Almost all spacecraft (including satellites) use hydrazine (MMH, UDMH or Aerozine 50) for rotating around itself to keep pointing in the right direction (see attitude control, reaction control system).
When used as a bi-propellant, hydrazine is usually combined with N2O4, which is also super toxic.
It is not just the military that uses these things. Everyone uses it because it is the best performing high thrust (not ion engine) non-cryogenic (storable) propellant. It being hypergolic (self igniting) is a bonus for reliability.
The military actually switched to solids for ICBMs and SLBMs.
The F-16 has a hydrazine APU, and I would not be surprised if the F-35 does the same thing.
> The F-16 has a hydrazine APU, and I would not be surprised if the F-35 does the same thing.
The F-16 has an EPU not an APU, i.e. an Emergency Power Unit vs an Axillary Power Unit. Lacking an APU is an exception when it comes to jet aircraft and necessitates a few changes. Relevant here is that an APU can provide power in an emergency, so the role is played by the hydrazine powered EPU for the F-16.
This makes hydrazine somewhat more of a rational choice for something you expect to use rarely. If it were expected to be frequently used then it would have to be frequently refilled and that would necessitate all ground crew wearing the full body hazmat suits you see in the photo for the X-37b here as well as many other complex safety precautions.
The F-35 has a conventionally jet fuelled APU[0] so it has no need for an EPU or hydrazine.
Interestingly Concord didn't have space for an APU (due to the shape of the empennage and placement of a rear fuel tank). I have seen pictures of a hydrazine powered EPU on one of the prototypes, but this was never going to make it into service as certifying carrying something as toxic as hydrazine - even back then - would be nigh on impossible. This is the question that starts the most epic thread about Concord[1] (warning - you may get sucked into reading all 103 pages!)
The EPU on the F-16 is actually quite interesting itself and is a good fit for what is needed with 70s technology.
Redundant systems are normal on aircraft and the F-16 has a particular need for hydraulic and electrical power as its inherently unstable airframe needs various onboard systems to keep it stable and flyable.
If the main generator disconnects from the bus or the hydraulic pressure drops[0] the EPU will automatically operate to provide electrical and hydraulic power. It can run from engine bleed air, but if the (single) engine has failed then pressure will be provided from the hydrazine system.
It achieves this using a 70% solution of hydrazine in water as a monopropellant, which is decomposed over an iridium catalyst. The water helps keep it stable, and cools the catalyst when it boils, keeping it around 850C and the high pressure gasses are fed into the EPU.
This has the advantage of being light (25L of hydrazine and simple as only a single liquid), reliable and fast acting (~2s to max power).
pprune is the goto site whenever anything interesting happens in aviation (and the pro's there are very aware that it's where the journalists will start looking when there's an incident).
I suspect the F-35 does not use hypergolics, because they land on aircraft carriers. There's only so much risk you can tolerate on such a large, high-value asset. Nukes, sure. Hydrazine? Do we absolutely have to? If not, take a pass.
Rocket fuel typically uses either monomethylhydrazine (MMH) or unsymmetrical dimetehalhydrazine (UDMH - the more common of the two).
The link you're responding to is about tetrafluorohydrazine, which is some kind of hydrazine and fluoride. I think it's mentioned in Ignition! but I can't remember. I just remember John Clark (the author of Ignition!) being very very hesitant and even frightened of working with fluoride based fuels.
I'm not really sure how how it's tetrafluorohydrazine is relevant to the X37-B though.
You remember the Crew Dragon test that exploded? The orangeish smoke cloud? Don't breathe that. That uses NTO + MMH.
"On 24 July 1975, NTO [dinitrogen tetroxide] poisoning affected three U.S. astronauts on the final descent to Earth after the Apollo-Soyuz Test Project flight. This was due to a switch accidentally left in the wrong position, which allowed the attitude control thrusters to fire after the cabin fresh air intake was opened, allowing NTO fumes to enter the cabin. One crew member lost consciousness during descent. Upon landing, the crew was hospitalized for five days for chemical-induced pneumonia and edema."
>There was this amazing article in 2010 about "chemical compounds i will not work with". Tetrafluorohydrazine was one of them:
I remember reading that article it was interesting. But it's funny that hydrofluoric acid (HF) was not mentioned since it seems to be incredibly dangerous.
Periodic Videos on Youtube has a new video about hydrofluoric acid. Professor Martyn Poliakoff mentions HF is feared by people working in chemistry. He also said that even a small drop of HF on skin will cause a heart attack (and eat through your skin).
