Micro Capsules / Micro Space Planes for Micro Orbital Launch Vehicles

kbd512 · 2020-11-28 19:59:01

All,

I'm starting a new topic for this subject and moving posts to this thread, per request from SpaceNut. I originally posted this content under the "Unconventional Ways to LEO" sticky. I see value added capability through the development of this technology.

In addition to our traditional orbital class rockets, I think the US should continue to develop micro capsules and micro space planes for both commercial and military purposes. The Virgin Galactic LauncherOne immediately comes to mind. In order to extract the last few seconds of specific impulse, we'll need miniature staged combustion engines using an oxidizer / fuel combination, such as LOX and sub-cooled LPG, that retains the bulk density of LauncherOne's LOX/RP1 propellant combination with a slight specific impulse boost and the ability to take advantage of autogenous pressurization to eliminate COPVs, simplifying manufacture of the rocket stage hardware and flight operations. The use of a standard commercial fuel that does not require special processing is an added bonus. LPG does not appreciably degrade over time, nor does it coke engine components.

The initial goals behind such a technology development program would be creation of an unpressurized single-person or small parcel delivery vehicle for retrieval by an awaiting spacecraft for various civil and military missions. The space plane, in particular, is intended to flight qualify lightweight CNT and BNNT structural composites and heat shielding fabrics, to permit this very light weight glide-capable reentry vehicle to ascend to orbit via air launch, transfer its occupant or parcel to an orbital space station, and then reenter and land on a runway like a conventional light aircraft. Everything would be as simple and lightweight as possible- a no frills personal spacecraft. Subsequent program goals would include air capture and reuse of the booster stage to reduce operational costs.

kbd512 · 2020-11-28 20:00:15

GW Johnson wrote:

The "microcapsule" idea would look about like a single-seat scale-down of Gemini with its somewhat-propulsive service module. It would be about the size of a Mercury capsule, which itself had no propulsive service module.
Neither was capable of automated rendezvous with a space station, although Gemini came close, falling short in avionics, not propulsion. The difference would be some more propulsive capability in the service module, plus modern avionics, so that rendezvous with the space staton becomes possible.
What you are really talking about here, is a scaled-down Dragon, 1 seat instead of 7 seats. There, the propulsion is in the casule, not the service module, which is power and cargo capacity only. Plus aerostability during early launch abort.
At about $85-95M for a Falcon-9/Dragon launch, I don't see much savings to be obtained by developing a smaller version of the capsule. For one thing, there are no man-rated somewhat-smaller rockets available to launch it. For another, desired payload always grows. Spacex's price is already lower than anyone else in the industry. So why not just go with it?
I'm not at all sure how you would build a spaceplane significantly-smaller than X-37B, and still have one seat aboard. Even if you did come up with such a design, with what slightly-smaller rocket would you launch it? Why not go with what you already have, and come up with an "X-37C" that has a seat instead of a payload bay? And fly it with the same Atlas-5 (or whatever replaces Atlas-5)?
Or just use Sierra Nevada's Dreamchaser. 3 seats, but as I said, payloads always grow, they never decrease. It also launches with the Atlas-5. Or eventually it will.
GW

kbd512 · 2020-11-28 20:01:12

kbd512 wrote:

