This web page last updated 9 Jan 2023
Using the Astron Omega 1 Engine as a Compressor and Using COPVs and Inflatables as Aircraft Structural Elements
This sub-page to www.ResearchGate.net is duplicated at www.rocketslinger.com also. Here, we briefly add corrections, comments, and additions to what was described and discussed at https://www.researchgate.net/publication/365964188_Propulsion_Designs_Using_Novel_Nested_COPVs_and_the , with the full title being “Propulsion Designs Using Novel Nested COPVs and the Astron Omega 1 Engine”. This new paper (here) then discusses how COPVs and inflatables could be used as structural elements in selected parts of an airframe. COPVs could double up as not only structural elements, but also as compressed-air sources for filling a to-be-launched-from-the-aircraft orbital rocket, or other rocket, with chilled or liquefied air or oxygen as a propellant and oxidizer. This could be called a “poor man’s air-breathing rocket”, with the liquid air (or oxygen) having been harvested at higher altitudes, reducing the weight of the aircraft (plus rocket cargo) at take-off. If the aircraft is powered by liquid hydrogen or liquid methane (for fueling otherwise-mostly-conventional jet engines), then a large on-board super-chilled liquid hydrogen (or methane) tank could serve as a “cold-source” for chilling compressed air (or oxygen). Would the added mass of required support gear (to include or possibly to include air compressors, oxygen concentrators or generators, regulators, valves, pipes and hoses, refrigerators, and heat-exchange devices) be so large as to negate all of the takeoff-mass-savings to be gained by filling the rocket in-flight with harvested liquid air or oxygen? This hard-to-answer question isn’t answered here. What is described in a fair amount of detail, is this: What design elements could be used in an aircraft, to dual-use COPVs, not only as compressed-gas sources, but also, as structural elements, to make these tradeoffs more attractive, here.
Much-lower-pressure inflatables (“gas bags”) are also briefly discussed here as structural elements for aircraft, as well as buildings. They could also be used as parts of “adaptive structures”.
The first (or preceding) document in this series is at https://www.researchgate.net/publication/365964188_Propulsion_Designs_Using_Novel_Nested_COPVs_and_thehttp://www.rocketslinger.com/COPVs/1st COPVs Document
As before, as with other sub-pages of www.rocketslinger.com, the intent here is to “defensively publish” propulsion-related (and “misc.”) ideas, to make them available to everyone “for free” (sometimes called “throwing it into the public domain”), and to prevent “patent trolling” of (mostly) simple, basic ideas. Accordingly, currently-highly-implausible design ideas (usually marked as such) are sometimes included, just in case they ever become plausible, through radical new technology developments (often in materials sciences).
Dear Reader, excuse me as I will often slip out of stilted formal modes of writing here. I have no boss or bosses to please with these “hobby” writings of mine, so I’ll do it my way! I’ll often use a more informal style from here on in, using “I”, “we”, “you”, etc. “We” is you and me. “You” are an engineer, manager, or other party interested in what’s described here. Let’s thwart the patent trolls, and get ON with it!
In descending order of importance (as ranked by Yours Truly, of course), here are the major changes, corrections, and embellishments that I would like to address here:
‘1) The 1st COPVs DocumentI wrote while assuming that compressed air would be saved in a wing-mounted assembly, never having even dreamed of the idea that COPVs could double up as structural elements of an aircraft. See Figure #10 in said previous document for a sample of my previous thinking. Most of the document below will concern the details about just HOW one might integrate COPVs (pressure vessels in general) into the structure of an aircraft.
‘2) The 1st COPVs DocumentI wrote with the idea that stored compressed (in-flight-harvested, chilled, possibly liquefied) air would be used to propel the rocket-launching aircraft, the entire aircraft, to a higher altitude (above the normal service ceiling) for launching the rocket. I now think that it makes MUCH more sense to add harvested air (or more-pure oxygen) TO THE LAUNCHED ROCKET ONLY (or at least primarily), in the name of efficiency. More details (not many more, about this) are discussed further below.
‘3) Before, I wasn’t aware of “oxygen concentrators” and “oxygen generators”, or nitrogen-oxygen separators. Now that I’ve learned about such things, I suspect that it might make sense to add such things to the “load” carried by the rocket-launching aircraft. These could be used to purify the oxygen (v/s simply compressed air) to be loaded to the to-be-launched rocket, of course. I (sadly) have no ideas to add, here, about how to scale such devices up, for our needs here, while keeping them (these devices) lightweight. I also don’t know which is our best choice. So I’ll provide some links, and leave it at that. See this grab-bag of links; some being more relevant than others… https://www.atlascopco.com/en-us/compressors/products/oxygen-generators and https://eurasiantimes.com/equipped-with-on-the-go-oxygen-chinese-soldiers-look-to-outdo/ and https://www.aviationconsumer.com/industry-news/editorial/o2-concentrators-inogen-aviator-is-tops/ and https://en.wikipedia.org/wiki/Oxygen_concentrator and https://en.wikipedia.org/wiki/Nitrogen_generator#Membrane_technology . Note that as far as I know, you have only 3 basic choices: Oxygen “concentrators”, oxygen “generators”, and nitrogen generators (this last one produces oxygen as the main “by-product”).
