Hacker News Reader

As a working engineer in the aerospace industry with an amateur rocketry background, I highly recommend that you refine the scope of your project before you sink in a lot of resources. Iterating on high power solid rockets w/ parallel development on a small scale pressure-fed liquid is probably the most direct path to success.

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.

Cheers for this! Don't worry about the negativity, it's something I've come to expect from subject matter experts since this is a very long process I'm going down fraught with danger and legislation.

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.

> 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.

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.

>If you can safely handle the dangerous fuels it's a much easier route to a liquid fueled rocket engine.

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

In general, I would agree with you.

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.

> in the grand scheme of dangerous fuel and oxidisers combinations, Kerosene and Hydrogen Peroxide are significantly safer to handle than traditionally used hypergolic mixtures:

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!