AeroGav

Ammonia / Hydrogen Peroxide propellant properties?

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I'm starting to mess around with modded KSP again,  and am brainstorming for a near future,  Space Shuttle 2.0 concept.

To this end I've installed Ferram Aerospace and Real Fuels.

The orbiter is going to have liquid ammonia tanks in the fuselage feeding a nuclear thermal rocket.   The TWR can be below one as it will use wings for lift in the upper atmosphere,  and I'm proficient at doing these "wave rider" style ascents.

Why Liquid Ammonia , and not Hydrogen ?

  • It is storable, so this can double as our OMS system.
  • It is liquid at room temperature with a modestly pressurized tank, which is a good thing given that the Columbia disaster was precipitated by a chunk of ice breaking off a cryo tank.
  • Relatively non toxic, at least compared to the hypergols
  • Unlike Methane,  it won't leave carbon deposits  sticking to the inside of the reactor.    Scraping those off is a job for someone you don't like.
  • It is much denser than liquid hydrogen.    This is important because Ferram does not model compression lift, so lifting body designs like Skylon that have plenty of internal volume and reasonably good hypersonic lift/drag ratio aren't possible.     The fuselage needs to be slender like on a conventional supersonic jet.

FWIW,    NTR are commonly quoted as giving the following ISP with different propellants - 

Liquid Hydrogen  - 900

Methane - 640

Ammonia - 520

.

However,  we've also got some liquid volume in our wing tanks,  what to put there ?  Due to icing, cryogens are out of the question.   Ammonia also appears to be out - the pressures to keep it liquid at room temperature are not large, but too high to make a mass efficient non-cylindrical tank.       

One option was Kerosene.   Combined with a bit of LOX tankage in the fuselage,   we could run a Kerolox engine to assist the NTR during the early part of the ascent, when the craft is most heavy with fuel.

However,   we could fill them will High Test Peroxide instead.      This could be injected into the Ammonia stream that's just been heated by the reactor as an "Afterburner", rather like the LANTR proposal, again during the early part of the ascent.

 

2NH3 + 3H2O         =   2N+   3H2O      

 

Any idea what kind of ISP, propellant ratios and thrust i can expect in this config ?

Stoichiometric   hydrogen/oxygen  has a propellant ratio of  1KG hydrogen being burned with 8KG liquid oxygen.       Actual rocket engines run rich, to take advantage of he lower molar mass of hydrogen,   ratio of 5:1 or 6:1 .

LANTR   could run richer still,  3 to 1 or less,  because combustion does not have to supply all the heat to expand the products, thanks to the reactor.

According to this PDF,  https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930085381.pdf  page 41,      the ISP of this combo when burned as a chemical rocket is rather low ,  253 seconds, but same source quotes hydrolox as about 345, which also seems low ball - are these sea level ratings?.   Unlike most fuels,  Stoich gives best ISP,  with Ammonia about 42% of the propellant by mass. 

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19950005290.pdf

As regards the afterburner,  i'm wondering if we can meaningfully extrapolate anything from the LANTR data - 

f9CbKGv.png

TWR doubles at a mixture ratio of one (an oxidizer volume only 20% of that which gives best ISP in  chemical hydrolox),  while ISP only drops a third of the difference between the hydrogen NTR value and the chemical hydrolox value.

So,  dodgy guesstimation time -

NTR (Ammonia) ISP - 520

Ammonia / Peroxide ISP - 330 

Afterburner ISP - 460 ish

Not bad for relatively dense, room temperature propellants (the alternative are hypergolics).

What about TWR ?

The in-game NERV engine appears to be based on 1960s technology,  with a mass of 3 Tons and 60kn of thrust.     If we look at its late 80s counterpart,  Project Timberwind,  it does slightly better -

https://en.wikipedia.org/wiki/Project_Timberwind    (nothing to with Justin Timberlake)

Timberwind 45  has half the mass (1.5 tons)   and thrust has improved just a bit,  to 441kn

That's still only half the TWR of the Space Shuttle Main engine,   and the Merlin 1D (nothing to do with boy band One Direction) that SpaceX use on their Falcon series,  has a TWR 50% higher than the SSME.   But still,  Timberwind is nowhere near the lead sled that is NERV.

On the other hand,   Orbital Velocity in stock KSP is only 1/3 real life, so we don't want our engine too overpowered.   Why not install real scale solar system ?  Well,   then you run into FAR's inability to model compression lift and  before you're halfway to orbit,  you'll be seeing lift to drag ratio below unity.

