Skylon’s SABRE Engine Passes a Big Test | Hacker News Reader

Skylon’s SABRE Engine Passes a Big Test

universetoday.com

140 pointssohkamyung44 comments

In case anyone was confused by the article's description, here's the Wikipedia:

"SABRE (Synergetic Air Breathing Rocket Engine) is a concept under development by Reaction Engines Limited for a hypersonic precooled hybrid air-breathing rocket engine. The engine is being designed to achieve single-stage-to-orbit capability, propelling the proposed Skylon spaceplane to low Earth orbit. SABRE is an evolution of Alan Bond's series of liquid air cycle engine (LACE) and LACE-like designs that started in the early/mid-1980s for the HOTOL project.

The design comprises a single combined cycle rocket engine with two modes of operation. The air-breathing mode combines a turbo-compressor with a lightweight air precooler positioned just behind the inlet cone. At high speeds this precooler cools the hot, ram-compressed air, which would otherwise reach a temperature that the engine could not withstand, leading to a very high pressure ratio within the engine. The compressed air is subsequently fed into the rocket combustion chamber where it is ignited along with stored liquid hydrogen. The high pressure ratio allows the engine to provide high thrust at very high speeds and altitudes. The low temperature of the air permits light alloy construction to be employed and allow a very lightweight engine—essential for reaching orbit. In addition, unlike the LACE concept, SABRE's precooler does not liquefy the air, letting it run more efficiently.

After shutting the inlet cone off at Mach 5.14, and at an altitude of 28.5 km, the system continues as a closed-cycle high-performance rocket engine burning liquid oxygen and liquid hydrogen from on-board fuel tanks, potentially allowing a hybrid spaceplane concept like Skylon to reach orbital velocity after leaving the atmosphere on a steep climb."

https://en.wikipedia.org/wiki/SABRE_(rocket_engine)

>After shutting the inlet cone off at Mach 5.14, and at an altitude of 28.5 km, the system continues as a closed-cycle high-performance rocket engine burning liquid oxygen and liquid hydrogen from on-board fuel tanks

the benchmark of today - SpaceX - separates the first stage at Mach6-8 at 65-80km height. Thus, the SpaceX second stage has less delta-v to add and don't have to carry all that weight - the SABRE would naturally be bigger than the 2nd stage for the same payload. The economical space related case of HOTOL/SABRE single-stage-to-orbit pretty much disappeared for a foreseeable future when SpaceX started to recover the 1st stage. That not to say about suborbital flights SF-Shanghai though. Or even "just" hypersonic as SABRE tech seems to successfully deal with one of the major/key obstacles for it (and that is huge, i'm in no way trying to dismiss their work). And one can see how SABRE can be used in some cases as a convenient 1st stage, i.e. by being able to launch from any big airport instead of only specially designed spaceports (such a 1st stage would probably be better than that https://en.wikipedia.org/wiki/Pegasus_(rocket)#Carrier_aircr...).

Imagine putting SABRE on the first stage though - the engines would be heavier, but using air instead of carrying oxygen, for the full burn of the first stage. The payload mass fraction would be dramatically higher without carrying the oxidizer mass on board.

It is possible though cost&complexity seems high - we theoretically can even today bundle a bunch of SR-71 engines and probably stretch them beyond designed Mach 3.3 for the short time. Having low thrust-to-weight (SABRE promises up to 14, SR-71 had 6) we'd need either a lot of them for VTOL which leads to high cost, or we're limited by the size of maximum realistically possible hypersonic capable plane, plus the plane body being the additional weight. For example VTOL calculation - say engine weights 1 ton, we can lift off 13 ton of fuel and payload. It will use 40 ton of O2 from the air. For rocket engine - 1 ton engine can lift off 100+ ton, and if we just take the 13 ton fuel plus 40 ton O2 we'd have 45 ton budget for the rest (body plus payload). In reality you'd need higher fuel ratio, and this is why VTOL for atmospheric breathing engine pretty much isn't an option .

Going beyond pure rocket engine for the 1st stage i think air-augmented rocket (http://astronautix.com/g/gnom.html) being simpler (thus cheaper) would be the next step that would get us closer (specific impulse wise) to what SABRE is targeting.

I think the benefit of launching horizontaly is overstated. Any airport would still need to handle LOX and hydrogen which could be pretty dangerous. And the airport is not necessarily going to be in the right place for launch.

Also traditional rockets have most of the forces acting vertically. A horizontal launch space plane must also deal with a completely different set of forces.

One might argue that a 3km runway is harder to obtain than a single launch pad.

Also, I wonder if the traditional safety requirement of an East coast is still necessary: that's an additional constraint on location. Plus the need to be closeish to the equator won't change.

