LV-N what's it good for

[Zoidos]

9 hours ago, kBob said:

So I get a contract to test the LV-N nuclear engine: "nifty," I think, "never really played with them before and it will be awhile before I reach that tech level," so I jump at the contract.  I replaced the poodle on my run-about with it and head for the Mun.  If it works out I'll just be careful not fulfill that contract for awhile.  But hmmm, it's way slower, heavier and seems to use about the same amount of fuel (though I'm just eyeballing the fuel gauge not doing detailed flow rate comparisons).  What is this engine best for?

They are a lot more efficient than simple LFO-fueled engines. (LV-N has an ISP of 800, the poodle has only 350 I think). 

I use them mostly for interplanetary transfers. All of my interplanetary shuttles are nukes. The only thing (in stock) more efficient are ion engines, but due to their ridiculously low thrust makes them better suited for people who are a lot more patient than me.

[suicidejunkie]

Yep.  The problem you had was unknowingly carrying many tons of payload in the form of useless oxidizer.  If you drop the oxidizer from the design, you can replace that tonnage with a full science lab, an ISRU rig, and then perform the same mission profile and accomplish a lot more.

 

If you have a mix of LF&O and both an LV-N and a LV909, you get more dV by burning off the oxidizer first with the chemical engine to lower your mass, and then burning whatever LF is left with the LV-N.

If you've got rocket fuel tanks with default filling, then that means having the LV-N burn only the 0.00 units of LF left over at the end.

[AeroGav]

Let's try and break this down in a more scientific way.

Whilst most people use an LV-N to replace a Poodle, the Poodle is a 2.5m engine with 250kn thrust.  In the sort of interplanetary application for which you'd consider a Poodle anyway, the lower thrust of the LV-N isn't an issue, but let's take a more direct comparison - the terrier.  Both are 1.25m motors and both give 60kn, but are useless in thick atmosphere.

The Terrier weighs 500kg and burns 20kg fuel per second*( i am including tank mass here too)

The LV-N weighs 3000kg and burns 8.59kg fuel per second.

The break even point is 3 minutes and 40 seconds, or an FT800 LF/O tank.   If you are running your terrier for longer than that, or carrying more fuel than that per engine, you'd be better off switching to an LV-N.  

Now, a very light ship that's pretty much capsule only, gets 4k dV out of that much fuel so a terrier is a good choice to go anywhere.

OTOH if it's a big heavy payload, a 4 minute Terrier burn might not even get you a Munar flyby.

[Ozymandias_the_Goat]

I use it for efficiency on IP burns, and if turned upside-down, it looks like a giant ice cream cone.  Now seriously, the LV-N is pretty heavy, so I stay away from it on small ships, favoring the LV-909 terrier for it's lighter mass.

[Waxing_Kibbous]

5 hours ago, Renegrade said:

I generally don't use 'em anymore.  ISRU bases basically cut round-trips in half delta-v wise, and the miserable TWR means really long, inaccurate burns, or spamming nukes until you have a craft every bit as inefficient as a chemical one.  Plus the stock system is kinda small vs. the specific impulse of chemical engines... it's not necessary.

Besides, sending my Duna station to Duna on four Skippers at 1.85-3.35g was a lot more fun than drooling it out there at 0.2g on a nuke-based platform.  And cost about 20k less

I made a DunaBus-N crew carrier as a test - the LV-N "all the way there and back" model is actually bigger and slower and more expensive and requires more fuel than the Poodle-based "refuel via ISRU" model.

A bit OT, but this made something click in my brain- it seems if you depart for a planet at an optimal transfer window then land at it, the optimal transfer window back home is quite some time away, so might as well do something, and that something could be making fuel. I need to figure out the whole ISRU thing- are the small ones worth using in such a capacity?

[ZooNamedGames]

Is it bad that whenever I read this thread title to myself I sing "LV-N... what it good for- HUH" like that one song that goes "War... what's it good for". XD  .

But seriously, the LV-N is a great engine for larger crafts over longer durations. Its much like the Xenon engine in that it's exceptionally weak but has a far greater efficiency than any other engine. It's an important member of my space program!

[suicidejunkie]

The small ISRU can be used in some situations.

On the surface, the small ISRU with a good engineer is about equal to a large ISRU with no engineer.  (Terrible, in other words, but functional even with a low mass budget)

In orbit, the small ISRU throws 80% of your ore mass out the airlock and you can't turn a net fuel profit unless you're shuttling ore up from Gilly or possibly Minmus.

[cantab]

5 hours ago, AeroGav said:

Let's try and break this down in a more scientific way.