One major "known unknown" (thanks, Donald Rumsfeld)  is the combustion speed of ammonia / HTP mixtures.    LANTR  injects oxygen  after the throat, at the start of the bell nozzle itself, so as not to cause back pressure/choke problems for the reactor which is optimised for pure NTR operation.     But,  flow in the bell nozzle is supersonic,  so not a lot of time for combustion.   If combustion takes too long,  the mixture will have travelled some distance down the nozzle before reacting,  and thus will not get to expand as much as it should before exiting the nozzle.

 

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13 minutes ago, Steel said:

According to this post you get an ISP of about 260 s for HTP(95%)/Ammonia mixture.

He's giving a sea level rating of 380 to LH2 LOX,  so just under 310 in Vacuum?

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8 hours ago, AeroGav said:

This is important because Ferram does not model compression lift, so lifting body designs like Skylon that have plenty of internal volume and reasonably good hypersonic lift/drag ratio aren't possible.


If you're basing a next generation space craft on the limitations of a low fidelity simulation built on top of a low fidelity simulator game...  Then you're basing your choices on a model that bares no useful relationship to reality.   Might as well use an Ouija board.

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1 hour ago, DerekL1963 said:


If you're basing a next generation space craft on the limitations of a low fidelity simulation built on top of a low fidelity simulator game...  Then you're basing your choices on a model that bares no useful relationship to reality.   Might as well use an Ouija board.

 

Derek,  there's a couple of ways of reading this statement.   

Hostile reading 

  1. "you are not aware of the limitations of the game" 
  2. "this is not a worthwhile exercise so you should cease and desist"
  3. because "this kind of fanboyish  garbage is annoying "

More liberal interpretation :

That you also think Ferram is not perfect and the issue I identified with hypersonic aerodynamics is a show stopper in your opinion.   Or something like that.   

 

The thing is there is not much actual information in your post which makes it more likely to be read as a put down than something constructive.   Also,   from our previous dealings with each other,  If you had anything to say about this project,  it wouldn't be positive !

 

I'm struggling with modding engine config files anyway.    Might take another look at this next week,  if i decide it's worth it.

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3 hours ago, AeroGav said:

The thing is there is not much actual information in your post which makes it more likely to be read as a put down than something constructive. 


The thing is, there's all the information there that you need.

If you choose to treat bare facts as hostile or a put down, that's something to discuss with the man in the mirror, I bear no responsibility for your choices.

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19 hours ago, AeroGav said:

Liquid Hydrogen  - 900

Methane - 640

Ammonia - 520

520s for ammonia sounds a little high to me.  Based on some calculations I did several years ago, I'd say it's more like 450s.
 

19 hours ago, Steel said:

According to this post you get an ISP of about 260 s for HTP(95%)/Ammonia mixture.

FYI, the "Bob B." posting in that forum is me.

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5 hours ago, OhioBob said:

520s for ammonia sounds a little high to me.  Based on some calculations I did several years ago, I'd say it's more like 450s.
 

FYI, the "Bob B." posting in that forum is me.

I got my figures from this site, http://www.projectrho.com/public_html/rocket/enginelist.php#ntrsolidcore

it mentions 3000k, and quotes

Exhaust velocity (H2) 8,093 m/s
Exhaust velocity (CH4) 6,318 m/s
Exhaust velocity (NH3) 5,101 m/s
Exhaust velocity (H2O) 4,042 m/s

 

BTW, don't go to that site unless you don't mind losing an afternoon.

 

When you divide those exhaust velocities by 9.8m/s this converts into an ISP of 825 for Hydrogen,  644 for Methane and 520 for Ammonia.    I'm all for low balling the numbers a bit and playing it safe,  not only is this thing carrying people,  it's going in an atmosphere and is meant to be re-usable.   However  Project Timberwind in 1991 supposedly had 1000 ISP from hydrogen.

 

Regarding LANTR's afterburner,   it is correct that adding even one eighth of the amount of oxygen as required to burn the Hydrogen stoichiometrically doubles the mass flow, because oxygen is so much denser than H2.

However, is that the ONLY factor?  Bear in mind,  the oxygen never goes through the reactor, it is dumped into an afterburner at the top of the nozzle.     The combustion of the hydrogen and oxygen must raise the temperature of the gases , promoting greater expansion.      I mean, if combustion of 4KG liquid oxygen with 1KG liquid oxygen is able to take these materials from cryogenic to hotter than the core of an NTR, even though half the hydrogen is not reacting because we're pig-rich,    then if we're starting with gases that are already at  2700k from passing through a reactor, then they're going to end up even hotter surely?

