back to article Nuclear fusion firm Pulsar fires up a UK-built hybrid rocket engine

UK nuclear fusion outfit Pulsar Fusion has fired up a chemical rocket engine running on a combination of nitrous oxide oxidiser, high-density polyethylene fuel and oxygen. The acceptance tests of the UK-built rocket were conducted at COTEC, a UK Ministry of Defence site at Salisbury Plain in southern England. We spoke to CEO …

  1. bombastic bob Silver badge

    Fusion rocket engines - the gist

    Starting with hybrid engines, later evolving into fusion ones. Interesting.

    Although it is PLAINLY obvious that a proper fusion-powered rocket engine would maximize efficiency, it will still need "a something" to fling out of the tailpipe at high velocity, as does the ion engine.

    I suppose there are many ways of "flinging" but the only way I can think up looks a LOT like a standard engine, but 90% of the gamma+neutrons from the reaction would be absorbed by some hydrogenous liquid, like water, methane, or ammonia [which happen to be pretty abundant in our solar system] and then be expelled out the back end like regular rocket exhaust. "Impulse engine"

    Current rocket tech runs at a temperature close to melting the engines for max efficiency and single-use. Obviously we want the re-usable kind. So efficiency MIGHT have to suffer a bit. Unless... you use the propulsion fluid itself to MAKE A LAMINAR BOUNDARY LAYER on the insides of the engine! It's something related to what is already being done, i.e. use fuel to cool the rocket nozzle. In any case some clever spark will hopefully come up with a design that captures as much energy from the fusion reaction as possible, and THEN flings it out the back in a way that maximizes utilization of kinetic energy (proportional to v-squared, how much energy is needed) and momentum (mass times velocity, and how you get thrust) along with fuel weight/mass and the overall weight/mass of the rocket itself.

    (An ideal ratio of fuel use vs thrust vs reactor capacity just has to exist)

    Anyway, just thought I'd mention that. Looking forward to something that ACTUALLY WORKS. 2025 - was that for the FUSION engine?

    NOTE: a distance of about 30cm in liquid water is sufficient to absorb about 90% of gamma, and about 1 meter for 90% of neutrons. SO you would need an engine large enough to have the equivalent of liquid "that thick" to absorb most of the radiation and generate propulsion. The logistics of the placement of the fusion reaction itself might be the hardest part, but if you can just get most of that radiation into a hydrogenous liquid with a cooling layer protecting the metal parts, you SHOULD be able to get some very efficient thrust out of a reasonably sized engine.

    1. druck Silver badge

      Re: Fusion rocket engines - the gist

      Bob, you are correct it has already been done, the F1 engine vented the fuel rich exhaust from the turbo pumps into the main nozzle to form a protective boundary layer. However things have moved on since the 60s, with the full-flow staged-combustion-cycle Raptor engine being far more efficient in terms of both specific impulse and thrust to weight ratio, even if a single engine can't compete with the F1 in terms of total thrust.

      1. bombastic bob Silver badge

        Re: Fusion rocket engines - the gist

        Right, the basic idea is that you need to accelerate the mass you have at as high a velocity as you can get, meaning that the "burn" temperature will probably need to exceed the melting point of the engines for it to become efficient. The F1 (as I recall) burns kerosene+O2 which is heavier/denser than the H2+O2 used by the other stages. Granted the kerosene produces heavier exhaust and lower burn temp, but it's still hot enough to melt the engine. And so "a way" to keep from melting the nozzles needs to be there.

        My assumption, in essence, is to blast water into a layer at the sides of the engine, then light off the fusion reaction in the middle near the focal point of a parabola (also surrounded by cooling liquid so that it does not melt either). The resulting temperature of the liquid would give you the 'v' part of the 'mv' impulse, and the overall energy of the reaction would increase the K.E. of the liquid to get you as high a 'v' as you can possibly get (thereby minimizing the mass of liquid needed to get thrust).

        There were several fission based rocket engines tested in the 1950's and 1960's that were test-fired but never flew. It used nuclear fuel to heat liquid H2, but I think using water would have been a better design.