The UK is looking at West Coast locations for a new Spaceport.

I think one of their big advantages over SpaceX is noise pollution. Nobody is going to be launching Super Heavy near significantly inhabited areas just because of the noise.

Mach 5 at 28km and mach 6 at 70km are not all that different. Mach slows down with altitude. And specific altitude numbers dont matter much if you are aiming for orbit. All that really matters is horizontal velocity. The first stages of both schemes are relatively slow. Both get the bulk of thier orbital velocity from thier second stages.

SpaceX takes a very non-aggressive approach with its first stages. When they detach they arent moving nealy as fast as other rocket first stages. That is done so they dont slam back into the lower atmosphere but it means relying upon second/third stages to do the horizontal work. By the raw physics, it isnt the most energy efficient approach. It is a compromise to facilitate recovery.

Even if reusable rockets have them beat cost wise. This could be an ideal way to get passengers to orbit and back with less G forces.

These guys don't disappear - they have been around forever with their Skylon plane.

Just a heads up, it's a long way from testing one component of an engine on the ground to getting a full engine demo going to then testing it in the air to then build the plane then integrating engine - then getting orbital trips working with reentry!

I am curious how much private capital they have been able to attract (outside of govt contract players). Obviously if this is really revolutionary then they will but this always felt like a long term / govt kinda of cool - tech forward but pork barrel project for the UK.

More of their background from a somewhat more balanced source - at least the headline put revolutionary in quotes.

https://www.bbc.com/news/science-environment-36773074

They do claim to have the "best engineers" in the industry - so beating out big players like rolls royce, PW, CFM, spacex, blue origin, ariane aerospace - so that is a positive they have.

These things take time, but it's not the complete story, Virgin Galactic has been around since 2004, so the same year GMail launched, without producing a single passenger flight.

Blue Origin has been around for almost 20 years, and they have a few suborbital flights to their credit, and an engine that has yet to fly.

SpaceX, on the other hand, has been around since 2002 and achieved orbit in 2008, and have completed a lot of milestones since then.

I suspect the biggest difference between these companies is not talent or vision, but sens of urgency

Sense of urgency lets one leverage the best current technologies and take the best compromises within the time and monetary budget. But this is incremental innovation. It fails at tackling novel concepts where the paths forward are not so clear. You can't incrementally tunnel through a wall.

At one point maybe SABRE is ready and the next SpaceX comes along and will build a spaceship with it. The spoils of innovation seldom accrue with the inventors.

> The spoils of innovation seldom accrue with the inventors.

We are British, why change the habit of a lifetime ;)

That said, critical aspects of the design are protected and the private investors (big scary defense contractors etc) would no doubt sic the lawyers on anyone that attempted to rip it off.

Some ideas also have a tendency to be leapfrogged by a combination of lesser novel ideas used in a new way, the idea of a plane as a first stage was probably great until SpaceX showed up and landed a Falcon9 first stage to reuse.

"Virgin Galactic has been around since 2004"

I'm 54 - Sabre/Skylon were in the news when I was in high school!

I think the name Skylon was first used for this project in 1993 [1], so unless you repeated quite a few years, i doubt that's true.

RB454/HOTOL could have been in the news back then, though. I remember having some sort of brochure for HOTOL back in the mid-80s.

[1] https://ui.adsabs.harvard.edu/abs/1993SpFl...35..162V/abstra...

Yeah - you are probably correct - basically the same thing though albeit done by a different company.

>I suspect the biggest difference between these companies is not talent or vision, but sens of urgency

Well that and the SABRE engine is a completely new design and SpaceXs engines are based on engines created in the 1960s and refined since then.

Its comparing apples and oranges.

I think that “spaceplanes” where a great idea until SpaceX landed a Falcon9 first stage, after that point they are mostly a complication.

. . . it's a long way from testing one component of an engine on the ground to getting a full engine demo going to then testing it in the air to then build the plane then integrating engine . . .

True, but my understanding is that the heat exchanger is the critical piece of difficult technology/engineering. With that, they have the potential to revolutionise industries even if none of the rest comes to pass.

Exactly, there is talk of it having significant impact even if it never flies a mile.

People gloss over things like building a turbine engine as easy - it is not - it's been done, yes, but for these guys to build, qualify, validate and get an engine flying on passenger planes is a HUGE undertaking even ASSUMING this critical piece of tech was perfect.

To also then build the plane? I'm curious to see what their re-entry technology looks like - feels pretty critical path to me.

What are these applications and industries that will be revolutionized? I'm serious - I've heard this will revolutionize hypersonic cars. OK.

