Author Topic: tripropellant rockets  (Read 46919 times)

Offline space_dreamer

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tripropellant rockets
« on: 02/05/2009 02:28 pm »
I have been reading about of Wikipedia.
( http://en.wikipedia.org/wiki/Tripropellant_rocket )

It says - A mixture of lithium, hydrogen, and fluorine produced a specific impulse of 546 seconds; the highest ever of any chemical rocket motor.

An Isp of 546 is high enough to design a signal stage to orbit vehicle SSTO. Does anybody know, why an engine for this combination of fuel not being developed?

Offline Analyst

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Re: tripropellant rockets
« Reply #1 on: 02/05/2009 02:38 pm »
Fluor is highly reactive and nasty to work with.

Analyst

Offline Jim

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Re: tripropellant rockets
« Reply #2 on: 02/05/2009 02:38 pm »
I have been reading about of Wikipedia.
( http://en.wikipedia.org/wiki/Tripropellant_rocket )

It says - A mixture of lithium, hydrogen, and fluorine produced a specific impulse of 546 seconds; the highest ever of any chemical rocket motor.

An Isp of 546 is high enough to design a signal stage to orbit vehicle SSTO. Does anybody know, why an engine for this combination of fuel not being developed?


The propellants and exhaust are extremely toxic.

Offline Jorge

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Re: tripropellant rockets
« Reply #3 on: 02/05/2009 02:42 pm »
I have been reading about of Wikipedia.
( http://en.wikipedia.org/wiki/Tripropellant_rocket )

It says - A mixture of lithium, hydrogen, and fluorine produced a specific impulse of 546 seconds; the highest ever of any chemical rocket motor.

An Isp of 546 is high enough to design a signal stage to orbit vehicle SSTO. Does anybody know, why an engine for this combination of fuel not being developed?


Because the propellants are a royal PITA to handle.

Fluorine is extremely toxic and corrosive. It reacts with just about everything so only a few metals are suitable for containing it. It is hypergolic with most fire-extinguishing agents. There is no effective way to put out a fluorine fire.

Liquid lithium is hypergolic with air. Also horribly corrosive. There are no flexible materials (e.g. gaskets) that can survive liquid lithium; all joints must be welded.

The lithium fluoride in the exhaust would cause environmental problems. It's worse than SRB exhaust.
JRF

Offline mmeijeri

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Re: tripropellant rockets
« Reply #4 on: 02/05/2009 02:44 pm »
The propellants and exhaust are extremely toxic.

I read somewhere that the hydrogen has to be kept very cold and either the fluorine or the lithium (or both) has to be kept very hot. Not very practical, even if the exhaust products weren't toxic.
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Offline space_dreamer

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Re: tripropellant rockets
« Reply #5 on: 02/05/2009 03:41 pm »

Because the propellants are a royal PITA to handle.
Fluorine is extremely toxic and corrosive.
Liquid lithium is hypergolic with air. Also horribly corrosive.

The lithium fluoride in the exhaust would cause environmental problems. It's worse than SRB exhaust.


That’s a real shame.

This paragraph is pretty interesting-

Robert Salkeld, studied a number of designs using such engines, both ground based and a number that were air-launched from large jet aircraft. He concluded that tripropellant engines would produce gains of over 100% in payload fraction, reductions of over 65% in propellant volume and better than 20% in dry weight. A second design series studied the replacement of the Shuttles SRBs with tripropellant based boosters, in which case the engine almost halved the overall weight of the designs. His last full study was on the Orbital Rocket Airplane which used both tripropellant and (in some versions) a plug nozzle, resulting in a spaceship only slightly larger than a Lockheed SR-71, able to operate from traditional runways.

Offline Nick L.

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Re: tripropellant rockets
« Reply #6 on: 02/05/2009 04:22 pm »
Another problem with these fuels is that lithium and fluorine are fairly expensive and relatively rare (compared to LH2/LO2/RP1 for example), which would make any LV that uses such a combination that much more expensive.
« Last Edit: 02/05/2009 04:22 pm by Nick L. »
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Offline kevin-rf

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Re: tripropellant rockets
« Reply #7 on: 02/05/2009 05:22 pm »
A second design series studied the replacement of the Shuttles SRBs with tripropellant based boosters, in which case the engine almost halved the overall weight of the designs.

[humor_tag]
OMG you just solved all the Ares performance problems ;)
[/humor_tag]

What is the ISP of mono propellant H2 when heated with a nuclear reactor again?
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Offline GuessWho

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Re: tripropellant rockets
« Reply #8 on: 02/05/2009 06:56 pm »
Ideal Isp goes roughly as 17.4*sqrt(Gas Temp in Kelvin).  Thus at 2500 K, the Isp is 870 seconds.  Nozzle losses will reduce this by 5% or so.  Reasonable operating temperatures are in the 2500-2800 K range given material limitations.

Offline cheesybagel

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Re: tripropellant rockets
« Reply #9 on: 02/06/2009 01:53 am »
If you are going for hazardous rockets, my personal favorite is the pebble bed nuclear thermal rocket with LH2 as the ejection mass ala Project Timberwind. T/W ratio of 30 and 890 Isp at sea level. LN or CO2 as the ejection mass would increase thrust at cost of Isp. It isn't very different from a pebble bed nuclear reactor. Many countries have the technology required, including China.



Offline Patchouli

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Re: tripropellant rockets
« Reply #10 on: 02/06/2009 02:05 am »
I have been reading about of Wikipedia.
( http://en.wikipedia.org/wiki/Tripropellant_rocket )

It says - A mixture of lithium, hydrogen, and fluorine produced a specific impulse of 546 seconds; the highest ever of any chemical rocket motor.

An Isp of 546 is high enough to design a signal stage to orbit vehicle SSTO. Does anybody know, why an engine for this combination of fuel not being developed?


Because the propellants are a royal PITA to handle.

Fluorine is extremely toxic and corrosive. It reacts with just about everything so only a few metals are suitable for containing it. It is hypergolic with most fire-extinguishing agents. There is no effective way to put out a fluorine fire.

Liquid lithium is hypergolic with air. Also horribly corrosive. There are no flexible materials (e.g. gaskets) that can survive liquid lithium; all joints must be welded.

The lithium fluoride in the exhaust would cause environmental problems. It's worse than SRB exhaust.

The engine also would be single use which would completely defeat the purpose of having such a high ISP stage for SSTO.