‘4) Much of the previous document (1st COPVs Documentconcerned the use of borosilicate “pressure domes” (or pressure arches) inside (or used as a part of) pressure vessels, as a weight (mass) savings. I then examined the idea in more detail, and tore it to shreds, as being a BAD idea! All this while I was NOT aware of a NEW development in materials science, which is described here: https://phys.org/news/2022-12-toughest-material-earth.html “Say hello to the toughest material on Earth” From there, "The toughness of this material near liquid helium temperatures (20 Kelvin, -424 Fahrenheit) is as high as 500 megapascals square root meters.” This is an alloy made of chromium, cobalt, and nickel (CrCoNi). Also, “CrCoNi is a subset of a class of metals called high entropy alloys (HEAs).” Perhaps HEAs of the future will serve as NAKED (needing NO composite over-wrap?) pressure vessels? These would MUCH speed the exchange of thermal energy across the walls of the pressure vessel!
I don’t off-hand know what the strength or “toughness” of these HEAs might be at higher temperatures. However, these HEAs just MIGHT be able to make the idea of the borosilicate “pressure domes” in the walls of a pressure vessel become viable (as a costs savings for the presumably high costs of the HEA materials). See Figure #4 (“flattened view”) of the 1st COPVs Document
‘5) Search the 1st COPVs Document for the search-string “trash gas”, to see where I documented the idea of filling a COPV with a combustible gas, purging it with an inert gas (like nitrogen), and then filling it with pressurized air. This is an inferior idea as compared to what is documented here: https://steelheadcomposites.com/combined-propellant-pressurant-vessel-cppv-concept/ See the sliding piston here inside the pressure tank, which can keep gasses strictly separated from one another. Fill one side with one kind of gas while purging the other side! Yes, now we are cooking with gas!
‘6) Search the 1st COPVs Document for the search-string “mattress”, to see where I documented the idea of shaping low-pressure airbags with internal restraints. In more detail, the quote from there is: “If one is worried about distortion in internal space-layers between the layers of our air-tight bags (Kevlar or other-material-based), as we fill them, then think of your mattress, with internal tie-back strings and button-dimples (buttons being “washers”, if your will, like on bolts), holding layers in restraint, preventing too much bulging.”
Well, now I know more. I know of a source with more details about this sort of thing! See https://www.researchgate.net/publication/235213999_Air-Inflated_Fabric_Structures ; especially their heading “DROP-STITCHED FABRICs”, which concerns the equivalent of the internal string inside your mattress, tied to buttons (“washers”, load distributors) on the outsides of your mattress…
The rest of this (above) document is somewhat relevant here, or is good “FYI” material. I suspect that relying much on this kind of assembly for aircraft structural material isn’t viable, for concerns about strength and reliability. More on this later (further below). However, it (the above) says “Fabric air beams are examples of air-inflated structural elements that are capable of supporting a variety of loads similar to conventional beams. To date, seamless air beams have been constructed using continuous manufacturing methods that have produced diameters ranging up to 42 inches.”“
Also it says… “The air beam has a cylindrical cross-section and its length can be configured to a straight or curved shape such as an arch.” Also… “Woven structures are generally designed to operate at pressures up to 20 psi while triaxial braided and axial strap-reinforced braided structures are generally capable of higher inflation pressures.”
Before diving into the details of HOW we could do these things, let’s go through a reasonably long summary of where we’re going to go to. Let’s think of COPVs (and gasbags) as long, cylindrical “logs”… Now we’ll build ourselves (at least partially) a flying log cabin out of these logs! Much of the focus (further below) will detail how we join the “logs” together. In older, more primitive days, mosses, lichens, and mud (whatever was at hand) were used for “chinking” the logs. See https://www.weatherall.com/blogs/log-home-blog/the-history-of-chinking ... OK, let’s not get side-tracked! Much further below, we’ll address “chinking” (more like mounting or securing, or mortaring) our COPV-logs together.
Our rocket-launching aircraft may launch its rocket(s) in one or more styles. Dropped off of the wing-bottom of a single fuselage like “Cosmic Girl”, or off of the common wing-bottom between two fuselages of a “catamaran of the sky” such as the Stratolauncher, AKA ”Roc”, or out of the rear (in the style of a C5 Galaxy or a C130), or out of the bottom like a bomber (B52, for example). These choices are somewhat relevant to just WHERE we might like to build PARTS OF the aircraft out of our COPV-logs.
Where would using COPV “logs” as part of the aircraft structure clearly be a BAD idea? The entire undercarriage, for the entire length of the aircraft. The nose section (cockpit etc.). The tail section and control surfaces there. The wings and their support structures. These are all OUT! If the wings are mounted low to the fuselage, we MIGHT safely use our “logs” for the walls and the roof (ceiling) of the fuselage in that (wings-mounting) area. If the wings are mounted HIGH to the fuselage, then COPV-logs should be excluded around the entire fuselage (in a ring-shape) around that entire area.
I don’t know just HOW MUCH COPV storage space might be needed, for this entire set of ideas to be practical (or if it is even practical to begin with). I suspect that we would NOT need to press into the margins, but an available margin MIGHT be between the strong undercarriage, and a flat internal floor of a working space, say, 1/3 or so up from the bottom of the cylindrical fuselage-cavity. Call this the “sub-floor” (or “below deck” area), perhaps. Depending on the internal load to be carried, I think this is generally a bad idea to locate load-carrying COPVs here. So this leaves us with large sections of the walls and ceiling (roof) of the fuselage, where we could double-use COPVs as structural “logs”. I suspect that this should be plenty enough space!