GW,
Gemini was the smallest all-metal capsule that America was capable of creating using 1950s technology. I'm sure it was great for its time, but it's not representative of current technology at all. Gemini was pressurized, it had an ejection seat because it was ground launched and the rocket was nowhere near as reliable as the ones we have today, it used an instrument panel that today can quite literally be a space suit helmet HUD projection fed information from a computer the size of an iWatch with even smaller sensors that can simultaneously process and record more data than Gemini's instruments ever could.
Claiming that a LearJet is the smallest practical jet we can build pretty much ignores aircraft like our Tomahawk cruise missiles, which are more than powerful enough to seat a single human in a lightweight ejection seat, attach landing gear, and include an instrument panel, after removing that weapon's 2,000 pound warhead. We have guided ordnance now, the size and weight of an artillery shell- albeit with 3 different types of fused sensor inputs that are thoroughly capable of outright destroying any lesser vehicle than a main battle tank, because it's quite literally accurate enough to hit a human in the head while they're riding a motorcycle across a battlefield- from 20+ miles away. In short, modern technology has moved on from what you knew, at break-neck speed. That ordnance has been tested in battle and used to kill single terrorists in crowds of people without using any kind of explosive warhead, sparing the civilian populace from the results of war. It turns out that merely striking someone in the head with an artillery shell falling to Earth at several hundred miles per hour is more than sufficient to end them. The alternative is even more gruesome, which is why we invented that new technology.
Dragon and Dragon Rider have pressure hulls, have built-in abort systems, and are launched from the ground by vastly larger and more expensive / complex rockets, so no, we're not talking about scaled-down Dragon technology. If Starship has no built-in abort capability with 100+ people on board, then strictly speaking, it's not necessary.
Here's our use case scenario:
I want to send two astronauts to the ISS as crew replacements. Do I spend $85M to deliver two people using Dragon Rider, or can I spend $10M to $15M and deliver them via individual capsules or space planes that don't require splashdown in the ocean and subsequent recovery?
That's why I don't want to "just go with it". Competition lowers prices. Elon Musk said the same thing, so I'm going to take him at his word. All tool-myopia aside, there's no practical reason why a smaller rocket can't be "man rated". It's a matter of appropriate testing. I don't want to "increase payload", either. That's another euphemism for increasing cost. There's an appropriate use for every tool in our tool belt. Adding another tool won't hurt the other tools. Beyond that, if we mass produce these small launchers, then we don't have to wait 6 months to send someone or something new to ISS. We can have that done in a week, perhaps a matter of days.

Terraformer · 2020-11-29 07:15:06

What was the name of that proposal for an inflatable reentry glider?

Ah yes, FIRST.

407 kg per crew. Not bad, and we can probably improve on it now. Launch from an airplane, land in a glider.

SpaceNut · 2020-11-29 10:26:19

There is the need and for 1 or 2 people to be able to quickly get to the orbital platforms of space and back would and should be cheap.
This new topic "develop micro capsules and micro space planes for both commercial and military purposes" of KBD512, is worth exploring in terms of what we have for the launchers which are in that arena.

Currently the large end of the plane would be the x37 or DreamChaser but I think you are looking even smaller....

We have discussed something simular long ago in Smallest Human Ascent or Descent Lander for Mars Or Earth

kbd512 · 2020-11-29 13:21:39

Terraformer,

Thanks for that addition. I'd never seen that one before.

SpaceNut,

Dream Chaser, which is capable of seating up to 7 people, is significantly larger than what I had in mind. Dream Chaser still requires launch aboard a $100M to $200M rocket. That's not economical at all.

Everyone,

I'm of the opinion that spending $80M to $100M to deliver 2 people to the ISS is a waste of money, even for a government agency with pockets as deep as NASA has. If Starship truly can launch for $2M per flight, then that's the type of improvement I'm after, but it remains to be seen if costs will ever be that low. I contend that the standing army to support Starship will probably cost that much per day to maintain.

If we can implement true assembly line manufacturing to build 1 rocket and 1 space plane per day, that will bring the costs down to the point where spending perhaps $1M per flight is a trivial amount of money for NASA, out of its $20B budget. When we can launch 1 person per day, then we're to the point that we're putting the same number of people in space who have ever flown in space up to this point in time, every 2 years or so. If Dragon only costs $85M per flight, then we can afford to send 85 people to space rather than 7, greater than an order of magnitude improvement. Tiny rockets and space planes lend themselves to manufacturing line production, enabling continuous improvement feasible with the likes of the Tesla Model 3, whereas gigantic rockets and spacecraft do not.

At $1M per attempt, we can also afford to scrub a few launches here and there without any significant impact on operations. We should have 3 crew members aboard the launch aircraft, 1 astronaut, and 1 ground monitor who coordinates the flight, so there's only 1 person dedicated to communications and operations of the flight vehicle and astronaut aboard it. We can afford to devote 1 person to support 1 astronaut. Once that astronaut is aboard ISS or some larger vehicle, then operational control will be handed off to the support team for the larger vehicle. An air launch platform with the capacity of StratoLaunch could send all 7 astronauts on their way per flight, so it would only have to fly once per week, remain well within its payload performance margin, and put less stress on the wing by dropping much lighter rockets.

Instead of having a few dozen active astronauts, we can afford to have a thousand or so, routinely fly them on shorter missions, and allow them to specialize. I want specialist scientists who are "the best" at a single task, that we provide pilot and space walk training to. We don't need them to be generalists with millions of dollars worth of training if we have so many that we can begin to implement division of labor.

