More SSTO Engines

[KerbalRocket]

I was thinking that it would be good if there were more stock engines like the R.A.P.I.E.R or even and engine that could use Liquid Fuel and Air Intake or just Liquid Fuel or maybe an Atmospheric Nuclear Engine, Oxidizer only Engine for using up excess Oxidizer. If you have more engine ideas please put them below and maybe a Modder will reach out to us.

[Aeroboi]

4 hours ago, KerbalRocket said:

I was thinking that it would be good if there were more stock engines like the R.A.P.I.E.R or even and engine that could use Liquid Fuel and Air Intake or just Liquid Fuel or maybe an Atmospheric Nuclear Engine, Oxidizer only Engine for using up excess Oxidizer. If you have more engine ideas please put them below and maybe a Modder will reach out to us.

I made this suggestion myself a while ago but my thread ended on the 3rd+ page.

I would like another rapier also. Personally I think 1.875m is better because 2.5m is to big and to OP and MH needs liquid fuel only adapters. Also, one shock intake can feed 3 rapiers so I think a 1.875m should do with only 1 intake. The other reason is that I still like that there's a building challenge how to do it with fewest parts. With 2.5m you would only need like 4-8 of them for the largest space planes I reckon.

I don't like nuclear jets because that would make Eve SSTO's suddenly possible, and, ultimately easy and the challenge for Eve is that it isn't easy
As for the oxygen engines, besides oxidizer you need a combustion fuel because oxygen alone doesn't burn.

 

[Ol’ Musky Boi]

On 3/24/2019 at 9:53 AM, Aeroboi said:

I made this suggestion myself a while ago but my thread ended on the 3rd+ page.

I would like another rapier also. Personally I think 1.875m is better because 2.5m is to big and to OP and MH needs liquid fuel only adapters. Also, one shock intake can feed 3 rapiers so I think a 1.875m should do with only 1 intake. The other reason is that I still like that there's a building challenge how to do it with fewest parts. With 2.5m you would only need like 4-8 of them for the largest space planes I reckon.

I don't like nuclear jets because that would make Eve SSTO's suddenly possible, and, ultimately easy and the challenge for Eve is that it isn't easy
As for the oxygen engines, besides oxidizer you need a combustion fuel because oxygen alone doesn't burn.

 

1.875m parts wouldn't be available to players without MH so a 1.875m RAPIER in the stock game would be out of place. Besides, I don't think that a 2.5m RAPIER would be overpowered at all, it'd just be like using 4 RAPIERS but with less parts.

I'm with you on nuclear engines, they'd make Eve too easy.

[sturmhauke]

You can make Eve easier, but I don't think you could ever call it easy. It still has higher gravity and a thicker atmosphere than Kerbin.

[JadeOfMaar]

Nuclear engines aren't going to make Eve easy. Consider this: nuclear jet engines are only known to accelerate a craft to Mach 3 and will easily fail as atmosphere thins out or already warms before entering the engine. (The exceptions I know being Near Future Aeronautics (2.5m nuclear engines only) or KSPI-E (very complicated, not a mod that most players can handle).) Also consider that nuclear engines are incredibly heavy and have to fight Eve's gravity and thicker atmosphere, moreover when you carry the weight of LF needed to operate when the jets become useless. 2.5m engines would not be OP. They would spare players the need to spam 1.25m ones. Anyone can spam RAPIERS at anytime if they feel like it, especially when they know how to engineer for optimal drag reduction.

The ideal solution for usefully dumping excess Oxidizer is to make or provide cold gas RCS thrusters (with the setting on by default to respond to throttle) powered by the fuel pressure (a thrust curve method can be applied for this, making it weaker as the tanks empty out). When Soyuz boosters separate, they don't use Solid Fuel, they vent extra Oxidizer.

The one other SSTO engine I'd personally recommend is a scramjet, the kind of engine that's dead up to Mach 4 and then works up to idk, Mach 13 (as far as construction materials and the intake itself will allow) but Isp will be pretty low (for a jet engine). It's on the same level as the SABRE, as I see it. Sadly, with the size of the stock planets (namely Kerbin) a scramjet easily becomes OP or much more dead weight and trouble than it's worth.
Mach 4 to 7 operating range...at stock scale... isn't much justification for the extra mass of the number of scramjets needed to reach orbital speeds and the extra turbojets needed to push them. At 2.5x and up, then it's undeniably worth hauling around. Orbital speeds start at Mach 11.

Edited March 26, 2019 by JadeOfMaar

[Aeroboi]

1 hour ago, JadeOfMaar said:

Nuclear engines aren't going to make Eve easy. Consider this: nuclear jet engines are only known to accelerate a craft to Mach 3 and will easily fail as atmosphere thins out or already warms before entering the engine. (The exceptions I know being Near Future Aeronautics (2.5m nuclear engines only) or KSPI-E (very complicated, not a mod that most players can handle).) Also consider that nuclear engines are incredibly heavy and have to fight Eve's gravity and thicker atmosphere, moreover when you carry the weight of LF needed to operate when the jets become useless. 2.5m engines would not be OP. They would spare players the need to spam 1.25m ones. Anyone can spam RAPIERS at anytime if they feel like it, especially when they know how to engineer for optimal drag reduction.

