NASA developing a new, eco-friendly propellant

[fredinno]

Unforunately the ISP of hot air is horrible....

[Rune]

The reason this is much better than hidrazine, actualy, is a complicated an interesting one.

Obviously the safety consideration plays a big part: not having to handle it suited in a special facility just before liftoff is sure a nice feature that will save a lot of money in spacecraft construction (handling toxic propellants is one of the reasons payloads cost as much as rockets).

But the others are more difficult to see. The ~20s more isp doesn't look like much... but any gram counts. Switching to this monopropellant may mean the difference between paying for a dual launch on Falcon, or needing a dedicated launch o a more expensive Arianne V slot. Likewise, that 40% greater volumetric efficiency means roughly 40% less tank weight... and that is actually quite the big gain.

As to monoprop vs biprop, sure, biprops get much higher Isp... but they need two feed and tank systems, not to mention the engine is at least twice as complicated. Twice the valves that can get stuck. MANY deep space missions have used monopropellant as their main propellant source, just because of that reason, and this way they could have as little as two valves in the whole propulsion engine, one to pressurize the tank and another to control the engine. All those things have weight.

So actually, for tiny dV requirements (like stationkeeping), or extreme endurance missions (like missions to the outer system), or just for simplicity's sake (cubesat propulsion sytsem), this monopropellant makes much more sense from a purely engineering standpoint. And in all those cases, the simplified handling during ground ops is going to save, literally, millions of dollars and a few lives too.

Rune. The most amazing thing is how it doesn't seem to have a drawback... that is not common.

[cryogen]

As to monoprop vs biprop, sure, biprops get much higher Isp... but they need two feed and tank systems, not to mention the engine is at least twice as complicated. Twice the valves that can get stuck. MANY deep space missions have used monopropellant as their main propellant source, just because of that reason, and this way they could have as little as two valves in the whole propulsion engine, one to pressurize the tank and another to control the engine. All those things have weight.

I don't think this is right.

The only deep-space missions that used monoprops were prehistoric ones, that were flyby-only. (To my knowledge). I don't know of any orbiter (high deep-space delta-v) that used monoprops.

The tank fraction isn't meaningfully higher for biprops than monoprop.

Biprops are very reliable; they have lots of space experience in GEO satellites. If you need more reliability, you can add redundant spares, since their weight is trivial (<4 kg for 400 N) compared to the fuel mass. Cassini did this:

[Rune]

I don't think this is right.

The only deep-space missions that used monoprops were prehistoric ones, that were flyby-only. (To my knowledge). I don't know of any orbiter (high deep-space delta-v) that used monoprops.

The tank fraction isn't meaningfully higher for biprops than monoprop.

Biprops are very reliable; they have lots of space experience in GEO satellites. If you need more reliability, you can add redundant spares, since their weight is trivial (<4 kg for 400 N) compared to the fuel mass. Cassini did this:

https://i.imgur.com/I57XqRel.jpg

New Horizons is kind of a probe right? And kind of current? Well, there you go: monopropellant thrusters only. If we had had this fuel 15 years ago, maybe now the scientists would be looking at a difficult decision between many KBO candidates for an extended mission, instead of the two that the probe can reach, even after scouring the heavens with Hubble.

I know bripropellant hypergolic engines are very light, very simple, their fuel keeps for a very long time in space, and they are very reliable: well, monopropellant engines are still more of all of those. Not every mission is an orbiter with sizable dV requirements. Cassini is a beast for an interplanetary probe, only the Phobos 1 and 2 missions by the Soviets were larger.

Besides, every manned spacecraft currently is loaded with highly toxic hydrazine and nitric acid for maneuvering thrusters, centimeters away form the people and accompanying them all the trip. By taking a small-ish performance hit, you could have a very reliable monoprop RCS system on the capsule, and all the dangerous high-performing stuff in an isolated service module.

Rune. Again, I'm still looking for a downside.

[cryogen]

New Horizons is kind of a probe right? And kind of current? Well, there you go: monopropellant thrusters only.

True, but that's only a flyby mission; it uses very little delta-v in deep space.

From a quick Google: MRO and MAVEN used monopropellants; Magellan used a solid rocket; and all of Galileo, Cassini, MESSENGER, Juno, Mangalyaan, Mars Express, and the future Europa Clipper and JUICE use bipropellants.

Besides, every manned spacecraft currently is loaded with highly toxic hydrazine and nitric acid for maneuvering thrusters, centimeters away form the people and accompanying them all the trip.

