HOTOL - Anatomy of a spaceplane engine

HOTOL was a 1980s British project to build a totally reusable Space Shuttle. The project was cancelled and as it existed in the pre-internet age it's hard to find information about it.
In this video, with the aid of an original patent, I go back to basics to explain how HOTOL's unique rocket engine would have worked.
The patent referred to in the video is available here:
patentimages.storage.googleap...
My original HOTOL video is here:
• HOTOL - Spaceplane of ...
For an explanation of why I think SSTO spaceplanes are the future of space travel check out my original spaceplanes video:
• Spaceplanes are the fu...
The background rolling Earth orbit video is from:
"ORBIT - A Journey Around Earth in Real Time"
• ORBIT - Journey Around...

[@jobob7158]

Rich, another outstanding video. I'll pass this on to my colleague, Adam Dissel (he's the president of Reaction Engines, Inc.). We've been teaching together at the AIAA short course on high speed air breathing propulsion. (I do the Air Turbo Rocket part, Adam presents the current Reaction Engines cycle and how it works, along with several other outstanding instructors in aerospace). I was especially gratified by your explanation of how the concept of "SSTO" got so stigmatized; that squares pretty much right on with my experience, when I was a young engineer working on NASP propulsion systems. I no longer use the term "SSTO" because its so burdened with misapprehensions. Instead, we use the term "high delta V missions". But you know what we mean. Keep up the great work!

[@Thumblegudget]

Thanks for the compliment. I would really like to see this engine or something like it fly someday. Maybe educational videos like this might help move the needle, if even just slightly.

[@PoliticalWeekly]

when the heck is skylon coming out?

[@recoilrob324]

@@PoliticalWeekly Always remember that never is just around the corner!

[@AR_434]

Thank you! This is one of the best aerospace videos I‘ve ever seen (and I‘ve seen a lot)! I hope this video and your channel gets the recognition it deserves.

[@Thumblegudget]

Thanks for the compliment! Tell your friends I guess. And hit the like button. Likes are absolutely everything to a small channel.

[@gilbertotron]

Amazing video. Small thing, the temperature measurement is kelvin, not degrees kelvin.

[@aigslmnop6559]

the difficulty I have with the concept is how does the tank not distort if the pressure increases since coolant is needed for fuel stability AND to rapidly cool air that gets hot as it moves through the compressor😮

[@rorypenstock1763]

Very interesting. Now I'm interested to know how Skylon's engines differ.

[@YaBoiNicho]

I second that

[@Platin_2004]

You broke down a lot of complex concepts very well, fantastic job!

[@benetedmunds]

Super-informative. I was a bit distracted by my brain shouting "Eureka!" repeatedly.

[@chrysincognitio3751]

As somebody whose rocketry experience is limited to sucking at KSP, I found this bloody riveting. Thanks.

[@LivakProductions]

The quality of this video is incredible, chapeau! Love the technical detail but simplicity.

[@daveherbert6215]

Brilliant, brilliant, brilliant. Great explanation, so clear. I love the idea of disappointing SpaceX fans. I'd like to see a single stage space plane exist. I hope that reaction engines succeeds in bringing this to fruition, though I have heard that they are getting funding from the military to build yet another missile. Keep up the good work. PS I wonder if Scott Manley has any thoughts on this, let alone the everyday astronaut

[@proph7543]

I don't have any specific source for this, but it's likely that reaction engines isn't going to build such a plane on their own, at least. Perhaps in concert with Rolls Royce and/or the government. Don't worry, though, because their precooler tech has a lot of engineers drooling. Even if it's just used in jet engines it would allow for hypersonic speeds, after all.

[@aigslmnop6559]

what's so wrong with a staged space launch like vss unity or stratolaunch it's what rocketeers do? 😮

[@zounds010]

Excellent explanation of the HOTOL engine, working your way up from first principles.

