What do you think about new nuclear engine?

[Richy teh space man]

I've tested it and its not bad, very fuel efficient for its thrust

[whatisthisidonteven]

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).

If you want a heavier NERVA with more thrust, look at NovaPunch's NERVA engine, it has roughly the same stats you requested.

[flyfire2002]

I think they should reduce the impulse in vacuum to 550-600. getting to the mun/min is WAY too easy now.

Just look at the real-life Ion engine. They share similar properties

[Ghery88]

I've looked through all the corresponding wiki pages, and I think it's a bit underpowered. Even Scott Manley was surprised. The 800 ISP is well within limits for a solid core nuclear engine, there are other designs which could have as high as 3000 while having a TWR around 60.

Anyway, I use it extensively for interplanetary transfers and for landings in vacuum.

[Khrissetti]

I built my first .17 Mun lander with the NERVA engine as my main orbiting stage and was surprised by how low the thrust is, I think I was spoiled by NovaSilisko's NERVA. Needless to say, circularising the orbit before I fell back into the atmosphere was nail-bitingly close.

I imagine it's brilliant for interplanetary work, though.

[segaprophet]

The NERVA is great, it's my standard transfer stage engine.

[azazel1024]

It worked well for me to get to Duna. I had a lot less fuel than I thought I'd need to make it there and it turns out I had just enough. Though I had to burn through my RCS tankage to get a close in orbit. An extra fuel tank for my 2nd stage should manage a 1 way trip and landing. I use three big'um fuel tanks stacked 3 high and rocket motors to achieve a ballistic launch from Kerbal, 2nd stage is NERVA with 2 fuel tanks which is enough to get a circular orbit around Kerbal, then achieve interplanetary escape velocity, eliptical orbit to Duna. Sadly I had to dump the NERVA after running dry and relying on my landing stage to actually decelerate enough to achieve Duna orbit, which burned through the half tank of fuel on the landing stage. Then the RCS thrusters had to be used to achieve a 1200km cicular polar orbit.

So one more tank for the NERVA is probably enough. I'll find out tonight!

PS I love the new A. SAS and RCS full size tanks to match the big capsule. Now if we can just have a big'um NERVA as well :-D

[SyX]

In my experiments, I have found it to be lacking and non-ideal for most purposes. Trips to Jool sure. Landing on Duna AND returning, sure.

But if, for example, you just wanted to get to Duna, you don't really need a very big rocket.

If you have some lucky transfers, you only need the 1 man pod, 400 litre tank, and the 0.5 mass engine - assuming that you can get this into space without any of it's fuel consumed.

Sticking a nuclear engine in the place of the small engine in this example actually yields less delta v. This is because the nuclear engine is monstrously heavy.

Basically, what I am saying is that the nuclear engine is good if you want to move a HEAVY craft in space. But since you don't need one for most things, it is incredibly niche.

[AmpsterMan]

I personally think the engine is perfect as is. Part of the balance of the engine IS that timing burns is more difficult. Also, using them as landing engines is less than ideal because of the funky designs you need to make in order to use them. I think their utility will be expanded when we will be able to leave a transfer stage powered by lv-n engines in orbit and randevous with it during ascent.

I think the balance of the engines lays outside of the numbers so to speak. It is similar to the aerospike in that respect.

[silent_prtoagonist]

I love them, swapping out the transfer stage engines on my 0.16 interplanetary designs makes them ridiculously over-powered. Burn times can be a bit...tedious, but it's a small price to pay.

An interesting point, a combination of a 1 kerbal pod and 1 meter half-tank has almost exactly the same dv with a nuke or a small lander engine. The extra weight of the nuke almost completely offsets the extra efficiency.

[OdinYggd]

The low thrust only means that compensating design measures are needed- for instance my Skynet series ring station simply had it's four LV-45 engines replaced by a group of 7 of these to end up with more than twice the fuel efficiency with only a slight handling penalty. The Skynets only use their engines anyway for changing orbital altitudes, I really could have left it as-is but I sometimes do send them on their own from LKO to Mun or Minimus.