A hydrogen,kerosene, and oxygen rocket will likely produce the performance needed for a near SSTO for a lot less trouble.
Burning kerosene during the early phase of the flight reduces the size and mass of the tanks needed.
See MAKS http://www.buran.ru/htm/molniya6.htm
« Last Edit: 02/06/2009 02:08 am by Patchouli »

Offline Patchouli

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Re: tripropellant rockets
« Reply #11 on: 02/06/2009 02:12 am »
If you are going for hazardous rockets, my personal favorite is the pebble bed nuclear thermal rocket with LH2 as the ejection mass ala Project Timberwind. T/W ratio of 30 and 890 Isp at sea level. LN or CO2 as the ejection mass would increase thrust at cost of Isp. It isn't very different from a pebble bed nuclear reactor. Many countries have the technology required, including China.


That engine may be too dangerous for an LV but it would rock for a lunar shuttle no more launching a new EDS for every lunar mission just refuel the nuclear ferry.

Also with a T/W that high if it can throttle deeply and quickly it would make a good lunar lander engine too.
« Last Edit: 02/06/2009 02:14 am by Patchouli »

Offline Jorge

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Re: tripropellant rockets
« Reply #12 on: 02/06/2009 02:33 am »
If you are going for hazardous rockets, my personal favorite is the pebble bed nuclear thermal rocket with LH2 as the ejection mass ala Project Timberwind. T/W ratio of 30 and 890 Isp at sea level. LN or CO2 as the ejection mass would increase thrust at cost of Isp. It isn't very different from a pebble bed nuclear reactor. Many countries have the technology required, including China.




And of course, if you want to go completely crazy, there's liquid ozone 15 and acetylene. But I'll let the co-author of that tongue-in-cheek proposal describe it himself:

http://groups.google.com/group/sci.space.tech/msg/3199d5be7e770f44

(The rest of the thread is worth reading, for tips on making the acetylene radioactive, etc...)
JRF

Offline khallow

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Re: tripropellant rockets
« Reply #13 on: 02/06/2009 03:10 am »
I remember at one point thinking, boy you should be able to shave some weight by using only the lightest stable isotopes for your propellant. Turns out for the usual stuff, carbon, hydrogen, and oxygen, we already are, aside from a minute amount of heavier isotopes. So you can shave somewhere around 0.1% off on the molecular weight by doing that.

Lithium on the other hand can be improved greatly by purifying the rarer lithium 6 from the more common lithium 7. That might boost the ISP of this tripropellant engine significantly, assuming it hasn't already been done.
Karl Hallowell

Offline zapkitty

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Re: tripropellant rockets
« Reply #14 on: 02/06/2009 05:37 am »
And of course, if you want to go completely crazy, there's liquid ozone 15...

Hmmm... my notes from way back have George telling me it was O-14 with those properties... which, it turns out, actually has a much shorter half-life... hmmm...

Offline hop

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Re: tripropellant rockets
« Reply #15 on: 02/06/2009 05:54 am »
And of course, if you want to go completely crazy, there's liquid ozone 15 and acetylene. But I'll let the co-author of that tongue-in-cheek proposal describe it himself:

http://groups.google.com/group/sci.space.tech/msg/3199d5be7e770f44

(The rest of the thread is worth reading, for tips on making the acetylene radioactive, etc...)
In a similar vein you have chlorine trifluoride, which was at least somewhat seriously considered as a propellant.

Offline space_dreamer

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Re: tripropellant rockets
« Reply #16 on: 02/06/2009 11:45 am »
Propellants of liquid ozone 15 and acetylene, as well as chlorine trifluoride sound like total no goers.

Is it possible that there is a propellant combo out there which hasn’t be discovered yet that would produce a Isp over 500 and be non toxic and relative easy to work with? Or has every combination been tried?

- And consequently the only way to have a reusable SSTO vehicle is either a scram jet, air breathing rocket or nuclear engine. All of which are expensive to develop.

Offline space_dreamer

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Re: tripropellant rockets
« Reply #17 on: 02/06/2009 11:57 am »
Patchouli

A hydrogen,kerosene, and oxygen rocket will likely produce the performance needed for a near SSTO for a lot less trouble.
Burning kerosene during the early phase of the flight reduces the size and mass of the tanks needed.
See MAKS http://www.buran.ru/htm/molniya6.htm


The MAKS concept looks ideal - but why would the Russian have been wasting time with Kliper then ACTS if MAKS was sitting there just waiting to be finished?

Offline Jim

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Re: tripropellant rockets
« Reply #18 on: 02/06/2009 01:03 pm »

Is it possible that there is a propellant combo out there which hasn’t be discovered yet that would produce a Isp over 500 and be non toxic and relative easy to work with? Or has every combination been tried?


Not really, it is just chemistry, it can be figured out by equations.  No need to "try" or test the combinations. 

Offline Jim

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Re: tripropellant rockets
« Reply #19 on: 02/06/2009 01:04 pm »

The MAKS concept looks ideal - but why would the Russian have been wasting time with Kliper then ACTS if MAKS was sitting there just waiting to be finished?

There are other considerations than ISP

Offline jongoff

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Re: tripropellant rockets
« Reply #20 on: 02/06/2009 03:15 pm »
A hydrogen,kerosene, and oxygen rocket will likely produce the performance needed for a near SSTO for a lot less trouble.
Burning kerosene during the early phase of the flight reduces the size and mass of the tanks needed.
See MAKS http://www.buran.ru/htm/molniya6.htm

One of the interesting ways of doing a LOX/Kero/LH2 tripropellant rocket in a sensible way was suggested by Aerojet in one of their TAN papers.  Basically, you burn LOX/Kero in the TAN injectors, and LOX/LH2 in the core chamber.  The Kero is not just adding density impulse for the early part of the burn (and also decreasing gravity losses by being able to burn off quicker than a higher Isp fuel), but it is also allowing the main engine to have a much larger expansion ratio than you could get away with for a booster engine--giving much better Isp and engine T/W...

And yes, I wouldn't want to be with 100miles of someone dumb enough to be messing with Liquid Lithium and Florine in a rocket.

~Jon

Offline mlorrey

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Re: tripropellant rockets
« Reply #21 on: 02/07/2009 03:15 am »

And yes, I wouldn't want to be with 100miles of someone dumb enough to be messing with Liquid Lithium and Florine in a rocket.

