NASA’s “Green” Fuel Seeks Safer Spaceflight By Finally Moving Off Toxic Hydrazine

Spaceflight is inherently dangerous. It takes a certain type of person to willingly strap into what’s essentially a refined bomb and hope for the best. But what might not be so obvious is that the risks involved aren’t limited to those who are personally making the trip. The construction and testing of space-bound vehicles poses just as much danger to engineers here on the ground as it does to the astronauts in orbit. Arguably, more so. Far more individuals have given their lives developing rocket technology than have ever died in the cockpit of one of them.

Reddish brown exhaust of hydrazine thrusters

Ultimately, this is because of the enormous amount of energy stored in the propellants required to make a rocket fly. Ground support personnel need to exercise great care even when dealing with “safe” propellants, such as the classic combination of kerosene and liquid oxygen. On the other end of the spectrum you have chemicals that are so unstable and toxic that they can’t be handled without special training and equipment.

One of the most dangerous chemicals ever used in rocket propulsion is hydrazine; and yet from the Second World War to the present day, it’s been considered something of an occupational hazard of spaceflight. While American launch vehicles largely moved away from using it as a primary propellant, hydrazine is still commonly used for smaller thrusters on spacecraft.

When SpaceX’s Crew Dragon exploded in April during ground tests, the release of approximately one and a half tons of hydrazine and nitrogen tetroxide propellants required an environmental cleanup at the site.

But soon, that might change. NASA has been working on a project they call the Green Propellant Infusion Mission (GPIM) which is specifically designed to reduce modern spacecraft’s dependency on hydrazine. In collaboration with the Air Force Research Laboratory at California’s Edwards Air Force Base, the space agency has spearheaded the development of a new propellant that promises to not just replace hydrazine, but in some scenarios even outperform it.

So what’s so good about this new wonder fuel, called AF-M315E? To really understand why NASA is so eager to power future craft with something new, we first have to look at the situation we’re in currently.

Literal Nightmare Fuel

The term “Nightmare Fuel” is Internet-speak for something that’s so terrible that you’ll lose sleep just looking at it. In the case of hydrazine, that’s not very far off. If this high-level summary of the dangers of hydrazine by the United States Environmental Protection Agency isn’t enough to give you pause, you’re either very brave or very foolish:

Symptoms of acute (short-term) exposure to high levels of hydrazine may include irritation of the eyes, nose, and throat, dizziness, headache, nausea, pulmonary edema, seizures, and coma in humans. Acute exposure can also damage the liver, kidneys, and central nervous system in humans. The liquid is corrosive and may produce dermatitis from skin contact in humans and animals. Effects to the lungs, liver, spleen, and thyroid have been reported in animals chronically (long-term) exposed to hydrazine via inhalation. EPA has classified hydrazine as a Group B2, probable human carcinogen.

That’s a risk of central nervous system damage and coma from short term exposure. But of course, that’s just talking about what happens if it leaks or spills around humans. What happens if there’s an explosion, and the hydrazine fills the air? The situation goes from bad to far, far worse.

In October of 1960, a prototype R-16 intercontinental ballistic missile fueled by a derivative of hydrazine exploded on the launch pad at the Baikonur test range in the Soviet Union. Between the monstrous force of the explosion and the deadly fumes which engulfed anyone who survived the initial blast, 78 lives were lost. The incident, known as the “Nedelin Catastrophe“, helped earn the R-16’s specific blend of nitric acid and hydrazine the nickname Devil’s Venom.

So given how dangerous hydrazine is, why do we keep using it? The simple answer is, it’s an exceptionally versatile rocket fuel. Some formulations of it are used as a hypergolic propellant, which means it will ignite immediately when combined with an oxidizer such as dinitrogen tetroxide. It can also be used as a monopropellant, where it gets passed through a catalyst bed that instantly breaks it down into a large volume of hot gas. In either form it’s extremely reliable and stable enough to be stored indefinitely.

The Little Green Giant

To be clear, AF-M315E isn’t intended to replace hydrazine in hypergolic engines like those on the SpaceX Crew Dragon. Rather, it’s designed to replace hydrazine when used as a monopropellant. As that’s how it’s more commonly used on American vehicles, NASA doesn’t see that as a limitation. Monopropellant thrusters are generally used on spacecraft for maneuvering and performing orbit adjustments, though they are occasionally used in more exciting applications. For instance, hydrazine monopropellant was used in the “Sky Crane” that delivered the Curiosity rover to the Martian surface.

A prototype AF-M315E thruster

So how does AF-M315E compare with hydrazine as a monopropellant? At least on paper, very well. Testing has shown that it’s more efficient, offering a 12% higher specific impulse (ISP). It’s also 45% denser than hydrazine, which means you can either bring more of it in the same sized tanks, or simply load less of it onto your craft and enjoy the mass savings. As a practical example, Aerojet Rocketdyne estimated that using AF-M315E instead of hydrazine on Curiosity’s descent thrusters would have allowed adding an additional 58 kilograms of payload onto the rover; an increase of around 6%.

Based on the improved performance alone, AF-M315E would be worth looking into as an eventual replacement to hydrazine. But the biggest advantage is how much safer it is for the humans who have to work with it. While it’s not exactly inert, handling AF-M315E only requires the sort of equipment you might use when working with a strong acid: gloves and a face shield. Compared to the full-body hazmat suits required when working with hydrazine, being able to perform propellant loading in this so-called “shirt sleeve” environment would be a minor revolution in how we prepare spacecraft for flight.

A scientist handling AF-M315E in a standard beaker

If your spacecraft runs on hydrazine, it has to be transported with empty tanks and fueled prior to liftoff by a group of trained professionals in a secured location. This is not only a slow process, but an expensive one: filling even a small spacecraft’s tanks with hydrazine will easily add a six-figure line item to your budget.

But AF-M315E promises to change this paradigm completely. The propellant can be stored in plastic or glass bottles, and can be shipped through carriers such as FedEx. Any company, college, or even hackerspace, that has the technical ability to produce a CubeSat would also be able to safely load AF-M315E into their vehicle. The Department of Transportation is even looking at allowing craft filled with AF-M315E to be transported on public roads.

Not only would in-house fueling make building small spacecraft cheaper, but it would also reduce the workload for ground processing personnel at the launch site. Overall, this leads to less time on the ground and more time in space.

Real-World Testing

Luckily, we won’t have to wait too long before we know if this new propellant can deliver on its promises. On June 25th, a small satellite manufactured by Ball Aerospace and bristling with AF-M315E thrusters hitched a ride to space on SpaceX’s Falcon Heavy. It will spend a little more than a year in orbit, testing the performance of these thrusters and verifying everything works as expected.

As this is the first AF-M315E powered spacecraft in history, there’s plenty of unknowns to contend with. One of the main goals of the test is to see how the thrusters respond after sitting dormant for months on end. Since a spacecraft only fires its thrusters when necessary, it’s not uncommon to go months or perhaps even years between burns. Any propellant that hopes to dethrone hydrazine will need to be able to meet its ability to roar into action at a moment’s notice.

Even assuming everything goes well with this first GPIM mission, we won’t be rid of hydrazine overnight. As nasty as it is, manufacturers have decades of experience with it and have long since come to terms with the risks involved in handling it. The increased performance of AF-M315E will probably help convince aerospace manufacturers that it’s worth looking into converting their designs over to this new “green” propellent, but it may ultimately take pressure from the customer to get the ball rolling. Once the companies buying and operating these craft realize the time and money that can be saved by using a different fuel, you can be sure they’ll take it into account when shopping around for their next satellite.

35 thoughts on “NASA’s “Green” Fuel Seeks Safer Spaceflight By Finally Moving Off Toxic Hydrazine

    1. Not portobello mushrooms, turban cap mushrooms. And actually, they don’t contain any, but some of the chemicals in them metabolize into hydrazine once injested.

  1. IIRC, Hydrazine is the propellant used for “station keeping” of geosynchronous satellites.
    In other words, it has long term stability. What will be the life span of the replacement fuel.

    1. Any source of fuel is going to be dangerous. This happens to be less dangerous while offering better performance. Lithium batteries can be considered a fuel source (I mean, it’s a source of energy) , and they are relatively dangerous if not handled with some care, but they aren’t going to explode if lightly bumped. Hydrazine is really awful stuff but damn if it isn’t powerful and pretty well understood now a days.

    2. Nowhere does it say that you should be drinking the stuff, but it’s still a lot better than what we have now. The picture of the woman with a beaker of the new fuel would be a death sentence if she did it with hydrazine.

  2. I’ve had an object in my possession for many years that looks extremely similar to the picture of the A prototype AF-M315E thruster in this article. No one could ever tell me what it was. Now I’m curious again. It would be really cool if it turned out to be some sort of thruster.

      1. He left off blowing up the finish of the Boston Marathon. That’s pretty much the worst that can be done with a pressure cooker. I’ve seen a video of a guy disarming a field of improvised land mines made from pressure cookers.

    1. While FOOF is a very unpleasant chemical, from the same author there’s an even more relevant example. Chlorine Trifluoride.
      Originally tested for use as a rocket propellant, this was quickly stopped because it’s reactive with pretty much everything. It’s a better oxidiser than oxygen.
      Really, hydrazine is practically harmless compared to some of the chemicals used as rocket propellants.

  3. I was under the impression that the reason hydrogen was listed as a probable carcinogen is that usually before it gives anyone cancer, it gives them a bad case of dead.

    I was a bit surprised to see the Ball Aerospace logo looks exactly like the Mason jar logo. Sure enough, while they’re not currently the same company, they had spun off the glass can part, leaving a company that makes tin cans and spacecraft. Did somebody in management take David Bowie’s line about “Here I am floating in my tin can” a bit more seriously than anyone expected?

  4. On the last use of the Apollo Command Module for the “Apollo-Soyuz Test Project” in July 1975, the astronauts were exposed to hydrazine and nitrogen tetroxide fumes during re-entry by the failure to throw a switch at the correct time. It almost killed them, they were hospitalized for two weeks.

    https://en.wikipedia.org/wiki/Apollo%E2%80%93Soyuz_Test_Project#Re-entry_and_aftermath

    The mission was considered a great success, both technically and as a public-relations exercise for both nations. The only serious problem was during reentry and splashdown of the Apollo craft, during which the crew were accidentally exposed to toxic hydrazine and nitrogen tetroxide fumes, caused by unignited reaction control system (RCS) hypergolic propellants venting from the spacecraft and reentering a cabin air intake. The RCS was inadvertently left on during descent, and the toxic fumes were sucked into the spacecraft as it drew in outside air. Brand briefly lost consciousness, while Stafford retrieved emergency oxygen masks, put one on Brand, and gave one to Slayton. The three astronauts were hospitalized for two weeks in Honolulu.[18] Brand took responsibility for the mishap; because of high noise levels in the cabin during reentry, he believes he was unable to hear Stafford call off one item of the reentry checklist, the closure of two switches which would have automatically shut off the RCS and initiated drogue parachute deployment. These procedures were manually performed later than usual, allowing the ingestion of the propellant fumes through the ventilation system.[19]

  5. “while Stafford retrieved emergency oxygen masks, put one on Brand, and gave one to Slayton”…hmm, didn’t he get the safety briefing ? Remember to put your own oxygen mask on first before helping others, even though the bag may not inflate, oxygen is flowing.

    After shuttle landings, if memory serves, they would sniff the perimeter of the craft to determine toxicity levels of any residual reactants that might have leaked from the RCS nozzles.

    1. Early shuttle landings had large fans blowing the Shuttle for a half hour afterward to dissipate “noxious gasses”, before allowing the doors to open, or people approach.

  6. The State of Monopropellant Hydrazine technology 1968 https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680006875.pdf

    Detonability Study of Liquid Hydrazine 1994 https://pdfs.semanticscholar.org/9ce5/1082265a8738018a9d12c506d160e1fa2a60.pdf
    NASA couldn’t make Hydrazine detonate with C4 or high velocity impact, they set out to see what it would take to make it detonate.

    Requiring *extreme* measures to make hydrazine explode is one reason why it’s been used for so long. In other words, how it’s been depicted in “The 100” is totally wrong, just like 99.99% of everything else technical or medical on that show.

  7. “the sort of equipment you might use when working with a strong acid: gloves and a face shield.”

    And then proceed to show a picture of a woman handling a beaker full at eyelevel with her glasses perched at the tip of her nose (narrow reading glasses with just sideshields on top of that)…

  8. Does anyone know if it would a better choice for the catalytic reaction required on F16 systems? Not that it really matters, just curious since it is the other use of Hydrazine that I’m vaguely aware of.

  9. Hydrazine is used in the emergency power unit (EPU) generator on F-16 aircraft, getting a face-full of fumes from an activation gets you a trip to the emergency room to get your vitals checked and usually returned to duty in a couple of hours.

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