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2 hours ago, Xd the great said:

Did someone mention firing a nuclear rocket engine? In atmosphere?

You have over a thousand posts so I am sure you must know this by now,  but in case any person reads this and gets the wrong idea..      The exhaust of a solid core nuclear thermal rocket is not radioactive.   The fuel and the byproducts of the reaction stay inside the reactor,   unless it has a meltdown  It's going to emit x rays and gamma rays when operating because for weight reasons it's probably only shielded on the side that faces the crew module.  You don't want to get closer to a mile to this thing when the engine is firing, for that reason.   But  X rays and Gamma rays are not persistent,  as soon as the ship leaves the area or cuts its engine they are gone.

What the general public  fears about nuclear power is persistent stuff,  ie. when the environment gets contaminated with atoms of radioactive fuel or waste from a containment breach.    These atoms are unstable and each one will, after  a random period of time,  undergo fission and when that happens, and X ray or Gamma ray is kicked out,  hence the ticking geiger counters.    This is bad if it happens to be inside your body at the time,  because the contamination got into your water supply.

In terms of a  launch vehicle with an NTR,  there is obviously the risk of launch failure.   Apparently the reactor itself is built of very strong stuff and can be made to survive  a terminal velocity fall to the ground (that's why they are so heavy) but obviously any cooling systems will have been destroyed,  even shut down reactors produce residual decay heat as the reaction byproducts under go further decay to their final products.  The level of decay heat is dependent on how long the reactor has been run for and at what power level.    The reactors in a power station operate for months on end at high output,   so decay heat can be substantial after an emergency shutdown,  which is why Fukushima melted down after the cooling system failed even though the reactor was shut  down as soon as the earthquake hit.

Would i be having to fend off arguments like this if the thread was in "The Spacecraft Exchange?"

I am trying to build a mod shuttle system because all the stock ones i could come up with have been awful to fly and made no sense with the game mechanics.     The Role Play / Science Fiction aspects of this are just a bit of fun

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@AeroGav 

As much as I like ProjectRho I would take it with a grain of salt; although I have used it for reference in the past, some of its material is a little too optimistic for current technology or assumes higher levels of technology.

Re: exhaust: Mostly not radioactive though core erosion is a thing. More so in the early prototypes of Project Rover than in the final engines before the project was shut down though I don't know if it ever would have been solved 100% (100% meaning NO fuel ending up in the exhaust) but having said that, as you said it's for a game. People arguing against you doing this on those grounds ... just ignore them. It's your game and you can play it as sci-fi as you want. Who even knows if Kerbals are susceptible to radiation in the first place? 

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7 hours ago, AeroGav said:

I got my figures from this site, http://www.projectrho.com/public_html/rocket/enginelist.php#ntrsolidcore

it mentions 3000k, and quotes

Exhaust velocity (H2) 8,093 m/s
Exhaust velocity (CH4) 6,318 m/s
Exhaust velocity (NH3) 5,101 m/s
Exhaust velocity (H2O) 4,042 m/s

 

That could be then, they're basing their calculations on a hotter temperature than I did.  But taking temperature into consideration, they're numbers for H2 and CH4 seem a little low to me.

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11 hours ago, OhioBob said:

Here is another thread from many years ago in which we got into a big discussion about nuclear thermal rockets:

https://www.thespacerace.com/forum/index.php?topic=2878.30

 

Are you aware that your postings there were used as reference material for the original NTR engine configurations for Real Fuels? (although some of the isp/thrust ratings get munged a bit during tech level upgrades; I'm not sure they would survive proper vetting and I never got around to fixing them)

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12 minutes ago, Starwaster said:

Are you aware that your postings there were used as reference material for the original NTR engine configurations for Real Fuels?

Yep, @NathanKell told be about that.

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2 hours ago, AeroGav said:

You have over a thousand posts so I am sure you must know this by now,  but in case any person reads this and gets the wrong idea..      The exhaust of a solid core nuclear thermal rocket is not radioactive.   The fuel and the byproducts of the reaction stay inside the reactor,   unless it has a meltdown  It's going to emit x rays and gamma rays when operating because for weight reasons it's probably only shielded on the side that faces the crew module.  You don't want to get closer to a mile to this thing when the engine is firing, for that reason.   But  X rays and Gamma rays are not persistent,  as soon as the ship leaves the area or cuts its engine they are gone.