~Jon

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Offline robertross

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Re: tripropellant rockets
« Reply #22 on: 02/11/2009 12:44 am »
And of course, if you want to go completely crazy, there's liquid ozone 15 and acetylene. But I'll let the co-author of that tongue-in-cheek proposal describe it himself:

http://groups.google.com/group/sci.space.tech/msg/3199d5be7e770f44

(The rest of the thread is worth reading, for tips on making the acetylene radioactive, etc...)
In a similar vein you have chlorine trifluoride, which was at least somewhat seriously considered as a propellant.

Thanks Jorge & hop...I had a good laugh from those. I really miss my chemistry 101. And from that last link, I loved this point (among others):

"It is also hypergolic with such things as cloth, wood, and test engineers, not to mention asbestos, sand, and water-with which it reacts explosively"

Offline jongoff

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Re: tripropellant rockets
« Reply #23 on: 02/11/2009 01:52 am »
And of course, if you want to go completely crazy, there's liquid ozone 15 and acetylene. But I'll let the co-author of that tongue-in-cheek proposal describe it himself:

http://groups.google.com/group/sci.space.tech/msg/3199d5be7e770f44

(The rest of the thread is worth reading, for tips on making the acetylene radioactive, etc...)
In a similar vein you have chlorine trifluoride, which was at least somewhat seriously considered as a propellant.

Thanks Jorge & hop...I had a good laugh from those. I really miss my chemistry 101. And from that last link, I loved this point (among others):

"It is also hypergolic with such things as cloth, wood, and test engineers, not to mention asbestos, sand, and water-with which it reacts explosively"

I still think that George Herbert's gag propellant HOOOCCH was the best.  Poly-Acetyl Ozone.

http://www.retro.com/hooocch/acezone.html

~Jon

Offline mlorrey

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Re: tripropellant rockets
« Reply #24 on: 02/11/2009 02:03 am »
And of course, if you want to go completely crazy, there's liquid ozone 15 and acetylene. But I'll let the co-author of that tongue-in-cheek proposal describe it himself:

http://groups.google.com/group/sci.space.tech/msg/3199d5be7e770f44

(The rest of the thread is worth reading, for tips on making the acetylene radioactive, etc...)
In a similar vein you have chlorine trifluoride, which was at least somewhat seriously considered as a propellant.

Thanks Jorge & hop...I had a good laugh from those. I really miss my chemistry 101. And from that last link, I loved this point (among others):

"It is also hypergolic with such things as cloth, wood, and test engineers, not to mention asbestos, sand, and water-with which it reacts explosively"

I still think that George Herbert's gag propellant HOOOCCH was the best.  Poly-Acetyl Ozone.

http://www.retro.com/hooocch/acezone.html

~Jon

How about lithium and peroxide?
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Offline kevin-rf

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Re: tripropellant rockets
« Reply #25 on: 02/11/2009 02:39 pm »

I still think that George Herbert's gag propellant HOOOCCH was the best.  Poly-Acetyl Ozone.

http://www.retro.com/hooocch/acezone.html

~Jon

The Job listing page is equally good enough ;)

http://www.retro.com/general/employment.shtml

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Offline Patchouli

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Re: tripropellant rockets
« Reply #26 on: 02/11/2009 03:21 pm »

The MAKS concept looks ideal - but why would the Russian have been wasting time with Kliper then ACTS if MAKS was sitting there just waiting to be finished?

There are other considerations than ISP
Such as money plus relations with the Ukraine also MAKS only got a little farther then Orion is now.
The RD701 was tested and transition from tripropellant mode to bipropellant mode worked smoothly.
Though I think ACTS is now dead since the RSA and EU decided they should go their separate ways I didn't think it had much of a chance anyway.
 TsSKB and RSC favored the Kliper/parome a system over ACTS which was a Frankenstein creation that left holes in the cargo transportation end as far as Russia was concerned.
Russia doesn't like depending on other countries for services.

Lastly Kliper and ACTS were supposed to be able to go to the moon while MAKS is a pure LEO vehicle.

Still I bet they kick themselves for not finishing MAKS since MAKS-M and MAKS-D approach STS in some capabilities and would have given them something to compete with companies like Spacex and Arianespace with on equal grounds.

« Last Edit: 02/11/2009 03:37 pm by Patchouli »

Offline mlorrey

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Re: tripropellant rockets
« Reply #27 on: 02/12/2009 02:22 am »

Lastly Kliper and ACTS were supposed to be able to go to the moon while MAKS is a pure LEO vehicle.

Still I bet they kick themselves for not finishing MAKS since MAKS-M and MAKS-D approach STS in some capabilities and would have given them something to compete with companies like Spacex and Arianespace with on equal grounds.



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Offline Archibald

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Re: tripropellant rockets
« Reply #28 on: 02/13/2009 06:37 pm »
 a nice concept would be a Kistler K-1 with RD-701s (not NK-33 or NK-43)

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Offline tnphysics

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Re: tripropellant rockets
« Reply #29 on: 02/15/2009 01:22 am »
what about boranes?

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Re: tripropellant rockets
« Reply #30 on: 02/15/2009 02:13 am »
what about boranes?

Apparently very toxic. Silanes are apparently very promising, but also toxic.
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Offline gin455res

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Re: tripropellant rockets
« Reply #31 on: 03/09/2009 07:32 am »
Is it possible to get the effect of a tri-propellant with gelled fuels. For example if hydrogen was gelled with methane but the percentage of methane was stratified in the fuel tank so that there was lots of methane early in the burn and less as the burn continued?

And if we forget about fixating on maximum isp, is it possible to gell the hydrogen with alternate gelling agents that do not use up so much oxygen as methane. This would allow the fuel/oxidiser mixture ratio to vary less as the hydrogen/gellant mixture ratio changed.

In an article I found online, the hydrogen/methane (gelled) : oxygen ratio was 4:1 whereas the pure hydrogen : oxygen it was 6:1. Would there be any advantage in using alternative gelling agents so that this ratio would vary less as the mixture changed during the burn?

Perhaps, methanol, ammonia, nitromethane!!

Similarly, if there is a substance with a similar energy density/liter as methane but is far denser, then would it make any sense to gell this with methane in a similar stratified fashion? If the engine is running fuel rich then the effective energy densities would be less than that 'written on the can'  as there would be incomplete  combustion in the form of unreacted h2 and carbon monoxide. Some type of alcohol perhaps?

