DerekL1963

It *should* be before the engine, with the decomposed products ducted to the combustion chamber. But the current design of this engine shows it embedded in the combustion chamber.

Err... That completely fails to address the issue I raised, which isn't viscosity - that having your propellant tank completely open to the combustion chamber is monumentally stupid. You have tunneling problems from both ends, and tunnelling from the combustion chamber equates to rapid planned disassembly. And I'm having a problem visualizing any fuel mix that won't simply flow out the nozzle while the vehicle is being fueled yet will still flow past the restrictor you're trusting to prevent combustion from propagating into the fuel mass. That's a pretty steep order. From the reports I've heard, those don't work too well. They aren't designed for liquid flow, let alone at the rates a rocket requires - as the catalyst is in the surface layer it's stripped (eroded) away within a few seconds to a minute at best. Designing a functional cat pack, one that is structurally sound, allows sufficient flow, has sufficient performance, and which doesn't quickly strip is a *huge* challenge. And that's for a conventional cat pack - this system as the orders-of-magnitude-more-difficult issue of having to be compact enough to fit within a combustion chamber and will have a challengingly small 'depth' (as seen by the HTP flow). Between the challenges (and steep cost per flight) of a cat pack, the difficulty of obtaining HTP, and operating issues (such as needing to preheat the cat pack), pretty much nobody I've seen sticks with HTP long if they're serious about amatuer rocketry. It's just too difficult to work with and offers few significant advantages over NOX or LOX to offset it's disadvantages. And that's in conventional engines, this engine is... unconventional and has numerous significant (and likely difficult and expensive to solve, if they can be solved) challenges of it's own.

o.0 At least in the US, it's pretty straightforward, rocketeers do it routinely. - call Praxair or Airproducts and arrange for a delivery. You'll need an appropriately certified dewar and handling system/staff, which is non-trivial but doable. From everything I've read on various rocketry lists, the biggest problem is the smallest commercial delivery if frequently far larger than the hobbyist or amauter can use.

And that's not easy... Anything inside the tank (in the case of an S-II or S-IVB) needs to be able to survive a bath in deep cryogens while also posing no threat to the engines nor introducing dangerous slosh modes. (Oh, and not retaining pockets of helium when the tank is filled, nor pockets of cryogens when the tank is emptied.) All the equipment outside the tank needs to be broken down into components sized to fit through a tiny hatch, and shouldn't require a hundred times more man hours to be assembled than the programs provides across all occupancy periods. That's a *very* tall order. There's a reason why the 'wet' workshop was abandoned when a 'spare' Saturn V became available.

That rising curve is very pretty, but it's the stock market's estimation of value - which may or may not bear any relationship to reality or the amount of money a company is making. It's the numbers in the next panel down which are interesting - SpaceX is still eating capital at a frightening rate. A company that's making money in any significant amount doesn't need massive ongoing infusions of capital. https://www.axios.com/founders-fund-partner-leaves-to-launch-spacex-focused-fund-2466277199.html - the backstory here, if we ever hear it, will be interesting. But the tl;dr version is simple enough, SpaceX needs so much funding that someone is founding a company dedicated to supplying that need (and siphoning off their share via commissions).

Well, no. Unless the fuel tank is completely open to the chamber, which I had presumed you wouldn't do because it's monumentally stupid. HTP has disadvantages over LOX, period. That pendulum swings both ways.

On the other hand, if the density and cohesion is high - you'll increase the difficulty of feeding the propellant into the chamber. This will require higher gas pressure, thus likely bring back the problem of tunneling. TANSTAAFL. You can't consider only one variable in isolation. (And getting the propellant to inject, vaporize, mix, and burn is already going to be difficult enough.) You don't recommend using any combination that isn't hypergolic... based on what exactly? The near zero failure rate of igniters? The even lower failure rate if you use redundant igniters? Seriously, igniters are cheap, bone simple, lightweight, and well understood. To convince me that we should toss all that in favor of the operational expense and complications of using hypergolics you're going to have to do better than that.

If anything in the second stage propulsion system fails, you're boned. The real question here is more one of development risk (at the program level) than one of flight risk. A complex engine about which virtually nothing is known, vs. a simple igniter which is well characterized. It's silly to pretend the latter is a source of greater concern. It doesn't make a difference. If you've got gas pressing on a gel and an outlet for the pressure, tunneling is a potential concern. Regenerative cooling is tough, but well understood. The proposed engine is even tougher, and a complete mystery.

When evaluating failure modes, that it will fail is practically irrelevant - and a statement such as "can fail at the worst moment" is an appeal to emotion, not engineering. A proper evaluation considers the likelihood of failure, which in this case is damn near zero for a properly designed and tested igniter system. That being said, I'm with @Steel. This engine is way too complex for an amatuer effort.

To some extent, yeah. There's also more awareness of MMOD problem. There's also a great of hype.

That means "shuttles get hit more often" not "capsules don't get hit".

