Having trouble designing propulsion for my interstellar ship.

[Xuixien]

I have a lander design that can land on pretty much any of the low gravity planets (Moho, Duna, etc), + the command, habitation, and power sections of my ship. However I'm having trouble with propulsion. Here are two designs I had, one with argon engines (near future propulsion) and a fission reactor, and another using nuclear engines. I have problems with both designs

* The fission reactor never gets to full power, so I can't burn my argon engines at full thrust. The burns take forever, and I think this makes my maneuver nodes inaccurate.

* The nuclear engines, even with radiators, overheat too soon for a burn.

Looking for hints for alternative solutions or a fix for what I' doing wrong.

Edited October 28, 2015 by Xuixien

[Zophos]

What are you attaching the NERV engines to? My understanding is that large parts, and especially fuel tanks, make good heat sinks. You can then attach a radiator or solar panel to the tank to bleed off the heat received.

For example, I'm currently running a Duna mission that uses four of them, each attached to a good-sized LF tank sporting a gigantor. I have run the engines at full power for several minutes (six or more) without overheating problems.

[Xuixien]

What are you attaching the NERV engines to? My understanding is that large parts, and especially fuel tanks, make good heat sinks. You can then attach a radiator or solar panel to the tank to bleed off the heat received.

For example, I'm currently running a Duna mission that uses four of them, each attached to a good-sized LF tank sporting a gigantor. I have run the engines at full power for several minutes (six or more) without overheating problems.

A SpaceY interstage plate. If I add more radiators to the fuel tanks, will those bleed heat off the nuke engines?

[Snark]

Overheating problems are easy to deal with. Just attach some of the "active" radiator panels (the ones that fold and unfold) anywhere on the ship. They don't need to be next to the overheating component, they can be anywhere. While deployed, they actively (and rapidly) suck heat out of any components on the ship that are hotter than them. Problem solved. The only question mark is how many (and what size) radiators you need, which will depend on your heat load (i. e. how many LV-Ns you're running).

[Xuixien]

Overheating problems are easy to deal with. Just attach some of the "active" radiator panels (the ones that fold and unfold) anywhere on the ship. They don't need to be next to the overheating component, they can be anywhere. While deployed, they actively (and rapidly) suck heat out of any components on the ship that are hotter than them. Problem solved. The only question mark is how many (and what size) radiators you need, which will depend on your heat load (i. e. how many LV-Ns you're running).

I'm using 7.

[Zophos]

A SpaceY interstage plate. If I add more radiators to the fuel tanks, will those bleed heat off the nuke engines?

I haven't used the SpaceY parts, so I have no idea what their thermal properties are (specifically, how well they conduct heat). Mine are attached directly to the tanks, so the heat from each engine dumps directly into the big part. Here are the drilling/tug/tank sections, landed on Ike --- the rest is in orbit above at the moment:

The blue thing on the end of each boom is a procedural LF tank. With a NERV on the bottom and a gigantor on the side. It isn't particularly pretty, but it works just fine.

[Snark]

Overheating problems are easy to deal with. Just attach some of the "active" radiator panels (the ones that fold and unfold) anywhere on the ship. They don't need to be next to the overheating component, they can be anywhere. While deployed, they actively (and rapidly) suck heat out of any components on the ship that are hotter than them. Problem solved. The only question mark is how many (and what size) radiators you need, which will depend on your heat load (i. e. how many LV-Ns you're running).

I'm using 7.

Well, great, but I wasn't actually asking how many. All I'm saying is, try putting some active radiators on there as a test and run to see how it works. If you get a blowup, add more radiators. I'm guessing your 7 consist of one in the middle with six around it in sixfold symmetry? If I had to guess, I'd say putting on 6 of the medium radiators (the active foldable/unfoldable ones, not the static panels) would probably be plenty. That's a total guess though, would suggest testing it and upping the number if it's not enough.

It's important to use the active foldable panels, and not the static ones, because the active ones are the only ones that get the magic "suck heat out of parts everywhere on the ship" behavior. The static panels only help with the part they're directly attached to, and since you can't attach them directly to the LV-Ns, they won't help you much.

[Streetwind]

* The fission reactor never gets to full power, so I can't burn my argon engines at full thrust. The burns take forever, and I think this makes my maneuver nodes inaccurate.

Perhaps I can help you figure that part out, since I help out with Near Future.

To make reactors produce their full rated output, you need to:

- Initially wait for a few ingame hours. They are currently very slow at ramping up after being turned on. However, once they are turned on, you can still throttle them effortlessly between zero and maximum power, so there's literally no downside to just keeping them on forever. Therefore, just timewarp a bit before setting up a burn, until the reactor has completed its initial startup procedure.

- Actually throttle the thing up. When coming fresh out of the VAB, the reactor is set to 50% throttle, exactly like engines are. If you never touch the power setting, you'll only get half the rated performance even after the reactor has finished spooling up.

- Provide sufficient cooling through active radiators (Thermal Control Systems in stock KSP, or suitable mod parts). An insufficiently cooled reactor will overheat and lose more and more power output the higher the heat level grows. Each reactor lists a recommended radiator setup in its description, but keep in mind that some of the very large electric engines also produce large amounts of heat. This can cause reactors to start overheating a few minutes into the burn if you didn't bring enough radiator capacity for both.

If you checked off all those points and still don't get the output you expect, please come on over to the Near Future thread with some screenshots and we'll suss it out for you

(Reactor and heat behavior subject to change in future versions as the stock heat system evolves.)

Edited October 27, 2015 by Streetwind

[Climentina]

use can use alt+> to open the physics accelaration, if you think the argon engine takes 4ever

[Xuixien]

Thanks for all the help everyone! I'm sticking with liquid fuel + nuclear engines. Ideally I want my ship to be able to refuel off asteroids (do you even encounter those outside of the Kerbin area?) or at least send a lander onto a moon and refuel.

[Gojira1000]

I have yet to melt a NERVA system on burns of 10 minutes+ (I have managed some lovely glow, though) - I always pair 2 small or one medium radiator per engine (or a small + a gigantor).