Reaction Engines' Sabre rocket engine

True, I did and have worked there but not with the subs.
You can’t escape the influence of them though. I did find it alarming that the place I was working in had emergency tablet stores throughout the building that were to be taken in the event of a nuclear accident at the sub base!
Iodine-based I recall, hopefully yummy-cherry flavoured just to take the edge of impending radiation sickness.

This place is always an amazing journey.
Stranger, it is apparent that you are an expert in your field.
How would you suggest that Humanity establish an orbital presence?

SSTO for passengers and heavy-lift rockets for cargo?

We hear occasional rumblings from ‘on high’ that asteroid mining and space assembly is the way to create a viable long-lived space habitat. Can you estimate if and when this might happen? I appreciate your insight into this subject.

I don’t have enough direct experience or information about Russian and Ukrainian launch vehicles to make an authoritative comparison, but in my limited knowledge and reading there are a number of reasons why these vehicles are less costly (about half of Western space launch vehicles like the Delta or Ariane families) to build and operate:
[ul]
[li]Less complexity: These vehicles don’t tend to use cutting edge technology and narrow operating margins in order to achieve the highest possible performance per weight; instead, they have generous (by Western standards) operating margins with performance that is described by some as “disappointing” (although I’ll point out that the Energia-M had ~85% of the lift capacity of the Saturn V and the uprated version would have exceeded that by a generous margin)[/li][li]Greater robustness: I’ve read that when the Soviets shipped the R-7 rocket for the 1967 Paris Air Show, American engineers were stunned to see Soviet technicians literally walking around inside the unreinforced tanks and lifting the stages without the use of a strongback or spreader beams; by comparison, the Atlas tankage required positive pressure to maintain integrity (by design to minimize skin thickness) and even the more robust Titan II had to be handled with great are[/li][li]Designed for easy assembly and field service: Soviet rockets and weapons were often thought of as being very crude in their tolerances; however, “crude” misrepresents what is really an intentional design feature, as they are designed to be capable of assembly with minimal special tooling or exotic processing methods[/li][li]Maturity: the Russians tend to get a working design for engines, vehicle structures, and probably other systems, and keep evolving and refining; the Soyuz rocket family is over sixty years old and still functioning with what I believe is the highest success rate and by far the highest predicted reliability of any operating rocket family[/li][li]Reliability by robustness over redundancy: Western range safety and design standards tend to emphasize redundancy for all critical systems to avoid what are called “single point failures” (a single component which could result in catastrophic failure); however, this often masks the fact that if a component has an inherent fragility, putting two of them in parallel is not much more reliable; Russian systems tend to go for components of lower performance but that operate with much higher structure, thermal, and operating margins. Russian vehicles routinely launch in snowstorms and high winds which would violate allowable launch conditions and placards for American launch vehicles[/li][li]Minimizing payload processing and support: Russian payloads tend to be more robust and require less support (power, conditioning, protection from dynamic environments) than American satellites and space vehicles, and are generally designed for horizontal integration (rocket and payload are both on their sides, and can be mated without lifting the payload); American systems generally integrate the payload after the booster is erected with a large crane, which is more costly and time consuming[/li][li]Minimal range safety: A considerable portion of the operating costs of launching from a US range is satisfying all of the requirements for range safety (I have a set of safety requirements on my shelf for the Eastern and Western Range that comprises seven volumes of several hundred pages each, with requirements that are often subject to varying interpretation); this also includes an expensive, redundant flight termination system with its own telemetry system which is completely independent from the vehicle avionics; this is intended to allow range destruct if the vehicle flies off course. Russian systems tend to eschew command destruct for a more simple on-board autonomous system which will shut down propulsion if the guidance and control system goes out of control and accept the risk of a crash. Since Russian and Ukrainian launches typically occur over sparsely inhabited tundra and liability in those nations is much less than it is in the United States and Europe, this is viable.[/li][/ul]