[@proph7543]

Brilliant video! despite always having an interest in rocketry, especially these last few years, I've always been slightly confused on the specifics of a rocket engine's function, but your explanation has finally cleared up a few gaps! It's also nice to see some more HOTOL love.

[@user-lz1yb6qk3f]

Aerospike engine is uniquely suited for expander cycle. And it is simpler then double bell or expansion/deflection nozzle

[@glike2]

The presentation, narration, and technology is superb! Thank you!

[@RobSchofield]

Excellent! Yet another quality video, and about one of my favourite aerospaceframes. Keep it up!

[@adambarker173]

One of the best videos on KZbin! Please keep up the good work.

[@drawingboard82]

You are really good. For sure the best videos on hotol.

[@Thumblegudget]

Haha! You mean the only videos on HOTOL 😆

[@Thumblegudget]

But thanks, I appreciate the compliment.

[@marktompkins3180]

Excellent video!

[@robparker7110]

Keep up the good work!

[@populistrevolution5197]

THAT WAS AMAZING!!!!!!!

[@robparker7110]

Keep up the good work

[@JulianDanzerHAL9001]

4:50 that helps to a limited degree, pure rocket engiens and scramjets tend to have better thrust to weight ratios than jet engines or airbreathing rockets and any vehicle gets lighter as it uses up fuel so the mass is dominated by whatever you use first either way so either method ends up with surprisingly similar engine masses

[@patreekotime4578]

Thats interesting. One thing you didnt mention is that by using hydrogen as a coolant for the hypersonic airflow, it is also pre-warming the hydrogen before it even gets to the pre-burner. Brilliant.

[@sxmolin]

Yes it can be done!

[@DeltaR2023]

So underrated. I’ve thought about this idea before, however I had no idea that already existed. A question though, had they ever thought about reheating that excess hydrogen, and adding a variable nozzle to it?

[@Thumblegudget]

They did as a matter of fact. In later designs, after the patent was published, they incorporated a bypass ramjet into the intake system. You can see it in some of the later artwork. So many little extra things I could have included in the video!

[@DeltaR2023]

@@Thumblegudget Awesome stuff m8. As I said before, very underrated. Keep up the good work!

[@jocramkrispy305]

My goodness. Why on Earth did the algorithm take so long to show me this?

[@KennedyCopy]

Do one on Hotol vs. the new rotating detonation engine!

[@KaktusCzar]

Great content as always Rich. Super informative and technically correct for a project that nowadays not many know about. Just a remark if I may, when you say some 2 issues have had remained to be resolved on Hotol engine as frost control and nozzle. It is not just a nozzle as a single element but actually a complete second half of a thermal engine - the kinetic part. What we denominate as "nozzle" is conversion of build-up potential upstream into the useful kinetic - thrust. In preference of pressurized balloon, as you illustrated, with all these neat cycle adaptations and smart exchanging options, it is just augmentation of that potential before its final conversion. To convert then that 1st half into the useful kinetic energy you need a proper combination of CC-Nozzle as process end critical element. Unfortunately, the technology is still not there yet to meet the requirements for SSTO nor spaceplanes. On other youtube channel, you may find listed graveyard of projects and companies that have failed on the similar step. Either because of dealing with open form conversion elements as aerospike nozzles or because have selected wrong combination of CC-expansion.

[@KaktusCzar]

