LH2 fuel replacement... - ...NaH / NaBH4?

Josh Cryer · 2002-05-02 15:33:21

Hey guys, I was just thinking. The space shuttle uses liquid hydrogen and oxygen as fuel. Why couldn't the next generation space shuttle use something that contains hydrogen, yet is more ?compact? and stable (like NaH or NaBH4- both powdered forms)?

Could we convert these chemicals into pure hydrogen quick enough to sustain a rocket?

The problem with liquid hydrogen, is that volume-wise, you waste a lot of space while storing it. Even in liquid form, NaH beats hyrdogen 2 two 1 space-wise.

Canth · 2002-05-02 21:51:32

It is hard to feed a rocket powder however many liquid fuels are used as hydrogen substitutes. Also you don't need to convert the fuel to hydrogen, you just find one which reacts completely with the oxidizer and use that, it is more efficient. However if you meant making the powder into hydrogen and feeding the hydrogen into the engine this requires a lot of extra weight. There is no reason you couldn't dissolve the fuel in water at as much fuel to water as possibe and feed that into the engine letting it react with the oxidizer.
Also flourine is a much better oxidizer than oxygen in terms of preformance and the fact it is non cryogenic (you don't have to super cool it to make it liquid). The problem with flourine is it is toxic when in pure elemental form, while the rocket exaust wouldn't necisarily be toxic if the rocket exploded or crashed it could spread a toxic gas, not good. (flourine is the most reactive element)
Another thing you want is a light fuel (better preformance, lower weight) at least in general. So using lithium or another light element in place of sodium is more effecient. I think you are on the right track thinking about new fuels and propulsion methods. As far as chemical rockets go I favor flourine hydrogen or a similar high preformance fuel. Flourine and methane or kerosine will also work I beleive. Kerosine would allow greater fuel density and all the fuels involed would be liquid at room temperature simplifying things greatly in many ways.

C M Edwards · 2002-05-07 11:53:43

If you can be assured of sufficient heat from an outside source, such as in a solar thermal rocket, you can crack methane or propane to yield a rocket exhaust that is mostly hydrogen and pure carbon. This mixture is relatively light in terms of molecular weight.

Basically, the lighter the molecular weight of the exhaust, the more efficient a thermal rocket is going to be. That's one reason why hydrogen is among the best possible rocket fuels -- nothing is lighter. Electric rockets, like ion drives, can get even higher efficiencies, but they use other means than heat to accelerate their exhaust.

CME

Canth · 2002-05-07 13:23:27

I beleive electric rockets (like ion drives) get more thrust and higher effeciency from heavier fuels. Deep space one used xenon because it is heavy gaseous and extremely unreactive. Chemical and thermal rockets do work better with lighter fuels with small molecular sizes. I beleive the best fuel would be helium (monoatomic hydrogen being virtually impossible to make according to current theories) the only reason you wouldn't use it is the difficulty of keeping it liquified. It requires lower temperatures than any other known substance to liquify.

Mark S · 2002-05-17 13:30:42

Is there any way to store H2 in a more dense fashion than we currently do? It would do a great deal to cut down on the structural weight of the rocket if we could. Monatomic hydrogen could be denser than H2, but like somebody mentioned, it's probably not possible to make and store it. Hyrogen's low density makes me favor rocket-grade kerosene or methane for rockets.

It would also be advisable to look for an alternative to Liquid Oxygen, because the oxidizer makes up the majority of the rocket's weight. Hydrogen Peroxide is dense, but it has a lower ISp than LOX and there aren't too many engins that burn it. It's also pretty pricey. The best solution would be using oxygen from the atmosphere. If only we could get a working scramjet or LACE engine...

Canth · 2002-05-17 15:55:09

Actually monoatomic hydrogen is less dense than standard hydrogen. Even if flourine is more expensive than lox it is non crygenic and so it is gonna be cheaper to store. I gather the biggest problem is that flourine and many of its compounds are HIGHLY toxic. In the event of a failure there could be a major ecological disaster. Also the rocket exaust would be toxic. Flourine was used to test new fuels and I beleive that the Soviet's original design for a moon rocket used flourine as the oxidizer.
Kerosine is favored as the fuel for the next generation reusable launch vehicle, liquid oxygen the oxidizer.

mauk2 · 2002-12-10 22:57:26

If you HAVE to use chemical fuels for a launcher, then you want the most energetic mix you can get that is still dense enough to keep your tankage reasonable.

