What do you think about new nuclear engine?

[99TheCreator]

It's the best engine for long interplanetary missions, I couldn't have landed on Duna without it.

[Kiershar]

If the mission is not easy, nuke engines are gonna be needed. Definitely the best engine, makes the poodle and lv-909 obsolete because of the better specific impulse. Can land with it if you angle swept wings under as lander legs, better impact resistance than legs too. The only thing it can't do is bring you out of a strong atmosphere and achieving orbit post-lift off.

[AlternNocturn]

I stuck three of these things radially onto a big fuel tank with three smaller fuel tanks for my transfer stage. I got to Jool with enough fuel left to do orbital corrections. For Duna and Eve missions, you don't need anything more than the standard liquid engines. However if you're looking to go to Jool and beyond, or to Moho, you're going to need NERVAs.

[r_rolo1]

If the mission is not easy, nuke engines are gonna be needed. Definitely the best engine, makes the poodle and lv-909 obsolete because of the better specific impulse. Can land with it if you angle swept wings under as lander legs, better impact resistance than legs too. The only thing it can't do is bring you out of a strong atmosphere and achieving orbit post-lift off.

Actually , the nuke engine does not make the Lv-909 obsolete ( about the poodle ... it was always too weak as a alternative, even in .16 ). The nuke engine is surely a good engine, but it has the big con of being quite heavy compared with the rest of the 1m engines or even compared with the standard 1m fuel tank + 1m capsule weight. If you're trying to make a small rocket ,that can be enough of a reason to use the Lv-909 instead...

I stuck three of these things radially onto a big fuel tank with three smaller fuel tanks for my transfer stage. I got to Jool with enough fuel left to do orbital corrections. For Duna and Eve missions, you don't need anything more than the standard liquid engines. However if you're looking to go to Jool and beyond, or to Moho, you're going to need NERVAs.

If you just want to go to Jool, you can go on liquids only.

[AlternNocturn]

If you just want to go to Jool, you can go on liquids only.

Okay, so maybe you won't necessarily need NERVAs, but they're still really useful.

[Kiershar]

Actually , the nuke engine does not make the Lv-909 obsolete ( about the poodle ... it was always too weak as a alternative, even in .16 ). The nuke engine is surely a good engine, but it has the big con of being quite heavy compared with the rest of the 1m engines or even compared with the standard 1m fuel tank + 1m capsule weight. If you're trying to make a small rocket ,that can be enough of a reason to use the Lv-909 instead...

I calculated the delta-v of multiple setups with the lv-909 and the only reason to use it would be for very slightly better TWR, and if its TWR you need there's a lot of better options.

Of course, if your plan is to just go somewhere and land wherever then end the flight, any engine will do.

Edited October 9, 2012 by Kiershar

[r_rolo1]

Well, true and all, but you are forgetting that I'm talking of putting a small rocket up there with the nuke engine as part of the "payload" ( like in a interplanetary burn stage ). In those circumstances you can't only count with total dV , but also with the simple fact that your TWR at launch must be enough to leave the ground. You can definitely get more dV out of a nuke engine than of a LV-909 with the same fuel tank, but that comes at the cost of putting a extra 1.75 t in the rocket ( supposing all else equal ). If you're talking about a 20 t rocket that is a significant difference, especially if the TWR at launch with the LV-909 was already low ( as it should be in such a small rocket ). In those conditions you would have to increase the TWR to use the nuke engine in that design, a thing that means surely more engines and more fuel ... or simply use the LV 909 in spite of not being as dV efficient.

[Kiershar]

I don't know... if the first stage can't handle an extra 1.75 of weight maybe its a bit too minimalist. I find it very hard to justify using the lv-909; the only time i set them up is when the mission is so easy i'd rather do my burns faster than having extra fuels for contingency. If you restrict your first stage a lot then maybe the lv-909 is better in that situation, but that's with an artificial restriction that you set on yourself.

[r_rolo1]

Well, I can give a practical example: my Afrodite line. There is absolutely no way that putting up a nuclear engine in there would make any of those ships to work better than the LV 3 of them have.