Whilst most people use an LV-N to replace a Poodle, the Poodle is a 2.5m engine with 250kn thrust.  In the sort of interplanetary application for which you'd consider a Poodle anyway, the lower thrust of the LV-N isn't an issue, but let's take a more direct comparison - the terrier.  Both are 1.25m motors and both give 60kn, but are useless in thick atmosphere.

The Terrier weighs 500kg and burns 20kg fuel per second*( i am including tank mass here too)

The LV-N weighs 3000kg and burns 8.59kg fuel per second.

The break even point is 3 minutes and 40 seconds, or an FT800 LF/O tank.   If you are running your terrier for longer than that, or carrying more fuel than that per engine, you'd be better off switching to an LV-N.  

Now, a very light ship that's pretty much capsule only, gets 4k dV out of that much fuel so a terrier is a good choice to go anywhere.

OTOH if it's a big heavy payload, a 4 minute Terrier burn might not even get you a Munar flyby.

This is a really great way of looking at it, cutting out a lot of the complexity in considering dV and TWR requirements separately.

[SelectHalfling0]

For more efficiency over the terrier, the lvn needs to be used with very large mothership style vessels.

[AbacusWizard]

I find the nuclear engines extremely useful for large orbital-only "workhorse" vessels that I'll be using over and over again--tugs, cargo freighters, passenger liners, etc.--and refueling as needed (from orbital fuel depots which are themselves refilled by tankers from ISRU mining sites). If I'm designing a smaller vessel, or a one-use-only thing, or anything that needs to land, I'll usually just use Poodles or Terriers or Spikes instead.

[Xyphos]

See my signature below.

you use LV-N engines for interplanetary transfers, and perhaps orbital captures, depending on the celestial body. their Specific Impulse (ISP) is the highest out of all of the rocket engines available, making them the most fuel efficient engines available, with Poodle being the second best, followed by the Terrier in third.

Edited June 1, 2016 by Xyphos

[The Aziz]

Wow this topic got long. And more scientific and technical than I could understand.

Aanyway, before 1.0 I managed to land a returning from Duna flyby probe with ease. I thought I will crash in the water, but nah, gentle 6m/s splash, so back in time it was entirely possible to land on Kerbin with Nerv.

I crashed it on Eve though.

[cantab]

1 hour ago, The Aziz said:

Aanyway, before 1.0 I managed to land a returning from Duna flyby probe with ease. I thought I will crash in the water, but nah, gentle 6m/s splash, so back in time it was entirely possible to land on Kerbin with Nerv.

In 0.90 and earlier engines always made the same thrust, and just used more fuel flow rate in atmosphere. Since 1.0 they have instead always consume fuel at the same rate, and produce less thrust in atmosphere. So a Nerv-powered Kerbin landing probably won't be possible any more.

[Kerbonaut257]

So basically since its ISP is 800 or whatever, it has more than double the "range" of other engines, given the same fuel/mass ratio. Meaning if your ship weighs 40 tons and 20 tons of that is fuel, the LV-N will have more than double the dV. However, due to its weight, that makes it harder to get a good fuel/mass ratio. It also doesn't have super high thrust, meaning your transfer burns will be longer. 

 

But all that being said, they're totally worth it if you want to build a ship that can go many thousands of dV in a single stage. 

[Spaceception]

On 5/31/2016 at 1:32 AM, The Aziz said:

Yup, much more efficient than poodles, much lower thrust, and don't forget to put some radiators, as they heat up really fast. And yes, used for interplanetary transfers.

Funny, I haven't had any problems with overheating, even at full thrust for prolonged periods of time.

Edited June 6, 2016 by Spaceception

[Mjarf]

The LV-N tend to overheat in older versions of KSP, but it seems to like they have slightly tweaked it's heat management in 1.1. It still gets quite toasty, but with good margin from overheating.

[The Aziz]

Well, after few minutes of burn nearby radiators start to glow, so I don't know. Useful, if you have some heat sensitive parts close to tanks.

[AbacusWizard]

Testing it out right now...

 

 

That's two atomic engines (paired to make total thrust force zero so it doesn't shoot off into an inconvenient orbit) with six Mk1 fuel tanks holding 2400 units of liquid fuel (plus a probe core, a battery, and four small solar panels). I put it into a 1000km orbit and opened up to full throttle.

 

 

RESULTS: managed to burn through the entire 2400 units of fuel with nothing exploding. The engines' "Overheat" meters didn't even show up in the lower left until about halfway through the tank. By my reckoning the total burn lasted about 13 minutes.

 

 

However, towards the end, the heat started seeping in towards the center. A few minutes after the fuel ran out, the solar panels started popping. Still, I'm surprised it took that long. I'm starting to think that in the future I may not actually need to attach radiators to my atomic engines.

