Is LV-N Nuclear and Ion Drive Now Realistic?

[Landge]

With the recent changes made to the upperstage vacuum efficient/atmos deficient engines to make them more realistic (LV-1, LV-909, & Poodle),

I was wondering are the LV-N Nuclear and the Ion Drive more realistic too? I'm playing career and have a long way to go before unlocking them.

Is the LV-N still the goto interplanetary transfer engine?

Will I still be able to fly my Gnat like this on Mun 0.90?

[Gaarst]

Nuclear and ion engines vacuum Isp are very similar to those of real life (although nuclear engines were never actually put on a rocket), at least in theory.

And nuclear is still the best for heavier interplanetary crafts in 1.0.2 (although they only use liquid fuel now) as long as you can manage the heat they generate.

Ion engines' Isp was severely reduced in atmosphere but are still at 4200 in vacuum.

[Mastikator]

http://en.wikipedia.org/wiki/NASA_Solar_Technology_Application_Readiness

Deep Space 1 and Dawn used the NSTAR Ion thruster.

http://en.wikipedia.org/wiki/NERVA

Nuclear Thruster were invented and developed, but never put into use because governments around the world are not super happy about nuclear material being launched into orbit. A shame, I can think of no nobler goal for nuclear waste than to be used to explore space. Instead it's used as bombs.

[Gaarst]

Nuclear Thruster were invented and developed, but never put into use because governments around the world are not super happy about nuclear material being launched into orbit. A shame, I can think of no nobler goal for nuclear waste than to be used to explore space. Instead it's used as bombs.

That's off topic but nuclear waste cannot be used for anything, reactors, engines or bombs, only thing we are able to do with it is store it underground and prey for it not to leak and to gently lose radioactivity over time.

[NathanKell]

Heh. They are nowhere near realistic, although their Isps are about right. The NTR doesn't have to worry about extremely-not-dense fuel and/or boiloff (and/or politics ) and the ion has about 1,000x the thrust it should last I computed it...

[Geschosskopf]

Using the words "realism" and "KSP" in the same sentecne is a non sequitur.

[arkie87]

Nuclear and ion engines vacuum Isp are very similar to those of real life (although nuclear engines were never actually put on a rocket), at least in theory.

And nuclear is still the best for heavier interplanetary crafts in 1.0.2 (although they only use liquid fuel now) as long as you can manage the heat they generate.

Ion engines' Isp was severely reduced in atmosphere but are still at 4200 in vacuum.

Interesting...

I was just designing a rocket to go to Duna and i put a LV909 (terrier) and a LV-N (Nerv) and the LV909 had more deltaV... and no matter how much payload or fuel tanks i added, the LV909 had more deltaV.

But now im thinking it only had more deltaV because i had oxidizer for the LV-N?

[Landge]

Heh. They are nowhere near realistic, although their Isps are about right. The NTR doesn't have to worry about extremely-not-dense fuel and/or boiloff (and/or politics ) and the ion has about 1,000x the thrust it should last I computed it...

Here is an excerpt from the link above...

NERVA rocket stage specifications[edit]

Diameter: 10.55 meters (34.6 ft)

Length: 43.69 meters (143.3 ft)

Mass empty: 34,019 kilograms (74,999 lb)

Mass full: 178,321 kilograms (393,131 lb)

Thrust (vacuum): 333.6 kN (75,000 lbf)

ISP (vacuum): 850 seconds (8.3 km/s)

ISP (sea level): 380 seconds (3.7 km/s)

Burn Time: 1,200 s

Propellants: LH2

Engines: 1 Nerva-2

I take this to be the rocket AND fuel tank combined!

Now here is KSP...

LV-N specifications:

Diameter: 1.25 meters

Length: 3.75 meters? EB (This was measured on screen by Eye Ball)

Mass: 3 tons

Thrust (vacuum): 60 kN ??? (82% less than NERVA-2)

ISP (vacuum): 800 (close enough to the real deal)

ISP (sea level): 185 ??? (51% less than NERVA-2)

Makes me wish I had the real NERVA in KSP! Minus the radiation. Wait there is none! I'd be willing to bet it doesn't have overheating issues either! Boiloff?

Using the words "realism" and "KSP" in the same sentecne is a non sequitur.

I know right. Makes me question why the development team selectively changed the rules of the game, not just on certain engines but other things as well, for the sake of "realism".

Edited May 5, 2015 by Landge

[panzer1b]

No idea about realism, but i think they are pretty fair and balanced as they are now in KSP.

Ions are similar if not identical to before if you discount the atmosphere nerfs. Unless you insist on using them on kerbin, duna, eve, or laythe surface, they are basically identical to what they were before, your ion choppah will still work on the mun (if it worked before). The only major change is that massless parts are nolonger massless, if you relied on massless crap to power them (such as z-400 battery spam), then forget about it, otherwise you should get very similar results.

