Aerojet's Hydrazine replacement, what about oxidizer?

[AeroGav]

As you've probably heard by now,  liquid fuels used in spacecraft fall into one of two categories

1) cryogenics - those relying on hydrogen or methane as the fuel, and oxygen as oxidizer.  Best ISP but can only be used for launch due to boiloff. Mid course corrections, return journeys must be fuelled by

2) storable propellants - stuff that's liquid at about room temperature.  Apart from the Kerosine/Hydrogen Peroxide combo used by the UK in the 1960s, this generally means really nasty stuff.  Hydrazine, fuming nitric acid and derivatives - corrosive, carcinogenic, toxic - and don't forget to put "highly" in front of each of those adjectives.  Technicians working with the stuff are more or less dressed in a full spacesuit down on earth, it's that bad.

Along comes the https://en.wikipedia.org/wiki/Green_Propellant_Infusion_Mission

which uses https://en.wikipedia.org/wiki/Hydroxylammonium_nitrate instead of hydrazine.

ISP is a percent or two higher, and it's significantly (40-50%) denser.  It's also less volatile and far less toxic - either this woman is very brave or it really is ok to swill about in an open beaker

Now, in KSP we have just 3 fuels

Liquid Fuel, Oxidizer, and Monoprop.

Given that there is no boiloff, and given that ISPs given seem a low compared with state of the art, and the high densities, i am guessing that LF/O are both meant to be storables.

LF cannot be Kerosine, because it wouldn't work in a NERV long term (after a while, soot would clog the heat exchanger).   Hydrazine or this new HAN fuel must be what we are dealing with.    Then again, RAPIER engines require a cryogenic to work, so that's a bit of a mess.

Anyway, second question.  Anyone who knows a bit more about chemistry able to speculate if this new HAN can be used with an oxidizer rather than just as a monoprop for better ISP,  and are there any oxidizer candidates with similarly friendly properties?

Are there any house rules you can use to try make KSP more realistic with regards to real world fuels?

1. treat LF/O  as hypergolics.   That means no use of the RAPIER engine as a house rule.

2. treat LF/O as as cryo.   That means,  any LF/O  used to power a rocket engine or RAPIER must not be stored in a wing/strake tank and any fuel in that tank must be jettisoned shortly after making orbit to simulate boiloff.      LF stored in wings or used to power whiplash, panther or LV-N is assumed to be Hydrazine or HAN.

[Streetwind]

8 hours ago, AeroGav said:

LF cannot be Kerosine, because it wouldn't work in a NERV long term (after a while, soot would clog the heat exchanger).   Hydrazine or this new HAN fuel must be what we are dealing with.    Then again, RAPIER engines require a cryogenic to work, so that's a bit of a mess.

Word of advice: don't try to make sense of something that is very clearly abstracted away from real chemistry.   You can find an analogue for the rocket engines (Aerozine 50, N2O4? something like that) but it very obviously breaks down when you look at any other engines. KSP is not modelling any specific propellant chemistry. It made up a fuel, gave it generic names, and assigned it whatever Isp's it needs to have.

As for your other question: John D. Clarke talks about experimenting with all sorts of ammonium nitrates in his (out of print) book "Ignition!", which you can find as a free PDF download around the web. He examined them for use as a monopropellant, and found them to be good candidates energy-wise, but sadly possessing unfortunately limited temperature tolerances that nobody would buy (they freeze way too easily in space).

Since the idea is at least 40 years old, I'm not sure what AF-M315E does differently today. Maybe they have found or synthesized a new additive that drops the freezing point way down, which was not available to Mr. Clarke. Or maybe he just never looked at the hydroxyl variant; he never mentions it by name anywhere. Though it is unlikely, considering that he reports testing a wide variety, and repeatedly expounds how reliably a trained propellant chemist can guesstimate the usefulness of a substance as a propellant just from one glance at its structural formula. Or maybe the propellant was discarded for yet different reasons, such as there being no suitable catalyst for it, or it being too aggressive to the engine, which modern science has managed to fix. Or maybe the poor temperature tolerance was simply no longer a problem - perhaps the tanks have simply gained heating elements. Who knows.