This is equivalent to having an officer corps (senior astronauts with generalist training and dozens of space flights) and enlisted corps (junior astronauts or specialists who perform specific duties related to their field of specialization). The senior astronauts, people like Peggy Whitson or Robert Behnken, have accumulated enough education / training / space flight experience / time in service to command an exploration class mission, but that doesn't mean we can't have a support corps who run various biomedical experiments, test specific new technologies, etc.

Currently, we can't afford division of labor due to the exorbitant up-front costs of education and training and rocket launches, but by spreading that out over time, we can employ a lot more people who perform useful specialized tasks. The US Air Force does the same thing. They don't expect a Lieutenant to command a squadron or a mission from the moment they walk through the door. Experience and exposure to different aspects of aviation is accumulated over time.

GW Johnson · 2020-11-29 13:37:25

Well, maybe we should not be too dismissive of 1950's technology. The SR-71 was a mid-1950's design, and no production vehicle has since come even close to matching what it could do. The closest was a flying Mig-25 prototype known then as EA-166.

Imagine what that 1950's SR-71 airframe and engines would be like, refitted with some modern avionics? Especially if we could get around the aging/cracking problem with its beta-phase titanium skins.

And don't go claiming X-43A and X-51A were counter-examples, because they were not! No experimental vehicle is.

I do take exception to the notion that something like a Tomahawk could be manned, replacing its "2000 lb" warhead. For one thing, the biggest warhead it could carry is/was a 1000 lb convenional warhead. The nuke was the W-80, which is actually smaller and lighter.

For another, that airframe was a cylinder 20 inches in outside diameter. There is no room to seat an occupant, in any position, much less include a "lightweight ejection seat", whatever that might be. (Most ejection seats are 500+ pounds, although a lot of that is driven by low speed/low-altitude requirements imposed on their design.)

That being said, what you come up with for lightweight capsules and spaceplanes depends upon what starting assumptions you make. That, more than anything else, determines your results.

If you assume a "clean sheet of paper", you implicitly assume that you will pay heavily for a full development cycle for your spacecraft, and also for the rocket that launches it, unless you can use an existing rocket. That stuff ain't cheap. Never was, never will be.

If on the other hand, you look at changes off of existing designs, you can relieve yourself of much of the development cycle costs. Especially if you can stick with existing launch rockets.

Regardless, whether a mini-capsule or a mini-spaceplane, you will need about 8 km/s out of your launch rocket, then either the launcher upper stage or the spacecraft must supply around 1 to 1.5 km/s delta-vee to rendezvous with ISS, or any other LEO space station. Then it needs a smidge more delta-vee for a de-orbit burn, and may or may not need a landing burn, depending upon exactly what you are designing.

Now, your craft will require electric power, and much more of it, if people are aboard. Your choices are batteries, fuel cells, or solar panels-with-some-battery. None of these are inconsequential in size or weight.

If people are aboard, you somehow have to design-in launch abort capability. Ideally, this should extend all the way from just sitting on the pad to just about station rendezvous. The demonstrated choices are launch escape towers and built-in spacecraft propulsion at multi-gee thrust levels. Neither of these is inconsequential in weight or volume.

And it should also include what to do during untoward circumstances during entry, as well as final descent and landing. That last item is still mostly unaddressed by all the designs that have ever been, including those out there right now. I say that despite all the stuff that got added to the Space Shuttle after the Challenger loss, none of which was worth anything to Columbia's lost crew.

The more stuff you do not reuse, the higher your operating costs will be, Spacex has proved that beyond a shadow of a doubt. But, know also that the bigger, heavier, and more expensive your craft will be, the more stuff you do try to re-use. And THAT gets very expensive indeed, due to the "tyranny of the rocket equation".

That's precisely why Gemini, Apollo, Soyuz, Dragon, and Starliner (as well as Orion, and whatever that craft is called that the Chinese fly) all featured/still feature throwaway service modules.

It's also why the kluged-up cluster that was Space Shuttle cost around $1.5B ($1990) per launch, once the real truth came out! Which is in turn why the Soviets decided not to use their Buran space shuttle clone, even though they had better, robot-capable avionics.

Many do not see the true technical difficulties involved in any sort of spacecraft design, but everybody understands high costs. Which when you include the development costs, exert a real push toward "differences-off-of-existing-designs", and away from "clean sheet of paper" designs. Ugly little fact of life, but there it is. Deal with it.

Which is why I suggested what I suggested in my earlier post. Obviously, this thread is really about "clean-sheet-of-paper" designs. So be it.

