Hydrazine
Published on Feb 16, 2008 at 12:34 am.
32 Comments.
Filed under rockets.
Hydrazine, N2H4, is a commonly used rocket propellant. The hydrazine molecule is basically what you get when you couple two ammonia molecules, by removing a hydrogen from each one. It is a reactive substance, and quite toxic. Hydrazine is a colorless liquid at room temperature. Its melting point is about 1° C, and its boiling point is 114° C. In that sense, it is liquid over about the same range of temperatures as water. However, hydrazine is much more reactive than water, and it has a flash point of about 38° C. It is a highly reactive reducing agent. There are several industrial and medical uses for hydrazine, but this is primarily a space oriented blog, so I’ll focus on its uses as a rocket propellant.
Hydrazine is considered a monopropellant, meaning that all you need is hydrazine and not some other chemical to mix with it. That is really quite useful. Most rocket fuels require an oxidizer. That means that you have to keep track of two chemicals and they have to be mixed in the rocket engine in just the right way to provide the desired thrust. Secondly, hydrazine does not need an ignition source. Again, most rocket fuels need to be ignited in order to burn. Igniting an engine in space is tough. Only a few rocket engines are designed to be stopped and restarted. Most fire until they are done, and then they are turned off, never to be turned on again. Using hydrazine as a propellant, you can fire the engine as needed, and then when you cut off the supply of hydrazine, the engine stops. If you turn on the hydrazine again, the engine starts. More hydrazine gives more thrust. Less hydrazine gives less thrust. That makes hydrazine a nice propellant for thrusters and maneuvering jets.
Interestingly, hydrazine has been used for rocket propulsion since the 1940s. Hydrazine hydrate (mixed with water and alcohol) was used in the German’s Messerschmitt 163B rocket interceptor. Today, it is used fairly regularly in satellite maneuvering and station keeping thrusters, the Space Shuttle, the Soyuz spacecraft, and in the Auxiliary Power Units aboard the International Space Station and the Space Shuttle.
So, how come we don’t see hydrazine used even more in spacecraft? Well, there are several reasons. One, the stuff is pretty toxic. Breathing hydrazine can cause coughing and irritation of the throat and lungs. Those effects can occur at fairly low concentrations. At higher concentrations, hydrazine can trigger tremors or convulsions. Ingesting hydrazine can cause tremors, nausea, neurological problems, and drowsiness. Hydrazine is very water soluble, and it can be absorbed through the skin. Prolonged exposure can cause liver and kidney damage, as well as damage to reproductive organs. Hydrazine has caused tumors in animal studies, and it is listed as a carcinogen. When the Space Shuttle lands, the astronauts don’t go piling out of it as soon as it comes to a stop. Instead, special trucks roll out to it to “safe” the vehicle. This involves removing any unused hydrazine and “sniffing” the air around the Shuttle to see if any hydrazine vapors are present. One concern is that traces of hydrazine may remain in the thruster exhaust ports and pose a hazard to the astronauts. It is better for them to remain on board the spacecraft than to be exposed to possible health problems. Only when the all clear is given do the astronauts emerge from the Shuttle. It was in part due to the risk posed by the hydrazine that the public was warned to stay away from pieces of debris from the Space Shuttle Columbia that broke apart and showered much of east Texas with debris. The hydrazine contamination issue was also cited as a reason to shoot down USA-193, an errant American reconnaissance satellite rather than letting it crash to Earth of its own accord in some random location.
Personally, I agree with some public warnings about hydrazine contamination with space debris, but hydrazine is so reactive, volatile, and with such a low flash point, that I think that most of the debris is probably cleansed in passing through the high heat of burn up in the atmosphere. But, apparently at least some of the hydrazine tanks from the Columbia survived passage through Earth’s atmosphere during reentry, so it is quite likely that the same could happen for USA-193. That would most likely be the biggest hydrazine danger, rather than just random pieces of debris being contaminated. Nonetheless, I would not go out and handle any pieces of the satellite without taking protective measures, just in case.
Hydrazine is also corrosive and reactive. It breaks down rather readily in the environment, so long term environmental damage from small spills is unlikely. But, these chemical properties mean that it is not something that can be stored for extended periods of time. But, the instability turns out to be something very useful for rocket propulsion.