[wumpus]

I don't begin to understand the point about NERVA.  The reason you use H2 in a NERVA is entirely due to its low mass.  You heat up the low mass H2, and get an extreme Ve out of it, thus giving you an ISP of 800.  If your "fuel" (really reaction mass) going into the NERVA is more massive than water, then you can't reach Hydrolox's ISP.  If it is more massive than kerlox's mix of H2O+CO2, than you can't reach kerlox's ISP.  The moment you aren't willing to bring H2 along, you can forget about NERVA.

Randal Monroe's graph of "how well I know orbital mechanics" could be equally labeled "how well I understand the rocket equation".  Understanding that is critical to understanding rocket science at all.  There's always more to learn from that equation, and it explains why you are stuck with H2 for a NERVA.

[AeroGav]

35 minutes ago, wumpus said:

I don't begin to understand the point about NERVA.  The reason you use H2 in a NERVA is entirely due to its low mass.  You heat up the low mass H2, and get an extreme Ve out of it, thus giving you an ISP of 800.  If your "fuel" (really reaction mass) going into the NERVA is more massive than water, then you can't reach Hydrolox's ISP.  If it is more massive than kerlox's mix of H2O+CO2, than you can't reach kerlox's ISP.  The moment you aren't willing to bring H2 along, you can forget about NERVA.

Randal Monroe's graph of "how well I know orbital mechanics" could be equally labeled "how well I understand the rocket equation".  Understanding that is critical to understanding rocket science at all.  There's always more to learn from that equation, and it explains why you are stuck with H2 for a NERVA.

I don't know if this reflects reality but the Interstellar mod allows NERVA to use different fuels.   As you say, there is a general trend of decreasing ISP with denser fuels, however, hydrazine is a standout because it dissociates in the heat of the engine and the products are low molecular weight.

Keeping things as simple as possible, perhaps instead of LF, OX, and MONO, we should have had -

Cryo - Low density fuel with high boil off.   Cannot go in wing tanks. 

OX -  High density oxidizer with low boil off rate.  Cannot go in wing tanks.   Insulated tanks available to decrease boil off, refrigerated tanks that eliminate it at cost of electrical power.

Storable - High density with zero boiloff.

.. and we could have the following engine categories

NERV  + Rapier  - can use only Cryo fuel.  Rapier also uses OX in closed cycle mode

Rockets (cryo ) - use Cryo + Ox,  Storable + Ox, or Storable only (mono thrusters) in descending order of ISP

Jets - can use Cryo or Storable fuel

[wumpus]

Interesting.  I knew there was a real fuels mod, but had no idea that interstellar had separate fuels *without* realism.  NERV+rapier makes no sense: the output from the rapier is already too hot for the NERV, and the whole point of the rapier is to cool down the input fuel (so it doesn't want the output from the NERV).  I'm assuming that it acts as a single engine.  For interplanetary flight they would make sense, as long as you used the NERV in orbit or transfers and only fed it hydrogen.

I wouldn't look to Interstellar for chemical information.  Maybe real fuels, but you will still likely need a sanity check.  Clark is obvious the ideal source, but I am wary of the legality of the pdfs floating around (I'd also assume that the original just isn't available.  Maybe some sort of interlibrary loan might be possible, but I wouldn't be surprised if they recommend the pdf).

[sevenperforce]

Less on KSP and more on propellant choices...

The Wikipedia article says that HAN can be used as a bipropellant, but it doesn't say how, and I can't figure out how that would work. It has both hydrogen and oxygen attached, so what would it be burned with? Pretty cool monoprop though. It is still toxic, volatile, and likely carcinogenic, but it isn't quite as bad as hydrazine.

For NERVA options beyond pure LH2, I rather like anhydrous ammonia. It is about as dense as kerosene, disassociates easily, and the nitrogen doesn't have the residue problem that CH4 would suffer from. In an NTR with ammonia you get a specific impulse significantly above the best possible hydrolox engines with a TWR that is much better than standard nuclear rockets. Ammonia decomposes endothermically with catalysis, making it a superb coolant for an expander cycle NTR, and it is just cryogenic enough to be self-pressurizing without requiring insulation or particularly careful handling. Finally, it would be extremely amenable to either LOX-afterburning or a supercharged ramrocket cycle, which could mitigate its TWR disadvantage. Finally, it is cheap and available practically everywhere. 