OK, that's enough of that. I just want y'all to understand a little about the surrounding milieu for what you want to try to do here. You will be ignoring those program-killing development costs for clean-sheet-of-paper designs! It takes a very rich outfit to actually do that. As Spacex and Blue Origin have also proven beyond a shadow of a doubt.

GW

Last edited by GW Johnson (2020-11-29 13:47:31)

SpaceNut · 2020-11-29 15:50:59

From what I remember the Dream chaser can be launch even by a Falcon 9 to orbit so there is no need for the expensive booster that ULA can provide for its use in the Atlas V..

If reusability as well is what we would want then a plane style booster and altered Dream Chaser sounds like a win, win; in that each should be quick turn to reuse.

You nailed the first set of data in this

GW Johnson wrote:

Regardless, whether a mini-capsule or a mini-spaceplane, you will need about 8 km/s out of your launch rocket, then either the launcher upper stage or the spacecraft must supply around 1 to 1.5 km/s delta-vee to rendezvous with ISS, or any other LEO space station. Then it needs a smidge more delta-vee for a de-orbit burn, and may or may not need a landing burn, depending upon exactly what you are designing.

What altitude is the 8km/s to and does it improve if the speed is increased to 9 or 9.5 so as to reduce the possible size of an upper stage that would be 2 plus stages if the capsule or bird is powered?

kbd512 · 2020-11-29 18:47:46

GW,

Apologies, but I forgot that the Tomahawk only had a 1,000 pound warhead. I never meant to suggest that that specific airframe could be retrofitted to become a fighter jet, just that that amount of weight is enough for a modern fighter made from modern materials and equipped with modern weapons. My point about Tomahawk's 2,900 pound launch weight, less 600 pound booster rocket motor, being more than enough weight to equip an airframe with a modern small jet engine, cockpit, ejection seat, avionics and sensors, and a couple of small bombs or missiles still stands. The Martin Baker Mk17 ejection seat weighs 36kg and is certified for use in aircraft with weights as low as 1,000kg, and it accommodates crew weights from 56kg to 123kg.

Mk17 Ultra Lightweight Escape System

That document was from 2013. Replace all that carbon fiber with CNT or BNNT, aerogel foam for support / comfort, and we can probably get that seat down to 18kg.

The 2020s are not the 1950s. A bomb that weighs less than a 155mm artillery shell contains at least 3 different sensors in it, the avionics to fuse the sensor inputs, which makes it accurate enough to hit a bowling ball moving at 40mph, it can glide for at least a dozen miles from 20,000 feet, and still packs enough explosive to outright kill anything short of a MBT, despite the fact that a small teenager can easily pick it up with one hand. That kind of capability didn't exist 10 years ago, never mind 70 years ago.

So, can we build a lightweight orbital reentry vehicle that absolutely minimizes all the "fluff"?

I think we can. The total absence of fluff makes the new vehicle cheap and simple to produce and operate. The flight avionics will be built into the space suit, with an umbilical that connects the suit to the sensors incorporated into the vehicle itself. The Space Shuttle era EMUs supposedly draw no more than 100 Watt-hours per hour, or thereabouts. We're using a MCP suit, so figure 100W maximum for the life support equipment and perhaps another 150W for the vehicle itself. Our new thin film solar panels weigh ~1kg per 1kW of output and the new Tesla batteries are about 386Wh/kg. I can't imagine at what point more than 1kW of power would ever be required. The AF-M315E monopropellant thrusters would only require a couple dozen Watt-hours of power to heat up their catalyst beds, at most.

SpaceNut · 2020-11-29 21:07:12

I should not be all that surprised when I happen upon another topic that related to delivery of just few crew to orbit.

The Case for a Small CEV

GW Johnson · 2020-11-30 13:16:46

Spacenut:

The 8 km/s is a nominal figure that gets you to a very low Earth orbit, more-or-less eastward launched, such as from Canaveral. That would be to something near 300 km up. The ISS is higher than that (about 500-600 km up, and rather sharply inclined off of eastward. So the direct requirement to the ISS orbit is nearer 8.3-8.5 km/s.

But, in order to rendezvous with a station already in that orbit, you have to enter an elliptical orbit, or series of elliptical orbits, with period(s) different from the station in its circular orbit. You wait it out in these intermediate orbits until the station is going to be at your apogeee when you are there, too.

That's when you circularize at that apogee, which puts you within a mile or two of the station, in the same orbit at the same speed. Depending upon how many elliptic "waiting" orbits you might need, the sum of the burns might fall in the 0.5 km/s class for delta-vee. But from that final close position, it's just small thruster burns to dock.