Offline mlorrey

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Re: tripropellant rockets
« Reply #32 on: 03/09/2009 08:18 pm »
Is it possible to get the effect of a tri-propellant with gelled fuels. For example if hydrogen was gelled with methane but the percentage of methane was stratified in the fuel tank so that there was lots of methane early in the burn and less as the burn continued?

And if we forget about fixating on maximum isp, is it possible to gell the hydrogen with alternate gelling agents that do not use up so much oxygen as methane. This would allow the fuel/oxidiser mixture ratio to vary less as the hydrogen/gellant mixture ratio changed.

In an article I found online, the hydrogen/methane (gelled) : oxygen ratio was 4:1 whereas the pure hydrogen : oxygen it was 6:1. Would there be any advantage in using alternative gelling agents so that this ratio would vary less as the mixture changed during the burn?

Perhaps, methanol, ammonia, nitromethane!!

Similarly, if there is a substance with a similar energy density/liter as methane but is far denser, then would it make any sense to gell this with methane in a similar stratified fashion? If the engine is running fuel rich then the effective energy densities would be less than that 'written on the can'  as there would be incomplete  combustion in the form of unreacted h2 and carbon monoxide. Some type of alcohol perhaps?

NASA's HEDM program researched gelling hydrogen with additives like aluminum, carbon, titanium and boron powders. All gave significant increases in IsP however questions remain about coking issues in any turbopumps used by engines burning these gells.
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Offline mlorrey

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Re: tripropellant rockets
« Reply #33 on: 03/09/2009 11:34 pm »
http://www.wickmanspacecraft.com/loxmono.html

Check this out, these guys are mixing LOX with kerosene at cryogenic temps to create a 'monopropellant'. Dont know how stable this mixture is, but it could save some tankage mass if you only need one tank, and making it pressure fed, eliminate turbopumping, you'd have the liquid equivalent of a solid rocket motor. Comments?
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Offline khallow

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Re: tripropellant rockets
« Reply #34 on: 03/10/2009 05:13 am »
http://www.wickmanspacecraft.com/loxmono.html

Check this out, these guys are mixing LOX with kerosene at cryogenic temps to create a 'monopropellant'. Dont know how stable this mixture is, but it could save some tankage mass if you only need one tank, and making it pressure fed, eliminate turbopumping, you'd have the liquid equivalent of a solid rocket motor. Comments?

How about outgassing? Seems likely that anything you vent would instantaneous burn at room temperature.

What few rumors I heard on this seems to indicate that this is a very unstable mix. For example, suppose I leave a little petroleum grease smear on the inside of a LOX tank. The grease will burn in the presence of LOX, but the energy released is merely that of the burning grease. In this LOX/kerosene mix, grease contamination might instantly detonate the whole mix (in the usual explosive sense with supersonic wavefront and everything). So this system, at least, seems much more sensitive to contamination than what we have today.

It might spontaneously react too. A very energetic cosmic ray (I love blaming these guys) or a static discharge somewhere in your plumbing might set off your propellant. You'd have to put in safeguards to keep a combustion wavefront from racing into your tank from elsewhere.
Karl Hallowell

Offline GI-Thruster

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Re: tripropellant rockets
« Reply #35 on: 03/12/2009 06:20 pm »
Anyone interested in using more energetic propellants will want to track the progress at Harvard and look for the SPESIF paper by Dr. John W. Cole (of MSC fame) and Dr. Isaac F. Silvera of Harvard entitled "Metallic Hydrogen Propelled Launch Vehicles for Lunar Missions" where you will find amongst other things, some raw numbers for such vehicles.  Given metallic hydrogen as a fuel, one could for example fly single stage to the moon with a 65 m high, 452 MT GLOW and land 45 MT on the lunar surface.

That's not your mother's hydrogen thruster. . .

Offline modavis

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Re: tripropellant rockets
« Reply #36 on: 03/12/2009 07:54 pm »
It isn't very different from a pebble bed nuclear reactor.

It's different in at least one very significant way.

The greatest virtue of the PBR that, unlike the tubes and rods and channels of earlier reactors, no elaborate structure is needed to position the fissionables. Given the flux of heat-transfer fluid needed, even in the worst case the maximum energy available to move the "pebbles" around is safely less than it would take to damage them, and there's no arrangement of pebbles that would choke the flow.

The flux of reaction mass through a NTR is much higher. The momentum per unit engine mass (aka "how fast does it tear itself apart if something goes wrong") is orders of magnitude higher. So it does need a structure that holds the fissionables in a fixed arrangement and maintains clear channels. And if that begins to fail, there is more than enough momentum around to turn a small flaw into a big one really fast.

I happen to think NTRs are promising, and we now know how to sinter fuel elements tougher than those in NERVA or Timberwind. But the comparison to a PBR is still disingenuous: the design principles are deeply different.   

 

Offline GI-Thruster

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Re: tripropellant rockets
« Reply #37 on: 03/13/2009 01:55 pm »
Just continuing on with John Cole's latest on metallic hydrogen. . .this is a state change reaction, going from atomic solid molecular releases 216 MJ/kg.  Temp for this is >5600K or 9600F with an Isp in the 1700's so John proposes cooling with liquid H2 or water.  There are several different case studies, the most efficient of which seems to be the two stage to the Moon, water cooled.  Nice tables with the winner seeming to be an Isp of about 900-1100 or the edge of what present day materials can handle.  Tables with Lunar mission requirements, dv per maneuver, mix ratios, mass fractions, comparisons with Saturn V, Titan IV, Delta IV-H and Atlas V, vehicle sizing calculations and charts including Shuttle, Saturn V and the stick for comparison.

Great paper to look for once AIP publishes.

Offline khallow

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Re: tripropellant rockets
« Reply #38 on: 03/13/2009 06:20 pm »
Thing is, as far as I know, you have to store metallic hydrogen under tremendous pressure, a million atmospheres or more. You probaby  can generate useful thrust from just about any gas at that pressure.
Karl Hallowell

Offline GI-Thruster

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Re: tripropellant rockets
« Reply #39 on: 03/13/2009 08:56 pm »
Karl, the first half of the paper concerns the experiments to create metallic hydrogen.  I doubt it's fair even to say they've created enough to know the answer to that but in general, it is being portrayed as "metastable" so it is stable with specific temperature.  Meaning, they think if they keep it cold, as in immersed in liquid H2, then it will stay in its metallic state.  Of course, if they're wrong, there's a big boom.

