Even if you do plan to carry craft docked, you could put ports on both ends of the subcraft and chain them.

[strongest_2hu]

The RCS tanks are for extended operations on orbit around various planets. Think it's overkill?

I think unless you dock extremely inefficiently you will either grow tired of the mission or lose it to an update before you run out of RCS fuel, and if you've got a kethane extractor you'll never run out. It doesn't take much to dock something like that to something similar, probably no more than 5 units of monopropellant or so, as long as you use the main engines to provide forward thrust (just shut a bunch of them down if there's too much thrust) and are able control the ship you're docking to: just switch back and forth between vessels to keep the docking ports pointed directly at each other (using command-module torque) while you drive it in with the mains.

If you're going to add RCS blocks for routine attitude adjustment, never forget that lander-can has the same form as a big RCS tank but weighs less and never runs out of torque. Command module torque is god's gift to kerbal-kind, use it early and often.

[CalculusWarrior]

Yes, you can remove the big RCS tanks, and possibly some of the engines (like the two on the side). Having less engines to suck up your fuel and less mass to push around will definitely increase delta-v.

[nhnifong]

Not related to increased deltav, but if you're going to be docking other large things to the sides of those big docking ports, and trying to thrust while they're connected, I suggest liberally strutting the docking ports themselves to everything in sight (not the RCS tanks)

[Killenger]

Put atmospheric engines that detach to aid its launch into orbit (you aren't showing your launch stage?) regardless, you can go full atmospheric and nuclear like SSTO's. Extremely efficient

[Djhcc26]

Loose all the rcs tanks on the side and put 2 large rcs tanks under your bigger nervas on the side. Additionally, drop the center nerva on your engine cluster and put a non gimbled stock engine that's 215 thrust. Get rid of all your batteries and put the smallest ones on the sides and some static photovoltaic panels next to it no more than 1 on each side so there's no probe death. That will raise your thrust to about 875 and keep you D/V in between 8300-8500. Keep in mind that after you dock it to the command module your D/V will drop to around 6k-7.5k depending on its mass. 1000 Kn is a little hard to do with that much weight short of editing config files your gonna have to deal with either lower D/V and higher thrust or lower thrust and higher D/V. You cant have both.

[John FX]

If you don`t mind mods the 2.5M NERVA from the NovaPunch pack is 300Kn so 3 of them would be 900Kn. I use them to power my stations about. They look good and are not overpowered compared to a ring of standard NERVA.

Not the best view, sorry.

Also, the pack is huge, extract just the NERVA engine part or it may take over your VAB...

[Shrike42]

Lighter is better; Once you're in orbit, you can get anywhere with just a few LV-Ns and a good tank of gas. Your Drive core currently could probably make the grand tour without any problems, and have enough fuel to do it twice. Lose the external orange tanks and half of those very-nicely placed engines, to save weight and make it easier to get into orbit.

[Conarr]

I think unless you dock extremely inefficiently you will either grow tired of the mission or lose it to an update before you run out of RCS fuel,... Command module torque is god's gift to kerbal-kind, use it early and often.

I'm not the best docker guy in the world, but I can get it done within a few minutes. I actually designed this off others I'd seen on the forums. I don't use RCS all that much anymore, actually only for my utility tug which goes and fetches the drop tanks then docks them to the station. I've just gotten so used to seeing them there, I didn't think of removing them.

The crew lander bolts on to the single docking port between the three tanks and has a command module - so I was utilizing that extra torque. Good comment though, I should have thought to add that in my original description.

Not related to increased deltav, but if you're going to be docking other large things to the sides of those big docking ports, and trying to thrust while they're connected, I suggest liberally strutting the docking ports themselves to everything in sight (not the RCS tanks)

You're absolutely right. I did stress test it. The drop tanks that snap on to the side dock ports are empty for interplanetary runs and weigh in at about 9 tons. The side docks don't even wiggle under full throttle. I originally had about 6 struts lashed all over, but backed it down after testing to reduce part count on the final ship (~420ish)

Put atmospheric engines that detach to aid its launch into orbit (you aren't showing your launch stage?) regardless, you can go full atmospheric and nuclear like SSTO's. Extremely efficient

Oh, sorry man, I didn't explain it well. I have a launcher that will push that junk into LKO. I'm looking to get the kN's up for running out to Duna or some other planets.

.... 1000 Kn is a little hard to do with that much weight short of editing config files your gonna have to deal with either lower D/V and higher thrust or lower thrust and higher D/V. You cant have both.