From the station going home, you need at the very least a deorbit burn. This is approximated by the "apogee burn" to put you from circular onto an ellipse that intersects station altitude at its apogee, and just grazes the surface at its perigee. All those in that class of perigee altitudes from around 50-60 km altitude down to a surface (or even subsurface) graze, will all have about the same delta vee from the station circular orbit. It's on the order of 0.1 to 0.2 km/s.

Which is why the total delta-vee to actually reach the station, and deorbit to go home, falls closer to 9 km/s than 8 k/s. If you need a landing burn, you'll need more delta-vee than that. If you rendezvous with anything else on the way, you'll also need yet more delta-vee. It is the designer's choice whether and how much of this delta-vee beyond 8 km/s comes from the launcher's upper stage, and how much must be supplied by the spacecraft. But one or the other MUST supply it!

Everybody:

I did a couple of oddball small spaceplane studies a few years ago that might have some bearing on what is being discussed here. They're posted on "exrocketman". Those are 2 March 2013's "A Unique Folding-Wing Spaceplane Concept", and 3 April 2019's "Pivot-Wing Spaceplane Concept Feasibility".

Both use fuselages that enter dead broadside, with my low-density ceramic heat shield material on rather flat bellies. Both are fairly small craft. They carry more than 1 person, so the designs could be scaled down.

The low-density ceramic heat shield is described in another posted article: 18 March 2013's "Low Density Non-Ablative Ceramic Heat Shields", which essentially contains the content of my paper on that material at the Boulder, CO Mars Society convention that same year. Highly experimental material, but it showed great promise.

GW

Last edited by GW Johnson (2020-11-30 13:19:55)

SpaceNut · 2020-11-30 18:02:19

Thanks GW for the knowledge to my question.
So rocket engines and fuels along with the structural dry mass is all part of solving to the acceleration to orbit that we require.

Shuttle was very heavy for what it could do for bringing that crew to orbit plus a 20 mT payload tucked away in the cargo hold. So can we make a small shuttle taxi to orbit and ignore the large payload cargo for just what we would need if we had to wait to come down or missed the rendezvous with the station or other orbiting location.

SpaceNut · 2020-12-03 21:06:32

Bump small seems to be catching on.

kbd512 · 2020-12-06 06:59:09

I've identified a particular use case for this type of solution, so now I'll explain a bit more about the optimizations for cost-effectiveness.

1. A carrier aircraft, such as the 747 or StratoLaunch, negates the requirement for ejection seats / rockets for launch pad abort scenarios that don't exist when the rocket in question is dropped from 30,000 to 40,000 feet in altitude. This vehicle is latched to the wing of a very large transport aircraft like a piece of outsized ordnance. The transport aircraft contains no ejection seats or other crew escape systems, so it's not strictly necessary for a single seat space plane. Both StratoLaunch and Cosmic Girl use 747 components since 747s have been relegated to cargo transport on account of the lower ticket prices associated with using twin-engined airliners with better fuel economy.

2. The booster and upper stage use LOX/LPG propellants because sub-cooled LPG can provide an oxidizer / fuel density impulse nearly identical to LOX/RP1, but with the added benefits of a meaningful specific impulse improvement and autogenous pressurization so high-pressure Helium or Nitrogen bottles are not required. Since both propellants will be at the same storage temperature, no insulation between the oxidizer and propellant tanks is required. A simple carbon fiber body with some type of aerogel foam wrap will suffice. LPG is a light hydrocarbon that does not coke engines the way RP1 does and it is not a specialized batch-produced fuel specific to rocketry.

3. The propellant tanks, rocket engines, and space plane are small enough to easily mass manufacture on an assembly line. A semi truck with a standard trailer can easily transport a LauncherOne-sized vehicle broken down into the space plane (wings removed), upper stage, and booster stage. This makes transport of the vehicle to the Mojave Space Port a much simpler prospect. The individual components are so small and light that simple hand-cranes could be used to assemble the complete vehicle stack onsite. The space plane itself is very small and light, so it can use any paved runway for landing. In an emergency, it could even land in a field.

4. The use of AF-M315E monopropellant for the thrusters means no special precautions are required for fueling the space plane itself or during recovery. Since the space plane falls in the weight range of a mini satellite, existing satellite thrusters are sufficient.

5. The complete total lack of specialized support infrastructure means any airport or military air base where a 747, LOX, and LPG can be delivered to can support a launch. This describes virtually every airport and military air base in the Western Hemisphere. Existing 747s can be converted to both carry cargo as a side job and support launches.