Note that the Soviets did not always adhere to these considerations, most notably with the Buran shuttle. The Buran system, designed in what appeared to be little more than an ego contest with the US, was so enormously complex and expensive to develop and operate that it is widely considered to have helped accelerate the economic failure of the USSR. (To be precise, the Buran system was in many ways somewhat better designed than the STS, but it also had some more complex elements such as the four liquid booster stages versus the Shuttle’s two SRBs, and the Soviets spent considerably more time testing and developing the system including design and partial construction of a second, presumably improved version of the orbiter vehicle.) Although operating costs on the Buran system are unknown (Buran was only flown once, and the Energia booster which propelled it to orbit was flown only on one other mission) but would likely have been in the same range as the STS minus the difference in labor costs.

There are certainly some lessons that can be learned from Russian launch vehicles and processing methods, but the American mindset is rooted in the notion that the highest performance is best, and reusability is the key to dramatically reducing launch costs, which would only be true if a vehicle were truly reusable (not refurbishable as with the Shuttle Orbiter or remanufacturable as with the SRBs) and was robust enough to be turned around with minimal processing.

Stranger

Stranger, your points are taken but to some extent you’re comparing apples and oranges when talking about spaceplanes vs. ballistic rockets. It would be pretty inefficient to use an air-breathing engine for a ballistic ascent, just as the numbers just aren’t there for a spaceplane powered entirely by rocket thrust. SSTO if achievable is highly desirable because staging and vehicle assembly impose their own penalties of complexity and ground costs. Pretty much only a spaceplane could possibly eliminate those (although some stage-and-a-half “plug nozzle” ballistic designs come close). Expendable rockets do make better economic sense as long as almost all of your traffic is one-way to orbit- more or less the reason milk bottles delivered and picked up by a milkman were replaced by disposable cartons. But a mature space economy will need more two way traffic. One factoid I read was that the Shuttle, cost overruns included, still made it 40x cheaper to return anything from earth orbit than any capsule alternative. Rockets are useful but they are to space travel what hot-air balloons were to aeronautics: the best that can be done at the time, but too limited to fulfill the hopes people have for the future.

It’s a bit of a hijack, but I do think the OP’s initial question has been satisfied. I’m a very casual observer of space technology, I watched the Apollo missions and many of the early shuttle launches. I have a vague understanding of what makes space travel possible, and that’s about it. My professional life has never intersected with science enough to have a stronger understanding, and my hobbies have never directed me into independent study.

With that background, coming at this more as a lay fan of space travel and taxpayer, it seems to me when I was a kid we had a huge team of some of the smartest engineers in the country and a large (comparative to today) portion of our budget being thrown at very difficult problems–and we had some spectacular successes.

Now it seems like anytime on any internet source I read, some new interesting technology is just proposed, all the most informed people immediately dismiss it as not worthy of spending. What exactly should we be focusing our resources on when it comes to space travel? Better low earth orbit satellites and more reliable launches of said satellites? Considering the large commercial interest in satellites I think that’s the stuff that should be left to private industry. It’s dismaying that while ultimately it will be a failure there appears to be more private interest in going to Mars than in the public.

I don’t even really know that we should go to Mars, but theoretically I think we could do a quick there and back trip in which the astronauts just barely brush up against their lifetime recommended radiation dosage. I think there are a lot of really qualified people willing to take that risk with their health to go on the trip. I think we’ve shown we can launch a lot of crap at Mars, there’s no reason to not be doing missions in vessels that could be human manned (but maybe initially just filled with sensors.) Now, I understand launching rovers and satellites is far different than a manned crew. But if we were willing to make an Apollo level commitment I don’t even think we need all that much “new” technology to actually get to Mars, we probably don’t even need any exotic new propulsion systems. Werner von Braun had sketched out what I thought was at least a semi-plausible idea for getting people to Mars (in the end he didn’t realize the thin Martian atmosphere would not allow his parachute landings, but I think his ideas on how to get rockets there made sense, at least to me.)