A log cabin is probably a bad analogy, but I couldn’t pass it up! Our COPV-logs might be better regarded as the siding, and the drywalls, of a “balloon frame” building. The siding and drywalls carry SOME, but not ALL, of the structural loads. A wooden frame carries the rest. Similarly, for what I describe here, there should be metal (aluminum most likely) periodically interspersed (in hoop-shapes or semi-circles) between (or among, supporting) the COPV-logs, to add extra strength and rigidity. These hoops should be located such as to span from undercarriage up through one wall, across the ceiling, down the other wall, and then back down (firmly mounted) to the undercarriage. Alternately put, hoops prevent our “logs” from rolling or sliding out of place.
This below drawing may not be needed for most readers, but is provided for clarity anyway.
So that’s a preview or over-view of our flying log cabin structure, with the fine details reserved for further below. What is the “big picture” of why we’re doing this? Where are we going with this?
Concerning “Reaction Engine’s Synergetic Air Breathing Rocket Engine (SABRE)”, we have this: https://physicsworld.com/a/air-breathing-rocket-engines-the-future-of-space-flight/ . From there, “The precooler can cool high mass-flow airstreams from temperatures above 1000 °C to ambient in less than 50 milliseconds, within a compact and low-weight design. It is formed from over 42 km of tubing, the walls of which are thinner than a human hair – thereby providing an enormous area for heat-transfer between the air and cooling medium.”
What I would now like to plainly state is this: I’ve never been able to verify this at any web site, but the Sabre space-plane MUST be getting its “cooling power” (transferred via helium) from its large tankful of super-cooled liquid hydrogen fuel. I see NO other possible choice! So for our “poor man’s version” of this, the jet engines of the (relatively) slow-speed airframe that launches the rocket, should be modified (or designed) to run on hydrogen or methane. See https://www.reuters.com/business/aerospace-defense/rolls-royce-successfully-tests-hydrogen-powered-jet-engine-2022-11-28/ and https://www.dgc.dk/sites/default/files/2021-06/Liquid_methane_aircraft2020.pdf . This large fuel tank full of bitter-cold liquid fuel could then power the entire aircraft, while ALSO serving (as this fuel warms up before being used) as a “cold source” (heat sink) for super-cooling in-flight-harvested compressed air (or oxygen).
I don’t have the expertise required, to discuss details about how this heat transfer (from compressed air to being-warmed liquid fuel) would best work. Nor do I want to research these details… It isn’t my focus here. It is just a useful ingredient to help make the entire idea here become possibly-practical. If “Reaction Engines” Sabre-jet can make it work in-flight, we can make a lower-tech version of this work! Yes? Enough said about that!
The same large tank of liquid hydrogen or methane can also be used to power a (fairly large?) number of on-board Astron Omega 1 engines (for compressing air and-or other gases, generating electrical power, and running an assortment of “whatever” other gear). The 1st COPVs Document
The Omega 1 is supposed to be able to run at “high altitudes”, but I’ve never been able to ascertain just HOW high such “high altitudes” might be. Some varieties of oxygen-nitrogen separators are also altitude-limited. The bulk of the “cargo bay” inside our aircraft will be next to impossible to securely pressurized with our “log cabin architecture” (I am near certain of that), and so, SOME sub-sections will best be pressurized. This may be as simple as a large rigid door (for getting gear and possibly also people in and out), or double doors and an airlock, perhaps, even, for holding in a fairly low pressure, inside something not much fancier than a pressurized kids’ “bouncy house”, with a high-volume low-pressure electric air pump for keeping it inflated. ***IF*** people are needed in-flight, inside the cargo bay, for attending to “persnickety” gear and-or the rocket and its cargo, they could be restricted to pressurized areas, and-or, wear oxygen masks, or even pressure suits. If any fuel-burning engines are used inside these pressurized areas (Astron engines for example), we’ll clearly have to constantly be bringing in fresh, new air, for getting rid of waste heat and waste gasses, as well as bringing in oxygen.
Getting back to the super-chilled tank(s) of liquid hydrogen or methane, now, please note that we know for sure that the Astron Omega 1 engines can run on these kinds of fuels (presumably after turning them to gasses!). So, even without cutting-edge new jet engines to burn such (gasified) liquid fuels, we could at least carry SOME smaller amounts of super-chilled liquid fuels, to serve for SOME of our heat-sinking needs, while fueling the Aston engines. If the cutting-edge new jet engines aren’t affordable, or spend too much time in development, we’ll need, perhaps, to rely on conventional petrol-based fuels instead (JP-4, JP-8), for the jet engines. We now have no giant heat sink any more, and emphasis would shift to on-board refrigeration, for cooling compressed, harvested gasses. For links concerning refrigeration, go towards the bottom of the section (here in this paper) at the “Adaptive Structures” section.
First, we’ll speculate as to what the optimum dimensions of the COPV “logs” might be, and then we’ll discuss how to secure them together. We’ll consider conventional (existing as of now) styles of COPVs, first. Then we’ll consider customizing the COPV designs, primarily for our structural purposes. That’s a quick preview.