Aren't you the one who said earlier, supersonic detonation and all that. . .very bad hair day for everyone within miles. . .

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Offline GraphGuy

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Re: tripropellant rockets
« Reply #41 on: 03/24/2009 08:38 pm »
http://www.wickmanspacecraft.com/loxmono.html

Check this out, these guys are mixing LOX with kerosene at cryogenic temps to create a 'monopropellant'. Dont know how stable this mixture is, but it could save some tankage mass if you only need one tank, and making it pressure fed, eliminate turbopumping, you'd have the liquid equivalent of a solid rocket motor. Comments?

Wouldn't mixing fuel and oxidizer in this manner turn the liquid engine into a bomb waiting to explode, even worse than a solid motor?  This would greatly increase your LOC numbers.  Also you might have problems if the density of LOX and cryogenic RP vary as you may have some settling when accelerating at multiple Gs.  If the fuel or the oxidizer floats to the top then you are in serious trouble.

Offline mlorrey

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Re: tripropellant rockets
« Reply #42 on: 04/01/2009 09:56 pm »
http://www.wickmanspacecraft.com/loxmono.html

Check this out, these guys are mixing LOX with kerosene at cryogenic temps to create a 'monopropellant'. Dont know how stable this mixture is, but it could save some tankage mass if you only need one tank, and making it pressure fed, eliminate turbopumping, you'd have the liquid equivalent of a solid rocket motor. Comments?

Wouldn't mixing fuel and oxidizer in this manner turn the liquid engine into a bomb waiting to explode, even worse than a solid motor?  This would greatly increase your LOC numbers.  Also you might have problems if the density of LOX and cryogenic RP vary as you may have some settling when accelerating at multiple Gs.  If the fuel or the oxidizer floats to the top then you are in serious trouble.

Technically, oxidation can only happen with both fuel, oxidizer, and HEAT. Cryogenic mixing of fuel and oxidizer LIQUID is theoretically nonflammable without a heat source or other form of shock (shock wave, electric arc, etc). You need to turn liquids into vapors (i.e. add heat) before you can ignite them anyways. Rocket engine combustion chambers are just very very efficient at doing this very quickly.
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Offline mars sts-107

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Re: tripropellant rockets
« Reply #43 on: 06/06/2009 02:26 pm »
I have been reading about of Wikipedia.
( http://en.wikipedia.org/wiki/Tripropellant_rocket )

It says - A mixture of lithium, hydrogen, and fluorine produced a specific impulse of 546 seconds; the highest ever of any chemical rocket motor.

An Isp of 546 is high enough to design a signal stage to orbit vehicle SSTO. Does anybody know, why an engine for this combination of fuel not being developed?


The propellants and exhaust are extremely toxic.

monomethal hydrozine and nitrogen tettroxide are toxic too and they use them

Offline Jim

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Re: tripropellant rockets
« Reply #44 on: 06/06/2009 04:11 pm »
I have been reading about of Wikipedia.
( http://en.wikipedia.org/wiki/Tripropellant_rocket )

It says - A mixture of lithium, hydrogen, and fluorine produced a specific impulse of 546 seconds; the highest ever of any chemical rocket motor.

An Isp of 546 is high enough to design a signal stage to orbit vehicle SSTO. Does anybody know, why an engine for this combination of fuel not being developed?


The propellants and exhaust are extremely toxic.

monomethal hydrozine and nitrogen tettroxide are toxic too and they use them

Not as toxic or hard to handle as flourine.

Offline mboeller

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Re: tripropellant rockets
« Reply #45 on: 06/16/2009 09:01 am »
here is a nice german website with informations about exotic tripropellant fuels:

http://www.bernd-leitenberger.de/raktreib3.shtml

the given exhaust velocities are not 100% correct but calculated with the program FCEA2. A comparison between FCEA2 results and real exhaust velocities can be seen in table1 .

Kapitel 7 shows mixtures of fuel
Kapitel 8 shows mixtures of oxidators
Kapitel 9 shows tripropellant and even fourpropellant (2x oxidator, 2x fuel) mixtures.
« Last Edit: 06/16/2009 09:05 am by mboeller »

Offline neph

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Re: tripropellant rockets
« Reply #46 on: 01/31/2020 08:44 am »
Necroing this thread to bring up another type of tripropellant...

There has been a [lot of research](https://www.intechopen.com/books/hydrogen-energy-challenges-and-perspectives/use-of-hydrogen-methane-blends-in-internal-combustion-engines) in H2-CH4 mixtures recently, but it's all in internal combustion studies. I've been thinking about a premixed LH2-LCH4-LOX rocket engine.

I suspect the benefits compared to either pure methalox or hydrolox include the elimination of the already limited coking of methane combustion, Isp increases compared to pure methalox, better properties for regenerative cooling than methalox, lower boiloff than pure hydrolox, and clearly substantial density improvements over hydrolox. Of course, I'm sure there's plenty of issues, such as the fact that your mixed fuel is probably more of a slurry than a mixture at the cryogenic temperatures that such a solution would require. Nonetheless, I wonder if the advantages wouldn't make it worth it.

Has any research been put into such an propellant system? If not a premixed fuel, what about a proper tripropellent system with a three-fluid injector plate?

Offline Seamurda

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Re: tripropellant rockets
« Reply #47 on: 02/01/2020 06:33 pm »
I've seen very many references to Salkelds papers on Tri propellant engines.

Does anyone have any copies of any of them?

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Re: tripropellant rockets
« Reply #48 on: 02/01/2020 07:27 pm »
Lockheed Agena and Bell engine (second stage & space vehicle) experimented with liquid flourine engines with some testing at the Lockheed 4000 acre Bonny Dune, Santa Cruz, CA test facility.

Some info on the web..