Still, they all use bipropellants for the main engines, not monoprops. In very large amounts too!

e.g.,

[TABLE=width: 600]

[TR]

[TD]Shuttle OMS[/TD]

[TD]MMH/NTO, 21,660 kg[/TD]

[/TR]

[TR]

[TD]Soyuz TMA-M (current)[/TD]

[TD]UDMH/NTO, 800 kg[/TD]

[/TR]

[TR]

[TD]SpaceX Dragon v2[/TD]

[TD]MMH/NTO, 1,290 kg[/TD]

[/TR]

[TR]

[TD]Boeing CST-100[/TD]

[TD]MMH/NTO[/TD]

[/TR]

[TR]

[TD]Orion Service Module (ESM)[/TD]

[TD]MMH/MON-3, 9,200 kg[/TD]

[/TR]

[/TABLE]

Edited August 23, 2015 by cryogen

[RuBisCO]

In other words, it's more likely to explode compared to keeping the fuel and oxidizer separate until they're in the combustion chamber of the engine.

Nobody likes uncommanded explosions in rockets IRL.

Then why is it going to ISS for space qualifications? They may have formulated the propellant and propulsion structure to insure a level of safety equal to that of hydrazine, yet have higher ISP, and be non-toxic.

[Ravenchant]

True, but that stuff is more dangerous to handle no matter how non-toxic it is.

Because it's basically a fuel-oxidizer stored in a single tank, it's quite unstable.

Not sure that's quite correct. Monopropellants such as hydrogen peroxide, hydrazine etc. typically thermally decompose when run through a catalyst material. There is no oxidiser to speak of.

[Bill Phil]

I suppose this is more economy friendly...

[SciMan]

@Ravenchant:

I was referring specifically to the "Nitrous Oxide Fuel Blend" (NOFBx) "monopropellant". It's not really even a monopropellant, because there's two different types of chemical in the mix.

That's why they call it "Nitrous Oxide Fuel Blend". Nitrous oxide is the oxidizer, and they're blending it with a fuel BEFORE they store it in the tank.

It doesn't take a genius to figure out that NOFBx should have a nasty habit of exploding/burning when unwanted. After all, that's kind of the entire reason most liquid fuel engines need separate tanks for the fuel and the oxidizer.

As for it being tested on the ISS? NOT going to happen. Not before being tested separately several times, at least.

It would also have to be man-rated, which means a bunch of successful ground test firings, probably several orbital test firings, and even then that's probably still not enough testing.

If all you're doing is testing a new propellant, you don't send it up to the ISS to test it. Instead, you do something like GPIM, and if it works, you're still 5-10 years away from getting it anywhere near man-rated unless you have an unlimited budget.

[RuBisCO]

SciMan,

Well it did pass a NASA safety review for going to a ISS: http://www.parabolicarc.com/2012/05/16/green-propellant-passes-iss-safety-review/

[SciMan]

Huh, guess they figured out some sort of stabilization additive or something. I don't follow this kind of stuff too closely (electric propulsion is more my style), so I'm not surprised at all that I'm wrong on this. Still, it'll be interesting to see what happens with stuff like Hydroxyl-Ammonium Nitrate and the other "Green" (aka. less-toxic-than-hydrazine) propellants.

Of course, I still think you can't beat a good electric thruster for orbital stationkeeping.

[Ravenchant]

Of course, I still think you can't beat a good electric thruster for orbital stationkeeping.

Agreed, though I doubt the intended use is for stationkeeping, especially with some companies beginning to move onto electric propulsion for geostationary sats. Probes and manned spaceflight, most like

[kerbiloid]

From ecological pov, "NH3...NO3" means "synthesized from ammonia"

which means "synthesized from natural gas and polluting the atmosphere with NOx and COx when being produced"

which means "to pollute the air not at the space centerm but at the chemical plant"

which means "to sweep the rubbish under the carpet".

[SciMan]

Agreed, kerbiloid. That's another reason I like electric propulsion. You can get away with using most anything, so long as you can ionize it and it doesn't chemically attack the engine when ionized.

[lajoswinkler]

I'd call it environmentally friendlier (maybe!), not eco-anything because it has nothing to do with counting fishes in a lake and other stuff ecology is dealing with.

It will probably require heavier engines. I can't say if there will be net benefit. It's too complex to figure out at this point and with so little data.

[kerbiloid]

I'd call it environmentally friendlier (maybe!), not eco-anything because it has nothing to do with counting fishes in a lake and other stuff ecology is dealing with. .

Yes, sorry. A wrong term.

[NuclearNut]

That is good, it is more efficient as far as tank mass goes, and presumably it does not require quite the safety precautions hydrazine does, but the main concern should be on cost relative utility. In space it really does not matter how non toxic your fuel is, there is nothing to be harmed there except spacecraft, no environment to be damaged. The more cynical side of me wants to say "this is just a PR stunt" and the more noble side of me wants to say "the lower toxicity is a side benefit".