It would also seem to me we should continually be trying to refine propulsion systems, but most people in the know seem to present (to me) this position that we’ll never, in all of human history, have propulsion systems much better than we have now. I find that difficult to believe.

As Lumpy said, we’re talking about a spaceplane here. Gravity losses are efficiently handled through aerodynamic lift.

Other organizations, like SpaceX, are already solving that problem. There’s no reason why every company has to have the same focus.

Large problems are solved in steps. It would be fantastic if Reaction Engines could actually prove their engine design. Sure, there are a lot more steps before getting to a viable space plane, but a space plane will never happen unless people are solving the immediate problems.

I have been reading up on this and it seems that what has been achieved is they got the engines precooler to work. This is a fundamental and important step as it allows the vehicle to be accelerated up to appx. Mach 5. Some of the Engineers can better explain this but from what I understand it very difficult to compress very hot, fast moving air and with no air to mix with the fuel, no acceleration.

There are Major hurdles to go,

No actual engine yet.

How do you close an air intake at 3800mph/6100kph? This is no small feat, doable but this has to go right first time every time on two engines simultaneously.

The big one for me is the re-entry plan. The vehicles body is supposed to be large enough the it can slow down in the upper atmosphere. This will supposedly heat the vehicle to only 1000 deg. Kelvin (1340f/727c) instead of the Shuttles 2000 deg. Kelvin, but the leading edges will still need internal cooling to remain intact. This is still hot and one little leak or hole and the thing is toast.

All of this can and probably will be done, I think it is fantastic, but I have to agree with Stranger in that over selling/promising is a bad idea. I do not think this vehicle will be delivering to a space station by 2022. They have been working on it for twenty years so far and have not achieved much.

Capt

I tend to feel there is a middle ground here. Reaction Engines have been plodding along with remarkably low levels of funding (compared to say the the money ploughed into various research programmes in the US space effort) and arguably have done a lot with little.

This reminds me so much of some efforts in high performance computing architectures. It would be true to say that the entire world of computer architecture has dropped down to a very few Instruction Set Architectures (ISA). x86 and ARM are the dominant ones. Both are pretty much the same basic ideas - one CISC, the other RISC, but other than that there are more features in common than divide them. Vector architectures have gone, SIMD has mostly gone (with a pale shadow of the idea living in the SSE instructions) and so it goes. Even 20 years ago there was really only one really new idea - MTA the multi-threaded architecture. It also plodded along with little funding and was never really able to deliver on its promise. (There was a totally weird event where MTA bought Cray, but this didn’t actually save the MTA architecture.) MTA lives on in a very reduced form as hyperthreading. The point is that at the time MTA was about the only game in town that had some promise of being the next leap. But it too relied upon external technologies to make it work. In particular compilers. The compilers never managed to get to the point where they could reap the possible rewards, and MTA faded away. (A similar story with IA64.) But, it was worth supporting MTA, and some of us still grieve its passing.

Reaction Engines might fall in a similar position. They are one of only a few new ideas, and for that alone they are worthy of some funding. Their reliance on a whole slew of materials advances is likely to scupper the current pie in the sky ideas, but that doesn’t mean that some of what they create won’t be of value. Whether some of the current almost SciFi materials in the labs ever come to fruition is difficult to say. There could be some of the needed advances in materials, but I would not be betting big money on it. But if there were, it would be nice to have at least some research done in technologies to exploit them that are not just more of the same. I really don’t think I will see a Reaction Engines powered craft reach orbit in my lifetime (and I intend living for rather a while yet), but I do rather wish I might.

Thanks for the fascinating responses here. Very much enjoyed reading the discussion.

As scientists based at Manchester Uni discovered Graphine, I wondered if there were possible applications for it here?