The ideal solution for usefully dumping excess Oxidizer is to make or provide cold gas RCS thrusters (with the setting on by default to respond to throttle) powered by the fuel pressure (a thrust curve method can be applied for this, making it weaker as the tanks empty out). When Soyuz boosters separate, they don't use Solid Fuel, they vent extra Oxidizer.

The one other SSTO engine I'd personally recommend is a scramjet, the kind of engine that's dead up to Mach 4 and then works up to idk, Mach 13 (as far as construction materials and the intake itself will allow) but Isp will be pretty low (for a jet engine). It's on the same level as the SABRE, as I see it. Sadly, with the size of the stock planets (namely Kerbin) a scramjet easily becomes OP or much more dead weight and trouble than it's worth.
Mach 4 to 7 operating range...at stock scale... isn't much justification for the extra mass of the number of scramjets needed to reach orbital speeds and the extra turbojets needed to push them. At 2.5x and up, then it's undeniably worth hauling around. Orbital speeds start at Mach 11.

So that's why we haven't got Scramjets, they operate to Mach 13, you only require Mach 5 on Kerbin And if used as a escape trajectory pusher inside the atmosphere I'd find it unrealistic tbh due to scale and real life application.
For RSS it would be a cool thing. Not sure if a Scramjet mod exists but I feel tempted to try something like it in RSS since you mentioned it.

Edited March 26, 2019 by Aeroboi

[JadeOfMaar]

@Aeroboi A few mods exist that carry scramjets. Mk2 and Mk3 Stockalike Expansion are the top pick, and OPT Reconfig makes the 2.5m OPT jet engine fit for use in RSS. OPT Legacy provides a whole new breed of SSTO engine, the late-game "WarpJet" which I devised and is inspired by an irl concept for a plasma jet engine.

[KerbalRocket]

I actually already use MK2 and MK3 Stockalike Expansion and all of the near future mods. , But I will check out OPT. 

[Redacted]

My issue with liquid fueled SSTO engines is that their all too similar. Increase the motors tonage / tech level yet its TWR, ISP and assent profiles remain almost identical. (safely scaled up with the tonnage) What is needed are motors with better profiles / stats, that perform better on larger ships as the tech level increase. Currently my MK4 transport uses 16 - 20 Broadsword engines which is an ridiculous amount. The higher part counts tends to make the MK4’s rather unstable and prone to sudden aerodynamic/ structural failure. Anything that can directly increase the motor performance, will indirectly reduce the part count.

The T1 Dart Aerospike really isn’t much better or worse than the Rapier / Broadsword. Sure each has their own nitch but Aerospike motors are too few and far between to be worth using on anything beyond MK2. Yet those that do exist (mods) don’t properly scale the motors relative the the nozzles physical surface area. Case in point, Linear vs Toroidal: Linear has a much greater nozzle surface area and should produce a much greater thrust but at the cost of a lower ISP.  However, all the Aerospikes I’ve tied use a similar if not the exact same profile and stats, just repackaged / rescaled for the weight of the motor. (Just like the other SSTO motors)

The “Air-Breathing” Nuclear  (ABN) engines have really horrible assent profiles which makes them unable to lift their own weight off the runway. Even at their ideal mach / altitudes the performance is very poor for the tech level / costs involved. This is further compounded by the fact that the ABN’s are not dual modal, thus becoming useless in a vacuum. IMO, even with the crap assent profiles, they’d be worth using ‘if’ they were capable of switching modes. (switch from air-breathing to liquid or LH2 fuels) For the life of me, I can’t recall ever reading of anyone even using ABN’s. That in itself says something and the mod developers should take note of this.

Edited March 31, 2019 by Redacted

[TiktaalikDreaming]

Regarding any Nuclear powered SSTO engines, you're inhibited by the fact that their always going to be heavy.  Without invoking super-science and fusion, you need large chunks if fissionable materials, plus even more mass in shielding, and then the only real advantage in atmospheric flight is longevity.  For any sort of system using air as the propellant (fans, ramjets, scramjets, etc) you're going to be stuck in the atmosphere, and fairly low in it.  So what you end up with is a radioactive craft that can stay aloft at speed for a long long time, but can't go higher without both losing thrust, and losing cooling, with resultant explosions.

If you take your propellant with you, then you can get really good ISPs out of NTPropulsion, but you get crappy TWR, which leads to really huge gravity loses getting up into orbit.  And that cancels out the usefulness.  Again, the mass required for fission fuel and shielding is going to kill the plan.  Lightbulbs are probably the closest to viable for ground launch, but they're not what I'd call based on proven engineering.  Most of the concepts are sorted, but there's serious concerns for various parts of the fissionable gas containment.  Similar concerns surround open cycle gas core as well, but seem a bit less insurmountable, but no-one in their right mind would start one of those up in an atmosphere (hell, they should be banned if they're even close to one, IMHO).  And that leaves things like the pebble bed as the best of the bunch, and when you have TWRs that low, you burn through a lot more propellant getting out of the atmosphere and into orbit.