        In short it's a way to get a bit more velocity by applying heat more efficiently to the "impulse fluid", and at much higher temperatures than you could get with a chemical burn. I expect fusion to be similar.

        yeah no doubt better engines exist now than the F1 used in Apollo, but the design principles of fusion or fission exclude combustion kinds of things. Heating needs to be done differently, and gamma capture by the "impulse fluid" would be extremely effective (and not melt engine parts so easily)

        years ago I figured out that a dense fluid that was heated and accelerated directly by fusion gamma and neutron radiation would give you the best fuel utilization efficiency, being as a heavy fluid does not need such a large tank to store it in...

        [to double thrust you must either double exhaust velocity or double the mass flow rate. doubling mass flow rate takes twice the energy. doubling velocity takes 4 times the energy. doing the math, yeah)

    2. The Basis of everything is...

      Re: Fusion rocket engines - the gist

      I remember reading stories about this as a kid - probably Heinlein, maybe others, referring to even though the engines use an "atomic pile" they still needed reaction mass to actually move the ship. And a couple of scenes with a bored crew, a half empty water tank and the things you can get up to in zero g...

    3. Jonathon Green

      Re: Fusion rocket engines - the gist

      I have no idea what kind of fusion this bunch are working on, but let’s say it’s inertial confinement…

      Letting my fevered imagination and hand-wave level understanding of how this stuff works have free reign then that strikes me as taking us a fair chunk of the way towards a less nightmare inducing variant of Orion, where rather than letting off a series of full-on thermonuclear bombs behind your ship to push it along you spit out a stream of dinky little pellets (Hohlraum?) containing a deuterium/tritium mix and “detonate” them with big-ass lasers[1].

      Or to put it another way, if you squint a bit, don’t look too closely, and crank your optimism up to 11 the National Ignition Facility[2] at Lawrence Livermore is actually a ground based prototype starship drive… :-)

      [1] Sharks optional…


    4. Anonymous Coward

      Re: Fusion rocket engines - the gist

      You want the highest possible exhaust velocity. What you should therefore throw out of tail of rocket is as far as you can manage is the gammas & fast neutrons from the fusion. For everything else I think fusion buys you much less than you might think: exhaust velocity depends on temperature you can raise reaction mass to, and limit of that is what you can contain in the engine. Suspect strongly that existing chemical rockets are already limited by this: you can have fuels which already burn too hot and so cannot be used even though they would get you high specific impulse. Using part of fuel itself to cool engine is clever idea (also old one) but since this must be cooler it reduces specific impulse.

      Fusion rocket is not magic bullet unless you eject fusion products directly in other words. In that case it is not only magic bullet but extremely effective weapon (is famous quote about this).

      Also ... if you can build a fusion rocket you have sustained, strongly exothermic, fusion. And if you have that you are then not building a fusion rocket you are using your device to heat water, make steam, and drive turbines.

      So these people neither have one nor are close to having one. What are they doing, in fact, other than extracting money from investors?

      1. swm

        Re: Fusion rocket engines - the gist

        You really would like to have an exhaust velocity be the speed of light. This means you need lasers that convert input power to light with a very high efficiency.

        1. Anonymous Coward

          Re: Fusion rocket engines - the gist

          Of course, if you have fusion power source then efficiency matters rather less as you have copious power: just use ordinary lasers. Or ordinary lights indeed.

          (Of course they don't have nor will they have such a power source any time soon but let us pretend, as they are pretending.)

        2. Loyal Commenter Silver badge

          Re: Fusion rocket engines - the gist

          Just don't stand behind it, because that also sounds an awful lot like a fusion-powered laser cannon.

          1. zuckzuckgo Silver badge

            Re: Fusion rocket engines - the gist

            Clearly it is essential to get started on a selective shark breeding program now. If we don't if we won't have one large enough to mount those new lasers on.