Nukes are basically teh same except for a slight increase in mass and actual heating problems. That said, if you know how to deal with it, the heating can be largely ignored. Nukes are right now actually more fair imo, they are still the ultimate in ISP (ions aside), but they arent as easy to use as they were before. Right now they work 100% fine for shorter burns, even without any heatsinks or advanced stuff, and for very long 10+ minute burns you might need radiators such as wings. Still, they are the go-to engine for interplanetary unless its an extremely lightweight (under 10t) ship where ions or even lv-909s make more sense.

[Landge]

No idea about realism, but i think they are pretty fair and balanced as they are now in KSP.

Ions are similar if not identical to before if you discount the atmosphere nerfs. Unless you insist on using them on kerbin, duna, eve, or laythe surface, they are basically identical to what they were before, your ion choppah will still work on the mun (if it worked before). The only major change is that massless parts are nolonger massless, if you relied on massless crap to power them (such as z-400 battery spam), then forget about it, otherwise you should get very similar results.

Nukes are basically teh same except for a slight increase in mass and actual heating problems. That said, if you know how to deal with it, the heating can be largely ignored. Nukes are right now actually more fair imo, they are still the ultimate in ISP (ions aside), but they arent as easy to use as they were before. Right now they work 100% fine for shorter burns, even without any heatsinks or advanced stuff, and for very long 10+ minute burns you might need radiators such as wings. Still, they are the go-to engine for interplanetary unless its an extremely lightweight (under 10t) ship where ions or even lv-909s make more sense.

No battery spam per se. I used 2 of the smallest inline batteries, 2 inline xenon tanks, and a SAS. "Allow Part Clipping" was not activated however there was a bit of right angle overlap getting the bottom ion to line up with the CoM and still have clearance underneath.

You have to really have to keep your eye on the descent speed, forward velocity, and battery life. Get too far ahead of the Ap and the ground will smack you like a bug hitting a windshield.

It took me perhaps a dozen tries. Probably more. I'd get frustrated and quit then come back and try again later before I finally made my first successful landing only losing a couple Cubic Octagonal Strut or two used for landing legs. Lost the bottom ion a few times as well.

As far as the NERVA - LV-N comparison I posted above, the NERVA has A LOT MORE thrust, both in vacuum and at sea level, compared to the LV-N.

The ONLY similarity that I can find is the ISP in vacuum. 850 vs 800. I can't make an accurate call on size and weight of the two based on the wiki.

I definitely don't want real world ion thrust. I'm just asking Squad to be consistent when they are changing the specs of the engines based on keeping it realistic.

If vacuum engines get nerfed in atmos, so be it. But give the other engines a buff if they deserve it based on real world counter parts.

I did some in game comparison experimentation with the LV-N based on the NERVA specs.

[stock] specs

ISP (vac)= 800

ISP (sea level)= 185

Max Thrust (vac) = 60

Max Thrust (sea level)= 13.05

[NERVA] specs

ISP (vac)= 850

ISP (sea level)= 380

Max Thrust (vac) = 333

Max Thrust (sea level)= 130.5

For the sake of not making the LV-N too overpowered (we don't want it to be too realistic do we?) I created this...

[Hybrid] LV-N stock max thrust w/ NERVA ISP ASL (380)

Max Thrust (sea level) = 23.5

Even using the stock 60 kN thrust in vacuum the sea level is almost double compared to stock.

Edited May 5, 2015 by Landge

[KerikBalm]

That's off topic but nuclear waste cannot be used for anything, reactors, engines or bombs, only thing we are able to do with it is store it underground and prey for it not to leak and to gently lose radioactivity over time.

Not true:

http://www.theguardian.com/environment/2012/jul/30/fast-breeder-reactors-nuclear-waste-nightmare

http://en.wikipedia.org/wiki/Breeder_reactor#Waste_reduction

Most nuclear reactor waste can in fact be used as fuel in new breeder reactors, which can consume the long lived radioactive elements, and the resulting waste has half lives of 91 years or less.

In particular we should have switched over to Thorium reactors long ago.

The current status of nuclear power in the world is appalling. The new high tech designs aren't being built, and ones from the 50's like Fukishima continue to operate and pose ever present safety hazards.

Breeder reactos won't melt down (its requires specific conditions just to keep the more complicated reactions going), and they can be fueled by the waste from the old reactors.

And when that waste is gone, they can use a thorium fuel cycle, which won't produce plutonium suitable for use in nuclear weapons, nor does it require enrichment uranium, which can also be diverted for nuclear weapons. The waste would be at basically background levels in ~200 years.

Also, all thorium can be used, as opposed to uranium where the usable isotope is a small fraction of uranium on earth, and thorium itself is more abundant than uranium on earth.

It could supply all earth's power needs at the current level for thousands of years...