In my research, the longest COPV design that I’ve seen is at https://static1.squarespace.com/static/5ca8e523ebfc7fd95c0c4fc1/t/5fb2cbbe44ad9171878b4010/1605553092670/COPV_Design_Report.pdf , where figure 4.18 (page 93) shows an 18-foot-long COPV design, but according to my reading of this source, it has never been built… For reference, https://steelheadcomposites.com/composite-pressure-vessels/ offers diameters up to 17 inches, and lengths up to 102 inches = 8.5 feet. And https://astforgetech.com/composite-overwrapped-pressure-vessels-copv-ultimate-guide/ says that “AST can manufacture forge and spin tooling for any diameter and lengths of up to 120 inches.” That’s 10 feet!!!! For type 3… From there… Type 3 COPV… ”COPVs with advanced fibers and metal liners are classified as type 3 COPV’s. Type 3 COPV’s from Advanced Structural Technologies, Inc (AST), in particular, feature a thin and lightweight 6061 aluminum liner, fully overwrapped with carbon fiber composite. The composite materials carry the structural loads.” (Emphasis mine). Also… “AST specializes in high capacity, high-pressure storage solutions up to 27” (69 cm) diameter and 120” (305 cm) in length.”
“Winging it”, then, for our design purposes (compromising between many factors), we might settle on COPVs 10 feet long, or slightly less. As possible “fillers” (if we want to stack or over-lay them in an interleaved order like bricks), we might also want to have some of them be “half-bricks” at 5 feet long, or slightly less. 27 inches (a tad over 2 feet) sounds like TOO thick for an aircraft wall! Maybe we should settle for 12 to 18 inches or so, for the diameters of our COPV “logs” here, IMHO (In My Humble Opinion).
The above idea concerning an interleaved or stacked brick-like arrangement may or may not be valid (optimal), depending on (possibly among other factors) how the “bricks” or “logs” interface to the metal “hoops”, as have been previously mentioned. This isn’t an avenue which I care to delve into, in detail.
As far as is concerned, HOW do we secure the COPVs, and fasten them to one another? We do NOT want to rip or tear the composite over-wraps, so we must proceed with utmost caution! I am thinking that we should tightly jacket them with a harness. Think of a harness in the style of fishnet stockings, but with far bigger gaps or voids… Or like “chicken wire”, with far larger voids. The jackets (harnesses) could be made of any suitable type of rope or cables. If metallic cables are used, they would most certainly have to be coated with plastics or artificial rubber, to prevent harsh surfaces from abrading the surfaces of the COPVs. In my mind, the BEST option would be to fashion the harnesses from tightly stretched flat artificial rubber “bungee cord”-type material, similar to the following type: https://www.uline.com/Product/Detail/H-3601/Cargo-Control/Rubber-Tarp-Straps-15?pricode=WA9585&gadtype=pla&id=H-3601 . Using such a harness will be of great help in holding the COPVs in place, without adding too much mass, and without adding too much insulation, either. Too much insulation will prevent the COPV from shedding the heat generated by freshly-compressed air, or compressed gasses in general.
Shock and vibrations will “jostle” our COPVs! We’ll want to prevent them from shifting around, and from spinning (rolling) around. Cross-ties of rope (from one COPV and harness) to another will help, as will ropes tied to the metal “hoops” as well (as were discussed further above). I am thinking ROPES here, not nuts and bolts, or other harsh, aggressive, metallic fasteners, in order to NOT abrade the COPVs, of course.
This will appear “jury rigged” or “unprofessional”, but who cares, or SHOULD care, so long as it is FUNCTIONAL? I must now momentarily digress, and tell a “war story” on myself. As an EE test engineer, I often built test equipment that, um, didn’t look too pretty, at times. As in, I would resort to the use of “epoxy putty”, such as “Gapoxio”; see http://aplusbputty.com/ , for securing parts together, in an emergency. When accused of being “unprofessional”, I would simply ask, “Is ANY customer EVER going to say, ‘Well, I like the costs, performance, reliability, and even the appearance of this computer or other electronic gear, here, but I will NOT buy it, because I hear that it was tested on some UGLY looking test equipment’? Methinks NOT!” (End of digression.)
Under severe or prolonged shock and vibration, COPVs might STILL shift around, or spin, inside their harnesses. Tests and-or computer simulations might best be used to clarify these issues. ONE possible option might be to (very cautiously) attach (glue) a “glue wart” at at least one carefully selected location on the COPV, with holes in the “glue wart”, which can then be tied to the harness.
A “glue wart” could be fashioned as follows: A cup-like hollow container (of any shape) made of artificial rubber (or similar non-aggressive,soft material) has voids in it, through which small pipes span from wall to wall, through the walls. Pipes could be made of thin aluminum, or moderately-heat-tolerant plastic, because the pipes will shortly be subjected to the (self-heating or exothermic) heat of curing epoxy “potting compound”. Keep on reading…
This “glue wart” is now filled with epoxy “potting compound”, to be slightly over-flowing (being thick, the compound will hold a good “meniscus”). See https://www.henkel-adhesives.com/us/en/products/encapsulants/potting-compounds.html ... To save a few dollars, the potting compound could be “cut” (diluted) using plastic pellets (AKA “nurdles”), in the same style as concrete is “cut” using gravel or rocks. The near-overflowing glue meniscus (ideally not TOO polluted at the top layer, with TOO many “nurdles”) is now held upright, while mated to the (coming down from above) COPV, for over-night (or at least multi-hour) curing. After the curing process, the protruding pipes are cut off, and “reamed out” (especially if metal pipes are used) to prevent harsh edges from abrading our ropes (or strings). Many “glue wart” pipes at many angles will allow us many choices on how to tie the “glue-wart” to the harness.
This (gluing the glue-wart to the COPV) may or may not be optimal. Tests and-or computer simulations should illuminate this matter. If gluing is NOT optimal, there’s another simple variation of this idea available to us: Form a (or form several per COPV) “glue-wart(s)”-like soft-surfaced conformal “warts” that are NOT glued into place, but are simply held tightly in place by the tightly-stretched (rubbery) harness. My personal bet is that this is probably the best choice (use no glue). Solid-state lubrication power (such as chalk), or other lubrication, between so-called “glue warts” and the COPV surface may be desirable, to prevent abrasion of the COPV surface.