Also there is not much support neither from industry neither from governments to technically deal with any new energy conversion/nozzle concepts. Last serious attempt was for mentioned NASA X-33 linear aerospike and since then it is pretty much dead end. Currently, you have sizeable companies/organisations either dealing with conventional and advanced rockets or spaceplane engines - that 1st "potential" half- and then a few tiny companies trying to breach the gap between the conventional bell nozzles to altitude (pressure) adaptive ones. Nozzles except they are mentioned conversion elements they are also interface between the internal aerothermodynamics and the external one. In wall-bounded types that interface is found on the nozzle exit (if the flow is not separated), whereas in open form as aero spike/plug interface occurs for the whole length. As such those units are also susceptible to any external exciters as atmospheric conditions, strong jet winds, presence of other exhausts, angle of attack etc. Hence, to finally get them into air seems better to use them on a simpler engines, as small rockets, in order to get them to some TRL before trying to apply them for bigger systems. And once when they get to that, to go to spaceplanes it will need additional steps which probably will consist of novel materials, zirconium based for temperatures with additive manufacturing, electroformed regenerative cooling, and especially active flow control if to be mounted on a winged horizontal fly vehicle. I also believe the spaceplanes are the future but it appears that current state of the industry is still not favoring them and environment is not ready to put serious effort in development of advanced kinetic conversion alternatives to bell nozzles.

[@jocramkrispy305]

Along with Bristol University, Reaction Engines ran E/D nozzle tests (and published the results) to enable them to validate their CF results. later, Airborne Engineering tested their advanced nozzle design for the SABRE 4 engine which effectively provides an E/D nozzle for atmospheric flight, and a bell for vacuum flight

[@Matyanson]

Now I'm curious what you thinnk about aerospike engines

[@thomasciarlariello3228]

In of a March 2019 by invite only to an MIT engineering conference I presented a proposal for a muon catalyzed fusion rocket engine for spaceplanes originally designed by Noguchi and Songsu of early 1940s Hamgyong province where a Dewar of liquified cryogenic deuterium fuel was connected to beryllium alloy reaction chamber nozzle coiled in around electromagnet coils to focus cosmic ray muons for fuel to have prevented exceeding of Curie Point while alpha particles would have been deflected.

[@thomasciarlariello3228]

Dr. Mitchell Swartz who published my MIT peer reviewed articles on such a subject during the 1990s agrees with me on how my articles are Prior Art on Jerome Drexler Patents.

[@Astroponicist]

What is it's max payload to LEO? It looks like it would be best used as a passenger transport to Low Earth Orbit for transfer to A Lunar, or Martian cycler vessel. The Starship is starting to look like it will be doing lots of heavy freight, & mass transport as it's capacity is said to be 100 passengers.

[@thomasciarlariello3228]

Excellent design since it is only way diborane or boron hydride could be used for a jet fuel.

[@GLORY-TO-ENTROPY]

what do you think about 2 stage spaceplanes?. The first stage gets it up to let's say mach 3 or 4(with all the turbine engines and ramjets), then the next stage uses a combination of rocket and scramjet engine to get to orbital speed. The split velocity would ideally be where the metals couldn't handle the heat, and tiles are needed. Both planes could be connected by a simple rope like a glider, thou a heat resistant one.

[@Thumblegudget]

Ha! They’re a video in themselves. They’re really expensive to develop, because you’re developing two aircraft, and operationally they’re a nightmare. Separating two aircraft at supersonic speeds is very dangerous. Using aerodynamics to slow down and turn around the first stage for recovery is also very tricky. Seriously if you want two stage I think you’re better off going the SpaceX route. That said, the exception is something called suborbital payload deployment, which is where a HOTOL or SKYLON like vehicle does a once-around to land back at the launch site but never quite reaches orbital speed. In this case the payload has a small second stage booster attached. This would be a way for such a spaceplane to deploy heavier payloads, or for early operational flights.

[@aigslmnop6559]

the keyhole missions operated at 120km altitude and electric propulsion craft operate in vleo, it's not a stretch to include an electric element in every stage and any space launch involves risk air breathers are inherently safe from the atex perspective

[@Schroinx]

Interesting.Now UK has a new gov, it could be something for EU and UK to fund as a common project.

[@davidsasse40]

What about a detachable turbojet scramjet ramjet to get you to 25km and mach 5 then the rocket only space plane detaches and goes into orbit. The multijet "piggyback" could detach and glide or fly back to the surface for reatachment and reuse. This keeps the weight of the engine tanks and fuel for the very energy intensive first stage on the detachable drone. The weight saving of all that fuel tanks and engine that detach are considerable.

