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AHeroReborn

question with the NERV

Question

i have found that delta V decreases when i add more than one Nerv, i i guess it's a choice in between crap burn times and slightly above average delta V without building a huge rocket. also any tips on designing a NERV powered interplanetary shipwould be welcome.

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They are heavy, which explains the dv loss.  But you can get some great fuel economy with them.  Increasing the number decreases your burn times, so you won't need as many radiators.  

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Figure out something else to do for 10 minutes while the engine burns.

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IMO, they're well and truly worth the burntime in stock game if you're headed inside eve, or outside dres.

The ISP(hilariously low compared to RL) is just too good, almost 3 times the nearest chemical rocket. There's no other way to push a mass too heavy for practical ion drives to any respectable delta-V. 

With some of the more exotic drives out there in mods, maybe not so good. 

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If you need plenty of margin in dv(2.5km/s~3km/s), Nuke is better for TWR under 0.6. Poodle is better for TWR over 0.7.

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4 hours ago, AHeroReborn said:

i have found that delta V decreases when i add more than one Nerv, i i guess it's a choice in between crap burn times and slightly above average delta V without building a huge rocket. also any tips on designing a NERV powered interplanetary shipwould be welcome.

Remember to use liquid fuel tanks, not rocket fuel tanks. The LV-N doesn't need oxidizer. If you carry around a lot of useless oxidizer, that would explain why you're not seeing good dV results...

 

1 hour ago, Lelitu said:

The ISP(hilariously low compared to RL)

It has exactly the Isp of the RL engine it is based on.

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Just now, Streetwind said:

It has exactly the Isp of the RL engine it is based on.

True, the NASA design was 850 seconds (slightly higher than the KSP design)

Later designs, never built, range up to 5000 seconds for gas core nuclear thermal rockets.. Not simple to build, and never been done, but damned efficient.

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4 hours ago, AHeroReborn said:

i have found that delta V decreases when i add more than one Nerv,

Any mass added that's not fuel will decrease delta v.

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3 hours ago, Lelitu said:

True, the NASA design was 850 seconds (slightly higher than the KSP design)

Later designs, never built, range up to 5000 seconds for gas core nuclear thermal rockets.. Not simple to build, and never been done, but damned efficient.

Do you think the KSP NERV is a "gas core nuclear thermal rocket"?

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Posted (edited)

I only use the NERV when I really need the delta-v, compromising in TWR and doing multiple passes to burn at periapsis.

Yes, an efficient NERV-Spaceship has to have crappy TWR. To keep it playable, I usually try not to get it below 0.2 (wich is pretty low).

If you wanted to squeeze decent TWR out of NERVs, your dry mass increases a lot and you could as well use POODLES or TERRIERS, wich are a lot cheaper, to get the same delta-v.

Edited by Physics Student

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10 hours ago, Lelitu said:

True, the NASA design was 850 seconds (slightly higher than the KSP design)

Later designs, never built, range up to 5000 seconds for gas core nuclear thermal rockets.. Not simple to build, and never been done, but damned efficient.

These kind of sci-fi engines are covered pretty well in a variety of mods. Atomic Age, Near Future, the Mk2/3/4 expansions, probably hundreds of others.

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Posted (edited)
On 3/16/2017 at 10:09 PM, Physics Student said:

Yes, an efficient NERV-Spaceship has to have crappy TWR.

0.44 isn't what I'd call crappy, although "efficiency" is in the eye of the beholder. Save a little bit of oxidiser and you've got the option of RAPIER emergency landing boost, too.

NOYwtKP.jpg

 

On the conventional rocketry front, a well-built 0.625m asparagused LFO robolander, stuck on an asparagused NERV transfer stage, itself on top of a Poodle circularisation stage, lifted by a good asparagused booster, should be able to approach 20,000m/s delta V while still carrying a useful payload, without being too painful to fly. The start of the NERVA stage is at TWR 0.14, but that improves fairly quickly as the fuel burns off.

 

duTxW3X.png

nJEdzOQ.png

The NERV bit of that is actually only onion staged; I had enough DV for Moho return, so I didn't see a need. Asparagus that stage as well and you'd squeeze a bit more out of it. Replace the fuel hoses with advanced tweakables and you'll get a bit more again.

Edited by Wanderfound

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On 3/15/2017 at 10:30 PM, bewing said:

Figure out something else to do for 10 minutes while the engine burns.

Second this.  Get multiple monitors so you can leave KSP running and keep an eye on it while you're doing something else.

My record so far was nearly 40 minutes for a capture burn at Moho.

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1 hour ago, Loren Pechtel said:

Second this.  Get multiple monitors so you can leave KSP running and keep an eye on it while you're doing something else.

My record so far was nearly 40 minutes for a capture burn at Moho.

I have been long suffering from a problem that when I'm too focusd on the other thing I'm doing, suddenly an explosion scared the crap out of me.

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Get Kerbal Alarm Clock and set a "pause" alarm before you tab away, just in case?

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On 16/3/2017 at 2:30 AM, bewing said:

Figure out something else to do for 10 minutes while the engine burns.

That's one of the situations in which I use MJ autopilot. Now that we have the point-to-node SAS, there isn't much of a difference in setting SAS in that mode, firing up the engines and time warping than using MJ autopilot (and timewarping). 10 minutes at 4x timewarp (assuming your ship is rigid and stable enough, otherwise choose 3x timewarp) it's two minutes.

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well thanks everyone! Ill play FTL or something while KSP is doing its thing.

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