Anyway, back to the topic.

The LV-N has an unrealistically low TWR.

The ion drive has a ridiculously unrealistically high TWR.

Both Isps are realistic in absolute terms, but proportional to the dV needed to get somewhere in the Kerbal's system vs ours, they seem too high:

http://i.imgur.com/AAGJvD1.png

dV from low Earth orbit to orbit of the Moon: 3,900 m/s

dV from low Kerbin orbit to orbit of Mun: 1,170 m/s

3.33x as much IRL

dV from low Kerbin orbit to Jool intercept: 1,930 m/s

dV from low Earth orbit to Jupiter intercept: 6,570 m/s

3.4x as much IRL

To be "realistically hard", Isps should be nerfed to about 1/3 realistic values.

IRL, chemical rockets can get up to about 450s .... in KSP, the highest is now... 350? it used to be 390... but I think with the rebalance... its 350.

The fuel tanks in KSP are also really heavy, and the engine TWRs low. The best mass ratio is about 9:1, but IRL, you can get closer to 20, and do it with a much better TWR....

So... its not really comparable to just look at an Isp of 800s, and call it realistic or not.

[Red Iron Crown]

Heh. They are nowhere near realistic, although their Isps are about right. The NTR doesn't have to worry about extremely-not-dense fuel and/or boiloff (and/or politics ) and the ion has about 1,000x the thrust it should last I computed it...

I thought the historic NERVA had a much higher atmospheric Isp, though I could be mistaken.

The ion thrust is ridiculously high, but I consider that a gameplay concession as we have no way to reasonably simulate weeks or months long burns.

[78stonewobble]

Not true:

The current status of nuclear power in the world is appalling. The new high tech designs aren't being built, and ones from the 50's like Fukishima continue to operate and pose ever present safety hazards.

Sorry for off-topic. Ever present safety hazard, on the level of the chance of an airliner hitting you, while walking your dog or there abouts right? Because, deaths from nuclear powerplants, including the disasters, are drops in the ocean compaired to coal (still over 10.000 deaths a year in the US alone) or just car usage (1 mio. dead year and up to 50 million wounded a year is the global estimate) and thats for the 50's tech you mention.

[SymbolicFrank]

Nuclear Thruster were invented and developed, but never put into use because governments around the world are not super happy about nuclear material being launched into orbit. A shame, I can think of no nobler goal for nuclear waste than to be used to explore space. Instead it's used as bombs.

The interesting part is, that most probes contain about a kilogram of Plutonium, to power their generator. Because even probes that operate close to the sun tend to have a trajectory with gravity slingshots. So they regularly pass the Earth at about 100 km. Which is a lot more toxic than the Uranium in a NERVA.

Btw, I agree that we should switch to Thorium reactors and new models like Pebble Bed Reactors ASAP. But Breeder reactors, while they sound great, are tricky. Do use, but with caution.

Edited May 5, 2015 by SymbolicFrank

[Tw1]

I did some in game comparison experimentation with the LV-N based on the NERVA specs....

I think you missed something. Look again at the stats you posted earlier:

NERVA

Diameter: 10.55 meters

Length: 43.69 meters

Mass (empty): 34 tons

Thrust (vacuum): 333.6 kN

ISP (vacuum): 850 seconds

ISP (sea level): 380 seconds

LV-N

Diameter: 1.25 meters (about 12% of NERVA)

Length: 3.75 meters? (about 8.5% of NERVA)

Mass: 3 tons (about 9% of NERVA)

Thrust (vacuum): 60 kN (about 18% of NERVA)

ISP (vacuum): 800 (close enough to the real deal)

ISP (sea level): 185 ??? (51% less than NERVA-2)

If you look at it this way, the LV-N is loosely a 1/10 NERVA by stats, apart from the thrust, and the sea level ISP.

This ignores the square-cube law that would happen if you were to scale something down, really. But a lot of things in KSP are super dense...

[metaphor]

The mass of the real NERVA was about 6.8 tons, for a vacuum thrust of 333 kN and Isp of 850 s.

There were also other nuclear engines in planning, like the SNTP (Space Nuclear Thermal Propulsion) program, which had an engine with a mass of about 1.6 tons, a thrust of about 120 kN, and an Isp of 930-1000 s.

More info

[Laie]

NERVA rocket stage specifications[edit]

Diameter: 10.55 meters (34.6 ft)

Length: 43.69 meters (143.3 ft)

Mass empty: 34,019 kilograms (74,999 lb)

Mass full: 178,321 kilograms (393,131 lb)

I take this to be the rocket AND fuel tank combined!

Indeed it is. That 34t include the weight of a ~20m³ hydrogen tank. The shuttle's external tank has comparable size, but more complicated plumbing due to being an LF+O tank. Still, just as a ballpark figure, we're talking about something on the order of 15-20t for the tank alone.

