How to Design, Build and Test Small Liquid-Fuel Rocket Engines (1967)
risacher.org
risacher.org
I'm starting University in September as an adult student of Computer Science and I'm planning to start a model rocketry society with the goal of putting a 9ft tube above the Karman line and recovering it safely.
I'm still deciding on fuels, but I'm strongly considering a hypergolic combination of catalyzed pure hydrogen peroxide and kerosene (I've already been granted a recipient competent authority from the explosives department for the storage and transport of usable quantities these for the use in a model rocket).
The primary reason for hypergolic fuels is because it doesn't require a complex combustion chamber / ignition set up. You can mix them together at ambient pressure and temperature and they will spontaneously combust producing heat, steam and pressure. If you can safely handle the dangerous fuels it's a much easier route to a liquid fueled rocket engine.
One of the difficulties in the UK is going to be finding somewhere to launch from: we don't have large swathes of unowned, unmonitored land and the restrictions the CAA (rightfully) place on launching near cities means that it'll have to be out in the sticks somewhere. I'll probably have to convince a farmer to let us blow up a couple rockets on the back of a fallow field a few times before we get a successful launch off the ground.
I'm trying to plan as much as possible and get all the requisite licenses (I already have a CAA unmanned surveillance drone operator ID, as well as exemption from the need for a flyer ID because I have my flight competency certificates, and exemption from the 400ft amateur flight ceiling as long as I issue a NOTAM (notice to airmen) 1 week before any test flights, and I'm insured by the UK Rocketry Association) in the hopes that people will "take me seriously" when I found the society.
I'm also working behind the scenes to set up partnerships. I've been in contact with Starchaser Industries and a few other aerospace companies nearby to have them sponsor the program, show us around their rocketry factories and hopefully give us contacts at their company we can bounce ideas off to see if there's anything we've missed, or any hazards we are hugely mispredicting.
https://www.bloomberg.com/news/articles/2020-03-17/the-u-k-s...
There would be bits of rocket everywhere in a 20m radius (which we would be dutiful in picking up since it's useful to study for next time) and there is unlikely to be any sort of crater, but there would be a small kerosene fire we would have to put out (so providing and testing fire suppression equipment in the form of extinguishers and blankets will be important).
Realistically, we'll be flying something around the 30-40KG mark so we'll have to get it certified by the CAA: http://www.largemodelassociation.com/resources/over-20kg-sch...
I feel like with a youthful charm and the right paperwork from all the respective government divisions (The Explosives Division at the Health and Safety Executive, a certified model design from the Civil Aviation Authority, and our insurance as operators / flyers with the CAA) it won't be too hard to talk a field landowner in to it, in return for a token payment and an offer of a few cool afternoons seeing model rocket launches on the back-end of one of their fields.
Thought you might be interested.
Thanks a lot for this, it sounds useful, I wonder if we could time the launch so that the satellite could receive telemetry (as a back up to the integrated avionics failing due to rapid pressure or temperature changes, or shock)
https://www.bis-space.com/branches/regional/bis-west-midland...
I went to some talks organised by them a few years ago. Many of the members worked on rocket propulsion for a local company and had connections to the Rocket Propulsion Establishment.
This kind of glosses over the whole hypergolic fuels are necessarily poisonous toxins that boil your skin if you touch them. To react with each other so quickly, they basically have to react with just about everything else as well - including human saliva, the liquid on eyeballs, and the liquid in your lungs.
This (extremely 60s styled) video is full of useful information about how dangerous hypergols are: https://www.youtube.com/watch?v=Zha9DyS-PPA
If you're dealing with umsymettrical-dimethylhydrazine and dinitrogen tetroxide, you're going to be in a world of pain trying to produce them, handle them and get them close enough to use in an engine without being so close that the fumes spontaneously ignite. Not to mention that the dinitrogen tetroxide boils at ambient temperatures, etc, etc.
Obviously, I was glossing over the danger (not something I do in real life when handling dangerous fuels, but probably something I do when writing a short comment on Hacker News) and anyone seeking to work on Rocket Engines needs to ensure that they consult with subject matter exports before, during and after any construction or launch preparations begin.