NFPA 58 - Standard for the Storage and Handling of Liquefied Petroleum Gas - 1995 Edition

LPG could potentially be synthesized from syngas using a catalyst:

A highly stable and efficient catalyst for direct synthesis of LPG from syngas

Synthesis of LPG from synthesis gas

Beyond use in small rockets, LPG produced from DME could serve as a synthetic replacement for gasoline to reduce emissions, eliminate the need for fuel pumps, and improve the service life of piston engines. Unlike LCH4, LPG is storable on Mars at modest pressures. The LPG could be sub-cooled just prior to launch to provide RP1-like propellant bulk density and a modest specific impulse improvement over RP1. It's the only fuel that works in gasoline / diesel / gas turbine / rocket engines and high temperature fuel cells without substantial modifications to existing designs. LNG is great if you have all the infrastructure built to use it, but we're starting from zero on Mars, so a storable fuel would be really nice to have.

tahanson43206 · 2020-12-06 08:12:00

For kbd512 re #14

SearchTerm:LPG Liquid Petroleum Gas as a storable fuel for Mars or Earth applications

SearchTerm:UseCase for small launcher system

(th)

GW Johnson · 2020-12-06 13:23:36

LPG is a mix of light hydrocarbons, not a straight species. It is dominated by propane, but there's butane and a whole lot of others in there, too.

Its composition is not spec-controlled. Which makes its detailed properties (all of them!) variable from batch to batch, like gasolines, but actually a bit more variable.

This is not an issue when burned as stove gas or heating fuel, as those burner "just don't care" what they burn in detail. It could very easily be a problem in a liquid rocket engine, especially in the turbopump systems, and maybe in the safety systems trying to detect incipient problems.

So, I'll give you one guess why Spacex chose liquid methane (a pure substance with always the same characteristics) instead of LPG.

GW

kbd512 · 2020-12-06 15:36:26

GW,

LCH4 is not a pure product, either, nor anything close to it. It has to be refined, same as LPG, specifically because it contains heavier hydrocarbons, one of them being Propane, and other unwanted impurities. Here in the US, we deliberately mix other hydrocarbon products with it, namely Mercaptan. The generous tolerances of the HD5 Propane purity specification does not preclude corporations from manufacturing higher purity Propane mixtures. Air Liquide, which supplies Hydrogen and other cryogenic liquids to NASA, manufactures 99.9% pure Propane. I believe Air Liquide calls their product "CHEMGAZ 2". Matheson Gas manufactures a 99.999% pure Propane product that contains 8ppm of other species of hydrocarbons.

Whereas the HD5 spec calls for 95% pure Propane, the spec for LNG is 85% to 95% pure Methane.

Liquefied Natural Gas: Understanding the Basic Facts

Natural Gas Spec Sheet

INTERSTATE NATURAL GAS—QUALITY SPECIFICATIONS & INTERCHANGEABILITY

NATURAL GAS SPECIFICATION CHALLENGES IN THE LNG INDUSTRY

LNG Blue Corridors - Gas Quality

Manage contaminants in LNG feed gas and cryogenic processing—Part 1

So, I'll answer your "one guess" question as to why SpaceX chose LCH4:

1. Methane is the lightest and cheapest hydrocarbon available <- Primary reason
2. Methane is available from a variety of sources, albeit with substantial impurities, unlike RP-1 <- Secondary reason
3. Methane can be synthesized using the Sabatier reaction, even though it's a very energy-intensive process <- Tertiary reason

There's just one problem with it. It doesn't store at all without active cryo-cooling, which requires additional input power just to hold onto whatever you've already processed. That is not the case with LPG, which would remain liquid at night on Mars, at zero vapor pressure, even at the equator of Mars. There's no issue with the purity of LPG, either. We know how to economically produce greater than 99% purity LPG and do so for industrial and commercial purposes. We don't do that with LNG because we can't. LPG actually has fairly rigid purity specifications, whereas, to the best of my knowledge, LNG has none. There are GCV specifications for LNG in the US and it can't contain toxins like Mercury or Hydrogen Sulfide above a specified limit, but the impurities of the product are negotiated with individual customers at the point of sale.

RobertDyck · 2020-12-06 15:59:15

kbd512 wrote:

LCH4 is not a pure product, either ... the spec for LNG is 85% to 95% pure Methane.