I have a lot of posts myself, but don't expect NTR engines to be fired in all but the highest parts of the atmosphere.  Of course this has more to do with the low thrust they have, and that any time they can be even used as a last gasp to put the things in orbit would likely be well outside the atmosphere (I've let my kebal tugs claw their way into orbit, but don't recommend it).

Isp (NTR with water mass) = 412

Isp (maximum water temperature + rich H2) = 450 (SSME)

Seems a bit high for NTR water, although new materials *might* allow for higher nuclear temperatures (although I really doubt you want your nuclear core to melt...).

https://arstechnica.com/science/2018/10/new-material-could-up-efficiency-of-concentrated-solar-power/

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Well,  here's the config i finally settled upon -


,

Spoiler

 


+PART[nuclearEngine]:FOR[RealFuels_StockEngines]
{
    @name = nuclearEngine-trimodal // If you're using the stockalike configs the original name would have conflicted
    @author = NovaSilisko, Starwaster, AeroGav
    @title = LV-N Atomic Rocket Motor, trimodal
    @mass = 0.85

    @description = Despite the big scary trefoil painted onto the side of this engine, its radioactive exhaust, and tendency to overheat, the LV-N Atomic Rocket Motor is harmless. Mostly. This one can inject LOX into the nozzle stream to increase thrust at the expense of fuel efficiency.

    MODULE
    {
        name = MultiModeEngine
        primaryEngineID = Regular
        primaryEngineModeDisplayName = Regular
        secondaryEngineID = Afterburner
        secondaryEngineModeDisplayName = Afterburner
    }


    @MODULE[ModuleEngines*]
    {
        @name = ModuleEnginesRF
        PROPELLANT
        {
            name = LqdAmmonia
            
            ratio = 100.000000
            flowMode = STACK_PRIORITY_SEARCH
            DrawGauge = true
        }
        !PROPELLANT[Kerosene] {}
        !PROPELLANT[LqdOxygen] {}
        !PROPELLANT[LiquidFuel] {}
        !PROPELLANT[Oxidizer] {}
        %engineID = Regular
        @minThrust = 0
        @maxThrust = 110
        !atmosphereCurve{}
        atmosphereCurve
        {
            key,0 = 0 520
            key,1 = 1 300
        }
    }

    MODULE
    {
        name = ModuleEnginesRF
        engineID = Afterburner
        directThrottleEffectName = powerflame
        runningEffectName = powersmoke
        thrustVectorTransformName = thrustTransform
        exhaustDamage = True
        ignitionThreshold = 0.1
        minThrust = 0
        maxThrust = 196
        heatProduction = 100
        fxOffset = 0, 0, 1.0
        PROPELLANT
        {
            name = LqdAmmonia
            
            ratio = 116
            DrawGauge = True
            %resourceFlowMode = STACK_PRIORITY_SEARCH
        }
        PROPELLANT
        {
            name = HTP                
            ratio =  70
            DrawGauge = True
            %resourceFlowMode = STACK_PRIORITY_SEARCH
        }
        PROPELLANT
        {
            name = EnrichedUranium
            ratio = 0.00000000001
        }
        atmosphereCurve
        {
            key = 0 420
            key = 1 330
        }
    }
    !MODULE[ModuleEngineConfigs],*{}
    MODULE
    {
        name = ModuleAlternator
        OUTPUT_RESOURCE
        {
            name = EnrichedUranium
            rate = -0.0000000005
        }
        OUTPUT_RESOURCE
        {
            name = DepletedUranium
            rate = 0.0000000005
        }
        OUTPUT_RESOURCE
        {
            name = ElectricCharge
            rate = 3.0
        }
    }
    MODULE
    {
        name = ModuleGenerator
        //resourceThreshold = 0
        isAlwaysActive = true
        OUTPUT_RESOURCE
        {
            name = ElectricCharge
            rate = 1.5
        }
        OUTPUT_RESOURCE
        {
            name = DepletedUranium
            rate = 0.0000000005
        }
        INPUT_RESOURCE
        {
            name = EnrichedUranium
            rate = 0.0000000005
        }
    }
    RESOURCE
    {
        name = EnrichedUranium
        amount = 5
        maxAmount = 5
    }
    RESOURCE
    {
        name = DepletedUranium
        amount = 0
        maxAmount = 5
    }
}

.