Because hydrazine is unstable, it can be easily broken down. All it takes is a catalyst, such as iridium, to cause the hydrazine to break down into ammonia, nitrogen, and hydrogen gas. The process is extremely exothermic (meaning that it releases a lot of heat when hydrazine breaks down this way). With a sufficient flow of hydrazine through a chamber containing the catalyst, the temperature in the chamber can very rapidly reach extremely high temperatures. That means that the gases produced in the reaction become extremely hot. Gas takes up nearly a thousand times the volume of liquids to start with. Then, if you heat the gas, it expands even more. That is how rocket and jet propulsion works. A solid or liquid is burned, and the combustion byproducts are hot expanding gases. These gases are then expelled at high velocity from the rocket engine (or jet engine). This hot rapidly expelled exhaust provides the engine’s thrust.
But, normally, a rocket or jet engine needs a fuel and an oxidizer. For a jet engine, the oxidizer is simply oxygen from air intake into the engine. For a rocket, though, the oxidizer is carried on board. Sometimes it is liquid oxygen, and sometimes a very reactive oxidizing chemical. Liquid oxygen is a cryogenic fluid that requires special handling. Oxidizing liquids also are exceeding corrosive and also require special handling. But, without the need for an oxidizer to burn the hydrazine to produce the hot gas, the engine can be simpler. A quick squirt of hydrazine can produce a quick burst of gas expelled. That makes hydrazine a very attractive propellant for attitude thrusters or station keeping thrusters.
But, even though hydrazine can be used as a monopropellant, it can also also be used with an oxidizer such as nitric acid to produce an even more powerful thrust. Hydrazine is so reactive that when used with a suitable oxidizer, there is no need for any sort of ignition system. The fuel and oxidizer just spontaneously ignite and burn. Propellants like this are called hypergolic propellants. An even more powerful derivative of just straight hydrazine is monomethyl hydrazine (CH3NHNH2), which is used with nitrogen textroxide as a hypergolic propellant. (This is the form used in the Space Shuttle’s thrusters).
I am not a chemist, but I thought that I’d look up some information on hydrazine because of all the news recently about the decision to shoot down USA-193. Possible injuries to people on the ground from hydrazine released in an uncontrolled reentry of that satellite was cited in many of the news reports as a major source of concern in reaching that decision. What I have written here is not to be taken as the authoritative expert fact sheet on hydrazine, but I hope that I’ve explained it sufficiently for people to get an idea of what the substance is, why it is used in spacecraft, and what concerns exist when spacecraft crash back to Earth with hydrazine aboard.
-Astroprof
Vossinakis Andreas on February 16, 2008 at 3:43 am: 1
Very good research, thanks for sharing
Vossinakis Andreas
Thessaloniki, Greece
DavidG on February 16, 2008 at 5:50 am: 2
I recall from a friend that certain racing organizations banned the use of Hydrazine in otherwise open fuel classes in the late 1970s. We often wondered if the ban was due to an accident/event or if it was proactive.
I think people were considering it as an additive. From what little I knew of it then, I thought they were nuts. Now doubly so.
Spankermatic on February 16, 2008 at 9:22 pm: 3
Interesting and thorough article. Thanks for that.
Calli Arcale on February 16, 2008 at 9:29 pm: 4
In addition to simplifying the rocket engine (by omitting either oxidizer or igniter), hydrazine is also much more storable than the best liquid alternatives, such as LH2 and kerosene. Its most popular oxidizer, nitrogen tetroxide, is also more storable. This feature is the main reason why it is the primary propellant for nearly every spacecraft’s on-board thrusters. The Soyuz main engines use it. Voyager 1 and 2 use it. And liquid ICBMs use it too. That was what made the Titan so much better than Atlas; Atlas had to be loaded with kerosene and LOX prior to launching against Soviet targets, which made its response time very slow. Titan could be loaded with Aerozine-50 and N2O4 and then left in a silo for months, ready to launch at a moment’s notice. Periodically, they be serviced, but they stood ready to fire for years. The drawback is that it’s heavy and lacks the high specific impulse of cryogenics or even kerosene. But if you want missile readiness, it’s either that or solids.
The Russians knew this, and when they designed a rocket to beat the threat posed by the American Atlas (kerosene/LOX), they opted for hypergolics. The R-16 would carry unsymmetrical dimethyl hydrazine (still popular in Russia today — Soyuz, Progress, the ISS, and the Proton heavy-lift booster all use it) and nitrogen tetroxide. The awesome danger of such a rocket became painfully apparent one day when, under serious pressure from the Kremlin, a tiny mistake was made during preflight testing. The R-16 rocket, surrounded by technicians, engineers, and dignitaries including Field Marshall Nedelin. The resulting disaster bears his name. The Nedelin Catastrophe killed over a hundred people, including the field marshall. The lucky ones died in the fireball; others died over the next month or so as a result of burns, smoke inhalation, and exposure to the toxic propellants of the R-16 rocket.