    5. Eclectic Man Silver badge

      Re: Fusion rocket engines - the gist

      Not a fusion device, but the Russians are working on a nuclear powered cruise missile:

      One allegedly blew up recently:

      After 'hyperdrive' (and for Star Trek fans, 'warp drive'), fusion rockets, as I recall, have been the mainstay of science fiction writer for decades.

      1. Anonymous Coward

        Re: Fusion rocket engines - the gist

        Cruise missiles like this are air breathing and so have no real upper bound on reaction mass: as long as you can heat the air you can keep going. Nuclear power therefore good option for this: you use air to cool reactor and also to drive missile, giving you really no limit on range, and thus a specific impulse which is for all useful purposes infinite. Exhaust tends to be a bit radioactiv though. One idea for Pluto was that it could fly around over enemys cities dumping fallout once it had used all its warheads I think.

  2. tony72

    Smart move

    The market for launch vehicle already seems to be getting really crowded, and one feels there's going to be a major shakeout at some point. But focusing on components for rockets seems like a smart move.

    Strange though, this polyethylene/lox engine doesn't seem to be mentioned anywhere on Pulsar Fusion's website, and all I can find on it online is articles with pretty much the same info as this Reg article, presumably all based on the same press release. The only mob I can think of that's flying hybrid solid fuel engines is Virgin Galactic, I wonder if these are comparable.

    1. Stork Silver badge

      Re: Smart move

      I think Copenhagen Suborbitals used something like that

  3. Anonymous Coward
    Anonymous Coward

    No! No! N2O!

    Apparently nitrous oxide is a fairly potent greenhouse gas, though unless this technology ends up in personal jetpacks or some other consumer nonsense the threat seems likely to be dwarfed by agricultural emissions.

    1. Chris G

      Re: No! No! N2O!

      If the engine is working, there won't be any nitrous oxide coming out of the back end, it will have provided the oxygen to enable the polyethylene fuel to burn.

      I ought to mention here that burning a plastic like HDPE at the temperatures in a rocket engine using a oxidiser should produce only water vapour and a relatively small amount of carbon dioxide, so still some green house gas but nowhere near as noxious as some rocket fuels.

      This is worth a read;

      1. the hatter

        Re: No! No! N2O!

        When I'm explaining it to folk with a scientific background, but not up on their rocket science, is that I'm sure they're familiar with the horrible smoke from burning plastics, but they also know from simple flames such as candles, that when you get badd smoke that's just because you're not doing an efficient burn. That problem with burning plastic is fixed in hybrid motors because they're no longer oxygen-starved, hence none of those bad combustion products get to hang around, due to the heat in the reaction, breaking down most of those, and outputting more energy as the bonds holding the complex chemicals are destroyed.

    2. Loyal Commenter Silver badge

      Re: No! No! N2O!

      Polyethylene and oxygen:

      [CH2]n + 1.5n O2 => nCO2 + nH2O

      Where does the nitrogen come in? Answers on a postcard please...

  4. Anonymous Coward
    Anonymous Coward

    "What I've learned," Dinan told The Reg, "is that everybody knows how rocket engines work."

    ... well its not rocket science

    1. eldakka

      Leonard: Uh-oh.

      Raj: What's the matter?

      Leonard: Something's wrong, I'm not getting any gas. Anybody know anything about internal combustion engines?

      Sheldon: Of course.

      Raj: Very basic.

      Howard: 19th-century technology.

      Leonard: Does anybody know how to fix an internal combustion engine?

      Sheldon: No.

      Howard: No, not a clue.

    2. Jonathan Richards 1

      Kind of the point

      Rocket science seems to be much easier than rocket technology. Big stick go bang.

      1. Tom 7

        Re: Kind of the point

        Hybrid rockets are incredibly simple compared to liquid fuelled rockets. Basically you have a tube lined with your fuel with a hole down the middle and an igniter lining that and a choke at the bottom to increase the thrust. You set off the igniter while blowing the oxidiser into the top of the cylinder and away you go. I've spent a few Sundays at EARS near Cambourne Cambs watching people launch these things.