[viktor19]

I was just designing a rocket to go to Duna and i put a LV909 (terrier) and a LV-N (Nerv) and the LV909 had more deltaV... and no matter how much payload or fuel tanks i added, the LV909 had more deltaV.

That's because LV-909 uses LF+O mix, and LV-N uses just the LF, which makes oxidiser dead weight. Remove the oxidiser from the tank when you fit it with LV-N

[Tw1]

The mass of the real NERVA was about 6.8 tons, for a vacuum thrust of 333 kN and Isp of 850 s.

I stand corrected.

[KerikBalm]

Sorry for off-topic. Ever present safety hazard, on the level of the chance of an airliner hitting you, while walking your dog or there abouts right? Because, deaths from nuclear powerplants, including the disasters, are drops in the ocean compaired to coal (still over 10.000 deaths a year in the US alone) or just car usage (1 mio. dead year and up to 50 million wounded a year is the global estimate) and thats for the 50's tech you mention.

Its true that actual verifiable deaths are quite low.

Have you ever heard of risk homeostasis? http://en.wikipedia.org/wiki/Risk_compensation#Risk_homeostasis

Those reactors are very dangerous for a number of reasons, so they are operated very carefully.

But you can't deny Fukishima happened. You can't deny a design that can meltdown is more dangerous than one that cannot.

You can't deny plutonium is produced in significant quantities and must be carefully accounted for (nuclear weapon proliferation risk)

You can't deny the waste is hazardous, and will continue to be hazardous on a timescale far longer than the duration of any nation on Earth.

You can't look at just the deaths from acute radiation exposure. You have to look at all the factors.

Heck... with Fukishima... there were 0 deaths to acute radiation exposure, but 1,600 people died due to evacuation-related causes (exacerbated by the tsunami's effects, sure), and there was signfican't amounts of radioactive elements released into the atmosphere - although the cancer signal will be hard to detect decades from now, and the ecological effects are very hard to determine.

I'm not anti-nuclear, I think people that are anti-nuclear have had the perverse effect of making nuclear power less safe - because by blocking the construction of new reactors, the old ones are kept online much longer.

We should have tax incentives and such to transition to thorium reactors.

The whole Iran energy deal thing would be a non-issue if Thorium power development hadn't been shut down in the 60's

Tell the Iranians that they can have schematics for a thorium reactor, and then if nuclear energy is all they want, they can completely disassemble all centrifuges for enriching uranium.

[Kuu Lightwing]

Thanks for that NERVA stage stats, guys. If I'm not mistaken, with about 50 ton payload it would have roughly 8000 m/s delta V, which is gorram amazing!

[magnemoe]

I thought the historic NERVA had a much higher atmospheric Isp, though I could be mistaken.

The ion thrust is ridiculously high, but I consider that a gameplay concession as we have no way to reasonably simulate weeks or months long burns.

LV-N and some other engines has very low surface ISP of game play reasons, they wanted to differentiate the atmospheric and vacuum engines.

- - - Updated - - -

The interesting part is, that most probes contain about a kilogram of Plutonium, to power their generator. Because even probes that operate close to the sun tend to have a trajectory with gravity slingshots. So they regularly pass the Earth at about 100 km. Which is a lot more toxic than the Uranium in a NERVA.

Btw, I agree that we should switch to Thorium reactors and new models like Pebble Bed Reactors ASAP. But Breeder reactors, while they sound great, are tricky. Do use, but with caution.

Most important reason for no nerva use is no large interplanetary payloads. if you only use small probes in KSP you have no need for the LV-N.

Lots of mars mission plans has included nerva.

[Red Iron Crown]

LV-N and some other engines has very low surface ISP of game play reasons, they wanted to differentiate the atmospheric and vacuum engines.

Pre-1.0 it hardly mattered, the LV-N had a better Isp than any chemical engine by 1700m altitude on Kerbin and at any altitude on Duna (Eve was another story though). I haven't run the numbers in 1.0, but I'm sure it is a good bit higher as the LV-N's atmospheric Isp has been nerfed, plus with thrust scaling it's going to be weak until the atmosphere gets really thin.

[Laie]

Duna's atmosphere is really thin, it barely exists. Last time I checked (v0.90), the LV-N had ~750 ISP in one of Duna's deeper craters. Or was that on ordinary terrain of approx. 3000m elevation? The ISP at ~1500m still was >700, though, I'm certain of that.

With 1.0, the atmospheric ISP has gone even worse, but not by much. I still expect an ISP of 700 or better. That would give you, what, like 50-55kN on the surface? I don't think that will be a make-or-break issue.

[NathanKell]

It's far from impossible to have on-rails thrust, Orbit Manipulator has done it for over a year...

[m4v]

but it might be a pain to make an useful user interface for plan a trajectory.