Is there any reason to not use nukes for interplanetary anything?

[panzer1b]

Well as the title says, as much as ive used about every engine in the game (except those puny ant engines i cant find any use for), i cant seem to find any reason to use anything but a nuke (or a cluster of them) for interplanetary burns. Is it just me, or is the ISP difference so massive between the nuke and other engines, that aside from extremely massive loads (not that ive ever flown anything bigger then 200t past LKO), or landers, all engines but nukes feel pointless in terms of efficiency. Ofc you can still get reasonable dV from other engines, but nukes let you more or less do the same trip as a normal engine with roughly half the fuel, or more payloads.

Ofc nukes arent for the patient, as burns can take roughly 10 minutes or so to jool or farther (i usually use 1 nuke for 20 tons of mass), but even still, unlike ions, nukes actually have enough thrust to move stuff at a respectable rate.

Anyways, is there ever a reason to not use nukes for interplanetary, or perhaps a reason to use other engine types instead of nukes (that isnt the obvious cut down part count or moving 1000t ships).

[7499275]

Launch weight increase, nukes are heavy. Therefore it will take a larger launcher to put it in orbit and if you're in career, they're expensive.

[smjjames]

Launch weight increase, nukes are heavy. Therefore it will take a larger launcher to put it in orbit and if you're in career, they're expensive.

Perhaps, but would the pros outweigh the costs?

In science mode and sandbox, the actual monetary cost doesn't matter though.

[panzer1b]

Launch weight increase, nukes are heavy. Therefore it will take a larger launcher to put it in orbit and if you're in career, they're expensive.

Valid point, but aside from funds, does it ever make sense to not use them (im from the era before career even existed, so i still play sandbox all the time).

[JimmyAgent007]

They are worth it in my opinion. More so if you are using the same ship over and over. Leave it in orbit and then just refuel so you dont need to lift the nuke engines more than once. Personally I never use any other kind of engine in space. Landers and Launchers are different but any long distance moving I do is with Nukes.

[Caelib]

I encourage you to experiment with delta-V using different engines and configurations using the Kerbal Engineer mod. If you're launching extremely heavy payloads, then a single nuclear engine is usually the most efficient approach. However, if you're willing to use probes, I have found that building very small is the most cost-effective approach and you don't even need to use nuclear engines. I've build 4-stage probes that can literally go anywhere in the whole system for a launch cost of ~25,000 funds (and that includes science parts) and it DOES NOT use asparagus staging or any fuel lines.

A lot of people get bored with KSP and take a break - when I get bored, I start experimenting with builds to see how small/efficient I can make things and it has been very rewarding. Don't underestimate the ion engine, it's extremely efficient and means you can build small and go far.

Edited February 13, 2015 by Caelib

[Rakaydos]

Smaller designs can use the even-more-efficent Ion engine effectively

[7499275]

They are worth it in my opinion. More so if you are using the same ship over and over. Leave it in orbit and then just refuel so you dont need to lift the nuke engines more than once. Personally I never use any other kind of engine in space. Landers and Launchers are different but any long distance moving I do is with Nukes.

Agreed, if you are leaving in orbit yeah they are totally worth it. Or if its a long haul with a big load. I just hate having to lift nukes off the planet again, because of the weight.

[pizzaoverhead]

If your mission profile requires a fast insertion burn, using lighter, higher TWR ratio engines may be more efficient than clustering LV-Ns. Other reasons include price, not having a big enough payload, and not having them unlocked yet. Beyond that, their huge ISP is hard to match. The right tool for the right job.

In reality, you don't want your crew or electronics bathed in more radiation than they're receiving already, and shielding is heavy, so you get some interesting design decisions:

http://www.projectrho.com/public_html/rocket/radiation.php

Edited February 16, 2015 by pizzaoverhead

[mitko]

If your ship is lighter then 8 tons or so you are better off using 48-7S, and if it's lighter than a ton the PB-ION is better.

[r_rolo1]

It depends of the mission profile ... in other words, how much dV needed, the TWR expected for the burn and the useful payload weight ( oh, and the ammount of time/ patience you have avaliable for burns also might make a difference in here ). If you want to send a 0,5 ton mini sat to Duna, attaching a 2,5 ton nuke engine to it makes no sense, for a quick example.

[rkman]

Launch weight increase, nukes are heavy. Therefore it will take a larger launcher to put it in orbit

To get the same dV with a 909 as with a LV-N, it needs 3 times as much fuel, which is much heavier than a LV-N.

payload mass : 7.3ton (mk1-2 + hitchhiker + parachute)

LV-N : 4400m/s dV, mass 18.5ton

909 : 2470m/s dV, mass 16.8ton (same amount of fuel as above)

909 : 4400m/s dV, mass 34ton

[panzer1b]

If your ship is lighter then 8 tons or so you are better off using 48-7S, and if it's lighter than a ton the PB-ION is better.