Sorry to nitpick, but that means LCH4 is not LNG. The acronym "LCH4" means liquid CH4, which is pure methane.

kbd512 · 2020-12-06 17:42:45

Robert,

What I should have written was: "LNG is not a pure product, either, nor anything close to it." Apologies for using the terms interchangeably. The spec for LNG is 85% to 95% pure LCH4. LH2 isn't 100% pure Liquid Hydrogen, either, nor is LOX 100% pure Liquid Oxygen. It's a mostly pure product and for sake of understanding we refer to it by its nominal chemical formula, even though it's never 100% pure. I'm sure you already knew that, but if you didn't, then you do now. What we manufacture here on Earth is LNG, not LCH4. The overwhelming majority of the product is LCH4, but it's never 100% pure.

SpaceNut · 2020-12-06 17:53:40

When a fuel is a mixture is hard to keep a consistent thrust ratio when the mix ratio needs to vary.

GW Johnson · 2020-12-08 18:26:56

I looked in my 1987 Marks' Mechanical Engineer's Handbook, in chapter 7 about fuels, and found a nice section about gaseous fuels. There seems to be "natural gas" in multiple forms, "liquified petroleum gas" sold to a variety of product specs, and a variety of "manufactured gas" fuels.

Natural gas exists in two major forms, the raw material as it comes out of the wells, and the commercial natural gas product that is actually put into the gas pipelines.

The raw material out of the well varies quite dramatically in composition and heating value from well to well, and (I presume) over time from any given well. It is dominated by methane (~60-90%), but there's lots of ethane, propane, and butane (5-15% each), and higher hydrocarbons. There is also often lots of nitrogen (up to 30% or so), carbon dioxide (up to 30% or so), various sulfur compounds, particulates, and even water.

The article said this highly-variable raw material is processed to remove some of the non-methane materials, and often blended to achieve the heating value they want (in the vicinity of 1000 BTU/cu.ft). The article didn't say how it was exactly processed, but I know that condensibles are easily removed at elevated pressure with suitable chilling. Particulates can be settled-out in a stilling chamber. You can't do much about nitrogen except blend a high-nitrogen gas with a low-nitrogen gas to achieve the desired heating value.

The processed gas is sold into the pipelines per multiple product specs. Heating value is more important than exact composition, usually. Methane usually varies from 85 to 95 volume percent. Most of the rest is ethane, propane, and butane.

I rather doubt this kind of "methane" is what Spacex is using. They most likely are paying the premium price to get real technical-grade methane.

The propane and butane removed from natural gas to create pipeline-ready grades are the feedstock for "liquified petroleum gas" products, which includes specs for commercial "propane", commercial "butane", and commercially-sold mixtures of the two, all of which are considered to be "liquified petroleum gas" products. The ethane is feedstock for chemical plants.

Exactly how much methane is in your commercial natural gas product, how much propane is in your commercial propane product, how much butane is in your commercial butane product, and what the proportion of propane to butane is, in your mixed liquified petroleum gas product, all depend upon the spec to which you buy it (or more usually the outfit from whom you buy it). There is no one spec for any of these commercial products.

Further, none of these commercial products would ever qualify as a relatively-pure technical grade material. That was not addressed in the article. You would pay a premium price for technical grade products bought to an actual technical-grade spec. The commercial product folks only care about price, heating value, and that it does not unexpectedly liquify. Heating value would not be your prime requirement in that technical-grade milieu, composition would be. You have to pay for the extra processing to achieve it.

GW

Last edited by GW Johnson (2020-12-08 18:27:50)

kbd512 · 2020-12-08 18:42:35

GW,

One of the primary suppliers of cryogens to NASA, Air Liquide, manufactures technical grades of Oxygen, Nitrogen, Hydrogen, Helium, Methane, and LPG. So yes, I would presume that slight premiums are being paid for nearly-pure oxidizers and fuels. However, it could also be the case that an outfit like SpaceX is using commercial grades of oxidizers and/or fuels to absolutely minimize launch cost, but I doubt it. The main point is that LPG is storable at atmospheric temperature in a stainless steel can, whereas LOX / LH2 / LCH4 are not. LPG confers the benefits of autogenous pressurization, just like LCH4, impulse density near LOX/RP1 when sub-cooled the way SpaceX does LOX/RP1 and LOX/LCH4, improved specific impulse over LOX/RP1, is significantly cheaper than RP1, and LPG burns about as clean as LCH4. It's not quite as good as LCH4 as a rocket fuel when it comes to specific impulse, but millions of LPG refining and storage sites are in successful operation around the world. LPG is also a viable replacement for gasoline and diesel if synthetically manufactured using syngas and solar thermal power. Heck, they've powered airliners with LPG. LPG provides roughly 2.5 times the BTUs of LCH4 in the same storage space.

