PSA: Nerv's become useful above 10km in Kerbin atmo

[A_name]

I made some tests (bonus shameless plug of my all liquid fuel SSTO).

Conclusion: As the title says, above 10km Nerv engines come near their peak performance parameters in terms of thrust and ISP. Useful for spaceplanes. Next step is to test this on Duna and Laythe.

[Foxster]

Yup, most (all?) the engines that have lousy sea level thrust get useable low down at like 10km, so no need to only use them in space.

[Old Foxboy]

Get ready to go to jail for nuclear pollution of Kerbin's atmosphere...

[Wanderfound]

Get ready to go to jail for nuclear pollution of Kerbin's atmosphere...

Pre-1.0, I would regularly use the nukes as takeoff boosters for my interplanetary SSTOs...

[Sharpy]

Thanks, that's some pretty interesting news. I had waited to activate them at 50,000, it seems needlessly. 13km for 700 ISp is no longer wasting fuel.

[ajburges]

Ya engines see 98%+ vacuum performance once you hit that first barometer color shift.

The interesting thing with nukes is they make an acceptable ultra high plane engine. You can get enough lift for level flight going 1.6 km/s at 35 km. At that height there is practically no drag.

[Francesco]

Since you're using Kerbal Engineer, you can simply check the engine's performance on a atmospheric body without even leaving the VAB/SPH, by using the altitude slider displayed by the 'atmospheric' button

[Red Iron Crown]

In 0.90 it outstripped any chemical rocket engine in Isp by 1700m, pretty much always good to have it burning. Now in 1.0 with thrust scaling and wide asparagus designs being less desirable it's a bit trickier, but with LV-N equipped spaceplanes I typically wait to light them up until the jets start to die.

[Laie]

Yup, most (all?) the engines that have lousy sea level thrust get useable low down at like 10km, so no need to only use them in space.

Arguably even lower than that. Most vacuum engines don't provide the TWR you'd like to have early in the ascent, but ISP-wise, 5km is halfways to space. If the nozzle has a free field of fire, you may as well use it.

[Michael R]

Yup, most (all?) the engines that have lousy sea level thrust get useable low down at like 10km, so no need to only use them in space.

I recently did similar testing with all the low-sea-level-ISP engines to confirm their utility at 10-12km. I have found that I can pretty reliably put 1300 to 1400 m/s dV on my rockets' launch stages, and I'll be high enough to stage and use these engines efficiently. It's made me love the Rhino.

[Arkalius]

Get ready to go to jail for nuclear pollution of Kerbin's atmosphere...

Nuclear engines don't spew out any nuclear waste. The real NERVA would just be spitting out hot, clean Hydrogen gas.

[ajburges]

NERVs are based on solid core Nuclear Thermal Rockets engines. They are not the same engines as project Pluto.

Liquid and gas core nuclear thermal engines are where you have nuclear waste discharge. But those also get better ISP: 1040-1200 s and 2400-4000 s respectively if they use the same scaling to real life as the NERV.

Look up the Wikipedia article on Nuclear Thermal Rockets. It's a shame budget concerns over a Mars mission killed the program.