What leads you believe that?

Which, with the current throttling scheme, will virtually guarantee combustion instability - while still not solving the problem of ensuring complete mixing of fuel and oxidizer. Figuring out some way of evening out the flow (without causing too much backpressure into the cat pack) will go a long ways towards solving both issues. You absolutely need an even feed across the entire face of the oxidizer injector. Seriously, as you've already shown the performance of this design is marginal. You can't afford to have any significant amount of propellant go unburned if you hope to get anywhere near the theoretical performance of these propellants.

You already said that in the portion of your previous message that I quoted. Repeating it does not address the issue I raised. Again, scale isn't the issue here - lack of mixing is.

In theory. It remains to be seen if the theory is correct. Especially since "decreasing burn area" != "burn quenching". What those fluid dynamics look like to me is "there's no mixing, so most of the oxidiser mass is wasted and there's a lot of combustion in the nozzle and even so most of the fuel is wasted". And that's setting aside the extraordinary difficulty of matching fuel pressure to chamber pressure.

It's also worth pointing out that for all the piffle spread about (in the US) about "escaping religious intolerance" and "fleeing oppression", those were the exceptions. During the grand era of colonization, colonies were very much engines of business and profit. Many of the uninhabited, unexploited regions of the Earth are largely that way largely because there's nothing there to exploit of sufficient value to be worth the trouble.

Then, frankly, you don't understand any of my comments . Nobody spends billions to trillions of dollars on massive infrastructure projects without an expectation of commensurate return. It's all about the economics. Period. 0.o The people who are investing in fusion research are doing so with a positive and well defined economic (and political) goal, it's neither pure science nor pie-in-the-sky. Exoplanet hunting costs down in the rounding errors of the sums you're proposing to spend - it's completely irrelevant. Yep. The billions-to-trillions of dollars required to establish and the billions more per annum to operate ISRU infrastructure only makes sense if you have a present and ongoing demand for the output - "build it and they will come" doesn't apply here.

So, let's try this again. I didn't ask your definition of "commercial exploitation". I asked, who pays? If you can't answer that question, then you're just blowing smoke. Had I said anything about self sustaining, you'd have a point. I didn't. In fact, they won't be self sustaining, they almost certainly *can't* be self sustaining. (No chip fab for just one example.) That's why they cost trillions of dollars in the first place. Even at SpaceX prices, building and sustaining a lunar colony is going to be hellishly expensive. Not to mention, once you get past the smoke blowing and buzzword spouting and actually look at the technology, there's a lot 3-D printing can't do. Among them, well - pretty much anything that has to do with building heavy mining machinery. 3D printing isn't a magic wand, it's a real technology with very real limitations. Said limitations are expanding, but it's nowhere near the point where starting a lunar colony from essentially scratch is anything but fantasy. (And that should have been space exploitation is about economics.)

Without explaining who the market is (that is, who is buying the materials), then "commercial exploitation" is just a meaningless buzzword. It's going to take a LOT of vehicles flying about to make the trillion dollar cost of those mining colonies worth it. Define the destinations for those vehicles, and who is paying for them and their missions. Ditto for the colonies. Space exploration isn't about engineering, nor is it about fanboy fantasies. It's all about the economics. Who pays? And why?

Both are very good ways of blowing yourself up. While HTP isn't good for building actual bombs, it's still dangerous stuff and not very tolerant of mishandling. There's a reason why it's not sold in quantity except to "companies or government institutions that have the ability to properly handle and utilize the material". "Not good for building bombs" != "safe to handle". Not just the BATF, but state, county, and possibly municipal authorities will take an interest as well.

I'm on a private [very serious] amatuer rocketry mailing list (I.E. actual builders and operators) and the difficulty of obtaining HTP is a frequent topic of discussion, to the point where no design that uses it is regarded as viable.

Well, since we're talking about "every piece of hardware" (I.E. entire mission modules)... My statement "Nobody builds flight spares" holds. 0.o No offense, but this statement makes zero sense whatsoever - because regardless of the mode (EOR or Heavy Lift), each and every part is going to be absolutely key to mission success. Is a fantasy mission where what real world concerns aren't addressed by vast increases in budget are simple airily hand waved away.

Yes, checkout is difficult. However, combustion instability won't be a problem; the injection is behind the catalyst bed, so as soon as the HTP hits the catalyst bed it will decompose anyway. 0.o The issue isn't whether the HTP is decomposed or not - it's uneven flow at the inlet face of the cat pack and thus potentially uneven flow at the outlet face.

The big thing it adds is a nightmarishly stupid level of complexity. Not in the wiring harness and control, but in installing and checkout. And a variable number of injection points just screams "combustion instability" to me.

Yup. And the computers most people know about crash, BSOD, lag to heck and back, etc... etc... The experience of the public with computers is not a pretty one. (Yah, a guidance computer is a very different beast than a consumer grade computer... But try and get the general public to grasp that.)