Nuclear engines

[Cannon]

is something changed with nuclear engines, i haven't played since 0.90?

it seems to me that it's not so efficient anymore, when i was landing on duna it used much more fuel than i expected

[Red Iron Crown]

They are heavier, at 3t versus 2.25t, but the bigger difference is that they use liquid fuel only, no oxidizer. Use LF-only tanks for best performance, or at least tweak out the oxidizer in LFO tanks.

[Gaarst]

They produce some heat (a lot for some and not enough for others), they consume only LF, no oxidizer, and they have been the source of quite a lot of, say, "discussions" on the forums lately, a significant part of which was complaining about the heat issue

[Starhawk]

Everything changed with Nervas since 0.90. They generate significant heat (I think that was nerfed somewhat in the last update), they are heavier, they no longer gimbal, and the ISP curve means they are almost useless at sea-level pressures. And, of course, they are liquid-only now.

Many felt that the Nerva was significantly overpowered in versions before 1.0, and the devs changed many of the engine stats for a number of engines during the great balance pass.

Happy landings!

[Snark]

They are heavier, at 3t versus 2.25t, but the bigger difference is that they use liquid fuel only, no oxidizer. Use LF-only tanks for best performance, or at least tweak out the oxidizer in LFO tanks.

Bearing in mind (yeah, I realize kinda obvious, but took a stupid mission failure for me to get this through my own skull) that if you just use a regular LFO tank and zero out the oxidizer, you're still only getting a bit under half the volume of the tank for fuel.

So definitely go for liquid-fuel-only tanks. It's worth noting that they've tweaked the 1.25m round LF tank so that it has a reasonable fuel volume and mass ratio now, so it's a viable option.

Edited August 4, 2015 by Snark

[Sharpy]

The ISp went down too, IIRC - though not by much.

Still, a craft composed of one NERV, two 1.25 LF Fuselages, a command pod and survival/reentry essentials easily runs 4000m/s of delta-V.

Radiators are available for the overheating woes.

[Red Iron Crown]

The vacuum Isp stayed the same at 800s. The atmo Isp dropped a bit but that hardly matters, only a fool would use the LV-N in thick atmo.

[Pecan]

Starhawk almost said it right, but I'd (mis)quote):

Everything changed with Nervas since 0.90...

Don't expect any engines to perform as they did. Don't expect part costs, masses, capacities or capabilities to be as they were. Especially don't expect any atmospheric anything to be what you're used to. Versions 1.0, 1.0.1, 1.0.2 and 1.0.3 changed almost everything.

[Skorpychan]

Bearing in mind (yeah, I realize kinda obvious, but took a stupid mission failure for me to get this through my own skull) that if you just use a regular LFO tank and zero out the oxidizer, you're still only getting a bit under half the volume of the tank for fuel.

So definitely go for liquid-fuel-only tanks. It's worth noting that they've tweaked the 1.25m round LF tank so that it has a reasonable fuel volume and mass ratio now, so it's a viable option.

Spaceplane parts, or the mod that lets you adjust fuel tanks to be all LF, LFO, or all oxygen.

Unsure why you'd want the latter, but it's there anyway.

[quietghost]

The big thing with NERVAs is that because they only use LF, there is far less mass as fuel to burn. Since dV is based on the mass of the fuel (more is better, but with diminishing returns) by the lack of oxidizer (which reduces fuel mass) there is less dV. The exact mechanism by which this happens is the flow rate for LF is much greater now, not because NERVAs were nerfed, but because previously flow rate was split between the LF and the Oxidizer. If the whole tank were just LF (i.e the oxidizer storage converted to LF storage) the performace metrics of the NERVA would be similar to 0.90. Of course they are also heavier, which only compounds the perceived nerfing.

[Xannari Ferrows]

At the very least they have more potential to become more efficient for super huge vessels.

[KerikBalm]

Well, not the Mk1 LF fusalages have a 9:1 mass ratio like all the other cylindrical tanks, so if you load up on Mk1 LF tans, you'll get nearly the same performance as before...

except that each engine is heavier...

So what we really got was a TWR nerf

[KingPhantom]

i'm looking forward to get liquid fuel only 2.50m tanks. the orange one only with liquid fuel....

otherwise i will mod them for me!

[CowsAreEvil]

If you are building a large ship 'Fuel tanks plus' is a mod that has liquid fuel tanks up to orange tank size. They make the LVN more viable for transfers to other planets.

If you are building a small ship then the LV909 might be worth considering.