Just use them in groups if your craft is too large to be propelled by only one. It doesn't take much to assemble an engine array out of 1 meter parts and tack it on where the older single engines sat.

[robly18]

Low thrust and long burn times can royally mess up well timed interplanetary travel.

For the moment, im sticking with the 'real' LFE's.

Hey look buddy. I'm a kerbal. That means I solve problems.

Not problems like "how to make a safe rocket", because who needs safety? I solve practical problems.

For instance, how am I gonna make me an efficient way to make interplanetary burns with an 800 specifil impulse?

The anwer... Use a NERVA

And if that don't work? Use moar NERVA

[Bluejayek]

I'm using it for my interplanetary transit burns and it works great. The delta-V I can get off one of these below 9600L of fuel is monstrous, as is required when you frack up and circularize an orbit in Jool's SOI with a moon going the opposite direction and have to fix it.

[VincentLaw]

I made the mistake of trying to push 7 fully filled Rockomax x200-32 tanks (22400 L) out of Kerbin orbit with just one nuclear engine... Over 4 hours of continuous burning later I reached Jool. Next time I will use more engines.

Some people were talking about it not having enough thrust for the high precision burns needed to get the right angles for interplanetary travel but there is a simple solution for that. If you get into a nearly parabolic escape from Kerbin (any direction will do) then you will have a convenient parking orbit around the sun that is nearly the same as Kerbin's orbit. After that you can accelerate time until you get to the right angle, and since the period around the sun is so long burning for minutes or hours really doesn't make a difference.

[Enture]

Anyway, I use it extensively for interplanetary transfers and for landings in vacuum.

Well, that's a thing that suddenly started to bug me yesterday: basically, a NERVA is a nuclear reactor opened at one end (correct me if I'm wrong!), ejecting a highly radioactive hydrogen flow... in orbit, it's fine. But 1) Doesn't using them on a landing stage mean lethally irradiating your landing site? and 2) what happens after the spent engine burns up upon reentry, or crashes on the surface? Again, dispersing radioactive materials everywhere, isn't it?

Some people were talking about it not having enough thrust for the high precision burns needed to get the right angles for interplanetary travel but there is a simple solution for that. If you get into a nearly parabolic escape from Kerbin (any direction will do) then you will have a convenient parking orbit around the sun that is nearly the same as Kerbin's orbit. After that you can accelerate time until you get to the right angle, and since the period around the sun is so long burning for minutes or hours really doesn't make a difference.

Great tip, thanks!

[RoboRay]

Well, that's a thing that suddenly started to bug me yesterday: basically, a NERVA is a nuclear reactor opened at one end (correct me if I'm wrong!), ejecting a highly radioactive hydrogen flow...

Yep! It's a hydrogen-filled nuclear reactor with a deliberate leak.

in orbit, it's fine. But 1) Doesn't using them on a landing stage mean lethally irradiating your landing site?

Yes. Not immediately lethal, but potentially to levels dangerous for long-term exposure.

Furthermore, due to the weight of radiation shielding, the reactor itself is almost certainly not shielded on the sides, and is absolutely not shielded on the bottom (big, open nozzle, remember?), so it's quite dangerous to approach. I wouldn't want to climb down a ladder right next to one.

and 2) what happens after the spent engine burns up upon reentry, or crashes on the surface? Again, dispersing radioactive materials everywhere, isn't it?

Quite so. Try to dump your expended nuclear engines into Jool or the Sun, or at least leave them in a safe, stable parking orbit so that they can be recycled in the future.

Or possibly try soft-landing them with parachutes somewhere near KSC, to be re-used on later missions.

Edited September 24, 2012 by RoboRay

[Markus Reese]

Aww, curse it. Now I will need to plan my landings better. I had planned on nuc jettisons on re-entry. But now I will need to change my designs... hrm....

[VincentLaw]

Well, that's a thing that suddenly started to bug me yesterday: basically, a NERVA is a nuclear reactor opened at one end (correct me if I'm wrong!), ejecting a highly radioactive hydrogen flow... in orbit, it's fine. But 1) Doesn't using them on a landing stage mean lethally irradiating your landing site?