> He also said that even a small drop of HF on skin will cause a heart attack
I really wish people in the know wouldn't spread stuff like this.
HF isn't untreatably deadly like dimethylmercury.
HF is a strong acid and should be treated as such. Most effects of HF are quite treatable as long as you haven't managed to somehow convert it into elemental fluorine gas.
They key is that you have to know that you've had an HF incident.
What IS nasty is that an HF burn probably doesn't hurt until far too late. HF reacts with calcium and can inactivate pain neurons. And, while a small droplet won't do it, a large HF burn can cause a heart attack because it soaks up a lot of the free calcium in your bloodstream.
So, when you go in for treatment for an HF burn the doctor needs to start giving you calcium gluconate in order to resupply your calcium.
HF is nasty, but not so nasty that semiconductor fabs work terribly hard to get rid of it. Piranha etch (HF and HNO3 at 70C) is bog standard and people work with it every day.
Constrast this to Arsine gas (AsH3--flammable and toxic--oh, the joy!) which everybody works to get rid of.
I don't believe I've ever been in any hardware store that sold hydrofluoric acid in any concentration. Care to expand on what you meant?
Now - hydrochloric acid or sulfuric acid - both those (and some other relatively nasty chemicals) can be easily purchased at many hardware (and other) stores; the first is commonly known as "muriatic acid" (pool acid), while the second is sold (usually at auto parts stores, but there are some hardware stores that sell it too) for lead-acid battery "replenishment" (if the acid in them becomes too diluted from "topping up" with distilled water over time).
But HF? No - I certainly can't see where that would be allowed to be sold in any concentration to the ordinary public...
In low concentration, it's in various cleaning products, rust removers, that kind of thing. In some places, you can buy glass etching cream which also contains HF.
Dumb question from someone who knows very little chemistry; is it possible for a malicious actor to use some sort of distillation process to take that 1% solution and concentrate it into something much more dangerous?
The fun part in the video is when they neutralized the HF with sodium carbonate to make sodium fluoride which is used in toothpaste. Keeping in mind the concentration again.
It's acidic, not less dangerous. If you get one of those other acids on you, you will know, immediately. Whereas HF will just absorb through your skin without appearing to cause any damage, but will kill all the tissue in it's path and start dissolving your bone underneath.
One of the near misses in terms of potentially fatal spacecraft accidents involved fumes from hydrazine and dinitrogen tetroxide entering the cockpit of the Apollo capsule returning from the Apollo-Soyuz docking in 1975. The astronauts survived after two weeks of hospitalization, thankfully.
Dr. Lowe's Things I Won’t Work With is on the top 10 best blogs out there. What an utter joy! His writing style is a breath of fresh air for the sleepy journal-club style articles. He is funny, informative, and interesting. A great addition to the world of science advocates. I love his blog. Some favs:
Can’t Stop the Nitro Groups :"... this new paper’s introduction includes the phrase “In our continuing efforts to introduce as many nitro groups associated with a tetrazole ring as possible. . .” and to most organic chemists that’s roughly equivalent to saying something like “In our continuing efforts to spray as much graffiti on the snouts of salt-water crocodiles as possible. . .”[0]
Sand Won't Save You This Time: "It is, of course, extremely toxic, but that’s the least of the problem. It is hypergolic with every known fuel, and so rapidly hypergolic that no ignition delay has ever been measured. 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."[1]
Hexanitrohexaazaisowurtzitane: "Hexanitro? Say what? I’d call for all the chemists who’ve ever worked with a hexanitro compound to raise their hands, but that might be assuming too much about the limb-to-chemist ratio." [2]
Yeah, it's an amusing article but it's not about Tetrafluorohydrazine and there don't seem to be any others in the series that are. Tetrafluorohydrazine also doesn't seem to be the same thing as hydrazine which is used as a fuel in some spacecraft.
The article does mention tetrafluorohydrazine being added to FOOF which is the actual subject of the article and a comment mentions tetrafluorohydrazine being used as an oxidizer for rocket fuels.
When used as a bi-propellant, hydrazine is usually combined with N2O4, which is also super toxic.
It is not just the military that uses these things. Everyone uses it because it is the best performing high thrust (not ion engine) non-cryogenic (storable) propellant. It being hypergolic (self igniting) is a bonus for reliability.
The military actually switched to solids for ICBMs and SLBMs.
The F-16 has a hydrazine APU, and I would not be surprised if the F-35 does the same thing.