[@gilbertotron]

Honestly don't know how this channel has so few views when there are clowns out there spouting utter nonsense with millions of views. Thanks

[@thomasciarlariello3228]

U.S. Patent #5101622 of April 7, 1992 by Alan Bond

[@rogerphelps9939]

Over 30 years of snaillike progress..

[@juanlu3958]

Mega super sonic plane(2mach) carry with subsonic ramjet engine spaceplane=best single stage to orbit vehicle so far.

[@juanlu3958]

you can design a mega plane can stuck spaceplane at the head of airplne.

[@aigslmnop6559]

reserving coolant to precool oxidant precludes fuel that doesn't require as much such as the new methalox chinese rocketry successful laumches

[@thomasciarlariello3228]

Liquid air cycle engine or synergistic air breathing rocket engine is described by Patent #5025623 and to handle cryogenic fuels such as Diborane one could consider Patents by Xcor for their "Lynx" spaceplane titled "High speed Check Valve suitable For Cyrogens" to remember how my dad's brother worked on similar engine for "Dyna Soar" designed to skip on the upper atmosphere. "Liquid Air" by T. O'Conner Sloane described how Victorians used cryogenics to condense oxidizer for earliest Prior Art .

[@jocramkrispy305]

hotol didn't use a liquid air engine

[@thomasciarlariello3228]

You miss the point completely how Alan Bond's Reaction Engines Ltd. condensed oxidizer from atmosphere to liquify air.

[@jocramkrispy305]

@@thomasciarlariello3228 No, you miss the point entirely, it doesn't liquefy the air. It *isn't* LACE.

[@thomasciarlariello3228]

Ever See Alan Bond's Reaction Engines Ltd. commentary. Arthur Clarke's commentary, and American Institute of Physics on liquid hydrogen fueled Aerospace, etc. since liquid air cycle is synergistic air breathing if one pays attention to patent documents cited.

[@jocramkrispy305]

@@thomasciarlariello3228 The patents for LACE are listed, because they are prior art - they also cool the incoming air, often using cross flow radial pre-coolers. But a key realisation Bond made was that liquefy the air was not only unnecessary, but detrimental, as they require deeper cooling and heavier plant.

[@aleksanderkuncwicz7277]

Nuclear energy would make a good space plane fly on match head of nuclear tnt would blow up as much as a grenade,so does sombody just make a smaller gas nozzle for nuclear feul.

[@KennedyCopy]

If they moved the Hotol factory to California, would it be called the Hotol California?

[@philoso377]

Just about each statement Elon is saying was heard in Motorola before 2009. Including this: “the best component is no component”.

[@JulianDanzerHAL9001]

"if we threw away the airplane after every flight..."

[@philoso377]

@@JulianDanzerHAL9001ask him this question: so why did we discard soda bottles?

[@JulianDanzerHAL9001]

@@philoso377 we do kinda recycle them sometimes

[@philoso377]

@@JulianDanzerHAL9001 is “kinda” means “fashion but action or resolution ”?

[@JulianDanzerHAL9001]

@@philoso377 kinda means it varies depending on the type of bottle, location, state of the bottle and the level of recycling varies as well

[@bhuvanachandrabr4890]

Was kinda convincing but how do you convert the excess heat to work even with after cooler or pre cooler , u have too much heat exchanged how do u get rid of it , cuz there is got be somewhere for all that heat to go ? ... And when your pre heating the fuel u instantly vaporize it ... Which is good cuz it burns better , but won't that just mean u now have heat of the entire engine+forth coming heat by chemical reaction on the same nozzle now ? ... How's that good ? ... Isn't it more heat than what we can handle ? ... Cuz that's the exact reason we started cooling the engine in the first place ! ... Seems highly impractical to me ... More like some cold war era junk design , like ekrano plane or something or the star fighter 104 , basically which never saw service and so were disbanded ... ! ... No offense , the money could be used better than here ! ...