I’m not sure how anyone would even begin to make that kid of assessment The STS (and presumably Buran) are the only vehicles that have every been designed to collect a payload from orbit and return it to space, and owing to the limitations of the Shuttle in not being able to achieve orbits high enough to collect most satellites or return with a heavy payload the capability was only used once in its thirty years of operation. But regardless, the “two way traffic” for future space exploration and exploitation is expected mostly limited to human cargo and experiments; not only does return and refurbishments of satellites to Earth’s surface not make economic sense (since a large portion of the cost of a satellite is getting it up to orbit) but it actually makes more sense to recycle and refurbish at least the mechanical components of satellites already on-orbit, as it is cheaper to ship up the relatively light avionics, replacement batteries, stationkeeping propellant, et cetera than the heavy satellite chassis and mechanisms. Returning resources (such as processed “rare earth” elements or bulk metals) can be done much more cheaply with aerobraking capsules designed for single use from in-situ materials than the small payload capacity of a space plane.

This its down to the meat of the issue with regard to a crewed Mars mission; most people–even very smart people who lack direct experience with space propulsion and habitation systems–have a conception of a crewed interplanetary mission as just being a somewhat bigger version of Apollo that just has a longer duration and covers more distance. But in fact, that time and duration make the problems of such a mission fundamentally more challenging than Apollo. Apollo was, to make the analogy, like a week-long backpacking trip in which the hikers can carry everything they need in a rucksack and are never more than walking distance from some kind of civilization, and can survive for a few days even if they lose nearly all of their gear. Going to Mars is like an Antarctic expedition by comparison; the sheer bulk of resources, equipment, logistics, et cetera required and everything needed to haul it along with the expedition party in order to allow it to be self-sustaiing for two years (which is longer than anyone has even spent at Mir or the ISS, and without periodic resupply) is overwhelming given the current state of orbital launch and space habitation technology.

I don’t doubt that we could send a crewed mission to Mars (and in fact have worked on studies for the logistics to support such an effort). But the cost would be enormous, on the order of US$500B for a mission with an acceptable degree of risk (~98%) and well in excess of 99% of that cost would go to just keeping the crew alive and functional. Even a “low cost” mission done at higher risk–say, US$150B with a 90% success rate, the value in terms of scientific return is tiny in comparison to what could be gained by spending the same amount on unmanned probes and robotic vehicles. This begs the question of what we would be getting for the enormous cost aside from national prestige and claims of inspiring people to hope for the future (although even during the height of the Apollo program at no time did even 50% of the population support spending money on space exploration of any kind). Of course, we spend more money on even less useful efforts like non-functional social aid, pointless foreign wars, agricultural subsidies, and giant bureaucracies which perpetrate an illusion of security. But regardless, you are not going to see public support for crewed exploration at such enormous costs just for the sake of planting a flag or on the basis of abstract desires to “explore new worlds” or “ensure the survival of humanity”, as the vast majority of people simply don’t give a flying fuck about any kind of future unless it is returning something back to them in the near term. And the failure of a one shot crewed exploration effort at a cost of hundreds of billions of dollars would likely spell the end of any crewed space exploration for the foreseeable future.

I don’t know where you are getting this, but “most of the people in the know” are well aware that not only are there better propulsion systems that are feasible, but that with a concerted effort we could already have had them at a state of maturity to be using them today. Nuclear (fission) thermal and nuclear electric propulsion systems are entirely possible, albeit technically challenging, and if they had been pursued consistently from the 'Sixties onward it is not an unreasonable assertion that we could have had such systems in operation decades ago, and that such capability would facilitate practicable crewed exploration by virtue of reducing the amount of time spent in the space radiation and free fall environment, as well as providing the haulage to bring the necessary supplies and equipment. And that gets to the core issue of crewed exploration; we need to develop the necessary technology to make crewed missions much less costly, lower risk, and more functional than they can possibly be with chemical propulsion systems.