Well i generally dont touch craft below 10 tons, so i guess for my own methods of going to space, they are indeed the best engines. Probes are at least for me, using RCS for propulsion most of the time. This is because most probes i make are missiles, and i need to have full RCS control to guide them onto a target, + the monoprop engines are rather good in terms of thrust and efficiency at least for such small payloads). Ions are great, but like most engines are extremely limited to very small payloads, as while i have used them on a few occasions, i dont quite like aesthetics of the expanded solars, and using teh non-tracking panels is difficult and requires massive part numbers. Probes yes, but anything above 5t is unbearable in terms of burn times. If a burn to jool from 100km takes over 10 minutes, it measn i totally need way more engines.

As for landers, this is more or less the one spot i use non-nuke engines, as nukes are very heavy, and suck in atmosphere. Also lifters cant use nukes for obvious reasons, but i think most of us know this.

[cicatrix]

Finally I reached the point in my career that I don't need to care about money. I can launch really expensive crafts and I frequently choose TWR over Isp. I just can't stand 10-20 minute burns with LV-N so I simply lift larger fuel tanks to orbit, refuel them and use some nice powerful engine to get me where I want.

[Jouni]

When I was playing with the 6.4x Kerbol System, I frequently used Skippers and KR-2Ls for the first part of an interplanetary transfer burn. TWR requirements were higher than in the stock game, because delta-v requirements were around 3x higher, while orbital periods were just 2x longer. In the stock solar system, delta-v requirements are so low that high-TWR Kerbin departure stages don't make sense, except perhaps when you're diving close to the Sun directly from LKO.

[Laie]

I don't have the figures handy, but if you plan to run the engine for more than 2000m/s, it's always either the nuke or the ion that's coming out best (or so close to best that the miniscule savings don't justify the search for a better solution -- unless you enjoy the search itself, but then you wouldn't be asking). Craft size hardly matters, because the nukes are still rather small. If the next best engine would need one FLT-800 worth of fuel to get you there, the nuke plus half as many fuel will be just as heavy and take you further.

Look at Nuke. Look at FLT-400. Yes, it really makes sense more often than not.

Money makes this a little more complicated. But considering that the saved fuel doesn't need to be taken to space in the first place, nukes also become the most economical solution very quickly.

[Tank Buddy]

The higher Isp rocket motors have a higher maximum possible Delta V (there is a graph for it somewhere here \/).

Really it comes down to:

• How much Delta V you need
  
• What you want your burn times to be like (TWR)
  
• If it easier to just go with lighter engines (LV-Ns are heavy)
  

Edited February 13, 2015 by Tank Buddy

[Sirrobert]

When I'm moving probes, a single half 1.25m fuel tank with a 909, or 48-7S is MORE than enough. And way lighter and cheaper than the equivilant deltaV with a NERVA. (as in, with a NERVA you'd double the weight)

It's not exactly efficient when your engine is heavier than the entire rest of the rocket

Edited February 13, 2015 by Sirrobert

[zarakon]

LV-N's are harder to design in due to their size and the way the fairings split off

[Empiro]

As always, it depends on what you're trying to do and where you're trying to go.

If you're launching a science probe that's on a 1 way trip, then the craft is just a few tons, and you don't need more than 1500-2000 m/s delta-V. A 909 is more than sufficient.

If you're doing the Jool-5 with a giant crewed craft with landers and so forth, then of course you'd go with the nuke engine.

[LethalDose]

I only use nukes on vessels that are going to be operating in space for long periods of time (tugs, and such). IMO, the NERVA's abysmal TWR makes it more trouble than it's worth for most simple transfer stages. Having a decent TWR can save a substantally save burn dV, Which makes those graphs really misleading. It's also a bit harder to design the vessel around the 1.25m size.

Basically, in my games nukes have their place, but it's not for everything under (around?) the sun.

[tsotha]

I don't normally use nukes for Duna, Eve, or Moho. Duna and Eve aren't much harder to get to than the Mun and don't require that kind of high efficiency. A skipper will do just fine.

As for Moho, killing 3500 m/sec with nuclear engines is long and boring. I'd only use nukes if I were planning multiple assists to get me down to a reasonable closing speed.

[StrandedonEarth]

After going through 0.23-0.25 saves using a 4-nuke lander almost everywhere (also augmenting the transfer-tankers' 4 nukes), for .90 I decided to challenge myself by NOT using the LV-N. I was also not going to use the RTG, but they're just too goshdarn convenient. So far, it's no big deal, I just have to send out more tankers. The shorter burn times (and not needing a kick-burn to raise Ap) are nice

[Brainlord Mesomorph]

Ions are way too expensive for career mode.

Its nukes for me!

I even have a nuclear lander!

[GoSlash27]

panzer,

As you point out, nukes are awfully good for the job of interplanetary mass movers. This is as it should be; nukes are really that good.

So long as you're within the happy weight range and job description, there's no good reason to not use them. Any limitations you put on their use for the sake of game balance or realism would have to be self- imposed (like it is here on Earth).

I have a lot of safety and political constraints for how I employ nukes.

Best,

-Slashy