[kerbiloid]

Btw, in KSP turbojets also use LiquidFuel, with IntakeAir (presumably, oxygen).
Not sure if turbojets can use hyperholics. At least, pure ones.

LiquidFuel: density = 0.005. unitCost = 0.8, hsp = 2010
Oxidizer: density = 0.005, unitCost = 0.18, hsp = 1551
MonoPropellant: density = 0.004, unitCost = 1.2, hsp = 3000

Water (in CRP): density = 0.001, hsp = 4183 // specific heat capacity (kJ/tonne-K as units)

LV-T30 ratio:  LiquidFuel = 0.9, Oxidizer = 1.1

I.e. their density is 5 times greater than water, ~5000 kg/m³. and fuel:oxidizer ratio ~1:1.

Edited May 22, 2016 by kerbiloid

[PB666]

21 hours ago, wumpus said:

I don't begin to understand the point about NERVA.  The reason you use H2 in a NERVA is entirely due to its low mass.  You heat up the low mass H2, and get an extreme Ve out of it, thus giving you an ISP of 800.  If your "fuel" (really reaction mass) going into the NERVA is more massive than water, then you can't reach Hydrolox's ISP.  If it is more massive than kerlox's mix of H2O+CO2, than you can't reach kerlox's ISP.  The moment you aren't willing to bring H2 along, you can forget about NERVA.

Randal Monroe's graph of "how well I know orbital mechanics" could be equally labeled "how well I understand the rocket equation".  Understanding that is critical to understanding rocket science at all.  There's always more to learn from that equation, and it explains why you are stuck with H2 for a NERVA.

 

16 hours ago, wumpus said:

Interesting.  I knew there was a real fuels mod, but had no idea that interstellar had separate fuels *without* realism.  NERV+rapier makes no sense: the output from the rapier is already too hot for the NERV, and the whole point of the rapier is to cool down the input fuel (so it doesn't want the output from the NERV).  I'm assuming that it acts as a single engine.  For interplanetary flight they would make sense, as long as you used the NERV in orbit or transfers and only fed it hydrogen.

I wouldn't look to Interstellar for chemical information.  Maybe real fuels, but you will still likely need a sanity check.  Clark is obvious the ideal source, but I am wary of the legality of the pdfs floating around (I'd also assume that the original just isn't available.  Maybe some sort of interlibrary loan might be possible, but I wouldn't be surprised if they recommend the pdf).

I cant point out all the ways you are wrong, first an ISP of 800 is an archaic ISP for a nuclear thermonuclear If that rocket was built today it could easily be 20 or 30% higher. Almost all the engines have got an ISP boost over the last 40 years. 

Why use hydrogen versus other fuels, why not use hyperglolics? 

The problem is two fold with a third caveot, The highest ISP nuclear rockets will need to run a long period of time, heating and accelerating as much as is structurally possible. 

The problem is that heat, time and high pressures on smaller and longer nozzle. Hyperglolics will ionize  after radioisotopic heating and deionize  along the metal surface before they exit the rocket, that means they also reionize on the metal, and that iincludes oxygen and nitrogen free-radicals, what you would have over the long burn times of thes rockets is a loss of structural integrity. To counter this you would need a larger bell and including the problem of reactive disintegration of the fuel. You would need further isolation of the fuel lowering the heat and pressure. One reason to use hydrogen is that it deionizes it very inefficiently degrades the metals. 

When those hyperglolic passes by the radioisotope which has a peak temp of 4000k it will not be in its final form. First it becomes :C: H H: H. O: .N:, and all sorts of variants therof, bi- and triatomic species. As these species accelarate the lose their energy of ionization and they combine. The total mass of the hyperglolic doesn't matter, howver the bell shape and reaction chamber will matter. That is a benefit with hydrogen, it only has 2 electrons in its molecular orbital and one in its atomic natural outer shell, when you spilt there are only a few species of known mass. This gives you a better means of optimizing design. But ISP on an NTR is due to heat transfer oer unit time to fuel mass, total. So that whatever fuel you have, if you provide the contact area to heat, ionize that fuel so that it ultimately accelerates you can achieve that exhaust velocity. 