Such “glue warts” (with or without glue bonds to the surfaces of the COPVs), with holes through them for tying them to the harness, can be tied, mortar-style, to form flat surfaces between one COPV “log” and another. “Glue warts” could ALSO be tied to rigid members spanning from one COPV to another, to help prevent “log-spinning” (COPV-spinning). It’s about time now for another drawing, then…
The anti-spin cross-bar could simply be rope-tied to the harnesses at both ends, and I’m not sure if they’d actually-really be needed, or not. Tests and simulations should help clarify such matters, of course. If the COPVs spinning inside of their harnesses is a REALLY serious problem, then the cross-bars could be secured to glued-down “glue warts” at both ends, for quite firmly solving the problem. This step might risk damaging the over-wrap if the airframe takes a severe jolt, though.
The harness should be installed with tension in the web of ropes (or, preferred in my mind, rubbery flat “bungee cords”), to constantly squeeze the COPVs. However, this “squeeze force” should leave plenty of safety margin for NOT crushing the COPV when the COPV is weakest, which is when the COPV is empty.
The tied-to-the-harness “glue warts” (whether or not they are actually glued in place) between the COPV “logs” (in the place of joining mortar, if you will) are, in my mind at least, vitally essential. They spread the loads at these contact points, to include loads arising from shocks and vibrations (jostling of the entire airframe). As previously mentioned, they may or may not be glued to the COPVs (I suspect it is best to NOT glue them). I also suspect that they should run the entire lengths of the COPVs. ALSO NOTE that there might be troubles with the COPVs sliding end-for-end within the harness. An appropriate “fix” for this (not illustrated) is to place a doughnut shape (torus) at the “shoulders” (ends) of the COPVs, like a horse’s collar, with the harness tension holding each “collar” in place. These end-collars should be made of pliable materials, of course, like what I’ve been calling “glue-warts” here.
Some fraction of the COPVs could be replaced by identically-sized-and-shaped low-pressure inflated airbags. Doing this might help prevent a sort of “dominoes effect”, whereby too many too-heavy and too-hard COPVs ALL slosh around together (with accumulated “sloshing” forces) if or when the airframe takes a severe jolt. Interspersing a few softer and lighter inflated airbags (as “dampers” of you will) may, for this reason, be a good idea. Again, test and-or simulations should help to illuminate this matter.
What materials might be used for such low-pressure airbags? I now repeat a short segment from my previous paper: Sierra Nevada makes inflatable habitats; see https://www.space.com/sierra-nevada-inflatable-habitat-moon-gateway.html , which says “The outside of the prototype LIFE habitat is comprised of a urethane pressure bladder, a nylon liner and a woven Vectran fabric restraint layer.”
It is now time to move on, to making some modifications to standard off-the-shelf designs of COPVs, to examine what sort of design modifications we’d like to make, in order to optimize the dual-use ideas here (storing compressed gasses, while also using the COPVs as structural elements). Note that so far, in my descriptions here, I’ve not addressed how we might (most likely, or most often, end-on-end) “gang together” standard COPVs, into one common gas-storage space. High-pressure hoses (and standard tank-ports) should do fine, I suppose, for linking standard COPVs together. “The Google Which Knows All Things” can help you with high-pressure hoses, so I’ll not even bother to provide links about these.
Now suppose that we want to join COPVs end-on-end for both structural and gas-storage purposes, at the one and the same time, while not adding much mass. See https://steelheadcomposites.com/hydrogen-storage/ , which shows “…large-port enables variable fittings and in-tank regulators” The port end here (in this case) of a COPV is a substantial size-fraction of the COPV diameter. It’s not much of a stretch of the imagination to imagine that an outer thread could be added to the large port there, and that COPVs could then be coupled end-to-end, to join the COPVs into a common tank, both structurally and for holding their contents in common. Male threaded parts on the tank-ends, females on the couplers… One could even use reverse thread on half of the ends of both the males (tanks) and females (couplers) as an option to avoid the need for spinning the entire tanks while assembling them end-to-end. Ports could be simplified to simply be openings to permit fairly high-volume gas-flow, from one tank to the next. If the female couplers are made extra-long (with a gap between the threads), a port (or ports plural) could be added there in the middle of the coupler, for interfacing to high-pressure hoses, as well. The female-female coupling could be turned into a “T” joint (fitting), that is.
If shock and vibration is too dangerous for mechanically stressing this mostly-rigid threaded joint between the tanks, then the mechanical load could be spread out a bit. I can provide drawings if needed (email me at RocketSlinger@SBCGlobal.net if needed), but I am hoping that a verbal description here will be enough. Create, in your mind’s eye, a conforming-shaped doughnut (torus) with soft padded surfaces where it contacts the COPVs, and spans the gap between tanks. The hole in the torus accommodates the male and female threads, and the female coupler. The torus’s OD (Outer Diameter) should NOT exceed the diameters of the tanks being joined. Now cut the torus in half, with the cut-line being parallel to the coupler length. Shave off maybe1/2 inch or 1 inch of torus-material along the cut-line, to make sure we have some split-torus compression space available. Deburr and round the edges of the cut, of course. Or just build the two halves separately, and don’t make a cut!
