Author Topic: Next best propellant for abort engines after hydrazine et al  (Read 10198 times)

Offline adrianwyard

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I couldn't find the answer to this elsewhere so apologies it's common knowledge.

If hypergolics like hydrazine and nitrogen tetroxide were for some reason eliminated from a future vehicle, what would be the next best alternative propellant? Let's assume the task is abort engines, so mass, volume, and reliability/simplicity are still paramount.  Is anything close?

To my knowledge SNC is the only company proposing to use something other than hypergolics or solids for this purpose, with their propane/nitrous Orbitek engine. Anyone care to guess how that might perform compared to the others?

Offline Burninate

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It sounds like the question you're trying to ask might need some more constraints.

Hydrogen/LOX, kerosene/LOX, methane/LOX, and solids are all propellant options, but they are not really propellant options to directly replace hydrazine & NTO, they're not in the running for the much-vaunted 'green propellant'.  That's because LOX is mildly cryogenic and storing it long-term is a moderately complicated engineering problem we have not tackled in orbit yet, & the solutions are quite likely to only going to be worthwhile for large propellant volumes.  Hydrazine/NTO, hydrazine-based monopropellant, and inert nitrogen monopropellant, by contrast, are storeable at routine temperatures and pressures indefinitely, and permit extremely simple, lightweight, low-thrust engines.  These are engines that are small enough to spread out over the craft and use for RCS & in-space maneuvering fuel.

Only a few rockets still use hydrazine for any purpose other than tiny orbital thrusters - the Proton and some of the other Russian LVs.

So -
What type of ignition?
Monoprop or biprop?
How many vacuum restarts are permitted?
What type of Isp?
How thermally stable?

There are, as I understand it, a lot more fuels in the possibility space than there are oxidizers, so might as well start there.
« Last Edit: 03/14/2015 08:38 PM by Burninate »

Offline nadreck

Hydrogen peroxide/RP-1 it could easily be used for both RCS systems and larger engines. Alternately hydrogen peroxide and RP-1 for a high thrust engine and just hydrogen peroxide for RCS.

Drawbacks of H2O2 are instability at high temps and a freezing point near the same as water. Advantages are self ignition with RP-1 and many other fuels, and relatively high density.
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Offline adrianwyard

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Thanks, Burninate. I was thinking of limiting the question to just abort motors - where hydrazine is very much in use today (SpaceX Dragon, CST-100, Blue Origin).

Offline Damon Hill

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Offline Burninate

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Random notes on oxidizers from half an hour of googling:

So for conventional oxidizers, we have:
NTO, nitrogen tetroxide - problematically toxic, the standard in orbital maneuvering and also used in some liquid LVs
LOX, liquid oxygen - problematically cryogenic, the standard in liquid LVs
AP, ammonium perchlorate - mildly toxic, the standard in solid rockets
N2O, Nitrous oxide - pushed as bipropellant, as hybrid rocket oxidizer, and mixed into blended fuels as "NOFBX" liquid monopropellant, one of NASA's favorites to replace hydrazine/NTO
HTP - high test peroxide - Used frequently early in rocketry, but unless refrigerated, prone to runaway thermal autodecomposition

http://www.redalyc.org/articulo.oa?id=309429107002 puts forward:
ADN - Ammonium Dinitramide, fingered for replacing both the AP in solids and the hydrazine in liquid monopropellant, as part of an oxidizer-fuel blend
HNF - Hydrazinium Nitroformate, higher performance for solid rockets but needs research on stabilizing it

Next year NASA is launching the Green Propellant Infusion Mission, GPIM, using:
" a Hydroxyl Ammonium Nitrate (HAN) fuel/oxidizer blend, or AF-M315E."

http://www.spg-corp.com/nytrox-propellants.html & http://enu.kz/repository/2009/AIAA-2009-4966.pdf is trying to sell
Nytrox, nitrous oxide - LOX blends, pushed as self-pressurizing oxidizer for hybrid sounding rockets

http://adsabs.harvard.edu/full/2004ESASP.557E..23D pushes
AN, Ammonium Nitrate, as a cheaper, greener replacement or partial replacement for AP in solid rockets, and also as a solitary monopropellant.

http://www.diva-portal.org/smash/get/diva2:360054/FULLTEXT01.pdf works primarily towards stabilizing ADN, and notes six potential oxidizers, of which TNA / trinitramide seems to be their focus:
Quote
The dinitramide (1), trinitrogen dioxide (75), pentazole (77), oxopentazole (78), 1,3-dioxopentazole (79)
and the 1-nitro-2-oxo-3-aminotriazene (76) anions all hold considerable promise in all these respects. Finally, the neutral trinitramide molecule (25), the largest all-nitrogenoxygen compound known, was successfully synthesized and characterized
Trinitramide had been theorized long before being formulated.