        Being a cylinder of flaming gas resonance can turn the thing into a fiery organ pipe and the noise, light and smoke are something to behold. As the power can be controlled by restricting the amount of oxidiser you blow into the fuel these things can be controlled and I have seen a video of someone hopping one along a fence!

        I did see one 1/3rd size V2 using rubber as the fuel but alas something went wrong and it didnt get more than a couple of hundred foot up.

    3. captain veg Silver badge

      rocket science is overrated

      It is, after all, nothing more than Newton's third law.


      1. Dave 126 Silver badge

        Re: rocket science is overrated

        Rocket science is: Action, reaction, ballistics.

        Rocket technology is: rocket science AND materials science, complex fluid dynamics, chemistry, manufacturing, testing, data collection, metrology, meteorology, finance, regulatory frameworks, etc etc

        Of course the concepts of science and technology are artificial, and the history of rocket development saw theory and practice intertwined.

  5. Anonymous Coward

    Rocket science

    "The people that can build rocket engines are the people that have taken apart 20 engines that have failed..."

    As many have found, thinking of an idea is a lot easier than implementing an idea even if you're a rocket scientist. Sometimes you just need some 'rapid unscheduled disassembly' events to get it right. (see icon)

    1. David 132 Silver badge

      Re: Rocket science

      As is my custom on Reg articles concerning rocketry, allow me to highlight Ignition! by John D Clark. It’s one of the finest, most informative, and, yes, laugh-out-loud funny books ever written on the early history of rocketry up to the 1970s or so. Albeit that isn’t a very crowded field of literature, I’ll admit. But it’s very much worth a read.

      1. anothercynic Silver badge

        Re: Rocket science

        Indeed. That is one hell of a good read! :-)

      2. Gene Cash Silver badge

        Re: Rocket science

        Yes, and his estate has *finally* allowed it to be reprinted, replacing my samizdat PDF printout.

      3. Jonathon Green

        Re: Rocket science

        I’d also commend “ Strange Angel: The Otherworldly Life of Rocket Scientist John Whiteside Parsons” by George Pendleton. Where else are you going to find the early history of JPL, Aleister Crowley, and L. Ron Hubbard in a single non-fictional story…?

      4. RegGuy1 Silver badge

        Re: Rocket science

        Ignition: well what a stunning read! I had never heard of it before. Thank you!!

        If a man is splashed generously with [aniline], and it isn't removed immediately, he usually turns purple and then blue and is likely to die of cyanosis in a matter of minutes. So the combination was understandably unpopular, and the call went out for a new one that was, at least, not quite so poisonous and miserable to handle. (page 26)

      5. GBE

        Re: Rocket science

        As is my custom on Reg articles concerning rocketry, allow me to highlight Ignition! by John D Clark.

        That's indeed a fascinating book. I was very surprised by how much of the development of liquid fuel/oxidiser combinations was based on little more than educated guesses and trial-and-error experimentation.

  6. Tromos

    Flames came out of the right end

    That's good. Unless, of course, if they were meant to come out of the left end.

    1. el_oscuro

      Re: Flames came out of the right end

      Actually, it really should point to the ground if you want to go to space. If it starts point up towards space, you are having a bad problem and will not go to space today.

      1. david 12 Silver badge

        Re: Flames came out of the right end

        If you point straight up, you come back straight down: it's an elliptic orbit with minor radius of zero. If you want to stay up, you want to go into orbit, which means accelerating left (or right)

  7. Jan 0 Silver badge

    I have to say that that's the most underwhelming video of a conventional rocket engine that I've ever seen! I want shock diamonds and scary blue light!

    1. Tom 7

      That would be because its not a conventional rocket engine! And there were shocks at one point!

  8. MachDiamond Silver badge

    Doesn't scale well.

