Jump to content

PSA: Nuclear engine overheating


THX1138
 Share

Recommended Posts

@Regex, take a look at this.

Some juicy and very usefull info on the workings of various NTRs and the sorts. A couple of sections have pdf links to scanned NASA docs from back then when several of these engines were tested.

http://www.projectrho.com/public_html/rocket/enginelist.php#ntrsoliddumbo

Albeit being a DUMBO :P It functions the same as a NERVA or any other NTR engine really, no radiators used. Fuel flow is used to cool the engine/reactor.

(bad photocopy of a ) Rough schematic of Dumbo engine. Liquid hydrogen propellant enters top and flows through beryllium neutron reflector, cooling it. Flows upward through a Cold Gas Entrance into interior of a reactor tube. Hydrogen seeps through walls of tube, being heated by fissioning uranium. Hot hydrogen escapes through hot gas exit holes in bottom, entering exhaust nozzle. Beryllium reflector will have control drums (not shown)

dumbo15.png

So my question remaining: can the 1.0 heat system be modded, so that any liquid fuel can act as a radiator as long as you give enough throttle/give enough fuel flow.

This is what I like to know. Cause how it works now and has worked somewhat in the past is rather wrong.

Link to comment
Share on other sites

regex, I very much appreciate what you said elsewhere about enjoying a good engineering challenge. Version 1.0 is making us all re-think how we design our ships, and such challenges are the best part of KSP, in my opinion.

But I just don't like the idea of having to overcome a challenge that is rooted in some unphysical or erroneous implementation made by the devs (be it aerodynamic instability caused by improper implementation of heat shields, or overheating caused by a decision to make the nuclear engines run overly hot). I'll do it if I HAVE to...but I won't enjoy it.

Link to comment
Share on other sites

Flowing fuel already acts as a cooling system. If you have a fuel tank that is being depleted, it will cool. The effect is just not very noticeable at the moment, since its is not very much, and the heat from the engine will easily overpower the cooling, so the net heat still goes up. I have noticed this when I saw a strange "backdraft" on a few designs. The fuel tank would stop heating up, and start to cool while the engine was firing. After the engine stopped, and it was no longer getting any hotter, the fuel tank briefly reversed and started warming up again. This was because the net flow was positive again, and the engine was hotter that the tank, so it was warming it. Took me a few minutes to realize what was happening.

Link to comment
Share on other sites

But I just don't like the idea of having to overcome a challenge that is rooted in some unphysical or erroneous implementation made by the devs (be it aerodynamic instability caused by improper implementation of heat shields, or overheating caused by a decision to make the nuclear engines run overly hot). I'll do it if I HAVE to...but I won't enjoy it.
As far as NTRs are concerned, I think the heating is a fair balancing point (although, again, a dedicated radiator part would be welcome). The reasons being that LiquidFuel is essentially cryogenic kerosene (by density and other engine stats, IIRC) with the thermal properties of Aerozine 50 (the thermal info according to NathanKell). It's a super-fuel, nothing near cryogenic hydrogen in terms of storage and handling. Realistically, an NTR running kerosene would probably have a terrible isp. Also, while NTRs may actually be quite cool engines (they appear to be about mid-range in terms of chamber temperature) KSP glosses over the storage of cryo fuels, which require some sort of cooling mechanism in order to avoid boil-off.

I can't believe I'm saying this, but I feel the NTR heating is a balanced and interesting gameplay mechanic because KSP is not realistic. If this were Realism Overhaul the way the engine works now would be inexcusable.

Link to comment
Share on other sites

I wouldnt mind if it just got up to say 2000 K, but it has to have enough emmisivity to stay there by itself.

2K is lethal to the rest of the craft. You would have to insulate it really well from everything else. I don't think they actually changed that much about the LV-N, I just think the implementation of a proper heat system suddenly started taking into account the fact that they run HOT. I personally love it.

Why is it so hot? Who cares. Jeb probably bribed the engineers to put some extra Uranium into the engine, since he thought the "normal" non- overheating engine was "too dam slow".

We had Whackjob shoot insane monstrosities into an orbit, and you are saying we cannot figure a way to cool one measly nuke without a dev revision or boring stock radiators?

Link to comment
Share on other sites

I have found that a single nuke will not overheat the fuel tank it's attached too until after at least 5 minutes of burning. I have plenty of experience with nuke powered craft, and after a 5 minute burn it is often best to orbit around whatever planet your trying to escape and do a second burn anyways. Though we DO need a proper radiator. This new thermal system is amazing, but we obviously need a (real, not 50 wings) way to counter it.