A third issue is the absorption emmision frequencies of hydrogen, being fewer in the fact that you can accelerate hydrogen with rf. The means that if your vessel has solar panels, you can add rf to that systems and control in the ions much more easily than if you have alot spectrum to control. The problem with all of this is that NTRs are already extremely massive relative to their thrust. If you are going some place like the asteroid belt this comes in handy is that you always need more panel at your destination than you need when transferring. So  extra solar  panels and batteries for deeper space can be exploited for use in a hydrogen NTR. 

Getting a 1500 ISP NTR is plausible using hydrogen, the problem is doing that with the right mass/thrust ratio.

I never use NERVA in the game, the tanks are not designed for it, its not H2, there is no cryogenic recyler in the game, the engine is so heavy, and frankly if you are using gravity-well burns to perk your v, you really want an engine with a high TWR. Almost entirely i use mods with modern TWR and isp. This is not to say that there maybe a useful NTR in the future that is useful, but if you add up all the costs, in the game and rl, its not worth it. 

 

[Bill Phil]

1 hour ago, sevenperforce said:

Less on KSP and more on propellant choices...

The Wikipedia article says that HAN can be used as a bipropellant, but it doesn't say how, and I can't figure out how that would work. It has both hydrogen and oxygen attached, so what would it be burned with? Pretty cool monoprop though. It is still toxic, volatile, and likely carcinogenic, but it isn't quite as bad as hydrazine.

For NERVA options beyond pure LH2, I rather like anhydrous ammonia. It is about as dense as kerosene, disassociates easily, and the nitrogen doesn't have the residue problem that CH4 would suffer from. In an NTR with ammonia you get a specific impulse significantly above the best possible hydrolox engines with a TWR that is much better than standard nuclear rockets. Ammonia decomposes endothermically with catalysis, making it a superb coolant for an expander cycle NTR, and it is just cryogenic enough to be self-pressurizing without requiring insulation or particularly careful handling. Finally, it would be extremely amenable to either LOX-afterburning or a supercharged ramrocket cycle, which could mitigate its TWR disadvantage. Finally, it is cheap and available practically everywhere. 

Sugars have oxygen in them, alcohols too. They can be burned with oxygen.

I'd suggest hydrogen monoxide, at least for testing which oxidizer for the HAN.

[sevenperforce]

11 hours ago, Bill Phil said:

Sugars have oxygen in them, alcohols too. They can be burned with oxygen.

I'd suggest hydrogen monoxide, at least for testing which oxidizer for the HAN.

Ah, I misread the formula for HAN.

Sucrose (sugar) can burn because it has carbons linking the hydrogen and oxygen together. You add oxygen, which bonds to the carbon to form CO2 and leaves the oxygen and hydrogen to bond to each other. 

With HAN, however, you actually end up with two free oxygen atoms per decomposition. So HAN is an oxidizer, not a fuel, in biprop mix. Guess it could burn with just about any fuel then. HAN/hydrazine, anyone? **shudder**

[Jovus]

Point of order: At least for NTRs that have actually been built and tested (i.e. solid core NTRs in Project Rover) the core temperature is actually lower than that afforded by hydrogen combustion in, say, an RL10. The gains in I_sp come from the fact that you don't have to throw that heavy oxygen out the back.

[AeroGav]

3 hours ago, Jovus said:

Point of order: At least for NTRs that have actually been built and tested (i.e. solid core NTRs in Project Rover) the core temperature is actually lower than that afforded by hydrogen combustion in, say, an RL10. The gains in I_sp come from the fact that you don't have to throw that heavy oxygen out the back.

Since the thread has already drifted I hope you don't mind if I throw this in there.  My five year old son (ok it was me) drew this wonderful diagram showing how to combine NERV with SABRE tech

The first diagram shows a conventional jet engine, without afterburner. Eg. Wheesley, Juno, Goliath.  Intake, Compression, Combustion, Turbine stage to drive the compressor, nozzle.    Fuel economy is great but power is bottlenecked by the first stage of the turbine blades, which can only withstand a certain temperature without melting.   The world record, I believe , is 1600K and that's in a gas turbine power station with ceramic blades, airplane engines use metals to better survive in case of FOD.      Because of this, you can only inject enough fuel into the combustor to utilise about half the available oxygen, any more than that , things get too hot.    Note you can replace the combustor with a nuclear reactor and this makes a nuclear turbojet.