No, they are not. A spaceplane only provides lift in the atmosphere, at forward speeds at which it can function. Even a spaceplane that can achieve Mach 5 (about 3,800 miles per hour at 30 miles altitude) during ascent, which would require much more than just a hypersonic engine, is only making a fraction of orbital speed (~17,500 miles per hour at low Earth orbit). In between the difference the vehicle has to apply thrust to negate the downward component of acceleration due to gravity. (At orbit, the vehicle still experiences Earth’s gravity–hence why it doesn’t just fly off into space–but is moving so fast it literally falls above the horizon, which is a neat trick if you can do it) That thrust has to lift all of the mass at that point, including remaining propellant and the inert mass of the vehicle which goes into orbit. That inert mass of the vehicle, which for a spaceplane would include thermal protection systems, then aerodynamic surfaces, and all of the suboptimal mass-to-volume structure required to make and support a lifting shape versus a more optimal squat cylinder or spheroid, detracts from payload lift on a 1:1 basis. This is why SSTOs in general are such a contentious concept; although it is demonstrably possibly to construct a single stage vehicle which can get to orbit, carrying a significant amount of payload requires minimizing structural mass and getting high performance from the propulsion system versus a staged vehicle which can expend structural and propulsion system mass once it is not necessary. Spaceplanes unavoidably have a lot of inert mass by virtue of not being able to be optimized for weight-to-volume which overwhelms the advantages of lift, even using air breathing propulsion for the first few minutes of flight.

I don’t see where I’ve said anything different, and in fact this is exactly my point. Just because Reaction Engines has achieved one technical milestone with the SABRE engine does not mean that all other hurdles will fall away and they will be flying to orbit in short order. They have made one notable accomplishment in overcoming a technical challenge, but the article cited by the original poster makes it sound as if everything that follows is cake when in fact there are numerous other problems that are equally challenging.

While I’ve work on several studies (again, largely to support the logistics for surface to orbit transfer) and have a somewhat more than casual interest in the topic, I wouldn’t call myself an expert on space habitation, and at the state of technology and experience even the experts vary widely on opinions of what is required to develop habitation technology.

A reusable SSTO is often assumed to be necessary to achieve cost-effective access to space, but the technical challenges and limitations are such that I don’t think it should be considered requisite to achieve this, especially when partly reusable two stage vehicles at high volume production rates can be flown for a fraction of the cost of developing an SSTO which is sufficiently robust to not require refurbishment between flights. The notion of being able to launch to orbit with the same ease that we fly from city to city belies the physical difficulties of ascent and reentry. Unlike commercial aircraft which are constructed with substantial performance and thermal/structural margins, space launch vehicles will always be operating much closer to physical material capability limits, and no amount of imagination is going to alter the essential physics of this.

I would agree that launchers for people and small, delicate cargo are fundamentally different than those needed for heavy and bulk cargo, and should be separated accordingly. A high performance and high reliability two stage or parallel stage medium lift vehicle with a refurbishable lower/booster stage vehicle for the former should be the near term goal (and is essentially what the Falcon 9 and Falcon Heavy are), while a lower performing super heavy lift vehicle with somewhat relaxed reliability requirements (something akin to the Truax Sea Dragon) should be developed for heavy lift cargo. (It should be pointed out that while the test and margin requirements for reliability may be relaxed, going to lower performance tends to increase component robustness, and so even a “Big Dumb Booster” may end up being functionally as reliable as a more rigorously developed high performance vehicle.)

Permanent habitation in orbit or interplanetary space will unquestionably require in situ resource usage (ISRU) development and in space fabrication and assembly as a sine qua non capability. Even if we could get launch costs to a ridiculously low level (say, $250 per kg to LEO) it is still too costly to build large structures and provide supply logistics to orbit. And in order to develop that ISRU, we will need robotic and automated capabilities to do the exploration and resource recovery in order to allow people to remain in orbit indefinitely with the resources and protection to support habitation. So, while many space enthusiasts assert that people are the essential element in space mining and exploration, the converse is actually true; we need remote systems to do work in the hazardous conditions (radiation, extreme thermal conditions, et cetera) and do the heavy moving that people cannot do effectively in a vacuum and free fall environment so that we can construct structures and collect resources to sustain habitable conditions.