... With that disclaimer out of the way, in the grand scheme of dangerous fuel and oxidisers combinations, Kerosene and Hydrogen Peroxide are significantly safer to handle than traditionally used hypergolic mixtures:
- They are both liquids at ambient pressures and temperatures (don't underestimate the value of not needing highly pressurised canisters - above 2000psi in many cases - and cryogenic equipment, that's all mass you don't need to lift and failure states you don't need to control for)
- Storage and deployment of AVTUR (Aviation Turbine Fuels) is a well understood procedure with pre-certified canisters.
- Hydrogen Peroxide at sub-90%, and especially at sub 70%, purities is reasonably safe to store and handle, especially if you store it in an inhibited state and you're willing to have a suboptimal hypergolic reaction in return for a safer handling procedure.
- The pressures and temperatures created when reacting these two liquids together in a combustion chamber are extreme, but not so extreme as to be outside the remit of an amateur team.
This all doesn't mean that these are safe to handle - and failing to properly respect rocket fuel results in death for yourself and others - but it does mean that they're safer to handle.
In a perfect world I would manufacture solid state rocket propellants, but in addition to the negatives of not being throttle-able and being hard to early-terminate, manufacture of solid rocket motors is a criminal offence in the United Kingdom and getting an explosives certificate is a long, daunting task.
Are they? AFAIU the propensity for HTP to exothermically decompose was the main reason why it was abandoned in favor of IRFNA/NTO. I mean, if you're switching to something as nasty as NTO or IRFNA for safety reasons, whatever you're switching from has to be pretty bad!
See also the Kursk submarine disaster.
> Hydrogen Peroxide at sub-90%, and especially at sub 70%, purities is reasonably safe to store and handle, especially if you store it in an inhibited state and you're willing to have a suboptimal hypergolic reaction in return for a safer handling procedure.
IIRC in Clark's Ignition the opposite was mentioned, namely that higher concentrations have better resistance to decomposition, presumably due to lower amounts of impurities which can get the decomposition reaction started.
I'm not sure the switch to IRFNA/NTO is for safety reasons. There is simplicity involved - you don't need catalyst with them. The components themselves are easier to get by and to store. They however have their own nasty properties regarding safety. Also historically nitric acid was initially used with turpentine, which is a hypergolic pair.
Here are some comments on safety.
Yeah, good point, that's certainly an advantage.
> Here are some comments on safety.
> https://yarchive.net/space/rocket/fuels/peroxide.html
Coincidentally(?) those comments stop in the year 2000, when the Kursk put a dent in HTP enthusiasm. For a while at least.
Not that I have any good solution either. Seems all high performance liquid rocket fuels have some nasty downsides.
For small scale applications N2O + some light hydrocarbon like propane or ethane could be interesting. But that seems to be quite immature, so could be some showstoppers ahead in that path.
Union's space programme had uncounted casualties to something happening with H²O²
Highly concentrated / "pure" HP is an entirely different animal than what you buy at the drug store. It absolutely is not something to be toyed with.
It may still safer to use than the "typical" hypergolics, but it isn't "safe."
Have you thought about crowdfunding? I'd happily chuck in a tenner.
To launch a "9ft tube above the Karman line" you need - airframe structural design & analysis, avionics development & testing, recovery system " ", etc. The work that goes into a flight-ready airframe (separate from engine development) is massive. I don't know how to impress the scale of the project you're proposing, but you may want to take a look at some of the university teams attempting something similar: http://masa.engin.umich.edu/ (I'm not affiliated with UMich). Something to takeaway is how long it's taken to iterate on their systems, despite the steady stream of motivated students and university support/infrastructure.
I don't mean to be negative, but there needs to be a path forward if you're going to make the kind of progress you want. Again, I strongly suggest that you start flying smaller, simpler solid rockets now to iterate on airframe design and build flight experience as you consider liquid design choices.
One of the issues with solid rocket motors is that in the UK we can't manufacture our own solid rocket motors under the 1875 explosives act (supplemented by the EU Directive 2014/28/EU), so we have to purchase off the shelf rocket motors which are available in the UK.