I'll try out your other suggestions, but what you're saying here is what I was afraid of. I'm trying to squeeze every last ounce of performance and efficiency I can out of the ship, but I may be asking too much.

[M5000]

Having all those nuke engines doesn't inherently subtract from your dV. They all have the same Isp, so it doesn't matter how many you add. However, each engine DOES have some mass, so if you can bear with it, the MOST dV will come by removing all but one nuke engine. Burns will take quite a while, but there will be no unnecessary mass.

Your dV is NOT being subtracted by having more engines "sucking down fuel" that's not how it works, especially if they're all the same Isp. The dV WOULD be subtracted by the engine's mass.

That's what it's about. Specific impulse of the engines. Specifically, the average specific impulse of ALL your active engines. The thing is, the average Isp is NOT calculated the same way a normal average is. It's a weighted average, that considers the thrust of an engine, too. That's why simply adding a NERVA to a Mainsail won't get you much in the way of Isp. Since the Mainsail has more thrust, it has much more power over the final average Isp than the weaker NERVA.

Just sticking a bunch of NERVAs will not solve the problem, as they will build up to extra mass you're really not needing. If I were you, I'd stick a single KSPX NERVA on the end there and be done with it. Sorry, but Nova Punch's NERVA is most definitely O.P. It simply isn't possible to have an engine with that much thrust yet that high of a specific impulse. That's the whole point, fuel is annihilated to create thrust. You can only get so good.

[Killenger]

Oh, sorry man, I didn't explain it well. I have a launcher that will push that junk into LKO. I'm looking to get the kN's up for running out to Duna or some other planets.

Exactly, en-corporate atmospheric engines into its pre 20km launch stage and nuclear engines into its above 20km launcher stage and your launcher stage may almost take you to Duna. Your drive is pretty small really, you may be able to load that thing up with turbofans and get it to 20km off that thrust alone almost, if not use turbofans for an assist with a few skippers/mainsails for a first stage that gets to orbit/almost to orbit, next stage is nuclear and finishes off your orbit/gets you going to where you need to be, and your drive system finishes the job.

Just saying a bigger launch stage is not always better and I'm betting you have a huge dirty mainsail launcher stage. I've lowered alot of my launcher stage part counts by doing this.

Sorry to throw that all out there, I know this thread is not about the launch stage.

Edited June 15, 2013 by Killenger

[John FX]

Sorry, but Nova Punch's NERVA is most definitely O.P. It simply isn't possible to have an engine with that much thrust yet that high of a specific impulse.

Sorry, but it is not OP. It replaces 5 normal NERVA in a ring with the same ISP. 5x60Kn=300Kn. As ISP it stays the same the only difference is part count and weight. A standard NERVA weighs 2.25T so 5 would weigh 11.25T compared to the 9.5T of the NP NERVA so to offset the `definite OP` all you would have to do is put something that weighs 1.75T per engine on your craft. If you do that in less than 4 parts you have reduced your part count and not changed the thrust or weight or ISP of your craft.

If you want 1000Kn then the np NERVA does nearly this (900Kn) with low part count (3) and is not OP (add 5.25T total dead weight to offset the minor difference of the three engines)

[John FX]

Exactly, en-corporate atmospheric engines into its pre 20km launch stage and nuclear engines into its above 20km launcher stage and your launcher stage may almost take you to Duna. Your drive is pretty small really, you may be able to load that thing up with turbofans and get it to 20km off that thrust alone almost, if not use turbofans for an assist with a few skippers/mainsails for a first stage that gets to orbit/almost to orbit, next stage is nuclear and finishes off your orbit/gets you going to where you need to be, and your drive system finishes the job.

Just saying a bigger launch stage is not always better and I'm betting you have a huge dirty mainsail launcher stage. I've lowered alot of my launcher stage part counts by doing this.

Sorry to throw that all out there, I know this thread is not about the launch stage.

Lately I have been experimenting with a turbofan first stage and I have found that I can reduce my launch weight from 55T to 40T and change the mission from a Mun landing and return to a Duna landing and return with the same payload (If I add a parachute for the Duna landing)...

[zanzibar196]

Looks like you are building it upside down?

[Conarr]

Looks like you are building it upside down?

Yes, It is built upside down and the lift vehicle for it goes under. I've just removed it for clarity in the pics. Plus the struts to hold it all together with the lifter is quite ugly.