Need help: do I ignite LVN engines in high atmosphere or not?

[Cirocco]

Hi guys,

So I recently installed FAR and I noticed that my spaceplanes need a lot less thrust to make the orbital insertion burn than in stock KSP. This means I could save quite a bit of weight on my long-range spaceplanes by replacing the insertion burn engines (normally aerospikes) by LVN nuclear engines.

The thing is, I’m not too comfortable igniting nuclear engines in atmosphere. (yes I know there’s no in-game consequence, but the idea just rubs me the wrong way.) I have no problem igniting them the second I get to space since I figure at that point the magnetosphere and the amount of atmosphere between the exhaust and the surface will diffuse/redirect the radioactive particles to such a degree that they are no longer harmful. So I’m wondering: you guys think that igniting at 25-30km up is high enough to avoid any noticeable nuclear fallout below or should I always aim for orbital insertion first, then LVN’s once I go above about 75 km?

I’ve actually been toying around with the idea of a spaceplane with LVN engines and a separate stage for orbital insertion. Once it gets to orbit, it parks the orbital insertion stage (possibly on a refuel station or just letting it float in orbit) and goes off on the interplanetary journey. Once it comes back, we redock and take the whole thing back down to KSC. Could use that as an alternative.

Any thoughts on this? Is it a good idea? Will it work? Do you have any other, better suggestions? If so, do share!

[Dodgey]

As I understand it the LVN is a closed cycle nuclear reactor, the only radiation comes from the engine it's self. Blast away.

[Kasuha]

Starting at altitude of about 1200 m, LV-Ns are the most efficient rocket engines in game (surpassed only by jets in atmosphere).

Regarding your roleplaying, you're free to set up any restrictions you feel suitable. Real world NERVA engine had certain problems with radioactivity leaks as superheated hydrogen was gradually coroding cladding of nuclear material in the engine (they were marked as 'negligible' by official reports) and I can quite imagine if anyone tried to run nuclear engine on Earth, environmentalists would go nuts regardless whether it has or doesn't have any leaks.

On the other hand, playing the game without restrictions and using whatever physics is available is IMO much greater fun than restricting myself to Earth limitations. When I go playing a shooter multiplayer, I also shoot others without thinking if it's right or not.

[Red Iron Crown]

I don't mind burning LV-Ns in atmosphere, but letting them burn up on reentry is a no-no in my personal rule set.

[Dodgey]

Yea but environmentalists cringe everytime someone even mentions the word nuclear, I would like to know what the rate of corrosion was, it could add a service life to the engines for some extra realism if wanted, perhaps a mod could do it. I'm assuming that the time would be time spent burning, correct?

[Cirocco]

Well if they're closed-cycle I think I follow Red Iron Crown's logic: firing in atmosphere is okay (though I'll try to avoid doing it at low altitudes, just to make sure and because of the crap Isp at high ambient pressure) but having them crash/burn up/expose the reactor in any way is a no-no. As for the leaks, I can discount those simply by saying that kerbals are actually very good engineers when it comes to fail-safe equipment: no single component ever fails. They're just terrible ship designers at times

alright, thanks for the input guys. Though if anyone else feels they want to add their two cents, please don't hesitate to do so!

Edited June 2, 2014 by Cirocco

[KerbMav]

My rules:

No nukes in atmosphere, no reentering/aerobreaking/firing/...!

No nuke-ships are to get closer then 200km of Kerbin for prolonged periods!

Decommissioned nuke-ships are to be landed intact on Minmus!

[r4pt0r]

thread of mine from a month or 2 ago has good dialogue on the subject. http://forum.kerbalspaceprogram.com/threads/77306-Opinion-from-roleplayers-Does-the-LV-N-release-radioactive-exhaust

[Red Iron Crown]

KerbMav, your no aerobraking rule is a tough one, I almost always use LV-Ns on interplanetary ships and always aerobrake if possible at their destinations and upon return to Kerbin.

I generally don't use nukes on landers, even if there's no atmosphere.

[Cirocco]

Alright, after reading up on the subject I have decided that yes, I can burn in high atmosphere because the radioactivity in the exhaust would be either low or non-existant, but thick atmosphere is absolutely forbidden because of neutron backscatter.

nukes on landers is probably also best avoided, though I would be firing these on retroburns if I want to land spaceplanes on a planet/moon without atmosphere...

But then again, an advanced EVA suit could probably shield the user from the radiation for short periods of time at least...

[magnemoe]

If you use jets and lv-n I would wait with starting the lv-n as long as possible as the jets has better isp, with rockets you get better performance if you start them at 1.5-2 km

[Dkmdlb]

So I’m wondering: you guys think that igniting at 25-30km up is high enough to avoid any noticeable nuclear fallout below!

PedanticMode=True

Nuclear fallout is made up of the dirt, dust, and debris thrown into the atmosphere as a result of a nuclear explosion. If there is a very high-altitude explosion, there will be no nuclear fallout, because there is no dirt, dust, or debris involved in the explosion. Also, if there is an open nuclear reactor spewing radiation, there is no fallout.

It's the formerly safe material which has been made radioactive that makes up fallout.

[problemecium]

I'm happy to run my LV-Ns anywhere, but I don't ever ditch them to burn up in re-entry, although that's more because I imagine they're expensive than because I'm worried about fallout. These are Kerbals, after all; they're probably immune to the kind of radiation that would injure humans.

[KerbMav]

KerbMav, your no aerobraking rule is a tough one,

It is mostly restricted at Kerbin - and maybe Laythe for the uncertainty regarding the existence of life there.

Landing with nukes is no problem, as they are mostly rubbish in atmosphere anyway (esp. when using KIDS).

[Villageidiot]

I have no problem burning LV-Ns on non-Kerbin surfaces. The ambient radiation on any moon is likely 10x the possibility of any impact from the LV-N engines. Even a place like Laythe which is so close to a gas giant that the rads from it would be insane. Also, even Mars does not have a significant magnetic field to protect it from solar radiation so an LV-N would be nil impact there as well.

VI

[Boris_T_Roach]

Best way I've found to use nukes on my ships is to use the LH/LOX fuelled boosters to get the nuclear powered bit into a 130km * 5Km orbit, then dump the boosters and any supporting

structure and just use the nukes to circularise the orbit.

Keeps the debris count down too.

Boris

[Ayo99]

Above 20km, go ahead and use that Nuclear Engine

Feel free to use strap nuclear engines on your lander fro Minmus, Gilly and low-gravity surfaces.

NEVER USE IT TO LAND IN A ATMOSPHERE.

[cantab]

Well, despite the game description the LV-N *shouldn't* produce radioactive exhaust, at least no more so than the background radiation in any rocket exhaust.

Personally, considering I sat a Near Future Propulsion nuclear reactor on the launchpad and took it to meltdown to see what would happen, I don't think I care about the LV-N exhaust. Still, I've not fired it in atmo except during tests because I've not built anything intended to.

[Javster]

Yea but environmentalists cringe everytime someone even mentions the word nuclear, I would like to know what the rate of corrosion was, it could add a service life to the engines for some extra realism if wanted, perhaps a mod could do it. I'm assuming that the time would be time spent burning, correct?

Maybe they're just uNclear about Nuclear.

It's not always a danger.

[technicalfool]

Maybe they're just uNclear about Nuclear.

It's not always a danger.

There is a reason that MRIs are no longer called NMRIs. It's that word at the beginning. It scares people.

[Dodgey]

There is a reason that MRIs are no longer called NMRIs. It's that word at the beginning. It scares people.

I say we change it back, force people to learn.