"Bell liquid flourine engine


https://www.abbottaerospace.com/wp-content/uploads/2017/08/naca-rm-e53j20-Preliminary-Investigation-of-Performance-and-Starting-Characteristics-of-Liquid-Fluorine-Liquid-Oxygen-Mixtures-with-1-250x296.jpg

PART III : 1958-1959
10. Early High-Energy Upper Stages
Legacy of Suntan
https://history.nasa.gov/SP-4404/ch10-2.htm

ended up with hydrolox... to P&W then to GD (ended up with Centaur)


https://history.nasa.gov/SP-4404/ch10-2.htm
Lockheed was interested in hydrazine - flourine engine


paper
Handling Liquid Flourine in Rocket Applications
A. R. Kimball
Bell Aircraft Corporation

Kimball A.R. (1960) Handling Liquid Fluorine in Rocket Applications. In: Timmerhaus K.D. (eds) Advances in Cryogenic Engineering. Advances in Cryogenic Engineering, vol 5. Springer, Boston, MA
https://link.springer.com/chapter/10.1007/978-1-4757-0537-9_9

Offline Proponent

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Re: tripropellant rockets
« Reply #49 on: 02/01/2020 08:08 pm »
Fluorine, please, not flourine.

Sorry -- it's a pet peeve of mine.

Offline gin455res

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Re: tripropellant rockets
« Reply #50 on: 02/02/2020 09:36 pm »
I just did a 'back of the envelope' calculation that suggests a LOX ethanol/gasoline (E60) blend might have roughly the same Oxidiser/Fuel  ratio (by volume) as LOX/methane but it would be about 18% heavier.

I wonder if this or something similar like sub-cooled E60 but with propane or butane (not gasoline), might make an okay tri-propellant with methane and LOX?

Could a single gas-generator be used for both fuels during a launch?

How would it coke?

Would E60-ish make for a more or less economical gas-generator fuel?

If the industry is now comfortable with 37 engines on a booster, could one set of high thrust engines and another set high isp engines be employed together on a first-stage - (if the engine cannot switch fuels in flight)?


Or perhaps the E60-ish variant of the engine might be used on the booster and the methane variant on the upper-stage. Perhaps, giving a falcon 9 (or  Electron) equivalent but with less coking and better re-usability on the booster.

Offline Genial Precis

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Re: tripropellant rockets
« Reply #51 on: 02/05/2020 04:12 pm »
The thing is, methane is so hydrogen-rich that its Isp is substantially better than other hydrocarbons, burned with oxygen. Check out this 1986 survey of tripropellant concepts; it hasn't lost much relevance. Li and Be are too rare to be viable. Al and Si are the only thing competitive with H for burning with O. If you could densify methane or hydrogen by cheaply cramming them full of one of those, in a way that allowed such a good engine as Raptor to operate, preferably without complicating injection (unacceptably, I think) by turning them into gels, you could make a more compact (hence lighter, more payload) Starship/Superheavy.

Any substantial improvement from there basically involves a scramjet or nuclear thermal I think. And Starship has the potential to be so big and cheap that those are tough asks.

Offline edzieba

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Re: tripropellant rockets
« Reply #52 on: 02/06/2020 10:12 am »
For the "low-ISP-high-thrust fuel for takeoff only" tripropellant variant, it may make more sense to go the Thrust Augmented Nozzle route, rather than muck about trying to get an extra propellant injected into the main combustion chamber (or worse, try and massage it through the same propellant lines and turbomachinery).
« Last Edit: 02/06/2020 10:19 am by edzieba »

Offline Genial Precis

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Re: tripropellant rockets
« Reply #53 on: 02/06/2020 06:37 pm »
Al can't really be used as a separate propellant, to the best of my knowledge. You'd have to load it into the methane somehow. Which isn't exactly a tripropellant, but people have discussed mixtures here. And the point of using Al is that it's the only thing you can load into methane that doesn't reduce the Isp at all, and that works up to 67% by mass.

That said, I think it would increase the exhaust temperature, because Al2O3 isn't a gas and contributes nothing to thrust. To keep same Isp the other products need to move faster=hotter. Not sure if Raptor engines conceivably have room for that.

Offline gin455res

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Re: tripropellant rockets
« Reply #54 on: 03/11/2020 04:06 pm »
I think I read on here, that the cubed square law means that as rocket engines get larger they need less cooling.

Could tri-propellants take advantage of this once a certain size engine is reached by using only one fuel for both cooling and in the pump gas-generator?

For example, if the engine ran on LOX, kerosene and alcohol, could it reach a size where only the alcohol is needed for cooling (here the tri-propellant is purely used to improve re-usability by eliminating coking, not for density advantages)?

Offline Nilof

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Re: tripropellant rockets
« Reply #55 on: 03/19/2020 05:37 pm »
If you are going for hazardous rockets, my personal favorite is the pebble bed nuclear thermal rocket with LH2 as the ejection mass ala Project Timberwind. T/W ratio of 30 and 890 Isp at sea level. LN or CO2 as the ejection mass would increase thrust at cost of Isp. It isn't very different from a pebble bed nuclear reactor. Many countries have the technology required, including China.


That engine may be too dangerous for an LV but it would rock for a lunar shuttle no more launching a new EDS for every lunar mission just refuel the nuclear ferry.

Also with a T/W that high if it can throttle deeply and quickly it would make a good lunar lander engine too.

NTR for a lunar shuttle is not really a good idea either because the logistics are a PITA.

In vacuum, neutron radiation goes down as an inverse square law instead of exponentially with distance, and mostly unshielded multi-gigawatt nuclear reactors are REALLY neutron-bright during engine burns. Everyone in a lunar bases that it flies over or lands next to has to go into a radiation shelter.

On top of it, you only get an ISP advantage if all your reaction mass is hydrogen... which is the only thing which is in really short supply on the surface of the moon. If you have an oxygen source which is trivial for the moon, then hydrolox ISRU uses hydrogen from earth much more efficiently.

EDIT: holy necroposting
« Last Edit: 03/19/2020 05:38 pm by Nilof »
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline Nilof

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Re: tripropellant rockets
« Reply #56 on: 03/19/2020 05:39 pm »
I think I read on here, that the cubed square law means that as rocket engines get larger they need less cooling.

Could tri-propellants take advantage of this once a certain size engine is reached by using only one fuel for both cooling and in the pump gas-generator?

For example, if the engine ran on LOX, kerosene and alcohol, could it reach a size where only the alcohol is needed for cooling (here the tri-propellant is purely used to improve re-usability by eliminating coking, not for density advantages)?

RD-701 used hydrogen and no RP-1 for cooling iirc, though someone might correct me.
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline Proponent

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Re: tripropellant rockets
« Reply #57 on: 03/19/2020 08:34 pm »
RD-701 used hydrogen and no RP-1 for cooling iirc, though someone might correct me.