After a LOT of tinkering, I have reached the conclusion that the best possible set of chemical fuels for a HLV first stage is Diborane(B2H6) and Oxygen DiFlouride(OF2).

Diborane is about 6 times as dense as LH2, and is liquid at much higher temperatures, reducing boiloff.

Oxygen DiFluoride is about 40 percent denser than LOX, and is liquid at almost exactly the same temps.

Both are insensitive to shock, but are VERY poisonous. Also, the exhaust is not anything to be breathing.

All that is good stuff, but the real winner is the Isp: RP1 and LOX has sea level Isp of about 300. Diborane/OF2 has sea level Isp of about 400.

That is darn near the performance of LH2/LOX!

Imagine that beastly Russian rocket, the RD-170, reworked to burn this stuff! SeaLaunch fires the Xenit from out in the ocean anyway, the toxicity won't matter beans.

Now imagine a launcher with a first stage of 7 RD-173 variants burning DiBorane/OF2.

12,100,000 pounds of liftoff thrust, with an Isp of 400!

Whee!

nirgal · 2002-12-11 08:48:11

Wow! That is really impressive... Just how poisonous are these fuels? Would it be possible to use them when launching from a pad in the vicinity of populated areas (cape canaveral)?

Mark S · 2002-12-11 09:00:28

Fluorine had been considered during the space race as an oxidizer (?) necause the combination of hydrogen and fluorine actually gives an ISp around 600 seconds! But NASA rejected it based on its hazards, despite the performance benefits. I would think that Oxygen Difluoride would be no different.

Austin Stanley · 2002-12-11 15:15:31

There's good reason why flourine is not used as an oxidiser. It's toxicity cannot be overstated. Flourine, be it in it's elemental form (F2) or bound up with a diffrent chemical (HF, NaF, LiF, ect...), is very, very toxic. Especialy in the huge quantities we are dealing with here. The same applies to the other halogens, to a lesser degree as you procided down the periodic table. Even realitivily tame NaF has an LD50 esstimated as low as 20mg/Kg if ingested.

The most likely product of an flourine oxidies rocket, HF (Hydroflouric Acid), is much worse. It's a weak Acid with a pH around 1.6. It's toxicity is much worse, LD50 being around 1,300 ppm for inhalation. Worse, HF acid will easily penetrate skin and attack the tissue underneath. It's also deadly to aquatic life in concentrations around 60ppm, and it's probably not good for plant life as well. Even realitivly low doses of HF (or realy any flourine compound), can result in flourosis, a condition which results in various skeletal and dental problems.

I read a case study about someone who had a realitivily mild HF burn. In this case, the person recived a small splash (maybe 5cm^2) of a low (20% HF) solution. There never was any damage to the exterior tissue, however the HF had traveled right though his skin and attacked the underling tissues underneath. Treatment was very difficult, and only quick thinking and action by the doctor prevented the man from losing his hand, and possibly his life.

Not to mention the fact that HF will attack many metals and glass. Aliens wasn't a complete lie, just an exageration. HF acid realy does errode away at glass and other materials like no other acid (except maybe aqua regent, but I disgress).

Imagine a HLV in the Saturn V class, it's lift off would spew some 2 million kg of various toxic flouride products into the atmosphere and land around it's launch site. Of course for the bigger launch vehicles the problem gets even worse. The HF would probably do damage to the launch stand (maybe even the rocket itself), even if protected, as I imagine the violace of the launch would probably errode some of this. And the entire surrounding area would be innudated with HF. It would be danagerous to approach the launch site for quite some time, and I expect much (if not all) of the plant life would die. At a sight like cape-canavral the ocean would be polluted as well. And a sea launch would be horrible resulting in massive fish-kill.

No, we don't use flourine as an oxidant for good reason. It's just to dangerous to play around with. Even during loading, cryogenic oxygen or hydrogen is (in comparison), much, much safer than flourine. Maybe if the launch pad was in the desert it might be an option, but even then I doubt it. The risks and the pollution is just to great. We'd be better off using something like orion and nuclear bombs.