[magnemoe]

On 31.5.2016 at 5:59 PM, Renegrade said:

I generally don't use 'em anymore.  ISRU bases basically cut round-trips in half delta-v wise, and the miserable TWR means really long, inaccurate burns, or spamming nukes until you have a craft every bit as inefficient as a chemical one.  Plus the stock system is kinda small vs. the specific impulse of chemical engines... it's not necessary.

Besides, sending my Duna station to Duna on four Skippers at 1.85-3.35g was a lot more fun than drooling it out there at 0.2g on a nuke-based platform.  And cost about 20k less

I made a DunaBus-N crew carrier as a test - the LV-N "all the way there and back" model is actually bigger and slower and more expensive and requires more fuel than the Poodle-based "refuel via ISRU" model.

Note that if you use ISRU and bring the core stage to LKO you could refuel and have 2-3 km/s.
You could bring it to Minmus and top up the tanks for another 1 km/s, now going to Moho or Eeloo would be hard with something big. 
Note that an LV-N craft has the same benefit, here you would typical do the last 700 m/s on the LV-N and have 1 km/s in upper stage, now you refill in LKO, Minmus to top up and then slingshot past kerbin still help, an extra bonus for long burns as you can easy burn over an long time. 

[RizzoTheRat]

I use nukes as much as I can.  Obviously different engines are most efficient for different payloads, required TWR and dV.

Not got the spread sheet handy to check what TWR/dV this screenshot was for, but you can see that above 2.5 tonnes payload the NERV results in the lightest craft to achieve the required TWR.  This was pre 1.1 though, I should get round to updating it at some point.

As a result, I use NERVs for landers that are big enough, this one pushed its own fuel dump to Minmus orbit, hit landed in all biomes, transferred to the Mun, and then hot a few more biomes there.

Edited June 7, 2016 by RizzoTheRat

[Sereneti]

On 31.5.2016 at 10:17 AM, kBob said:

So I get a contract to test the LV-N nuclear engine: "nifty," I think, "never really played with them before and it will be awhile before I reach that tech level," so I jump at the contract.  I replaced the poodle on my run-about with it and head for the Mun.  If it works out I'll just be careful not fulfill that contract for awhile.  But hmmm, it's way slower, heavier and seems to use about the same amount of fuel (though I'm just eyeballing the fuel gauge not doing detailed flow rate comparisons).  What is this engine best for?

there are a breakdown about (afaik)20 tons.
the LV-N engine had a high-isp but a lot of weight.

this engine has a high ISP, that means that this engine can generate more energy from the same amount of fuel.

the downsice is: this engine weight round about 2 tons...
so you have to "burn" fuel to move the 2 tons of engine.

if you use a lighter engine, you can safe fuel from the lighter mass.
there is a breakdown about (afaik) 20 tons.
below that, its "better" (moar fuel effizient) to use a light rocket engine,
over that , its better to use a LV-N .

 

[kBob]

^Thanks everyone for all the interesting info, I think I'm learning more than I ever expected about rocket engines ;).  It was fun to play around with the LV-N once I realized the fuel requirement.  I restarted that career since I realized the settings were too easy so now I don't have that engine anymore, but I got the Mammoth instead which is actually a help for sending up my overbuilt rockets as it simplifies things.  Hopefully get the LV-N soon though, need to set up on Minmus and mine it for sci first; got side tracked playing with the Processing Lab but decided it wasn't worth the hassle just now...besides the engines are more fun to play with!

[rkman]

On 31-5-2016 at 10:17 AM, kBob said:

But hmmm, it's way slower, heavier and seems to use about the same amount of fuel (though I'm just eyeballing the fuel gauge not doing detailed flow rate comparisons).

The LV-N is about 3 times as fuel efficient as regular rocket engines (see the ISP numbers of the engines). 

So it saves you tons of fuel on far-away trips.

It doesn't help much with going to the Mun because you don't need much fuel anyway to go there, so the high mass of the engine offsets what you save on fuel.

[JoeNapalm]

10 hours ago, AbacusWizard said:

Testing it out right now...

 

 

 

Hey! I did that same test!:

Shame about Chad and Philman...

-Jn-

PS - I never use radiators on a NERV, and have never had a catastrophic heat problem...in vacuum.

Edited June 7, 2016 by JoeNapalm

[Archgeek]

10 hours ago, AbacusWizard said:

Testing it out right now...

I did some thermal testing myself, just a nearly-empty NCS, infinite fuel, a probe core, two panels, and various radiation solutions until it looked to be hitting equilibrium or about to blow the core (1100/1200):

Instead of putting engines in opposition, I burned retrograde to the sun and turned around if I managed to escape it after reversing orbit.  (Solar escape causes NaN-spam.)