I don't know, but on first principles, that might make sense.  The molar heat capacity of hydrogen may not be far off that or RP-1, meaning that the mass-specific heat capacity of hydrogen would be much higher.

Offline john smith 19

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Re: tripropellant rockets
« Reply #58 on: 03/21/2020 09:16 am »
I have been reading about of Wikipedia.
( http://en.wikipedia.org/wiki/Tripropellant_rocket )

It says - A mixture of lithium, hydrogen, and fluorine produced a specific impulse of 546 seconds; the highest ever of any chemical rocket motor.

An Isp of 546 is high enough to design a signal stage to orbit vehicle SSTO. Does anybody know, why an engine for this combination of fuel not being developed?


The propellants and exhaust are extremely toxic.
That pretty much sums up exactly why no one has built a vehicle to fly it.

You're also needing to handle both LH2 at -253c and Lithium at +180c before they start mixing together.  Burning it will give you HF which will react with any atmospheric water vapor to form hydroflouric acid which is used to etch glass.

Should you be interested in a viable tripropellant engine then later this year Reaction Engines Limited will start ground test of SABRE. As it runs on air/LH2/LOX it also is a tripropellant design but instead of switching fuels (the normal change) it switches oxidizers.

Air breathing Isp will be somewhere north of 3000 secs.
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Offline RanulfC

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Re: tripropellant rockets
« Reply #59 on: 06/05/2020 09:15 pm »
If you are going for hazardous rockets, my personal favorite is the pebble bed nuclear thermal rocket with LH2 as the ejection mass ala Project Timberwind. T/W ratio of 30 and 890 Isp at sea level. LN or CO2 as the ejection mass would increase thrust at cost of Isp. It isn't very different from a pebble bed nuclear reactor. Many countries have the technology required, including China.


That engine may be too dangerous for an LV but it would rock for a lunar shuttle no more launching a new EDS for every lunar mission just refuel the nuclear ferry.

Also with a T/W that high if it can throttle deeply and quickly it would make a good lunar lander engine too.

NTR for a lunar shuttle is not really a good idea either because the logistics are a PITA.

In vacuum, neutron radiation goes down as an inverse square law instead of exponentially with distance, and mostly unshielded multi-gigawatt nuclear reactors are REALLY neutron-bright during engine burns. Everyone in a lunar bases that it flies over or lands next to has to go into a radiation shelter.

On top of it, you only get an ISP advantage if all your reaction mass is hydrogen... which is the only thing which is in really short supply on the surface of the moon. If you have an oxygen source which is trivial for the moon, then hydrolox ISRU uses hydrogen from earth much more efficiently.

I think the 'ferry' is an orbit-to-orbit not a lander just FYI, I don't recall any suggestions, (serious ones anyway) for a lander. (Hence the "EDS" or "Earth Departure Stage" which in itself is "incorrect" since it would be E/LDS I suppose... :) )

Of course we now know that the pebble bed has worse internal drag than the NERVA and lower ISP than expected and they still had issues with uncontrolled hot-spots.. Eh we keep working on it :)

Quote
EDIT: holy necroposting

Ya, I actually started from the most recent and thought to review and WOW.. :)

Randy
[/quote]
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline RanulfC

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Re: tripropellant rockets
« Reply #60 on: 06/05/2020 09:18 pm »
I have been reading about of Wikipedia.
( http://en.wikipedia.org/wiki/Tripropellant_rocket )

It says - A mixture of lithium, hydrogen, and fluorine produced a specific impulse of 546 seconds; the highest ever of any chemical rocket motor.

An Isp of 546 is high enough to design a signal stage to orbit vehicle SSTO. Does anybody know, why an engine for this combination of fuel not being developed?


The propellants and exhaust are extremely toxic.
That pretty much sums up exactly why no one has built a vehicle to fly it.

Yep the few contractors who actually worked with the stuff were uber-glad the military lost interest in the idea :) Of course having said that they've been interested in a lot of gelled-metallic additive propellants for the last couple of decades and the only good thing to say is it's less likely to kill your ground crew and flight crew but arguably worse for anyone 'behind' you as it were :)

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline john smith 19

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Re: tripropellant rockets
« Reply #61 on: 06/07/2020 06:20 pm »
That pretty much sums up exactly why no one has built a vehicle to fly it.

Yep the few contractors who actually worked with the stuff were uber-glad the military lost interest in the idea :) Of course having said that they've been interested in a lot of gelled-metallic additive propellants for the last couple of decades and the only good thing to say is it's less likely to kill your ground crew and flight crew but arguably worse for anyone 'behind' you as it were :)

Randy
[/quote]
I thought gelled props were meant to be more safe than equivalent systems, while giving better Isp than solids.  Somehow thought they just never quite get over the line.  :(
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline RanulfC

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Re: tripropellant rockets
« Reply #62 on: 06/10/2020 07:34 pm »
I thought gelled props were meant to be more safe than equivalent systems, while giving better Isp than solids.  Somehow thought they just never quite get over the line.  :(

Well the gelled propellants they DO use are pretty effective it's just some (in the military in particular :) ) would like to see them be MORE effective... Often it seems without thinking through the outcomes :)

(I can understand this in many cases given what the 'military' is generally concerned with but in this case it was often JUST to get a few hundred pounds more of payload to LEO. And without batting the proverbial eye the report would usually go on to say "and it can increase operational capability significantly!" without remembering that they said just a few paragraphs before how toxic the exhaust would probably be :) )

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

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Re: tripropellant rockets
« Reply #63 on: 08/21/2022 10:31 am »
I just did a 'back of the envelope' calculation that suggests a LOX ethanol/gasoline (E60) blend might have roughly the same Oxidiser/Fuel  ratio (by volume) as LOX/methane but it would be about 18% heavier.

I wonder if this or something similar like sub-cooled E60 but with propane or butane (not gasoline), might make an okay tri-propellant with methane and LOX?

Could a single gas-generator be used for both fuels during a launch?

How would it coke?

Would E60-ish make for a more or less economical gas-generator fuel?

If the industry is now comfortable with 37 engines on a booster, could one set of high thrust engines and another set high isp engines be employed together on a first-stage - (if the engine cannot switch fuels in flight)?


Or perhaps the E60-ish variant of the engine might be used on the booster and the methane variant on the upper-stage. Perhaps, giving a falcon 9 (or  Electron) equivalent but with less coking and better re-usability on the booster.