To fasten the (presumably light-weight but strong) split torus to the coupled tank-ends, we could ‘A) most simply leave some grooves in the outer surfaces of the torus-halves for tightly wrapping the halves together with rope or cable. Simple!
Or we could ‘B) insert (firmly mount) metal pipe in one half of the torus, and inside-threaded pipe in the other. Bolt the halves together! Other options may be possible.
The assembled torus (if tightly installed) now spreads mechanical loading more widely across the tank-ends, reducing mechanical stresses on the threaded tanks-ends. With such port-ends on both ends of the tanks, as many tanks as are needed, could all be strung together, both for gas-contents and for structural purposes.
One could mentally make minor modifications to the above, to understand my next set of ideas here below (as before, please email me at RocketSlinger@SBCGlobal.net if needed, for more drawings or details). The only differences between what I now propose, and the just-now-described slight modifications to the “large-port” tanks at https://steelheadcomposites.com/hydrogen-storage/ , is that I would propose the use of steel only at the port-ends of the tanks, and aluminum liners along the lengths of the rest of the tanks (as a weight or mass savings). Also, we could get even larger ports, most likely, and do away with the half-tori for mechanical load-spreading at the port-ends. Total maximum gas-pressures retained may take a hit, here, but the trade-offs might be worth it. See more (text) details around Figure #8 in the1st COPVs Document
Just for reference, sticking to standard threads might be best. See https://en.wikipedia.org/wiki/National_pipe_thread , which goes up to 24 inches. As mentioned before, though, making half of the threads be reversed threads offers some advantages, in avoiding the need for spinning the entire tanks, when stringing them together.
So then I’m envisioning that the inside surface of our ugly-looking, “kludged” assembly of tied-together COPVs (and possibly airbags as well) “logs”, plus metal hoops, will remain naked and ugly. There’s no need to “prettify them up” with cover-panels, which will do nothing functionally for us, other than get in the way of thermal exchanges, and block access for gas-flow (pipes and-or hoses) and structural-maintenance purposes. Let them remain naked, at least on the inside! This is highly similar to common practice in civilian airliners v/s military aircraft. Airlines use cover-panels to keep things looking “pretty”, and to keep nosey passengers out of the plumbing and wiring. Military aircraft generally don’t bother with such panels.
Now how about on the OUTSIDE, where the COPVs (and possibly airbags as well) will be exposed to what, 500, 600 mph of airflow speeds? This may be dangerous! Just HOW dangerous, I don’t know! HOW MUCH do we need to shelter these elements from the relative winds? Versus, how much should they be EXPOSED to the winds, for cooling freshly-compressed air or oxygen? I just don’t know, and I am humble enough to admit it! (I am also PROUD of my utterly astounding humility, but let’s not go there right now).
For starters, maybe we could start with high-tech, tightly stretched fabric coverings, appropriately perforated perhaps, in a compromise between cooling airflow v/s protecting the COPVs from excessive high-speed winds, such as (repeated from earlier on), see https://www.space.com/sierra-nevada-inflatable-habitat-moon-gateway.html , which says “The outside of the prototype LIFE habitat is comprised of a urethane pressure bladder, a nylon liner and a woven Vectran fabric restraint layer.” We wouldn’t need the pressure-bladder urethane material, but the rest might be useful.
Now what about covering this fabric with airflow-friction reducing materials? It seems to me that biological evolution has pre-solved these kinds of problems for us, at least in water! See, as possibly a bit relevant, the following grab-bag of links: Low-friction dolphin skin? https://www.delftex.com/ is vaguely relevant but not of much help. https://www.researchgate.net/project/Dolphin-skin-and-hydrodynamics-of-dolphins is certainly helpful. So is https://www.sciencedaily.com/releases/2004/05/040517072242.htm .
However, put “sharks” and-or “airplanes” into your search-strings, and THEN you can holler, “Bingo!”. See low-friction airplane surfaces at https://cen.acs.org/business/specialty-chemicals/BASFs-AeroShark-low-friction-film/100/i8 for “BASF AeroShark”, and then see https://www.basf.com/global/en/media/news-releases/2021/05/p-21-204.html . THIS is the type of surface material that we might want to use in our (perforated?) outside coverings for our “flying log cabin”!
Another possibility is that the COPVs (and possibly airbags) could be covered, starting from the rear of these areas, with overlapping (rope-attached or string-attached?) fish-scale-like, light-weight, but somewhat air-permeable scales, made of lightweight materials, and then covered with this “BASF AeroShark” material. An alternate name for our “log cabins in the sky” might then be the “flying fish”! Goodbye (for now), and thanks for all of the fish!
Now to conclude this section, “for grins”, I will list inferior ideas that I collected along the way. Perhaps a reader or two might want to pursue avenues that I have dropped? Possibly for distantly related purposes? One idea was to encase (entirely or partially) our COPVs within rubber tires (creating a “tugboat in the sky”?), or similar low-pressure inflatables. This, IMHO, would be too heavy, too expensive, and-or, add too much thermal insulation to an already-bad situation, as far as is concerned, the ability of COPVs to shed the heat of recently-compressed gasses. However, an interesting link that I scared up is here: https://www.heuver.com/knowledge/otr/tyre-pressure-and-solid-rubber-tyres says that 9.0 bar is attainable! In truly giant tires, that is, when carrying a load. Unloaded giant tires might carry significantly higher pressures, safely. But I can NOT see any kind of good “fit” for this, for the uses discussed here.