Check out the MSDS (Material Safety Data Sheet) for HF here:
http://specchem-apps.alliedsignal.com/p … S/hfan.pdf

mauk2 · 2002-12-11 19:50:04

Nirgal: VERY poisonous. OF2 is not quite as mean as pure fluorine, but the difference is not worth bothering over. Plus, DiBorane is nothing to mess with either.

That said, NO, you would NEVER use this fuel mix anywhere near people. As I posted, launching a modified Zenit (sp) way out in the middle of the ocean would be the only way to do this. While the exhaust of such a launch would be very toxic, diluting it into a thousand cubic kilometers of sea water would do a handy job of dropping those concentrations, wouldn't it. A thousand cubic kilometers in the Pacific is literally like a drop in a bucket.

As for the info posted by Austin Stanley: Like I said, if you HAVE to use chemicals, this fuel mix is a very good compromise for a lower stage. I would prefer a sealed core NTR myself, Orion is just too hard to make work as of yet.

Austin Stanley · 2002-12-11 21:23:02

I have to disagree with mauk2 on this. Even for the smaller Saturn V rocket, the release of around 2 million kg of HF (or other flourine compounds, it's the disolved F- ions which do the dirty work, and they pretty much all disolve in water), could be expected to toxify 33 million cubic meters of the pacific (assuming 60ppm toxicity). And were talking total death in this region. The effects could easily be expected to be lethal as much as a cubic km from the sight. Given the nature of the ocean, however, this area would not be a true cubic km, but much more spread out. Maybe HF could be used in smaller amounts in the upper stages, but I think it is much to dangerous to use here on earth.

mauk2 · 2002-12-11 23:22:12

Austin Stanley: I am a trifle confused. Using your figures, 33 million cubic meters of water is about 3 percent of one cubic kilometer of water. A cubic kilometer of water is a LOT of water, and the ocean has lot of them.

Assume we have a launch with a thruster that used flourine, in whole or part, as the oxidiser in the first stage. The 2 million kilos of fluorine ions that is released is done so over a period of two minutes. Pulling some trajectory numbers from the air, at the time of burnout, lets say the booster is (conservatively) 100 kilometers downrange, and 50 kilometers high.

If the flourine falls back to the surface in a rough triangle, and the width of the plume at the furthest extent is 60 kilometers, then the toxic fluorine hits the ocean spread over an area of 3000 square kilometers, or three billion square meters. At 60 ppm as you state, the flourine will have a toxic concentration to a depth of 1 cm, averaged over that entire area. :0

The concentrations will be very high near the launch site, of course, but that simply means that the majority of the emission is spread over a large area of ocean at even lower concentrations than I assume above. Add in the fact that the fluorine will reach the water spread over time, and I would wager that most of the emissions would never reach the water in concentrations high enough to be toxic at all.

So, not to detract from the very, very poisonous nature of this stuff, the risk could be easily mitigated through the choice of a proper launch site.

Of course, if you're going to be SERIOUS about getting into space, then nuclear is the real option to pursue.

Austin Stanley · 2002-12-12 09:57:42

I understand your point mauk2, but here's why I still disagree.

#1. A 60 ppm toxicity is a VERY concervative figure. Although the data I have is for fresh water, I think it is safe to assume that nearly Everything exposed to that region of toxicity would die. It's certianly high enough to kill most of us humans. From fish to whales (low probability of them being at the launch site at the time, I know), and probably most of the plankton and other micro-organisims as well. Even when it has diluted down to 18 ppm (a cubic km away), it would still be very dangerous. You wouldn't want to drink such water, you'd get very sick. Sea life wouldn't be much diffrent. So seing effects out that far is highly likely. Concentrations as low as 2 ppm are supposed to cause fluorosis in humans, and I imagine bony fishes could suffer from this condition as well.

#2. You have to plan for a worse case scenario. A typical rocket launch would spread the flourine out over a wide area. Although higher impulse fuels like what we are talking about here would spend more of there fuel at lower alltitudes right higher specific impulse=(requires) a higher rate of mass discharge. But you must plan for a worse case-scenario, that is, the rocket blowing up on the pad, or something else like that.

#3. We're not just talking about one launch here, but many. The effects are multiplied over the length the booster is in use, which I hope will end up being much longer than the Saturn series of boosters.

#4. Launches are offten proposed to take place far out in the Pacific, where the sea-life densities are generaly lower and there is good isolation from inhabeted areas. But the logistics of such an opperation make me highly doubtfull. More-likely is a launch near a convient supply island, like some place in the Carribian or what not.