Flying in an air frame with these has several key issues: It won't be a solid test bed for our air frame weight, the centre of gravity will be offset, they aren't throttle-able, even the high specific impulse motors tend to have very short (sub 10 seconds) burn times, they don't generate shock cones, etc.
One of my personal inspirations is the UCSRPL: http://www.uscrpl.com/
I imagine we'll have to follow in their footsteps: progressively more complex builds following on from a relatively simple starting point.
The plan is to use as many pre-existing resources as possible, this means:
- Using purchased fuel and oxidiser combinations instead of synthesis
- Working on a software (virtualising the hardware) test bed for avionics, then progressing to breadboards, then to purchasing PCBs. It's worth mentioning that I will be a student of Computer Science, but I'm going in to this with a significant experience of real time programming and PCB design - previous companies I've worked at had embedded systems.
- Using a simple system for recovery, most likely pressure deployed drogues fitted in the air frame cone, and an emitter which enables us to find it post touchdown.
I also understand that it's likely going to take the majority of my degree to get this done. If we don't make it to the Karman line: that's also fine. I'm not daunted by the possibility of failure, I'm excited by it. We learn a lot from failure. The goal is to go as far as we can and develop our skills through iteration.
You're reiterating some of the differences between a solid & liquid rocket, but that's not what I'm getting at. If you wait until you have a flight-ready liquid engine (think in years) to test an airframe and other subsystems, those subsystems won't exist. Buy some COTS solid motors and iterate on your subsystem design; the flight experience is invaluable. Any smaller testbeds you fly will not resemble the final airframe, and that's the point. Flying a research liquid engine is risky, you need something cheap to unit test features in your onboard systems---recovery, tracking, DAQ, etc.
It sounds like your hardware experience will give you a head start; a lot of amateur rocketeers don't have that. Regardless, please consider starting small and starting now. Getting a small airframe in the air and recovering it successfully with your own avionics is the first hurdle, should be your first short-term goal. I've met several students (and professionals) that jump straight into spaceshot projects and burn out pretty quickly.
Some of the replies in this thread are ludicrous (barge launch?). Hypergolics are a bad idea on the hobby level, but others have already touched on that and I think you'll come to the same conclusion on your own. You mention a decrease in engine complexity (in my mind it's small) but you're trading that for a huge jump in infrastructure capability.
Lean on the engineering department at your university and recruit some younger guys to help out. It sounds like you're already familiar with the style/structure of other university rocket teams, and that's probably what you should aim for IMO.
They sold this book and Apollo photos and other things out of the back of hobby magazines in the 60s and 70s. China Lake is home to a Naval Air Station, a major R&D location for rockets and other flying things, so it's possible it was a side gig by some rocket scientists there, but that's just a wild guess.
[0]: https://www.amazon.com/Sidewinder-Creative-Missile-Developme...
Having a simulator to try these out would be very useful before trying anything practical. I'm sure it will be a complicated piece of code with heavy computation requirements
Simulating cooling channels//ablation for larger scale rockets is a major PTA though.
Purchasing LOX isn't too difficult, there are many vendors willing to supply large amounts of it, and a few vendors willing to supply small (experimental) amounts of it.
Storing LOX is the real challenge, you need to keep it at ~310f (~-190c) which requires a well insulated cryogenic storage chamber. Typical industrial sized storage tanks have a few metres of insulation to keep the heat out, and typical small-scale tanks have around 1-2 feet of insulation.
You're probably looking at a viable minimum storage container size of between 500-1000 litres (any smaller and your insulation layer will be so thin that you'll lose 10-20% of your stored oxygen as gases per day), with the typical minimal size being in the 2,500 litres range (which normally lose 1-2% of stored oxygen to gas per day)
You can buy very small containers (2l, 5l, 25l, etc, these are for nitrogen but you can get them for oxygen too): https://uk.vwr.com/store/product/2104367/liquid-nitrogen-dew... but these lose the liquid very quickly and you would likely want them delivered the same day you need them, resulting in a just-in-time delivery failure point.