Link to comment
Share on other sites

Well all engines give off heat, just that others dont tend to run as long. Still, cfg file says heat production figure is 240. Mainsail has 180! Proper figure should be say 60 as even "terrier" has 20.

But as there are problems with ISRU overheating, there should be a radiator of sorts. Or even just coolant pipes, like fuel pipes.

Link to comment
Share on other sites

Just a note for people using nuclear engines to keep an eye on the overheating because things have changed. I alt + tabbed out and came back to find I had no engines when previously they'd have been okay if left at 90% thrust (I have four grouped close together). Now they're overheating at 50% continuous thrust.

You need to cool them. Use some parts as radiators.

Link to comment
Share on other sites

It might be worth exploring the thermal debug options. I know there is a multiplier for radiative cooling. I haven't tested it yet, but increasing it might make nuclear engines somewhat more manageable.

I haven't checked, but could it still be fixed by editing the part.cfg file? Or does the new thermal system require editing something else?

Link to comment
Share on other sites

I haven't checked, but could it still be fixed by editing the part.cfg file? Or does the new thermal system require editing something else?
Basically you'd want to reduce the LV-N heat production by some amount. Wings are already fantastic radiators since their emissivity is 0.95, as opposed to the LV-N and Mainsail with 0.8. I don't think radiator parts will be the answer.
Link to comment
Share on other sites

This week, on

Criminally Negligent Engineering

Jeb: When we add the heat shield to the bottom of the Mk1 capsule, that's going to move the CoM backwards, right?

Bill: Nah...we'll arrange all the other equipment inside the Mk1 so that the CoM stays in the same place. Of course...it'll be unstable that way.

Jeb: Eh, no problem. We'll have Val fly that mission.

Bill & Jeb: Hahahahahahaha.

Jeb: How about the rebalancing of the nuclear engine? When we set throttle for 100% reactor power, how much fuel should we pump through it?

Bill: Oh, I don't know... Maybe 90% of what's needed to keep it from overheating?

Jeb: And we'll let Bob fly that mission.

Bill & Jeb: Hahahahahahaha!

Be sure to tune in next week for another episode of Criminally Negligent Engineering!

Link to comment
Share on other sites

I have to say, this new heating system is awesome. Finally an engineering challenge that doesn't involve dumb physics/rubbery rockets! We could certainly use some dedicated radiator parts but wings should fit the bill quite nicely for the time being. This is the realism that KSP deserves.

I finally agree with you regarding realism. This is a fun challenge!

EDIT: Hmm what about putting several lengths of girder between the nuke and other parts, like Discovery from 2001: A Space Odyssey ?

How are girders conduction-wise? I'll try that next!

Edited by moogoob
Link to comment
Share on other sites

I was a bit skeptical, but now I'm trying to overheat nukes on the kerbin launchpad...

... that does take pretty damn long, doesn't it? Maybe it's because I put 8 nukes on FLT400 connected to the big 3.75 tank, however those things are running for 30 minutes now and just don't stop. Atm they are at 1900* and the heating slows down to a crawl.

Link to comment
Share on other sites

I was a bit skeptical, but now I'm trying to overheat nukes on the kerbin launchpad...

... that does take pretty damn long, doesn't it? Maybe it's because I put 8 nukes on FLT400 connected to the big 3.75 tank, however those things are running for 30 minutes now and just don't stop. Atm they are at 1900* and the heating slows down to a crawl.

Try it in orbit. On Kerbin you've got air cooling to help.

Also, the atmo choking the thrust might lower heating too.

Plus, all the above is pumping heat into a big fuel tank - my busted batteries was on a small, thin one.

Link to comment
Share on other sites

They used up all fuel and then I had to use the cheat.^^'

Well, now i'm putting a ship with more nukes than necessary into space. Real spacecraft can get heat problems since they can't spread heat in space like they can do in an atmosphere.

Edit: Yeah, that's it. Died a lot faster.

Edited by Temeter
Link to comment
Share on other sites

Am I in backwards land? you mean to say running a NTR builds up heat?... Despite its propellant basically doubling as a coolant?... Yet RTG's don't generate any heat at all despite people clipping their built in decorative radiators inside their crafts without a second thought!? :huh:

engineering challenge or no this is rather unintuitive I believe I have some config editing to do...

Link to comment
Share on other sites

Something I can test tonight...

How well do the new aero-brakes work as Radiators for the Nuc?

Check the part cfg file and see what the emissiveConstant is. If it's less than 0.95, use wings instead.
Link to comment
Share on other sites

This thread is quite old. Please consider starting a new thread rather than reviving this one.

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...