The second picture indicates a jet engine with Reheat.  Eg. Panther.   Once we're past the turbine stage there is no temperature limitation, so we can inject fuel to use up the available oxygen.  However because the gases have already expanded some, combustion is taking place at a lower pressure and this means less of the heat is converted to mechanical energy.   Note you could do something similar with a nuclear turbojet.  At low altitude, there is likely more air available than the reactor will be capable of heating.  Higher up however, we can start to run into temperature limitations on the turbine (1600K) before we hit those of the reactor (3000k on modern pebble bed), also the air will have cooled some after expanding through the turbine section, that is after all how power is extracted to drive the compressor.    So, we can have a reheat stage in our nuclear turbojet analgous to the jet engine "afterburner".

The third picture indicates compressor bypass like we have on the Pratt & Whitney J58.  As we get very high up, ambient air temps start to rise again.  Since we'll be doing mach 3+ at these altitudes, we'll be getting substantial ram air effect compressing the air in the intake before it even gets to the engine.  In a  lot of ways that's a good thing, it helps to offset the very rarefied air at such altitudes.  But , when you compress a gas its temperature goes up, which can drive our turbomachinery over its thermal limits.   In such situations the J58 bypasses some of the compression stages to keep temperatures in check.   The "Whiplash" emulates this in game, but i see no reason why a nuclear turbojet couldn't also do this.

The SABRE (Rapier) engine takes a different approach, it uses the incoming LH2 fuel stream to cool the intake air allowing continued operation up to mach 5.  So, surely our nuclear turbojet could use increasing amounts of LH2 as a final measure to extend its operating envelope. After cooling the intake stream, the LH2 could be fed into the tailpipe to combust with the superheated air stream as an "after burner", increasing the exhaust temperature beyond the 3000k limit of the reactor core materials.  I forgot to indicate that you should probably heat the LH2 to 3000k with the reactor first before feeding it into the afterburner. 

Now , I think there's an upper limit to combustion temperature - breaking O2 and H2 molecules apart takes energy, it's actually the formation of H20 from these radicals that releases it.  And there is a temperature at which H20 cannot form , dissociating into free radicals.  But, I understand this is actually a goal of NTR designers, meaning they can get a lot more ISP from water propellant, since the molecular mass of all these radicals is much lower than molecular water.

As the spaceplane continues to climb more an more of the reactor heat is just going into the hydrogen stream , till eventually it's operating as a conventional nuclear thermal rocket.

 

Downsides -

With reactors , you got two choices.  You can shield it on all sides, like a conventional ground based or naval power plant.  This is extremely heavy.

Or  you can just use a "shadow shield", and only shield the side of the reactor that faces the crew compartment.   Anyone directly under it's flight path will get a nasty dose of gamma rays when the engine is in operation, since they're not protected by the shield.  Not sure the range on those - a mile or two?

Second,  re-usable spacecraft are extraordinarly maintenance intensive.  After landing, the technicians are going to need to crawl over every component with a fine toothcomb, they're going to end up glowing green, which is only OK if you're a Kerbal.   Maybe some automated piece of equipment could come up to the plane and lower lead plates around the reactor core before sending the techs in,  but i' m reaching a bit here.

[PB666]

11 hours ago, Jovus said:

Point of order: At least for NTRs that have actually been built and tested (i.e. solid core NTRs in Project Rover ) the core temperature is actually lower than that afforded by hydrogen combustion in, say, an RL10. The gains in I_sp come from the fact that you don't have to throw that heavy oxygen out the back.

Yes but oxygen can be more densely packed. I wont argue for use of Oxygen in the NTR, hydrogen IMO is the best for a variety of reasons. The real gains in Isp for H come with very high core temperatures, however the dramatically shortens the life of the core.

" 8300 ft/sec,” a hydrogen-fueled nuclear engine would “attain an exhaust velocity of 22,700 ft/sec " ft per sec can be converted by 0.302 meters per second.

8300 * 0.302 = 2506.6 (very poor for a modern rocket engine). 22,700 * 0.302 = 6856 (ISPg of about 690) would not justify the use of this NTR under any circumstance because chemical rockets, given the storage tax of Liquid H2, is higher. To make NTRs really useful you either need to switch to a different propellant or raise the temperature of the gas core interface. What you really want to achieve is the cracking of H2 into hydrogen that occurs between 1500 and 3000k at the same time you increase the chamber pressure to neat maximum.  