[@JulianDanzerHAL9001]

fuel has a lot more thermal apacity nad you cna heat it AFTER compressing it and well you can turn al ot of hte heat directly into work iwth a ismple expander cycle, its how every basic heatpump works the problem is jsut to make this work oyu ened a heatsink colder than your target cooling tmeperature nad that is already at liquification while a precooled high speed jet engien can get away with just cooling to the point where the engine stays at operating temperature for an airbreathing rocket engien you need to liuquify it because oyur comrpession ratio is so high that gas being compressed that much would heat up too much again and the only way to reach that pressure without using too mcuh energy is to only pressurize the very smal lvolume of liquified air regenerative coolign i ngeneral is absolutely a thing in rocket engines by the way while there might be better near future options this is an absolutely feasible and impressively elegant setup

[@thomasciarlariello3228]

Of March 2019 by invite only to an engineering conference held inside MIT's Electrical Dept. on Vassar Street of Cambridge, MA. I gave a presentation on a fusion rocket plane engine whereby cryogenic deuterium fuel flowing through a beryllium alloy reaction chamber nozzle coiled in around electromagnet coils to focus cosmic ray muons prevents electromagnet coils from exceeding Curie Point as alpha particles are deflected to form neutrons to enrich fuel. Earlier Dr. Mitchell Swartz affiliated with MIT published my articles on such a topic and Ruby Carat of Eureka California had posted transcript of my presentation online.

[@thomasciarlariello3228]

I based my Presentation's Prior Art cited on how Noguchi's Nitchitsu of Early 1940s Hamgyong Province had Patents #2134249, and #2156851 issued to an employee named Fritz Hansgirg whereby Hideo Hasagawa's memoir along with O.S.S. files described "Noguchi's Nitchitsu of Hamgyong had produced cryogenic deuterium aerospace fuels for NA to NZ" whereby United States Naval Intelligence Officers during WWII used cruel tortures to obtain such information. Also consider how Andrei Sakharov's muon catalyzed fusion began soon after Communists pillaged Northeast Asia during Fall of 1945 and how Luis Alvarez's muon catalyzed fusion began a decade later soon after United Nations Peacekeepers returned from ruins of Hamgyong Province. I had written a term paper on how laws of physics applied to social issues when I found am old photograph of an aerospace factory in of Manchuria from 1938 to 1945 so I put sources of old documents together to come to such a conclusion.

[@jasons44]

Good idea, but uk gov was very conservative and Short sighted

[@deeremeyer1749]

Uh...SR-71s routinely reached Mach 3.2. Literally "faster than a speeding bullet. And "air-launched" and manned X-15 "rocket planes" exceeded Mach 5. And still never got further than "halfway to space". Starting HORIZONTAL to go VERTICAL all the way to "orbit" is as perfect example of "wrong way thinking" as is humanly possible.

[@jocramkrispy305]

Orbit *is* horizontal. any effort expended vertically is wasted. X-15s got to space. They didn't get to orbit. (Flight 90 was the first such) But perhaps you need to watch again, as it is clearly stated that Mach 5 at 25Km is the point at which a stage can reasonably make it to orbit.

[@aigslmnop6559]

circularisation

[@JulianDanzerHAL9001]

the x-15 didn't make it anywhere near halfway plent vertical laucnehd suborbtial rockets these are baiscally completely unrelated variables you'd only correlate if you don't know anyhting baout hte pyhsics behind htem and only go by arbtirary historical examples this happens often certian design choices correlate for more complex reasons but people think they're directly related just because theyh appne to correlate its the same reason people think longrange planes have to be big

[@deeremeyer1749]

Remember that time when the British put a spacecraft in orbit? Any spacecraft? Me neither. Which leads to why Hotol's "place in the history of spaceflight" is SO "interesting". It's INVISIBLE.

[@jocramkrispy305]

1970 Prospero is still in orbit. The program had already been cancelled by the time it was launched.