    Virgin Galactic, once owned by Sir Richard Branson, found out that Hybrid rocket motors don't scale well. The one in Burt Rutan's Space Ship One didn't lend itself to a bigger version for VG's Space Ship Two. They are Nitrous/HTPB although they tried a nylon fuel with N20 moderated with Helium since the rubber motor ran far too rough towards the end of it's burn and they weren't getting the total impulse they needed to get to space. Simple enough, use the old definition of space that was lower. It was a Nylon fueled SS2 that broke up and crashed on Oct 31, 2014. One of the problems is the extra plumbing required eliminated a couple of passenger seats. That's 1/2 million bucks per flight in tickets.

    I've played with hobby hybrid motors and they were just too big of a PIA. I worked on pressure-fed liquid rockets that were much more reliable even though more complicated. I still play with my solid fuel rockets from time to time and may go out and watch some tomorrow morning at the local club launch.

    I wonder why they are using a two oxidizer approach.

    1. Tom 7

      Re: Doesn't scale well.

      Seen quite a few successful hybrid launches at EARS.

      1. ClockworkOwl

        Re: Doesn't scale well.

        Indeed, the Big EaARS I attended more than a few years ago had a Rattworks Tribrid* launch!

        It also had one of the best firework displays I've ever seen...

        The Robin Reliant shuttle used 6 Contrail O class hybrid motors, that are 6KN average thrust, 4 on take off, and 2 air starts...

        The video seems to show a very poor start, too much smoke and only diamonds at the end.

        6/10, not too impressive, but to be encouraged anyway!

        *Tribrid, is a hybrid (ABS/N2O) that transitions to Methanol/N2O:

  9. sitta_europea Silver badge

    Mass * Temperature => thrust.

    Chemical processes => tens of thousands of degrees K at best.

    Nuclear processes => tens of millions of degrees K minimum.

    Kinda obvious what to do when you look at it like that.

  10. John Brown (no body) Silver badge


    That SpinLaunch device looks interesting and wacky! Apart from the high tech control room, it looks sotra steampunk, like maybe the British Empire of the Victorian era may have used to colonise Mars :-)

    1. Oneman2Many

      Re: SpinLaunch

      Scott Manley has a video as to why SpinLaunch is extremely difficult both as a concept and for the payload.

    2. Ian Johnston Silver badge

      Re: SpinLaunch

      Their videos set off every bullshit detector I have. Why does the "Suborbital launcher" video keep cutting between some prototype device and CGI? Why does the "Orbital accelerator" video label a couple of random and unimportant things (AC motors and hydrodynamic bearings) while keeping completely silent about important stuff, like numbers? Why does the clamping system conveniently disappear from the video just before launch?

      They say that they will launch at 3000mph, which is 1300m/s and it seems that their centrifuge arm is 50m long. That's a centrifugal acceleration (centripetal for physicists who don't understand rotating axis systems) of 3400g. Even if they can build an arm capable of taking the loads, that means that every component with the launch shell has to be supported in a way which withstands 3400g.

      How do they release at the right time? Assuming the launch aperture is 1m wide, the vehicle's nose will pass across it in 0.8ms. At release, the vehicle is rotating at 26 rad/s: how do they propose to lose all that angular momentum?

      Still they have a vacuum, which will excite the hyperloop fanboiz who haven't yet learned critical thinking.

      1. TDog

        Re: SpinLaunch

        Well as the launch vehicle breaks the membrane keeping the air out of the vacuum chamber the air will rush in to the chamber. This will create a turbulent force on the rotating arm which I assume has sufficient aerodynamic properties not to excessively oscillate and snap.

        The electric motor could be used to slow the arm down as a brake but going from memory they were talking of several days to achieve full rotational velocity - so electrodynamic brakeing alone would presumably take the same time to slow it down - doubling the reuse time.

        Of course if the rotor is as light as is feasible then since most of it is travelling relatively slowly then releasing a projectile massing 20 times the mass of the rotor arm would result in well in excess of 95% of the energy stored being released in that projectile leaving relatively little to be dispersed.