Let’s now see how this might all come together, for an operational flight. Some elements here (such as throwing relatively pure oxygen into the jet engines to shorten the take-off) are repeated from 1st COPVs Document
We’re sitting on the runway. Our COPVs are mostly filled with high-pressure cooled air and-or high-pressure cooled oxygen, which has cooled down while sitting in the tanks (COPVs), or been forcibly cooled. Our to-be-launched rocket(s) is-are loaded and ready to go, minus compressed (perhaps liquefied) air or compressed (perhaps liquefied) oxygen, to be harvested and loaded onto the rocket(s) later, at higher altitudes. Given clearance, we taxi down the runway and (optionally) dump some oxygen into our jet engines, to speed the takeoff (and shorten the needed runway). There are lots of optional features here… Mix and match! We take off and gain altitude, perhaps hastening our departure using some of our compressed air and-or oxygen.
En route to an elevated rocket(s)-launching altitude and location (in better weather and-or closer to the equator), we replenish the compressed (perhaps liquefied) air and-or oxygen that we’ve expended during take-off and ascent. The gasses pre-cool a bit first, in our expansive fuselage-walls COPVs storage spaces, after being compressed (most likely by our on-board modified Astron engines, for example). Then the cooled, compressed gasses (air or oxygen) are (optionally) liquefied by thermal exchange with the aircraft’s super-cold supply of being-burned liquid hydrogen or liquid methane fuel. The liquefied air or oxygen is loaded onto the to-be-launched rocket(s). Optionally, right before the rocket(s) are launched, the launcher aircraft might burn some of its stored, compressed (perhaps liquefied) air or oxygen, to exceed its normal service ceiling. Finally, the rocket(s) is (are) launched.
Note that pressurized vessels are stronger. For a simple illustrative common-sense mental exercise, just think… Would you rather drive on flat tires, or on inflated tires? So in that vein, presumably rocket(s)-launching time (merely dropping the rocket(s) and then letting them light themselves up) is presumably a LOT less stressful to the aircraft, than taking off and landing. We can surely afford to expend a lot of COPV contents (and thus weaken the COPVs) at the top of the flight profile, and then re-pressurize (re-strengthen) the COPVs during descent. Land with pressurized (strong, but hot) COPVs, let them cool back down, refuel and reload the aircraft, rest, test all systems, replace, repair, and refurbish, and “rinse and repeat”! Done!
Just suppose that our rocket(s)-launching aircraft (through an emergency need, pilot error, or sheer accident or bad luck) finds itself in a horrible windstorm, and-or severe wind shear. Automated systems (to include structurally-embedded strain gauges, for example) could even detect such things, to be computer-automated, and blended with pilot commands. In an emergency, rather than losing the aircraft, the inflated structural airbags (if used as interspersed with COPVs) could be rapidly deflated. This would allow airflow to flow THROUGH the body of the aircraft, decreasing structural loads to the body of the aircraft. Areas (of the aircraft body) subjected to such semi-sacrificial, aircraft-saving uses could be carefully selected to minimize damage (especially water damage in wet weather) to the contents of the aircraft. But… Rather wet than damaged or destroyed! (I just hope that the lawyers will permit this!).
In passing, let me note that similarly, “semi-sacrificial floors” could be added to buildings. Rather than having the building be toppled in (for example) a hurricane, vent (deflate) some structural airbags! The “semi-sacrificial floors” could be thoroughly waterproofed (floors and ceilings both), and contain (hopefully water-protected) infrastructure, such as pumps, air handlers, water heaters, air conditioning units, heat pumps, and so forth. Such floors COULD even contain low-cost, lightweight, but high-capacity pressurized-air COPVs for energy storage! In passing, please note that some of the Old-Order Amish (in workshops to include wood-working shops) use high-pressure air, instead of electricity, as a power source for power tools, for religious and-or cultural reasons. High-pressure air, then, is sometimes called “Amish electricity”. See https://artdiamondblog.com/archives/2013/06/_source_kelly_k_18.html for example. Long live compressed air power!
Getting back to our semi-sacrificial sky-scraper-floors, and their contents possibly containing compressed-air energy storage, the following is HIGHLY relevant: See, in the popular press, https://www.pv-magazine.com/2023/01/06/storing-solar-power-with-compressed-air-storage-air-conditioning/ , which then links to https://www.nature.com/articles/s41598-022-26666-1 , “Cooling potential for hot climates by utilizing thermal management of compressed air energy storage systems” , which is also accessible at https://www.researchgate.net/publication/366470877_Cooling_potential_for_hot_climates_by_utilizing_thermal_management_of_compressed_air_energy_storage_systems . When emptying out the compressed air storage, for energy recovery, the cooling power of the expanding gases could be used to assist air conditioning, is the fairly straightforward idea here.
Here’s a concluding grab-bag of perhaps-vaguely relevant links. Note that some of them have to do with cooling (refrigeration), which could be relevant to our possible in-flight needs for cooling and-or liquefying air and-or oxygen. Precisely HOW would we use such things? I really don’t know!
Such links are at https://www.researchgate.net/publication/245529080_Some_issues_on_the_design_and_analysis_of_pneumatic_structures and https://www.researchgate.net/publication/286173742_Comparative_parametric_modelling_of_composite_tubes_and_composite_overwrapped_pressure_vessels and https://www.inceptivemind.com/new-more-environmentally-friendly-air-conditioner-uses-solid-refrigerants/25926/#:~:text=One%20class%20of%20solid%20refrigerants,%2Dto%2Dsolid%20phase%20change. Also https://www.sciencedaily.com/releases/2022/08/220822130431.htm Note that many of these “barocaloric” materials work at ridiculously high pressures. That means that they’re off limits for our practical uses. For example, see https://www.researchgate.net/publication/332510202_Colossal_barocaloric_effects_near_room_temperature_in_plastic_crystals_of_neopentylglycol 0.25 GPa here… GPa convert to bar = 2,500 bar is too high for us! See https://www.unitconverters.net/pressure/gigapascal-to-bar.htm for a handy converter. The root page here (https://www.unitconverters.net ) links to MANY handy converters, by the way.