 

ISP of 520 in NTR mode, SL 300 (assumed similar nozzle to RS25),  thrust of 110kn,  mass 0.85T

Yes one large engine makes more sense an am not sure you can put a critical mass of reactor together that small,  but it looks really silly unless you can mod something like a Rhino visual model on and i don't know how to do that.   Maybe all 3 turbopump/bell nozzles are running off the same reactor?

Thrust is 196kn in HTP Afterburner mode,  Vac ISP 420 and SL to 330.   I made an assumption that the extra mass flow and reheating effect of the combustion would make it less overexpanded.   NH3 flow rate is about the same in both modes.

I had a big rethink about the flow ratios for HTP afterburner.      Running an fuel : oxidizer ratio of 4:1 meant i was running out of liquid ammonia in the fuselage way before the wings were out of HTP, even if i stayed in afterburner mode the whole flight.   HTP is about twice as dense as Ammonia.       Thinking about it,   in a hydrolox engine the air fuel ratio is 2:1 and each oxygen atom combusting is heating  products with a total atomic weight of 20 by 3200k.     Assuming an NTR core temp of 2750K and stuff losing another 500 or 600 K from expansion by the time it hits the afterburner,  a small amount of LOX is able to bring the exhaust stream up to temp in LANTR.   But the exhaust products of a NH3 / HTP rocket have much greater atomic weight, so  i came up with a mixture that's only 60% rich of Stoich for the afterburner.Some small Kerolox boosters help us up to mach 1.5 or so.    Reliant engines are barely enough for a vertical launch - it comes off the pad like a Saturn V.     The modded NERVs also lack Gimbal,  but TBH it's not such an issue when you don't have the off - axis thrust the real orbiter did

Spoiler

 

J2IOpc9.jpg

 

IZaj66h.jpg

 

 

This kind of ascent is even worse for heating than re-entry, because you are heavy with fuel, and operating at a lower angle of attack (because you are trying to minimise rather than maximise drag).   But , the propellant heading to the engines go through a heat exchanger for some kind of cooling loop, an option that's not available on re-entry.  At least you're getting some heating of the fuel in exchange for all the friction.

 

VZ1xTkd.png

Science Lab in orbit , yay.   Now do that on a real scale solar system...   :-o

 

Edited by AeroGav
forgot 1 pic

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2 hours ago, Starwaster said:

Re: exhaust: Mostly not radioactive though core erosion is a thing. More so in the early prototypes of Project Rover than in the final engines before the project was shut down though I don't know if it ever would have been solved 100% (100% meaning NO fuel ending up in the exhaust) but having said that, as you said it's for a game. People arguing against you doing this on those grounds ... just ignore them. It's your game and you can play it as sci-fi as you want. Who even knows if Kerbals are susceptible to radiation in the first place? 


If the discussion is to be limited to game topics and isn't going to be about actual concerns about real life science and engineering...  Then it doesn't belong in the Science & Spaceflight sub forum.

That being said, the concerns about firing in atmosphere aren't limited to radioactive contamination.  If this thing is going to spend the majority of it's working life in space, then it makes no sense to fit it with anything but a proper vacuum nozzle... and that means firing it in atmosphere brings underexpansion and all it's associated problems to the table.

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53 minutes ago, DerekL1963 said:


If the discussion is to be limited to game topics and isn't going to be about actual concerns about real life science and engineering...  Then it doesn't belong in the Science & Spaceflight sub forum.

That being said, the concerns about firing in atmosphere aren't limited to radioactive contamination.  If this thing is going to spend the majority of it's working life in space, then it makes no sense to fit it with anything but a proper vacuum nozzle... and that means firing it in atmosphere brings underexpansion and all it's associated problems to the table.

Alright, fair enough.    I'm probably being too thin skinned or too much of a "snowflake" here.    I posted in this section of the forum hoping for more info on certain propellants  than i might get in SpaceCraft Exchange or on the Shuttle Challenges and Mission Ideas thread.          So,  this is where I am,  and if someone wants to criticise the entire concept and tell me i shouldn't undertake it at all that's part of the deal.    People who don't like the Space Shuttle,  don't like space planes, and who don't like nuclear propulsion in the ascent to orbit are a lot more likely to be of that opinion.     

I felt as though some of the comments were "cheap shots" and were just derailing the discussion, but in the end it's only my opinion and I need to man up and learn to take it.

As regards vacuum nozzles..    well, the real STS has them as will the SLS so if its a mistake i'm not the first person to do that.     Though the boosters provide most of the thrust up to 10km or so anyway, by which point vacuum nozzles are outperforming sea level ones,  and by that point it still has a very long way to go till orbit velocity.  