[wumpus]

14 minutes ago, PB666 said:

8300 * 0.302 = 2506.6 (very poor for a modern rocket engine). 22,700 * 0.302 = 6856 (ISPg of about 690) would not justify the use of this NTR under any circumstance because chemical rockets, given the storage tax of Liquid H2, is higher. To make NTRs really useful you either need to switch to a different propellant or raise the temperature of the gas core interface. What you really want to achieve is the cracking of H2 into hydrogen that occurs between 1500 and 3000k at the same time you increase the chamber pressure to neat maximum.  

To roughly double the ISP you would have to double the exhaust velocity.  Basically, you would wind up doubling the root of the temperature*pressure of the hydrogen (the rest of the Ve equation should be the same), or splitting H2 into H (which would help beyond the temperature needed).  Since the prototype was already run (for 6 hours) at 2000K, I imagine most of your supposed gains come from cracking the hydrogen (hopefully there exists a catalyst that won't melt under those conditions).

It sounds like a difficult thing to balance.  You want to keep the Hydrogen in the engine long enough to heat up to extreme temperatures and crack into H[1].  Hydrogen is pretty nasty stuff, I'd hate to think of what it is doing to that engine.  Also I don't think that KSP was all that wrong about NERVAs being low power: I know that NASA planned on at least two burns on going to Mars (although it might be to drop a fuel tank).  Having H2 (and especially H[1]) hang around in the engine can't be good, and less so at those temperatures.  Then there is always the issue of running your nuclear engine at those temperatures (and it obviously has to be hotter than the hydrogen).  Sounds like it will always be running at the edge of a meltdown.

[PB666]

1 hour ago, wumpus said:

To roughly double the ISP you would have to double the exhaust velocity.  Basically, you would wind up doubling the root of the temperature*pressure of the hydrogen (the rest of the Ve equation should be the same), or splitting H2 into H (which would help beyond the temperature needed).  Since the prototype was already run (for 6 hours) at 2000K, I imagine most of your supposed gains come from cracking the hydrogen (hopefully there exists a catalyst that won't melt under those conditions).

It sounds like a difficult thing to balance.  You want to keep the Hydrogen in the engine long enough to heat up to extreme temperatures and crack into H[1].  Hydrogen is pretty nasty stuff, I'd hate to think of what it is doing to that engine.  Also I don't think that KSP was all that wrong about NERVAs being low power: I know that NASA planned on at least two burns on going to Mars (although it might be to drop a fuel tank).  Having H2 (and especially H[1]) hang around in the engine can't be good, and less so at those temperatures.  Then there is always the issue of running your nuclear engine at those temperatures (and it obviously has to be hotter than the hydrogen).  Sounds like it will always be running at the edge of a meltdown.

Ionized hydrogen is nasty, no doubt, it blackens just about everything in space, but at its ionization temperature its less nasty than heating oxygen or carbon up to achieve the same exhaust velocity. It allows thise engines to run cooler to get the equivilant ISP, thats why hydrogen is used. You can get the same thrust/ISP with O, but you would have to allow the core to get many times hotter. 

Its not that hydrogen is good, its that the other choices are bad, lithium borohydride LiBH4 is an alternative, Lithium hydride or ammonia are other choices, none are specifically known for their safety or stability. 

The key point about hydrogen is that you want it to ionize and accelerate before it recombines, which will happen as atomic velocities laminarize in the nozzle, once along in the bell it can recombine. So you have to have a core, exhaust nozzle and most of the bell stable to the temperatures of ionized hydrogen. 

[todofwar]

On 5/22/2016 at 0:30 PM, Bill Phil said:

Sugars have oxygen in them, alcohols too. They can be burned with oxygen.

I'd suggest hydrogen monoxide, at least for testing which oxidizer for the HAN.

What the hell is hydrogen monoxide? 

On 5/21/2016 at 5:03 AM, AeroGav said:

As you've probably heard by now,  liquid fuels used in spacecraft fall into one of two categories

1) cryogenics - those relying on hydrogen or methane as the fuel, and oxygen as oxidizer.  Best ISP but can only be used for launch due to boiloff. Mid course corrections, return journeys must be fuelled by

2) storable propellants - stuff that's liquid at about room temperature.  Apart from the Kerosine/Hydrogen Peroxide combo used by the UK in the 1960s, this generally means really nasty stuff.  Hydrazine, fuming nitric acid and derivatives - corrosive, carcinogenic, toxic - and don't forget to put "highly" in front of each of those adjectives.  Technicians working with the stuff are more or less dressed in a full spacesuit down on earth, it's that bad.