Wikipedia's article on Monopropellants lists under new developments HAN, and an adaptation of ADN:
Quote
The EURENCO Bofors company produced LMP-103S as a 1-to-1 substitute for hydrazine by dissolving 65% ammonium dinitramide, NH4N(NO2)2, in 35% water solution of methanol and ammonia. LMP-103S has 6% higher specific impulse and 30% higher impulse density than hydrazine monopropellant. Additionally, hydrazine is highly toxic and carcinogenic, while LMP-103S is only moderately toxic. LMP-103S is UN Class 1.4S allowing for transport on commercial aircraft, and was demonstrated on the Prisma satellite in 2010. Special handling is not required. LMP-103S could replace hydrazine as the most commonly used monopropellant.[4]

It seems NOFBX had manifested a mission for 2013, but it may have been delayed or cancelled, while the HAN-fuel blend was the second green propellant to manifest an experimental mission (launch in 2016).

There's also testing of a water ice - nano-aluminum blend.

SO:
The commercially developed options for new liquid monoprop fuel blends seem to be LMP-103S (ADN/fuel), AF-M315E (HAN/fuel), and NOFBX (N2O/fuel).
« Last Edit: 03/14/2015 09:55 PM by Burninate »

Offline cdleonard

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As far as I know the Boeing CST-100 will actually use a LOX/alcohol engine. Is wikipedia wrong about this?
« Last Edit: 03/14/2015 09:51 PM by cdleonard »

Online kevin-rf

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You also have the option of white fuming nitric acid. It is hypergolic and not nearly as toxic as other options. You would not want to spoil it on your new shoes, but it is considered safer....

There once was an nsf thread extolling it's virtues. Five minutes with the search engine should find it.
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Offline Port

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http://en.wikipedia.org/wiki/Green_Propellant_Infusion_Mission

this!
IL's are amazing substances and chemists are barely touching the surface of what's possible (I'm working in this area)
The framework they exhibit in liquid state (yes thats the weird thing about them) makes them ideal for kinetically stabilizing something that seriously want's to go ooompf (like that Hydroxyl-Group on the nitrogen, man that one is really unhappy).

Offline adrianwyard

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As far as I know the Boeing CST-100 will actually use a LOX/alcohol engine. Is wikipedia wrong about this?

I heard Boeing switched to hypergols for the RS-88 on CST-100, but after some googling the only sources I can find for that are here at NSF, so I'm really not sure. CCDev 1 Milestone B4 looks like it might have been related to this switch, but I can't find anything definitive.

I suppose using LOX - or any cryogen - in an abort system adds the problem of boil-off and/or some means to replenish it.

Offline cdleonard

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Also, aren't disposable solids sort of ideal for an abort engine? Cheap and high-thrust.

The reason Dragon 2 is using hypergols is because they want to use the same engines to land propulsively even after spending months in space. It can also share the fuel with the attitude control system.

I guess CST-100 is using a liquid-fueled abort system because it's reusable?

Offline adrianwyard

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I guess CST-100 is using a liquid-fueled abort system because it's reusable?

That can't be the reason: the service module is discarded each flight.

A liquid/pusher abort system has the advantage (over solids) of being available for orbital maneuvering and de-orbit. But then storability is key, so cryogens are a problem.
« Last Edit: 03/14/2015 11:49 PM by adrianwyard »

Offline dkovacic

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I would also vote for HTP/RP-1, because HTP can be used for multiple purposes for any HSF mission (source of water, oxygen, fuel cell, mono-prop RCS). ISP is approximately the same as for NTO/MMH combination.

Let me put this this way - imagine being stuck in spaceship without propulsion, with days or weeks before any rescue mission can reach you. Which of chemicals mentioned above would you want to have in the tanks?

Offline RanulfC

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I would also vote for HTP/RP-1, because HTP can be used for multiple purposes for any HSF mission (source of water, oxygen, fuel cell, mono-prop RCS). ISP is approximately the same as for NTO/MMH combination.

Let me put this this way - imagine being stuck in spaceship without propulsion, with days or weeks before any rescue mission can reach you. Which of chemicals mentioned above would you want to have in the tanks?

While I agree with the first part I need to point out that the second part probably doesn't even matter as unless the systems is PLUMBED for access you can't GET to propellant in the tanks for use anyway :) I'm not sure anyone would consider it "cost-effective" to plumb a system for access on the off chance you 'might' need it at some point however if you've been designing for such operations as propellant transfer the chances go up greatly :)

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Offline Patchouli

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I would also vote for HTP/RP-1, because HTP can be used for multiple purposes for any HSF mission (source of water, oxygen, fuel cell, mono-prop RCS). ISP is approximately the same as for NTO/MMH combination.