The plane concept itself required a closed loop normal rocket engine - so you've got to have that AND the Sabre AND are doing single stage to orbit. I shudder to think of the mass fractions - how does carrying all this extra around make sense just from the physics - do you save that much in terms of LOX?

You speak as if the design has not changed over time. To be precise, the history dates back to American studies in the 50s and 60s which were not taken forward but that were picked up by Alan Bond in the UK and evolved, then later developed into the HOTOL design, and still later into Skylon/SABRE - with significant work undertaken throughout this history.

I think that there are some factors to give one faith that this won't just become another sad episode of unrealised promise to add to the history: the engine design has had significant verification along the way by authorities of the very highest credentials, is furthermore thought to be of sufficient promise to have attracted significant external funding, and finally has resulted in working hardware on the test stand that has not yet indicated that the expectations of success are ill-founded; it's getting to the point where the glaring flaw that some seem to want to be uncovered is increasingly unlikely to be found (I'd add personally I find it a little sad that amongst tech/space enthusiasts many seem so sceptical about SABRE when the facts suggests otherwise, and I wonder whether it would be a different story if it were an American project - I'm enthusiastic for anything that gets the human race off this rock, no matter where it comes from).

That said, I think it is important to separate SABRE and Skylon. The former as I've said is thought by many well credentialled people to have genuine promise, whereas the latter seems far more of a PR exercise to illustrate potential application of the technology. Nobody's actually building parts of Skylon yet as far as I'm aware, wheres they are building bits of SABRE and getting them signed off as workable.

Much of the “significant external funding” is coming from govt funded defense contractors - nothing better then selling star wars military dreams to politicians spending taxpayer money.

I’m glad research is happening - agreed on Sabre vs Skylon too. could do with a touch less hype.

Skyon's SABRE Engine Component Passes a Big Test.

Still very cool progress and quite the test setup.

How do you pronounce it? Sah-brey or say-ber?

Say-Ber

Say-ber, like the sword. [0]

[0] https://dictionary.cambridge.org/us/pronunciation/english/sa...

Haha if this was office reference

It is.

Everyone over here on HN seems to be quite negative about the SABRE engine. While there's very little evidence for this engine being useful for orbital applications, it is instead a very compelling idea for a Concorde and/or SR-71 replacement. Scramjet engines don't seem to be happening anytime soon (I just listened to a Queensland University researcher saying that their research may yield an actual engine in 4-5 decades). This idea of pre-cooling the incoming air seems closer to reality.

Here’s to a single stage to orbit craft a la Kerbal space program’s RAPIER engine (although it’s probably still not realistic to expect better than two stage due to the rocket equation)

Pretty sure KSP RAPIER is a fictional copy of the described SABRE engine.

The names seem to indicate that, both being similar kind of weapons.

Absolutely. https://wiki.kerbalspaceprogram.com/wiki/CR-7_R.A.P.I.E.R._E...

Looking forward to the integration test, if they get this to work it will be quite the engine.

Isn't it inevitable the SpaceX will (and already does) dominate the entire space industry?

Won't it be cheaper to launch on starship than anythign else even for very small payloads? Yes, I know about RocketLab but I wonder if they will be able to survive once starship is up and running.

European governments will continue to back Ariane because strategically it makes sense. Russia will bankroll energyia likewise. Dominance is not static and private capital will not entirely replace state actions.

A nitpick, Energiya doesn't make rockets this days, rather Soyuzes, Progresses, satellites, upper stages (Block D)... Launchers are made mostly by Khrunichev (Proton) and Progress (Soyuz-2).

Russia tries to develop new rockets, but so far it's really slow and quite expensive. It's possible that when NASA will stop paying for Soyuz transport to ISS, it will become even slower. It's not a particularly good time in Russia for new rockets paid by the state.

All true, but do you seriously think Putin will renounce a domestic space industry? They might pick jv partnerships like ariane to stay afloat. Or sell engines or something but i dont see them giving up. To your side of this, the cash flow to a russian space sector will end when a man rated launcher from the U.S. starts making regular trips to the ISS, I guess.

> do you seriously think Putin will renounce a domestic space industry?

Probably not. It's possible to bring the space industry to the state of aviation industry, but 1) some resources are still available to maintain some level (as you mentioned) 2) to keep the same level, one needn't spend too much effort and 3) there are some interested parties in Russia which wouldn't want too deep degradation of space industry (e.g. periodically some hints to that come from Samara).

So a likely outcome could be maintenance of some expertise, at least for military purposes, and possibly attempts to cooperation with foreign partners - China, Europe etc. No total destruction; "just" - potentially - another deep crisis.

It depends if we consider state sponsored agencies maintained for national security reasons part of the ‘space industry’. There are reasonable arguments either way.

Citations, please.

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