Hydrazine is very nasty stuff. Corrosive, too. The Soyuz vehicles used as ISS lifeboats have an on-orbit lifespan of just six months because the hydrazine eats through the seals in the propulsion system. Other spacecraft meant to last longer use more durable materials, but at a cost/weight penalty.
Freiddie on February 16, 2008 at 10:01 pm: 5
I like the chemistry here.
blue collar scientist » Blog Archive » Doesn’t Pass The Baloney Test on February 16, 2008 at 11:29 pm: 6
[…] Tanks containing satellite fuel have a fairly high probability of surviving re-entry intact. They have large surface areas compared to their mass, and they can slow down very rapidly and fall to earth without burning up in the atmosphere. If that happens in this case, wherever that tank lands becomes a toxic substances dump, without any of the environmental controls or monitoring that real toxic substances dumps have. If that happens to be my backyard, I’d be really ticked off. (Edit to add: The Bad Astronomer points out that Astroprof has an excellent post about hydrazine, if you want to consult it.) […]
Eddie Pasternak on February 17, 2008 at 2:53 am: 7
“…It’s melting point is about 1° C…”
Please fix this.
Martin on February 17, 2008 at 6:03 am: 8
“Auxiliary Power Units aboard the International Space Station”
There are APUs on the ISS too ?
Seb on February 17, 2008 at 9:47 am: 9
Great article, thanks.
Suggests:
“Oxidizing liquids also are exceedingLY corrosive”
John Takolander on February 17, 2008 at 12:33 pm: 10
Hydrazine is a common ingredient in Finnish municipal heating, also inother places, I believe.
Astroprof on February 17, 2008 at 1:20 pm: 11
Thanks for the catch, Eddie. Oops. I don’t normally make that particular punctuation mistake. I must just not have been thinking. I fixed it.
Astroprof on February 17, 2008 at 1:20 pm: 12
Martin, yes the ISS has APUs.
DElliott on February 17, 2008 at 3:55 pm: 13
Hydrazine is also used to power the F-16 Emergency Power Unit (EPU).
Chris Lintott’s Universe » Carnival of Space #42 on February 21, 2008 at 10:09 am: 14
[…] On the way into the atmosphere, be careful to dodge the remnants of the American spy satellite which had an encounter with a guided missile last night. Astroprof’s article, here, discusses hydrazine’s role in spacecraft. As you might expect, shooting down spacecraft also provides fodder for the space cynic, and Mars Odyssey joins in too. […]
skip on February 22, 2008 at 6:35 am: 15
Astroprof, you pointed out hydrazine’s affinity for and solubility in water. In the early 80’s hydrazine was still in use as an oxygen scavanger in power generating station’s high purity boiler water systems. At that time it wasn’t considered very hazardeous. PPE for operators who maintained the chemical addition systems consisted of a pair of rubber gloves and little else.
Marco Langbroek on February 22, 2008 at 10:00 am: 16
The chances that a random passenger aircraft with fuel tanks will drop on your head today are considerably bigger than the chances USA 193’s fuel tank would have dropped on your head. In other words: the hydrazine danger was certainly not a argument that we should take serious in justifying this 60 million dollar operation and it’s high media profile.
Charis Kosmas on February 23, 2008 at 2:10 pm: 17
For assessing the possibility for hydrazine to reach ground one neads to take into account that:
- the almost intact tank of Columbia that reached ground was empty because of its detachment from the pipework.
- We have also to note that the Columbia spaceplane was designd to wisthstand the reentry heat and to certain extent it did. The disintegration started well after touching the upper layers of atmosphere.
-the Columbia spaceplane was huge in comparison to a satellite!
- every hardware component of a manned mission has increased engineering margins with respect to simple satellites
- the tank in the case of Columbia was almost empty when started descent, meaning there was little reason fot it to explode.
treegod on February 25, 2008 at 10:40 am: 18
Good comments and great research. very informative. Now if we can just get to using this stuff in space and be able to keep it there as well. The less of that shit on Earth, the better!
Gilbo on February 26, 2008 at 5:43 pm: 19
I think the increased amount of space junk will be more of a problem than anything that may have fallen to earth.
Kent J on February 27, 2008 at 9:43 am: 20
Thanks for posting the new Ben Stein movie banner. I didn’t know about it and now i can spread the word.
Free speech should be included in science.