GW Johnson · 2020-12-09 20:21:20

The propane I use in my BBQ grill is an LPG product. It is roughly 98% propane, 2% butane, and traces of heavier hydrocarbons. The problem with it is storage pressures in the 200 psig class at 70 F ambient temperatures. Butane is closer to 50 psig at the same 70 F. Propane-butane blends fall in between. Those pressures are way too high for Starship's tankage.

The higher hydrocarbons show denser heating value storage capability. They are also less of the original natural gas out of the well, so the three discussed here are actually the most practical to recover. Spacex is using methane for its availability, and for the gravimetric (not volumetric) heating value. That is directly related to the energy release during combustion with oxygen.

Spacex has to use some sort of technical grade spec for its methane. There is no way around that, and still get repeatable performance figures during the turbopumping process. It simply costs what it costs to get that relatively pure methane, and the differential cost over commercial methane (pipeline-ready natural gas) is not "slight"! But, even so, that LCH4 and LOX are still far cheaper than any of the hydrazines, the hydrogen peroxides, the NTO's, and the nitric acids. And hydrogen.

I know what they were thinking: "methane is merely a dense form of high-performing hydrogen". And they would be right: there's four hydrogen atoms for every carbon atom in every methane molecule. That shows up the published Isp data for propellant combinations. LOX-methane is intermediate between LOX-hydrogen and LOX-kerosene.

Although I would caution you to disbelieve the Isp data in favor of chamber c* data. There's too much nozzle efficiency effects in Isp, none in c*.

GW

Last edited by GW Johnson (2020-12-09 21:23:32)

SpaceNut · 2021-01-17 15:36:15

Richard Branson’s Virgin Orbit flew a rocket to orbit Sunday in a test flight that marks the introduction of a new method for low-cost satellite launches and the likely shakeup of the aerospace industry.

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The flight was the company’s first successful trip to space, launching a small rocket from the wing of a 747 airplane flying over the Pacific Ocean. The company hopes to be a disruptive force in the launch market by offering a small, 70-foot long, two-stage rocket suited to take advantage of a revolution in satellite technology that is shrinking their size and lowering their costs. LauncherOne is a relatively small, 70-foot-long, two-stage vehicle that would be able to hoist payloads of up to a few hundred pounds — satellites that would range “from the size of a very big refrigerator to the size of a toaster oven,”
Instead of launching vertically from a pad on the ground, the company tethers LauncherOne under the wing of a modified 747 airplane, which carries the rocket to an altitude of about 35,000 feet. The rocket is then released, fires its engine and shoots off to space.
The “air launch” technique means the rocket is already above much of the atmosphere and traveling just under Mach 1, or the speed of sound, when it fires its engines.

This is the Pegasus launch style and it seems to have been solved by others....

GW Johnson · 2021-01-17 16:47:43

There is an advantage to air-launch toward orbit, but it is small for subsonic launch from a horizontal carrier. The effectiveness counts down from (1) very high speed at launch (low hypersonic or at least high supersonic), (2) angle close to 45 degrees at launch, and (3) high altitude (above 40,000 feet) at launch. The angle at launch is more important than you would think, because any vehicle that must pull up from horizontal, incurs enormous penalties due to an incorrect velocity direction (a vector addition problem), and to drag-due-to-lift (inherent physics of aerodynamic flight).

The original air-launched ASAT weapon launched from an F-15 doing about Mach 1 or even low supersonic, at a path angle upward very nearly 45 degrees. At altitudes above 20,000 feet. Near the top of its flight envelope (vicinity of 50,000 feet), the F-15 could not achieve path angles that steep. It's called "service ceiling", but the physics are actually quite fundamental. So it was more important to achieve angle than altitude. Speed was just limited to "around Mach 1" by the performance of the airplane, but shows up to first order, in the rocket equation that the weapon must satisfy.

I designed the "Minuteman" chase mission and "one-off" configuration for "Scout", that enabled the seeker on that ASAT weapon to actually work for the first time in a critical test. I did that way back in 1974. That mission flew in 1975, as depicted by the photo on the cover of Aviation Week magazine. We had the operational ASAT several years after that. Interesting work, if you are lucky enough to get it.

GW

Last edited by GW Johnson (2021-01-17 17:17:33)

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