In KSP an SSTO is a lot easier.  There's so little delta V required for orbit compared to Earth.  But NTRs will still have the same issues.  Using something other than LH2 for a propellant in NTRs lowers their ISP and raises their TWR, and that's close to what we see in KSP's NTRs.  But they only function for atmospheric flight because Kerbin is so small.  NTRs will always be for orbital and deep space use in my opinion.  They don't care what you feed them, but obviously there's limits.  

So, on to "why aren't there Oxidizer slurping NTRs?".  Realistically, you add NTRs to get better ISP than chemical rockets.  That comes at a price in TWR.  And for maneuvering after you'd got out of your gravity well, that's just fine.  A more extreme version of this trade off is the electrical drives, ion, plasma, etc.  Stuff all thrust, but truly awesome ISP.  Now, to maximize ISP in an NTR you use LH2.  There's just nothing that comes close to the low molecular mass.  And there's a chunk of your propellant that will dissociate at the high temperatures and result in some of your exhaust products being atomic hydrogen, half the mass again.  Mysterious liquid fuel could be anything, but assuming it's analogous to RP-1 aka refined kerosene, then it's molecular mass is much higher (and variable).  Again, some of it would break down and do strange chemical things during it's passing through a hot reactor core.  But, the end result is lower exhaust velocity (a given temp is a fixed amount of energy per molecule, so larger molecules are moving slower for the same temp).  This becomes a trade off, higher thrust (same energy, but now it's in higher mass, slower molecules, which results in higher momentum) but uses more mass, aka lower ISP.  But, by choosing NTRs, we already decided ISP was what we wanted.  So, anything other than LH2 is a secondary choice.  Now, the other issue is the effects each propellant has.  Carbon chains can cause coking.  When something like kerosene is heated really hot, it starts to break down, and the result is a mixed bag, but some of it will be carbon-carbon bonding, resulting in solids.  Considering graphite is a fairly common material in nuclear reactors, this is only likely to cause trouble if it starts blocking flows.  S, you probably can run NTRs on RP-1.  Even better would be methane, which doesn't tend to coke things, being just a single carbon with hydrogen.  Being the lightest hydrocarbon, it's also the preferred one for NTRs.

And here comes the problem with Oxidizers.  They oxidize.  At high temperatures, they oxidize a lot.  If you run liquid oxygen through a high temperature reactor core, the metal, including the fissionable fuel, and the carbon moderators, will start burning.  There are some metals that are immune (up to a point) for a while, but you'd need to make a lot of the systems out of this.  If you read up on the Russian/Soviet full flow rocket cycles, and how the Americans didn't believe it for a long time, you get a hint of the sort of thing I'm talking about.  But pushing oxidizer through an NTR would be worse.  It wouldn't be one pre-burner, one turbine, and then on to a balanced combustion chamber.  It would be everything.  And it's not like you can use exotic stainless as a fission fuel.  And, the whole thing needs to deal with neutron embrittlement, high temperatures, and retain it's strength.  I doubt there's any material known that covers off all the requirements for some sections.

But, it is KSP.  If you're fine with super science, just make a MM patch to pass oxidizer through the stock NTR.

[sturmhauke]

1 hour ago, TiktaalikDreaming said:

Regarding any Nuclear powered SSTO engines, you're inhibited by the fact that their always going to be heavy...

...But, it is KSP.  If you're fine with super science, just make a MM patch to pass oxidizer through the stock NTR.

 

I'll note here that the Kerbal Atomics mod meets all these requirements.

[wumpus]

On 3/26/2019 at 11:37 AM, JadeOfMaar said:

The one other SSTO engine I'd personally recommend is a scramjet, the kind of engine that's dead up to Mach 4 and then works up to idk, Mach 13 (as far as construction materials and the intake itself will allow) but Isp will be pretty low (for a jet engine). It's on the same level as the SABRE, as I see it. Sadly, with the size of the stock planets (namely Kerbin) a scramjet easily becomes OP or much more dead weight and trouble than it's worth.

Mach 4 to 7 operating range...at stock scale... isn't much justification for the extra mass of the number of scramjets needed to reach orbital speeds and the extra turbojets needed to push them. At 2.5x and up, then it's undeniably worth hauling around. Orbital speeds start at Mach 11.

The X-43 could operate from mach 4 to mach 7 (I think 6.8 was a more accurate number).  Top speed was mach 9.6, but that was "it appears that the vehicles acceleration was positive an non-zero, but the error bars are way outside that" and did not include any payload and quickly lost thrust.  But even these levels rely on Kerbin's low orbital velocity (although NASA clearly saw a path to an effective first stage via SCRAMJETS).