And note, this is not a matter of artificial restriction or not. I was just stating that IMHO the LV-909 wasn't obsolete because there was still a niche for it that the nuke engine couldn't handle well ( or at all ) due to the weight. In other words , there is a lower limit on rocket size for the usefulness of the nuke engine. It might be low enough to not matter much at this point, though ...

[Nao]

I'll agree on the subject with r_rolo1. The thing is Nuclear engines have terrible weight per kg of thrust, ISP matters of course but from what i calculated Nuclear would never be more mass efficient than LV909 above 1,08 thrust to weight ratio.

It's all about design goals and mehjeb really, if you play vanilla game 6000m/s Dv is 10minutes of thrust at 1ttwr, of course nuclears rock at smaller thrusts, but having to physically control the craft for more than half an hour can be too much sometimes, and there are planetary landings/ascents requirements for thrust.

Also food for thought:

small pod 2x nuclear engine 3x fuel tank + 0,15t of other parts : weight 12,2t Dv 5310m/s

small pod 2x LV909 4,5x fuel tank + 0,15t of other parts : weight 12,075t Dv 5230m/s

and just for fun:

small pod 2x RCStank + RCSthruster + smallSRB + bigSRB: weight 12,1t Dv 5300m/s (tri stage) , ISP of SRB:212 bigSRB:280 and RCS:255

I should probably play the damn game thou not do useless comparisons lol

[nhnifong]

I only bring it for long extended missions which may visit multiple planets. But if I'm just going to Duna or something, I get there quicker with a regular engine.

[ramses]

Well, yes I like them. Especially when they stay attached to your craft.

Somewhere in transit this one decided it did not want to be a part of my mission to Eve. I completed the mission without it.

IMO the thrust is too little. My 2c is both thrust and weight should be quadrupled. So that's Thrust 240, Mass 9. Then have it such that they will not work in atmosphere at all (for "safety" reasons).

Had the exactly the same thing happen to me. Was on my way to Eve, than all of a sudden, Bang! no Nerva?

[szpw]

It's a great engine for interplanetary transfers because of it's low fuel consumption. It does take a while though, and my interplanetary spacecraft use normal liquid fuel engines. It has proven capable of both Duna and Eve, but I still want to implement a nuclear engine in my Jool mission.

[Vanamonde]

I had a NERVA fall off for no reason as well. Fortunately, I heard the little poof noise and had a recent save I could load.

[Kiershar]

I'll agree on the subject with r_rolo1. The thing is Nuclear engines have terrible weight per kg of thrust, ISP matters of course but from what i calculated Nuclear would never be more mass efficient than LV909 above 1,08 thrust to weight ratio.

It's all about design goals and mehjeb really, if you play vanilla game 6000m/s Dv is 10minutes of thrust at 1ttwr, of course nuclears rock at smaller thrusts, but having to physically control the craft for more than half an hour can be too much sometimes, and there are planetary landings/ascents requirements for thrust.

Also food for thought:

small pod 2x nuclear engine 3x fuel tank + 0,15t of other parts : weight 12,2t Dv 5310m/s

small pod 2x LV909 4,5x fuel tank + 0,15t of other parts : weight 12,075t Dv 5230m/s

and just for fun:

small pod 2x RCStank + RCSthruster + smallSRB + bigSRB: weight 12,1t Dv 5300m/s (tri stage) , ISP of SRB:212 bigSRB:280 and RCS:255

I should probably play the damn game thou not do useless comparisons lol

Your comparisons are not good. Why is there 2 nuclear engines on a 12t design? You are complaining about thrust, yet the setup with the 2x 909 has less TWR than with 2x nukes...

mk1pod 1tons + 3 x 400L fuel (2.25t, empty 0.25t) = 7.75t

7848 * LN(Full nuke 10t / Empty nuke 4t) = 7191 delta-v, 0.6 TWR full

3825.9 * LN(Full 909 8.25t / Empty 909 2.25 = 4970 delta-v, 0.606 TWR full

There's no way the 909 is better than the nuke. If it is, it's because you over-designed your craft to fit it. The only legit pro-909 argument is that it's shorter, but even then its real easy to get around that.