#5. Technical considerations. As I pointed out earlier, HF will eat at pretty much anything, from most base metals, to glass and even concreate! How are you going to design a launch ship to deal with this extream corusivness. In fact, the entire concept of a gigantic launch ship, floating out into the deep-blue sea, and then launching a enormous rocket (the vessle itself being unmanned I should hope), gets less and less belivable the more I think about it. I suppose it's technicaly possible, but building bigger conventional rockets on land is probably a better solution.

mauk2 · 2002-12-12 16:59:59

Ok, responses;

1) Assuming my crude model of plume dispersal from above is correct, then it would be reasonable to state that wave actions would disperse the fluorine atoms into the top 1 meter of the ocean within five minutes. That would drop the concentration from 60 ppm to .6 ppm. well below the toxicity levels you mention here. Suppose that after a day the atoms are spread into the top 100 meters of the ocean. That drops the concentration to a meager .006 ppm.

The ocean is WAY deeper than 100 meters, too.

Would there be fish kills? Probably. But they would be minor indeed.

2) A worst case scenario could be handled by simply bringing along a few thousand tons of a neutralizing agent. This would also handily deal with the increased toxicity levels close to the launch ship. IE, instead of using water in your sound suppression sprays, use sodium hydroxide or some more compatible strong base. Neutralize the highest concentratioons of the mean stuff before it goes anywhere.

To deal with launch-pad blowups, we use a semi-submersible ship. The ship is protected by 40 feet of water from the explosion, and the dense, reactive fuels are neutralized by the same toxicity reducing sprays I mentioned before. It will be a big ship, ten or twenty thousand tons of a safety chemical would be no problem to bring along.

Oh, and if your fuel has a higher Isp, you need a LOWER mass flow for a givem thrust level, so there would be less exhaust at the launch site than with a less toxic fuel.

3) This is the most valid point yet.... I suspect using the toxicity neutralizing sprays would help a lot with this, but to be honest, for a long term HLV system, I'd advocate a nuclear option. It's going to have better performance and be cleaner.

4) The beauty of the Pacific as a launch point is the long stretch of clear water at the Equator. Launching from the Equator is very attractive if you are using a chemical launcher, because every little bit of velocity helps. for this reason, I don't see any huge obstacles to using the Pacific as the launch point.

5) Well, we are already building HUGE semi-submersible ships for other purposes: Take a look at this pdf on a big one that is going to be made even bigger next year.

http://www.dockwise.com/news....lin.pdf

That monster could be used as a launch base with only minor modifications, and I have seen designs for even bigger semi-submersible vessels.

Much of the resistance/corrosion problems could be solved by using teflon paint on the ship, and soaking it with a chemical neutralizer during and after launch.

I see this as a very doable thing, personally.

Of course, my true love is nuclear powered boosters. I have not tinkered on this chemical stuff for years. An Isp of 400 is TINY compared to the capabilities of nuclear.

soph · 2002-12-12 17:12:53

i dont think something that toxic will be looked upon with any more favor than nuclear systems. in fact, i think that they will make nuclear systems more favorable, which may or may not be a good thing, depending on your perspective.

Austin Stanley · 2002-12-12 22:48:32

I've looked into possibilties of neutralisation, but they don't look promissing to me. Flourine, like other hallogens, is very soluable in most compounds. There are only a few exceptions, such as BaF2, MgF2, PbF2. All three of these have fairly low Ksp (solubility constant) as well. In any case, precipitating the flouride ions out is not going to work well. The precipitate will simply sink and slowly dissolve as well. Perhaps it might be possible to capture it in big nets, but this seems highly dubious to me. I'm a chemistry major, but admitdly do not everything. Even-so, I don't know of any other means of removing flourine from aquious solution. Even today, flourine is produced by electrolisis of HF acid. HF is created by disolving Fluorspar (CaF2) in Sulphuric Acid (H2SO4) btw.

The dilution you propose would not be effective. The reaction plays out like this:
2NaOH(aq) + F2(g) -> 2NaF(aq) + H2O + OF2(g)
the reaction with HF would have no appreciable reaction (both would disolve in water). Remember for most flourine compounds it's not the acidity H+ ion concentration, but the F- ions that are the toxicity problems. Neutralising the acidity of the solution doesn't help. Besides, flourine is SO electronegative that it will litteraly attack the water breakng the O-H bonds. HF is also a weak acid, (meaing it does not dissasociate fully), so the more you neutralise the more goes out into solution.