        1. Anonymous Coward

          Re: SpinLaunch

          When they launch their projectile they suddenly have a centrifuge which is now hugely out of balance, suddenly running in air, with the ends of the arms moving at some significant fraction of orbital speed. This will not end well I think. Could deal with the balance problem by releasing a projectile in opposite direction, but then they must deal with the abrupt release of entire kinetic energy of that projectile when it hits whatever it hits. Which, also, will not end well.

        2. Loyal Commenter Silver badge

          Re: SpinLaunch

          This will create a turbulent force on the rotating arm

          Which in turn will create colossal amounts of heating, vibration, and most likely a huge shockwave. That's what we call, in common parlance, an explosion.

          ...then releasing a projectile massing 20 times the mass of the rotor arm would result in well in excess of 95% of the energy stored being released in that projectile leaving relatively little to be dispersed

          95% of the energy, but 0% of the angular momentum, which would be 100% transferred into the now hugely unbalanced rotor. I don't know if you've ever operated a centrifuge (I have), but the first, and most important thing you are taught is to make sure it is balanced. For the thing I used to use to rapidly settle finely suspended mixtures, the payload of the centrifuge, which weighed in the 100s of grams range, would have to be balanced to within a fraction of a gram, and that thing, which was mounted on great big rubber bushes bolted to a concrete floor to reduce vibration, only went to about 1,000 rpm.

  11. elsergiovolador Silver badge


    I have a feeling that this is already a legacy technology before it even got widely adopted.

    The future is in engines that bend time and space continuum in front of them and essentially make the rocket "fall" into it.

    That won't require having to emit anything from the rear, just like an object falling from the height does not have to do anything to orderly fall down.

    1. Uncle Slacky Silver badge

      Re: Gravity

      Join us at APEC if you'd like to know more:

      1. Anonymous Coward

        Re: Gravity

        In this presentation [a crank] will present some principles of active (non-reactive) propulsion drives. New methods do not require reactive mass ejection outside the vehicle. At first, we’ll consider examples of mechanical systems, later we will see analogs with electromagnetic propulsion systems. In both cases, mechanical or electromagnetic technologies, are presented as Aether density gradient.

        'Aether density gradient'! The cranks have their own crank conferences!

        Oh yes also

        In this presentation [a crank] discusses the possibility that while humans use radio communication, extraterrestrial intelligences may be using something more advanced, based on quantum superluminal communications. In other words, human beings may be on AM while aliens may be on FM.

        Ah yes, 'quantum superluminal communications': big impressive words for a thing which QM does not allow and which if it did allow would support causality violation.

    2. dajames

      Re: Gravity

      The future is in engines that bend time and space continuum in front of them and essentially make the rocket "fall" into it.

      Nice idea ... come back when you have a working prototype!

  12. Steve Graham

    Fusion? Fusion? Yes, we're working on revolutionary technology, but look at our rocket engine!

    They don't even have a Magic Leap video presentation.

  13. Ian Johnston Silver badge

    UK nuclear fusion outfit Pulsar Fusion has fired up a chemical rocket engine running on a combination of nitrous oxide oxidiser, high-density polyethylene fuel and oxygen. ... Unlike Rocket Lab's and SpaceX's powerplants, Pulsar's hybrid engine runs on high-density polyethylene fuel and oxygen. An oxidiser is required to make the magic happen.

    So is there nitrous oxide or not? The Pulsar Fusion website is non-committal. In fact it looks like a bunch of dreamers who claim they are about to produce power from fusion, cover their failure there with an ion thruster and cover their failure there with a bog standard hybrid rocket (see: Bloundhound and that Reliant on Top Gear). If they really could do fusion, why would they be pratting around with chemical rockets?

    1. Andy The Hat Silver badge

      I must admit that if you're "successfully" working on one technology why would you also be working on another system that has (basically) already been done, dusted and proved in multiple ways? Smells of smoke, mirrors and financial wizardry to me.

  14. batfink


    Does this mean the street price of nos will go up?

POST COMMENT House rules

Not a member of The Register? Create a new account here.

  • Enter your comment

  • Add an icon

Anonymous cowards cannot choose their icon

Other stories you might like