What is a NERVA?

[aceassasin]

In Harvesters recent post showing the changelog of the .17 experimentals in it was a new part called the NERVA engine i hear this all the time but i dont know what it is can anybody tell me

[Thobewill10]

The NERVA was a class of Nuclear thermal rockets (stands for Nuclear Engine for Rocket Vehicle Application). Nuclear thermal rockets have a much higher ISP than regular rocket engines, due to its use of a nuclear reactor to heat liquid hydrogen instead of pesky combustion.

[TheDarkStar]

NERVA stands for Nuclear Engine for Rocket Vehicle Application. It uses (like the name says) nuclear reactions to power a rocket. They were very efficient, and Wikipedia says it had an ISP of about 850.

[VincentLaw]

In the most basic sense, it has to do with Hydrogen being lighter than the water molecule (or others) that you get out of combustion, so you can accelerate it to higher velocities at the same material temperature limits. That's how you get a higher Isp than with a chemical reaction.

[nhnifong]

Why is it the velocity of the exhaust that matters instead of the momentum?

[VincentLaw]

If you have the same mass of propellant, then you would have the same mass going faster, so you have more momentum.

[NovaSilisko]

Why is it the velocity of the exhaust that matters instead of the momentum?

Well, remember, momentum is merely a measure of energy based around a given mass - the faster that mass is moving, the more momentum it has, and the more kinetic energy it can deliver. The faster the rocket exhaust velocity, the more "result" you get out of expending a given mass of propellant. Newton's third law at work!

[Fendleton]

In real life: NERVA was an experimental set of engines designed by NASA to update the Saturn 5 into a vehicle that could life much heavier loads, and send a crew to mars.

BECAUSE of this, the program was cancelled as soon as it became clear they'd made an engine that could be used for such a job (going to mars was deemed too expensive, so they cancelled everything that would let them get there).

Basically, instead of using a chemical reaction, you heat up your fuel (NERVA used liquid H2) using a nuclear fission reaction. This has unfortunate results if your rocket crashes and you're not using modern fuel rod designs (they actually tested this: they put an early prototype in a train car after modifying it to go critical so they could see what would happen. Environmental laws really weren't so strong back then.), and still isn't so nice even WITH modern rods... but it's a wonderfully efficient system. Far better than using an Ion engine in KSP, since we have to do things by hand, and ion engines are REALLY slow.

[Rickenbacker]

The NERVA was tested, though, in the Nevada desert, and it worked well. If NASA had been given a decent budget we could have had a Mars colony in the 80's!

Also, in a very Kerbal move, they even tested two of the NERVA reactors to destruction, with resulting nuclear mini-disasters to clean up...

[LaydeeDem]

This is a NERVA:

[softweir]

A very interesting thread which explains what a NERVA engine is to those not in the know, but it's ot really about KSP as such. So I've moved it to Off-Topic.

Edited September 17, 2012 by softweir
Spelling!

[Fuzzy Dunlop]

In the most basic sense, it has to do with Hydrogen being lighter than the water molecule (or others) that you get out of combustion, so you can accelerate it to higher velocities at the same material temperature limits. That's how you get a higher Isp than with a chemical reaction.

Thats not entirely true. The exhuast tempurature of a rocket engine shouldn't be limited by materials (ideally the exhaust shouldn't come into contact with anything). What limits the tempurature is the amount of energy that combustion can provide. Obviously a nuclear reactor provides far more energy.

[Ziff]

A very interesting thread which explains what a NERVA engine is to those not in the know, but it's ot really about KSP as such. So I've moved it to Off-Topic.

Softweir, HarvesteR wrote in his blog about the .17 Status Update that a Nuclear Thermal engine part would be included. So the discussion of NERVA is actually on-topic, I would think.

[kacperrutka26]

What is NERVA?? Some people mentioned it on the 0.17 update blag from HarvesteR but I don' know what it means? Can someone explain?

[RoboRay]

Nuclear Thermal Rockets ("NERVA" is the name for an American experimental NTR from the '60s and early '70s) use a sustained nuclear fission reaction to heat propellant, rather than chemical combustion. NTRs can be roughly twice as efficient as the best chemical rockets, with an I_sp approaching 900 seconds.

Edited September 17, 2012 by RoboRay

[UmbralRaptor]

It's from a series of solid core nuclear-thermal rocket (that is, a rocket that uses a nuclear reactor to heat up the propellant, rather than burning it) projects, mainly in the 1950s-1960s. Some of the earlier engines were tested, but none actually flew. Expected Isp seems to have slowly increased from 800 to 925 s.

Astronautix has lots of info about half way down this page

Edit: Huh, merged threads.

Edited September 18, 2012 by UmbralRaptor

[MaverickSawyer]

Nuclear Energy for Rocket Vehicle Applications. One of the most interesting prototype rocket propulsion systems ever designed, and the one with the most promise.