At the point that space habitation becomes self-sustaining and we no longer have to haul up resources from the Earth’s surface, many of the hurdles for crewed exploration of other planets fall away, and the technologies which would be required for this type of resource development and use will also contribute directly to interplanetary travel and exploration. But it doesn’t work the other way; going to Mars just to go there as soon as we can and doing the minimum technology development to make it possible does not return a space habitation infrastructure, and the opportunity cost in spending the initial effort on exploration detracts from the ability to develop the technology to make all manner of space operations (including crewed exploration) practicable.

I don’t oppose spending on developing space capabilities and performing exploration missions; quite the contrary, I think it would be a fantastic challenge and fiscal stimulus to put effort into these programs versus pointless international conflicts or corruption-laden “economic stimulus” packages that benefit the very people who created the problems to begin with. I think setting out a series of extremely difficult challenges, such as extracting resources, constructing self-sustaining habitats, and gaining more scientific knowledge about the solar system are all worthwhile goals from both an intellectual and practical standpoint. But jumping in and trying to do the hardest thing first with the most primitive capabilities is not the smart or effective way to do this, any more than you would begin to design a software system with a million lines of code by starting to program the user interface. This is exactly the lesson we should have learned from Apollo and the STS; going places and developing capabilities piecewise does not result in a program that has momentum to press inexorably onward. Apollo was dead as soon as Armstrong and Aldrin stepped on the Moon, not because the program failed in any technical sense, but because it didn’t offer a clear next step or useful benefits. But allocating money and effort into developing components of a coherent architecture that makes further development and exploration easier and cheaper, and may even return resources and practical knowledge at profit (as the telecommunications and Earth surveillance efforts have done now) makes it difficult for even the staunchest critics to oppose such programs.

Stranger

But a spaceplane wouldn’t immediately shift into pure ballistic mode once it exceeded its level flight ceiling, would it? Wouldn’t it continue to derive some lift as long as there was any substantial atmosphere?

The amount of lift that can be generated at a given Mach number is a function of air density and wing area. You do get the advantage of less drag at lower air density, but the radical drop of air density between 20 and 30 nm pretty much ensures that the amount of benefit you get from lift at that altitude is minimal, and as Mach number increases so does atmospheric heating. Making the functional wing surface larger means longer airfoils and more area to protect from shock wave radiative heating, and will also inevitable create more inert mass that has to be carried to orbit in addition to having to carry oxidizer for rocket propulsion above the altitude where sufficient oxygen can be scavenged from the atmosphere.

Conventional rockets try to get above the atmosphere as quickly as practicable (within vehicle controllability and structural integrity limitations) specifically to avoid this regime and minimize how much of the system is devoted to protecting against atmospheric heating even at the cost of having to carry additional fuel to combat the lack of tangential velocity. This is the reason rockets are not shaped like airplanes, and why, except for experimental vehicles, there are no successful rocket powered aircraft. (The Messershmitt ME 163 was not successful by any practical measure.) Far from making space launch vehicles operate more like aircraft, spaceplanes end up with the worst aspects of aircraft and rockets combined together. Making one which is functional, even with an air-breathing hypersonic ramjet is an enormous technical challenge, much less giving it enough payload and capability to operate as indicated in the Skylon promotional video.

A functional spaceplane is more likely to be a sort of delta-shaped lifting body with configurable wings to prove compression lift, like a blunt-bodied XB-70 ‘Valkyrie’. Frankly, it would make more sense to have an air-breathing return stage and a space launch vehicle upper stage (like the Soviet Spiral 50/50) but the technical difficulties with that program offer a cautionary tale about assuming that success with any single technology is going to resolve the gamut of technical problems with spaceplane configurations.

Stranger

Bumping this as it was a good discussion before and there’s some investment news. For the next round of funding Rolls-Royce are back in and so now are Boeing. So at least the story continues: