Slashdot Mirror
NASA Wants Green Rocket Fuel
coondoggie writes "NASA is looking for technology that could offer green rocket fuel alternatives to the highly toxic fuel hydrazine used to fire up most rockets today. According to NASA: 'Hydrazine is an efficient and ubiquitous propellant that can be stored for long periods of time, but is also highly corrosive and toxic.' It is used extensively on commercial and defense department satellites as well as for NASA science and exploration missions."
Everybody should read one book about rocket propellants: Ignition! by John D. Clark. Apart from it being a good (and hilarious at times) read, it'll also show you why this project will most likely end up being a waste of money.
Nitrous oxide fuel blend is a mixed mono propellent that's non-toxic and has 320-340s ISP. Max Vozoff, formerly of SpaceX, talks about NOFB in this episode of The Space Show. He think's it's a game changer.
I don't know if you've ever tried to obtain Halon lately but you'll find even if your system is still grandfathered it's nigh on impossible to get hold of, they've pretty much stopped making it. It's the same with the CFC's used by the shuttle's foam, being allowed to make it didn't mean the raw components are easy to come by. If they'd wanted to continue using CFCs they'd have to had to pay for a supply line to be available and maintained, whether they needed a lot or a little. The problem wasn't that they went green, the problem was that the alternative they chose wasn't the right one and they didn't want to invest the time and money working around that properly.
Hydrazine is described as corrosive and toxic, both of which will make it expensive to handle, require special pipes and tanks and so on. As far as I know, it's not
an environmental consideration -- it surely decays to nitrogen and water pretty fast.
I suspect this is about cost saving in the handling.
It's not really about being "Green". Hydrazine is very toxic and extremely unstable. It's terribly dangerous to work with even when things are going right, and when a launch goes wrong you may end up dropping a hydrazine-filled satellite in an urban area. That's not good, so you have to considerably overengineer the tanks (adding weight, reducing payload) so they'll survive reentry and not poison people.
So why do we use this devil of a propellant?
Normal rocket juice is two parts - fuel (eg H2, kerosene) and oxidizer (eg O2, N20). You flow both into your combustion chamber, strike a spark, and away you go. That's great for long sessions of high-power lift. The problem is it's terrible for fine maneuvering. Maintaining the proper mixture gets harder with small flows, your spark plugs wear out with repeated firings, and generally the whole bipropellant setup is big, heavy, and complicated, and you want your satellite to be compact, light, and as simple as possible for reliability.
So that's where hydrazine comes in. It's the same property that makes it dangerously unstable that makes it an ideal fuel when you need very low impulse and very high reliability. You just open a small valve on the line from the pressurized tank tank to the engine - that's your only moving part. The hydrazine flows into the combustion chamber where there's a catalyst. It instantly and very exothermically decomposes into ammonia, nitrogen and hydrogen gas. The very high temperature rise makes the exhaust velocity really high, which is great for efficiency.
Et voila, you have a rocket engine where the only moving part is the flow control valve. Since you want to do complex maneuvers, you can sprinkle a bunch of these little, simple, lightweight engines all over your craft instead of having a couple big complex (fuel mixing) ones with vectoring (gimbals and actuators are just more things to fail, plus now you need flexible fuel lines), and you can do your maneuvers in tiny bursts that are too short to even get a bipropellant engine to light off.
Similarly, the very low parts count makes hydrazine turbine engines very useful where maximum reliability is required - for instance APUs for hydraulic power used for the space shuttle, and on military aircraft for emergency backups.
Finding a safe replacement would allow much safer handling, lighter safety systems, and allow monopropellant engines to be used in places that they're impractical now.
When I was at school, one of the exam questions in S level chemistry was to estimate the maximum temperature reached if a stream of hydrazine hydrate was mixed with a stream of concentrated hydrogen peroxide. Of course, after the exam we had to try it... two carefully aimed pipettes over the centre of the biggest Belfast sink in the lab, three quarters full of cold water. I'm not disclosing how we released the liquids safely. If you can work it out, I'm not telling you anything you don't already know here. There was a white glow at the centre. I guess nowadays with the fear of terrorists no school exam would dare ask the question, whereas in those days I suspect the exam setter thought "Well, if they've done the work for S level, they deserve a little entertainment."
From scarped cliff or quarried stone she cries "A thousand types are gone, I care for nothing, no not one."
Politician storage is complex, expensive, and requires high levels of administratium, the heaviest element known. After long periods of storage politicians also decay into bureaucratium, which has a negative half-life and so becomes more massive over time.
Before you spout off about the ET insulation foam having been reformulated without CFCs, try reading the CAIB report (volume 1, Page 51), which specifically states that the portion of the foam that broke loose was the OLD CFC-based formulation.
http://caib.nasa.gov/news/report/pdf/vol1/full/caib_report_volume1.pdf
The story about the reformulated foam causing the Columbia accident is largely the doing of Rush Limbaugh, who seized on a lie from one of his typically ill-informed listeners, and kept repeating it until it became accepted as fact by everyone on the right.
http://mediamatters.org/research/200508090007
Remember "News for Nerds, Stuff that Matters"? Help make it a reality again! http://soylentnews.org
Hydrazine isn't used for heavy lifting rockets. It's for monopropellant thrusters. Satellite positioning, lifting and attitude control. The shuttle manouvering thrusters (Until recent retirement). That sort of thing. Very important in moving satellites around once they are up there.
Even more important - a hydrazine thruster is super-high-reliability. In space, pulling to the curb and calling AAA isn't an option (yet.) A liquid bi-propellant thruster is substantially more complicated than a hydrazine monopropellant one, and is more likely to have problems.
"Green" is the modern equivalent of "Safety First," which is a load of crap except for the safety alarmists (i.e. safety equipment vendors.) Mike Rowe is spot on with "Safety Third." I'd put Green at fourth. Every task has an attendant risk and cost. Environmental impact is a cost.
I'm all for developing less-toxic solutions, but a hydrazine monopropellant thruster is damned effective. It also shifts the system risk to the ground handling crews, where we can deal with it (as opposed to shifting it to on-orbit failures.)
"Kerosene + LOx = OMFG that is a LOT of Thrust!"
Yes but you can't store LOX for long periods, It want's to boil off. Hydrazine will stay stable for a long time, and another important aspect of hydrazine is it's hypergolic properties. This makes the engines very very reliable and simple to build. Just mix hydrazine and nitrogen tetroxide in a combustion chamber and it auto ignites. Or you can use a catalyst to break down the hydrazine, like in the shuttle APU. I know of no "green" propellents that can do this.