Non-conventional refrigerators have (for some time now) been able to use sound waves. See https://phys.org/news/2016-12-refrigerator-multistage.html , which then links to “Design and experimental verification of a cascade traveling-wave thermoacoustic amplifier”, which can be found at https://www.researchgate.net/publication/303598825_Design_and_experimental_verification_of_a_cascade_traveling-wave_thermoacoustic_amplifier .
See in the popular press, https://www.sciencealert.com/scientists-just-invented-an-entirely-new-way-to-refrigerate-things and https://hackaday.com/2023/01/06/salty-refrigeration-is-friendly-to-the-environment/ , which lead to https://www.science.org/doi/10.1126/science.ade1696 , “Ionocaloric refrigeration cycle” Or see https://www.researchgate.net/publication/366529710_Ionocaloric_refrigeration_cycle for the same...
Also (getting back away from refrigeration now) see https://www.researchgate.net/publication/304424721_Smart_Composite_Overwrapped_Pressure_Vessel_-_Integrated_Structural_Health_Monitoring_System_to_Meet_Space_Exploration_and_International_Space_Station_Mission_Assurance_Needs and https://www.researchgate.net/publication/353879171_New_Advances_and_Future_Possibilities_in_Forming_Technology_of_Hybrid_Metal-Polymer_Composites_Used_in_Aerospace_Applications/figures?lo=1 … For grins!
Also “for grins”, see an explosion test at https://www.space.com/lockheed-martin-space-habitat-explodes-video . “Habitat bursts violently at 285 per square- inch (psi), or more than six times the max operating pressure.” This means that it is rated for 47 psi or so, then…
I’ll be the first to admit that I’m a moderately well-self-educated non-expert, at best, here, concerning this topic. However, in the usual interests of thwarting “patent trolls” who might otherwise patent perhaps-obvious ideas, here goes! This concerns the rocket engine(s) for mid-air-launched rockets, more specifically, in my mind, at least. I suspect that we have a premium, here, on keeping things simple and light-weight. So… For whatever these ideas may be worth!
Cold liquid fuel (perhaps cold methane or cold hydrogen, or even cold refined kerosene) and cold liquid oxidizer (air or oxygen) might enter the combustion chamber insufficiently gasified, still be very cold, and be hard to keep lit. We might use a rocket-engine gas generator (see https://en.wikipedia.org/wiki/Gas-generator_cycle ) that is undersized, as a cost savings, or we might skip the use of such a thing altogether, and simply spray cold liquids (or even gas-liquid mixes) into the (top of the?) combustion chamber. In any case, we might have trouble keeping it all lit.
So here comes possibly-new-idea number one! Use a derivative of the Astron Omega 1 engine, and modify it. As previously noted in this document, the 1st COPVs Document
Idea number two here is as follows: See “Space Shuttle rocket engines” at https://en.wikipedia.org/wiki/RS-25 , which tells us that “A second hydrogen flow path from the main fuel valve is through the engine nozzle (to cool the nozzle).” Now suppose that we created a hollow-walled nozzle with (for example) an outer shell made of aluminum, and an inner wall of (for example) stainless steel (310S alloy, perhaps). The inner wall has tiny holes drilled in it, as well as “passive thermally activated flow-switches”. To understand details of what such “passive thermally activated flow-switches” would look like, see https://www.researchgate.net/publication/331556573_Designs_for_Passively_Thermally_Gated_Fluid_Flow_Switches , with a duplicate copy of this document also located at http://www.rocketslinger.com/Psv_Tgt_Fsw/ .
Cold (liquid, gasses, or mixed) fuel enters SOME of the segments of the nozzle (at the top or small-diameter end of the bell shape), within the aluminum and steel “sandwich”). So the combination of tiny simple weep-holes in the inner steel layer, and passively gated flow switches also, cools the nozzle walls, with cooling power inherently directed to where such cooling power is most needed. The same could be done with cold oxygen or air as well. If we slice the bell-shaped nozzle into many vaguely triangle-shaped (orange-peel-like) pieces, alternating fuel v/s oxidizer inside the “sandwich” slices, we can mix fuel and oxidizer somewhat well. Manufacturing the many identical or nearly-identical “orange peel triangle slices” might be assisted by 3-D printing. Fasten the segments together and hook them up! (If we chose to sandwich-convey ONLY fuel or ONLY oxidizer, the “orange peel segmentation” won’t be needed at all, of course.) Cold oxidizer and-or cold fuel now simultaneously cools the nozzle wall, while also adding combustion within the nozzle. Lengthening the nozzle (away from all of the combustion) with a more-conventional single-walled nozzle, to allow combustion to reach completion or near completion before exiting, would most likely be a good idea. Also note that this “hollow metal sandwich walls” idea could be used in the combustion chamber only, or the nozzle wall only, or both. There you have it! For what it’s worth!
That’s all that I have for now.
Stay tuned… Talk to me! My email is RocketSlinger@SBCGlobal.net
Back to main site at www.rocketslinger.com
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