Let me put this this way - imagine being stuck in spaceship without propulsion, with days or weeks before any rescue mission can reach you. Which of chemicals mentioned above would you want to have in the tanks?
It would be a good choice since it is relatively storable and everything is liquid at normal temperatures and pressures.
The only bad part is contamination of the HTP though you have to keep NTO and MMH free of any contamination as well so it doesn't really introduce many new issues.
As for use in OMS long term storage would not be an issue Soyuz has HTP thrusters in it's decent module and has no problems staying six months at ISS.
 
Even though they seem to come up short for sub orbital spacecraft is N2O rubber hybrids might be another ideal propellant for abort systems that double as OMS.

The minimum 1.7KM/sec of delta V a sub orbital spacecraft like SS2 needs to reach 100km is a ridiculous overkill for an abort motor.

« Last Edit: 04/25/2015 05:26 AM by Patchouli »

Offline adrianwyard

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...
Even though they seem to come up short for sub orbital spacecraft is N2O rubber hybrids might be another ideal propellant for abort systems that double as OMS.

The minimum 1.7KM/sec of delta V a sub orbital spacecraft like SS2 needs to reach 100km is a ridiculous overkill for an abort motor.

I recall people were critical of Dream Chaser's use of HTPB/Nitrous for its abort engines (which were also used for OMS and de-orbit). A couple of the factors were: thrust and startup time (in the case of abort, spare delta V is of no use if you can't use it to get out of dodge quickly). I'm not sure how fair a criticism this was, but we do know that the thrust to weigh ratio of Dragon's abort solution was far higher than DC's.

The last we heard from SNC is that they'd switched to Propane/Nitrous. I'm not sure if that combination fairs any better in terms of high-thrust in short order.
« Last Edit: 04/26/2015 09:31 PM by adrianwyard »

Offline adrianwyard

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Minor addition: A little googling confirms that UDMH and N2O4 are not shock sensitive, so any replacement would ideally match that quality.

That info came from the following useful brief description of propellants: http://www.astronautix.com/props/index.htm

Offline dafeixue001

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I'm paying attention to nofbx, I think it's a promising propellant .I haven't got any information about it since 2013.
 

Offline Rei

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I would also vote for HTP/RP-1, because HTP can be used for multiple purposes for any HSF mission (source of water, oxygen, fuel cell, mono-prop RCS). ISP is approximately the same as for NTO/MMH combination.

Let me put this this way - imagine being stuck in spaceship without propulsion, with days or weeks before any rescue mission can reach you. Which of chemicals mentioned above would you want to have in the tanks?

I don't think you're going to be arbitrary tapping into tanks in space and building homemade catalyst beds for decomposition, even in an emergency.  Unless the tank had some sort of system specifically designed for recovery of oxygen and water. In which case, why did you spend the money and launch mass building such a system rather than a proper water recovery / O2 generating life support system that's useful all the time?

Plus, it's technically possible to make life-support-useful compounds out of almost any propellant combination - run them over a hot platinum catalyst and you'll generally get a steady feed of their exhaust products, which often contain at the very least H2O, which you're probably splitting anyway in an oxygen generator. That doesn't mean that it's justifiable to include a system to do so, unless it's serving some other purpose (for example, using propellant in a fuel cell for power generation)

Really, though, my main issue with HTP is that it's explosive if you do anything wrong. There've been too many HTP handling accidents for my comfort. ISP is pretty bad, too.
« Last Edit: 03/26/2017 01:00 PM by Rei »

Offline Rei

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Minor addition: A little googling confirms that UDMH and N2O4 are not shock sensitive, so any replacement would ideally match that quality.

That info came from the following useful brief description of propellants: http://www.astronautix.com/props/index.htm

One additional thing I like about MON (aka what most people mean when they talk about N2O4) is that it works well with hydrogen free and low-hydrogen fuels. These tend to burn very hot. However, if you burn for example cyanogen with MON instead of LOX it drops the flame temperature by something like 300 degrees, at a cost of only something like 10 sec ISP (while gaining the other benefits of MON - non-cryogenic, high density, self-pressurizing, hypergolic with many fuels, etc). The ISP drop is much lower than when you burn MON with hydrogen-rich fuels. As for temperature, the extra nitrogen in the oxidizer helps dilute the exhaust, yielding more moles of lower temperature gas rather than fewer moles of higher temperature gas. Also, unlike advanced oxidizers, it remains fairly simple to synthesize in ISRU environments. If you're making fertilizer or the basic industrial acids locally, you've got MON (N2 + 3 H2 -> 2 NH3 (Haber), 4 NH3 + 5 O2 -> 4 NO + 6 H2O (Ostwald stage 1), 2 NO + O2 -> 2 NO2 (Ostwald stage 2); NO2 dimerizes to N2O4)
« Last Edit: 03/26/2017 12:54 PM by Rei »

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