The big problem with pad explosions is not the explosion itself (although of course those will be very bad), but the toxic release. A partialy submerged ship would obviously only increase these difficulties. Again, the launch system must be designed with the idea that a on-pad (or near-pad) explosion will occur and be designed to accept this. This is doubly true since these failures are among the most common anyways.

Well, I'm just dubious about supplying these huge ships out in the middle of the Pacific, what with the storms and what not out there. I have no doubt that such a ship could be built. It even could be protected from HF, but a wimpy coat of teflon sure ain't going to do it! Teflon is a thermosetting plastic IIRC, and it will surely melt from all the heat it will be subjected to, leaving the undersurface bare and unprotected. Even diluting the HF or percipitating the HF away will still leave you with a ship undergoing accelerated decay. Anyways, I grant that such a ship could be built, but building more Saturn V's would probably end up being cheaper than a fleet of these things. Another problem occured to me, where are you going to test the engines? No way the EPA is going to let you use the NASA sight in Mississippi (or was it Albama? I'm not sure and the name eludes me). A new site will have to built someplace remote. This applies to other new exotic big engines as well, something that needs to be considered.

Now as I said before I'm a chemist, not a rocket scientists. But I was under the impression that if you want to do a launch more with a higher ISP but the same ammount of propelent you would have either lower thrust (unaccaptable at lift-off), or higher mass consumption rates. Maybe you could point out where I'm wrong here.

Using HF in upper stages seems acceptable to me, as the quantities are generaly an order of magnitude lower, and the pollution is at high-alltiudes anyways. Of course there may be some flourine reactions with the upper atmosphere, but I know nothing about this, and won't speculate.

I have no problem with most nuclear designs though. Ironicly, they are much more eco-friendly that flourine engines.

mauk2 · 2002-12-15 21:38:07

I have no problem with most nuclear designs though. Ironicly, they are much more eco-friendly that flourine engines.

Heh. You have convinced me! Please go take a look at the Liberty Ship proposal I am working on when time allows, you are a bright fellow, see if I have screwed up the math or if I want to use alloys that are chemically impossible, or simila dopey things.

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#1 2002-05-02 15:33:21

Re: LH2 fuel replacement... - ...NaH / NaBH4?

#2 2002-05-02 21:51:32

Re: LH2 fuel replacement... - ...NaH / NaBH4?

#3 2002-05-07 11:53:43

Re: LH2 fuel replacement... - ...NaH / NaBH4?

#4 2002-05-07 13:23:27

Re: LH2 fuel replacement... - ...NaH / NaBH4?

#5 2002-05-17 13:30:42

Re: LH2 fuel replacement... - ...NaH / NaBH4?

#6 2002-05-17 15:55:09

Re: LH2 fuel replacement... - ...NaH / NaBH4?

#7 2002-12-10 22:57:26

Re: LH2 fuel replacement... - ...NaH / NaBH4?

#8 2002-12-11 08:48:11

Re: LH2 fuel replacement... - ...NaH / NaBH4?

#9 2002-12-11 09:00:28

Re: LH2 fuel replacement... - ...NaH / NaBH4?

#10 2002-12-11 15:15:31

Re: LH2 fuel replacement... - ...NaH / NaBH4?

#11 2002-12-11 19:50:04

Re: LH2 fuel replacement... - ...NaH / NaBH4?

#12 2002-12-11 21:23:02

Re: LH2 fuel replacement... - ...NaH / NaBH4?

#13 2002-12-11 23:22:12

Re: LH2 fuel replacement... - ...NaH / NaBH4?

#14 2002-12-12 09:57:42

Re: LH2 fuel replacement... - ...NaH / NaBH4?

#15 2002-12-12 16:59:59

Re: LH2 fuel replacement... - ...NaH / NaBH4?

#16 2002-12-12 17:12:53

Re: LH2 fuel replacement... - ...NaH / NaBH4?

#17 2002-12-12 22:48:32

Re: LH2 fuel replacement... - ...NaH / NaBH4?

#18 2002-12-15 21:38:07

Re: LH2 fuel replacement... - ...NaH / NaBH4?

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