I've been thinking on this one myself;  Engine clusters present the opportunity for heterogeneous engines;  If a mix of engines of different propellant types allowed for enough of a performance gain, it might make up for a difference betwixt mid performance GG cycle engines and high performance staged combustion engines.  Like matching a Raptor stage using a Vulcain and a Prometheus in a European context (a combination I mentioned in a thread over there).  If it does perform well enough, you could still get a vehicle up to or somewhat larger than New Glenn.  Though I'm not sure how this would impact stage dry mass.  The Ariane 5 core stage has an amazing mass fraction for a hydrogen stage (and I'm pretty sure that adds to its manufacturing costs), as do both Starship stages (using denser Methalox).  Would a stage with two common bulkheads for three propellants gain enough mass to counter the loss in vehicle length / barrel sections by swapping part of the hydrogen with methane?

One reason the Prometheus / Vulcain combination occurred to me was that the Prometheus has restart and throttle capabilities, allowing for a propulsive landing.  Some people in the Prometheus thread showed a rather startling asymtotic growth in first stage size if an all-Prometheus stage was pushed through moderate Δv and a landing.  Don't know if that would be better or worse with an improved ISP and worse mass fraction via a tripropellant system.

Offline edzieba

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Re: tripropellant rockets
« Reply #64 on: 08/22/2022 07:50 am »
The downside of heterogenous engine combinations is that all the engines not in use now add to your dry mass, eating away at the impulse gains of your added low-thrust-high-efficiency engines. If you are adding what is effectively an entire extra stage, it makes more sense to make it separable and discardable (or recoverable) rather than integrating it: you 'lose' the dry mass gains of a single enlarged oxidiser tank rather than two separate ones, but add on the dry mass benefits of discarding an entire additional propellant tanks and engines.
TAN designs get to sidestep some of this by using existing mostly existing engine mass (outer bell requires some additional plumbing and possible reinforcement) rather than adding new engine mass, and can gain the sea level thrust and exhaust stability benefits without heterogenous fuels.

Offline markbike528cbx

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Re: tripropellant rockets
« Reply #65 on: 08/22/2022 10:52 am »
I have been reading about of Wikipedia.
( http://en.wikipedia.org/wiki/Tripropellant_rocket )

It says - A mixture of lithium, hydrogen, and fluorine produced a specific impulse of 546 seconds; the highest ever of any chemical rocket motor.

An Isp of 546 is high enough to design a signal stage to orbit vehicle SSTO. Does anybody know, why an engine for this combination of fuel not being developed?

I didn't see any direct answers in the form of a quote from Ignition! by John D. Clark (1st ed. 1972)

Page 188 talks about Li-F-H triprop.

among other things it mentions:

"......Add to this the fact that liquid lithium is highly corrosive to most metals, and that it is incompatible with anything you might want to use for gaskets and sealing materials (it even attacks Teflon with enthusiasm), and you have problems.  ....."

Offline john smith 19

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Re: tripropellant rockets
« Reply #66 on: 08/23/2022 01:05 pm »
The downside of heterogenous engine combinations is that all the engines not in use now add to your dry mass, eating away at the impulse gains of your added low-thrust-high-efficiency engines. If you are adding what is effectively an entire extra stage, it makes more sense to make it separable and discardable (or recoverable) rather than integrating it: you 'lose' the dry mass gains of a single enlarged oxidiser tank rather than two separate ones, but add on the dry mass benefits of discarding an entire additional propellant tanks and engines.
TAN designs get to sidestep some of this by using existing mostly existing engine mass (outer bell requires some additional plumbing and possible reinforcement) rather than adding new engine mass, and can gain the sea level thrust and exhaust stability benefits without heterogenous fuels.
As does SABRE, by sharing significant sub systems (IE the pre-burner) between the air and oxygen modes of the engine

Most people think of a tri-propellant as a 2 fuel system but as SABRE demonstrates it can also be an 2 Oxydizer system as well.
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline Jim

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Re: tripropellant rockets
« Reply #67 on: 08/23/2022 02:21 pm »


Most people think of a tri-propellant as a 2 fuel system but as SABRE demonstrates it can also be an 2 Oxydizer system as well.

Not really.  It is only one, Oxygen, just different phases.

Offline john smith 19

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Re: tripropellant rockets
« Reply #68 on: 08/23/2022 04:20 pm »

Not really.  It is only one, Oxygen, just different phases.
Except one of those phases is also mixed with 80% N2.
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline edzieba

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Re: tripropellant rockets
« Reply #69 on: 08/24/2022 07:50 am »

Not really.  It is only one, Oxygen, just different phases.
Except one of those phases is also mixed with 80% N2.
That's more a diluent injection than an extra oxidiser (since N2 is pretty close to inert inside the engine, apart form some parasitic reactions). Diluent injections for air-breathing engines is not unheard of, usually via water injection into the comrpessor (the Harrier in vertical flight, the Skyburner YF-4, and proposed F-4X) but I can't recall any rocket engines deliberately adding any diluents beyond combustion products form a gas generator or preburner.

Offline libra

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Re: tripropellant rockets
« Reply #70 on: 08/24/2022 08:44 am »
Tripropellant rocketry ( as explored by Salkeld, Beichel, Lozino Lozinskyi and Mel Bulman)  is
- all rocket, not airbreathing
- kerosene + LH2 fuels with LOX oxidizer
- to get the best of both fuels
- high-thrust for takeoff
- high-energy for the ascent

Labelling an airbreathing system "tripropellant" because LOX+air+LH2 is either confusing or misleading.

"Tripropellant" historically is RP-1+LH2+LOX, not airbreathing.

Offline edzieba

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Re: tripropellant rockets
« Reply #71 on: 08/24/2022 12:26 pm »
That historic constraint is no constraint at all. There is no reason you cannot build a LOX/LH2/Propylene engine (so you can add a common dome or concentric tanks without the freezing/gelling risk), or a Peroxide/Butane/RJ-5 (to avoid handling cryogens), etc.
Whether any of these combinations works out in practice - just as with LOX/LH2/RP-1 - depends on the specific architecture it is to be used with.

Offline Asteroza

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Re: tripropellant rockets
« Reply #72 on: 08/24/2022 11:03 pm »
Didn't HMXHMX say he wanted to do a LOx/LH2/Propane rocket if he was going to make another stab at a new rocket?

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