No, The NERVA reactor is a closed system. The liquid Hydrogen propellant travels through isolated heat exchanger tubes and doubles as a coolant to keep the reactor from melting down. None of the radioactive fuel is expelled. Actually, the game should make the rocket overheat more at low throttle for this reason.

Edited September 24, 2012 by VincentLaw

[Promii]

Well, that's a thing that suddenly started to bug me yesterday: basically, a NERVA is a nuclear reactor opened at one end (correct me if I'm wrong!), ejecting a highly radioactive hydrogen flow... in orbit, it's fine. But 1) Doesn't using them on a landing stage mean lethally irradiating your landing site? and 2) what happens after the spent engine burns up upon reentry, or crashes on the surface? Again, dispersing radioactive materials everywhere, isn't it?

A nuclear salt-water rocket is closer to what you are describing. High thrust, high specific impulse, dirty as hell.

[OdinYggd]

No, The NERVA reactor is a closed system. The liquid Hydrogen propellant travels through isolated heat exchanger tubes and doubles as a coolant to keep the reactor from melting down. None of the radioactive fuel is expelled. Actually, the game should make the rocket overheat more at low throttle for this reason.

Something like this. It would be closest to what a nuclear warship or submarine is powered by and use the same flowchart as a PWR type reactor, but the heat exchanger for the secondary system heats propellant for thrust instead of boiling water for a steam turbine. Alternately, it uses a CANDU style reactor vessel with extra tubes inside to heat the propellant without having to circulate through the primary system.

Incidentally this also makes it easy to dispose of the "cold" heat from it- use a second heat exchanger to make steam for ship electricity. Then your 'idle' engine takes the place of your battery packs and solar panels, greatly offsetting the weight of the shielding on the 'crew' side of the unit.

Edited September 24, 2012 by OdinYggd

[JMBuilder]

I've compared the stock NERVA with the NovaPunch NERVA. I think that they both have unique advantages and are both fair. The stock NERVA has low thrust, high efficiency and is only somewhat heavy. The NP NERVA is more compact, has high thrust, good efficiency, but is WAY heavier. I like to use them in context with each other.

[antbin]

An interesting point, a combination of a 1 kerbal pod and 1 meter half-tank has almost exactly the same dv with a nuke or a small lander engine. The extra weight of the nuke almost completely offsets the extra efficiency.

Can any theory nerds explain the break-even point between weight and ISP? When should I pack a NERVA and less fuel, or an aerospike and more fuel?

The weight difference between a NERVA and aerospike is 1.5 tons, 300 fuel unit-equivalent. But the fuel mass will gradually decrease through a burn, while the NERVA stays heavy. Also, there's the Oberth effect.. if the low thrust means you're burning beyond your orbit periapse, you lose a bit of gravity assist efficiency.

Is there a design ratio of "Minimum NERVA burn time to make it worthwhile dragging an extra 1.5 mass along?"

[cardgame]

Every break-even point will depend on your mission profile and be ship-dependent, as far as I'm aware.

[thefamoushat]

The break even point will more likely be in function of the ratio of total mass to fuel mass. A spaceship with little fuel but a high SI engine will have the same deltaV capability as a ship with similar total mass but comparably more fuel and a conventional engine.

[Nao]

I would like to share the results of a little mathematic experiment i did recently, while designing interplanetary craft.

KSP's nuclear engines are indeed very efficient but getting anywhere on them can take a while. Thats why i wanted to push my TTWR (thrust to weight ratio) of full craft to be reasonably high for less tedious burns.

As it turns out LVT-30 engines are always more efficient for designs with TTWR above 1.

When using Toroidal Areospikes it's only 0,885 ttwr.

Even for designs having 0,5 ttwr , Areospikes will have better Delta V while total craft mass divided by cargo mass was below 1,6 (cargo is defined as total craft mass without engines, fuel, fuel tanks)

This of course is highly theoretical since you cant fit one and a half engine on craft , but for projects using more than 3-4 nuclear engines i would highly recommend checking if using one LVT-30 or Areospike would not bring better results.

I don't take any responsibility for errors in my math thou

If anyone will be interested i can post my spreadsheet and some pictures of 3d charts used.