Astroprof’s Page » Standard Missile-3 on February 27, 2008 at 6:38 pm: 21
[…] Last Wednesday night, while a lot of us were watching the lunar eclipse, the guided missile cruiser USS Lake Erie (CG-70) fired a missile to shoot down the defunct USA-193 satellite. The missile’s kinetic warhead struck the satellite at an altitude of 133 nautical miles, shattering the satellite. A cloud of expanding gas from the shattered satellite indicated that the hydrazine tank had been ruptured, which was the stated goal of the exercise. […]
Tin on March 3, 2008 at 10:02 pm: 22
Hi. On last saturday 1 march over the skies of Italy there has been a strange phenomena, a very bright object has crossed the skies of Northern Italy and part of Switzerland at aroud 23.45h. There are no scientific explanation yet, except some newspapers are talking of a meteoroid or bolide -4 magnitude. It has been seen by hundreds of people and heard like a thunder by a few also.
Well I’ve seen the light from the windows and like many others I’ve heard a hige crash after few second somewhere over the mountains, and since then there is a sharp smell of burning plastic in the air.
Could it be a piece of USA 193?
Astroprof on March 3, 2008 at 10:22 pm: 23
There’s no telling. Most likely it was a normal meteor. Most pieces of the satellite should have burned up, and there should not have been any smell. That was most likely a coincidence. That would be my best guess without additional data.
Bones B on March 17, 2008 at 10:29 am: 24
@Charis:
>>-the Columbia spaceplane was huge in comparison to a satellite
The 193 was reported to be the size of a bus, not the size of an Orbiter, but not your average TV Sat, either.
Mihail Fuhrmann on March 31, 2008 at 10:41 pm: 25
Calli Arcale,/all
Interested in a high mole reaction for the production of H2. Any leads?
Veronica on April 25, 2008 at 10:03 pm: 26
*Dear Astroprof*, I´m a student from Mexico. I study engeenery of ecology and I really liked your article. I´m doing an investigation project about satellites so I appreciate you could tell me your name to give some references of articles in my project.
If you can´t publish it here for any reason, this is my email: Veronik_rs@hotmail.com
I hope you could, thanks.
Brent on May 13, 2008 at 12:38 pm: 27
Astroprof,
You mention that Hyrdazine does not need an ignition source, only a catalyst in order to ignite. When used as a thruster in space, what sort of catalyst is used to ignite it? You also mention the high heat produced, and I’m curious what keeps the catalyst from disintegrating in the thruster.
And finally, since Hyrdazine has melting and boiling points roughly equivalent to water, how is it stored aboard a spacecraft that undergoes the extreme temperature changes of outer space, and yet remain in a useful liquid form? It seems too toxic to run this risk of storing it inside the temperature controlled craft.
Vanaussy on July 20, 2008 at 8:59 pm: 28
Since hydrazine has a boiling point of 113.5 deg. C and a freezing point of 1.4 deg. C, I would assume that the storage tank would be very well insulated. I would also assume that the tank would be heated by solar cells, with a temperature control system. That would keep the hydrazine in a liquid state, so it could be used for positioning. Now, how hot does the space shuttle get on re-entry? Several thousand degrees fahrenheit? If that is true, why wouldn’t the hydrazine tank reach the same temperature as the space shuttle and explode on re-entry, detonating the hydrazine? I think the U.S government wasted a lot of our tax money on this project!!!
Jmc10371 on October 29, 2008 at 10:39 pm: 29
I wonder if the shoot down of the USA193 was also used to show our ability to shoot down other nations spy satilites. I noted that it took the Presidents approval to proceed on this program! That hydrazine sounds like nasty stuff and not something that I want to store in my garage.
Recent Links Tagged With "n2h4" - JabberTags on November 9, 2008 at 4:19 pm: 30
[…] public links >> n2h4 Hydrazine Saved by mbwatts on Sat 08-11-2008 help please? Saved by nissling on Mon 13-10-2008 US to shoot […]
J_Sheley on January 16, 2009 at 1:17 pm: 31
Hydrazine decomposes to H2 and N2(NOT ammonia!) in the presents of a metal .
Platimnum,plalladium,nickel, ruthenium are typical hyrogenation catalysts- I have never seen irridium.
The driving force of this reaction is the formation of the low energy product, N2 NOT ammonia.
Yu ming on May 5, 2009 at 9:50 am: 32
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The product of hydrazine,Monomethyl Hydrazine (MMH),Uns- Dimethyl Hydrazine(UDMH) had been successfully used in Chang’e lunar probing satellite, ShenZhou Spacecraft as well as other Chinese satellites.
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