Along comes the https://en.wikipedia.org/wiki/Green_Propellant_Infusion_Mission

which uses https://en.wikipedia.org/wiki/Hydroxylammonium_nitrate instead of hydrazine.

ISP is a percent or two higher, and it's significantly (40-50%) denser.  It's also less volatile and far less toxic - either this woman is very brave or it really is ok to swill about in an open beaker

Now, in KSP we have just 3 fuels

Liquid Fuel, Oxidizer, and Monoprop.

Given that there is no boiloff, and given that ISPs given seem a low compared with state of the art, and the high densities, i am guessing that LF/O are both meant to be storables.

LF cannot be Kerosine, because it wouldn't work in a NERV long term (after a while, soot would clog the heat exchanger).   Hydrazine or this new HAN fuel must be what we are dealing with.    Then again, RAPIER engines require a cryogenic to work, so that's a bit of a mess.

Anyway, second question.  Anyone who knows a bit more about chemistry able to speculate if this new HAN can be used with an oxidizer rather than just as a monoprop for better ISP,  and are there any oxidizer candidates with similarly friendly properties?

Are there any house rules you can use to try make KSP more realistic with regards to real world fuels?

1. treat LF/O  as hypergolics.   That means no use of the RAPIER engine as a house rule.

2. treat LF/O as as cryo.   That means,  any LF/O  used to power a rocket engine or RAPIER must not be stored in a wing/strake tank and any fuel in that tank must be jettisoned shortly after making orbit to simulate boiloff.      LF stored in wings or used to power whiplash, panther or LV-N is assumed to be Hydrazine or HAN.

HAN is also a solid, so you need it in solution unless you mean to have this be an SRB. It's highly soluble in water, but I don't know if it would be usable as a saturated water solution. 

Edit: Wiki says they bind it to oligomers so it can be used as a liquid. So basically it's an ionic liquid. Might work, don't know of anyone mass producing the stuff. Also, as I suspected it's colorless, not sure what that lady is working with, looks like she's getting ready to run a mass spec or something so I doubt that is a HAN solution. 

Edited May 23, 2016 by todofwar
read the wiki

[Bill Phil]

9 minutes ago, todofwar said:

What the hell is hydrogen monoxide? 

HAN is also a solid, so you need it in solution unless you mean to have this be an SRB. It's highly soluble in water, but I don't know if it would be usable as a saturated water solution. 

Edit: Wiki says they bind it to oligomers so it can be used as a liquid. So basically it's an ionic liquid. Might work, don't know of anyone mass producing the stuff. Also, as I suspected it's colorless, not sure what that lady is working with, looks like she's getting ready to run a mass spec or something so I doubt that is a HAN solution. 

Sorry. That's water. Meant "peroxide".

[wumpus]

5 hours ago, PB666 said:

The key point about hydrogen is that you want it to ionize and accelerate before it recombines, which will happen as atomic velocities laminarize in the nozzle, once along in the bell it can recombine. So you have to have a core, exhaust nozzle and most of the bell stable to the temperatures of ionized hydrogen. 

Considering you need to maximize the pressure in the nozzle, and then maximize the output velocity (which implies mostly moving in the same direction), I suspect this will require heroic efforts to keep the hydrogen from recombining.

I think there is a reason that NASA's Mars plan from 2009 expected to use a NERVA* with an ISP between 875-950 and not 1500 (and as far as I know, the whole NERVA idea has come off the table since then).  http://www.nasa.gov/pdf/373665main_NASA-SP-2009-566.pdf

* there was also a plan using chemical rockets.  Unfortunately, most of the unsolved (non-political) problems with NERVAs are dealing with the hydrogen (unless you want >1000 ISP or something, or use something other than hydrogen).  This doesn't help you if you are planning on using hyrdox rockets (although certainly the James Webb telescope should improve zero-boiloff system greatly.  Maybe even enough to get this type of thing to work, maybe.