Why do i insist on building these annoying winged craft that fire their nuclear engines within the atmosphere ?  Because otherwise I don't see us ever having mostly SSTO or mostly reusable vehicles.  Also I just like building these kind of craft, but because of the forum i'm in as you point out i can't hide behind that shield.

 Flyback boosters or just learning to mass produce really cheap expendable launchers might be the better approach,  perhaps yourself  and @wumpus and @Xd the great think along those lines?

I had a similar thread concerning Lunar Oxygen harvesting,  someone kept posting one line objections.   He eventually declared his own position - that he was against visits to any celestial body, that we should focus on space stations and orbiting power arrays, which made his earlier postings more understandable from my point of view.   Everyone's entitled to their own dreams and opinions,  though if you insist on having the last word you could shoot back with "this thread is about your idea, mine are not up for discussion"   and  " opinions got nothing to do with it,  it's about cold hard facts " (the facts back me up AND YOU;RE WRONG  being strongly implied :-)

 

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Alright,  I'm in a much better mood now that the damn thing is finally finished  than I was after two days of editing CFG files in Notepad and reloading KSP every time the game bugged out.

If you think this thread should be moved,  let's tag a mod and get it done.   

I'm wondering what to try next.    Non nuclear looks like it's pretty high on the list.

So, no cryogens in wings, and I want to avoid nasty hypergolics that made the space shuttle so expensive to service (all the technicians having to wear space suits just like the astronauts).   Should the fuselage tanks be allowed cryogens?  Unless we have Kero/HTP at 250 seconds as our sole fuel,  i guess we'd have to allow that.   Ice hitting the wings and causing another Columbia disaster ?  Well,  I suppose it could have been designed out with enough effort,.   More robust materials on vulnerable TPS sections even if they require active cooling as a result.  Or better tank insulation /warmed skin layer to inhibit ice formation.    Also, SpaceX seem to consider Methane and Oxygen to be storable propellants now.

So -

1. Kerosene in wings,   Methalox in fuselage , boosters of whatever.  Have kerolox and methalox engines on orbiter, the kero ones providing a bit of extra slam down on the deck

Or

2. Hydrolox fuselage with Kerosene wings.

Not all the Kerosene gets used on launch,  some (and some LOX) is kept behind for use in orbit as OMS - also verner thrusters can run off this stuff.

 

What about my objection to Hydrolox on account of density?    Well the thing is , hypersonic lift/drag ratio is no longer important.    In KSP, wings can assist ascent using low TWR  NTR and jet engines.  But since we're using neither,  its easier to just have a high TWR and get out of the atmosphere ASAP.   Only unlike the original shuttle,   this one does not need to crossrange glide on re-entry to land back in USA after being in an inclined orbit over  enemy territory to deploy a spy satellite  .   I suppose we''ll keep the wings so we can still call it a shuttle.

Given all this, might as well have an external tank...  but i don't think i can handle the off-axis thrust this comes with, atmosphere or no.

 

So I'm tending towards 1)   if we can get by on Methalox ISP..

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5 hours ago, AeroGav said:

As regards vacuum nozzles..    well, the real STS has them as will the SLS so if its a mistake i'm not the first person to do that.


No, the Shuttle had compromise nozzles because they had to perform useful from sea level to orbit while also avoiding the problems with underexpansion.  They could get away with this because the SRB'd did most of the heavy lifting lower down.
 

3 hours ago, AeroGav said:

So, no cryogens in wings, and I want to avoid nasty hypergolics that made the space shuttle so expensive to service (all the technicians having to wear space suits just like the astronauts).


Only the hypergolics techs had to wear SCAPE suits, and that only when hypergolics were being handled.  (They cleared the OPF or VAB during those periods.)  It was a contributor to overall expense...  But not the only one.  Far from the only one.
 

5 hours ago, AeroGav said:

I had a similar thread concerning Lunar Oxygen harvesting,  someone kept posting one line objections. 

Factual errors don't usually take more than one line to correct.  Any assumptions about my motivations are, again, something you need to discuss with the man in the mirror.  I am not responsible for your assumptions.

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5 hours ago, AeroGav said:

and I want to avoid nasty hypergolics that made the space shuttle so expensive to service (all the technicians having to wear space suits just like the astronauts).


Something else that occurs to me... "saving money" and "nuclear propulsion" are not concepts to be found on the same vehicle.  Nuclear is expensive.  The handling and safety precautions even more so.

Edited by DerekL1963

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