Meet The TM65 Liquid Propellant Rocket Engine

While we’re reluctant to say it for fear of being misinterpreted, the new liquid fuel rocket engine being built by Copenhagen Suborbitals is one of the most impressive, daring, and nearly the sexiest machine we’ve ever seen. Although the engine hasn’t been fired yet, [Peter Madsen], Chief launch vehicle designer at Copenhagen Suborbitals, gives an amazing 18-minute-long rundown of the function of each and every tank and tube of the TM65 in this video.

When the TM65 engine begins its firing sequence, valves attached to tanks of alcohol and liquid Oxygen are opened. The Oxygen pours directly into an injector manifold that atomizes the liquid in the combustion chamber, while the alcohol makes a much longer trip down to the engine bell, flowing between the double wall of the chamber and nozzle for cooling. Once the alcohol and Oxygen in the combustion chamber ignite, two gigantic tanks of Helium are opened and the gas is forced down to a heat exchanger at the end of the nozzle, increasing the temperature and pressure of the Helium. The Helium is then routed to the tanks, pressurizing them and forcing fuel and oxidizer into the combustion chamber at 40 liters per second. This entire process happens in only eight seconds; after that, the rocket attached to the TM65 will be on its way upward.

We’re not going to say the TM65 is the best engine ever seen on Hackaday; we’ll leave you to decide that. We can’t wait for the video of the test fire to hit the Internet, though.

52 thoughts on “Meet The TM65 Liquid Propellant Rocket Engine

  1. And, unfortunately, that is why this idea is DOA. Helium is a mined resource, not manufactured. There is only so much of on Earth and we’re already starting to hear complaints from scientists and industry that things like party balloons are causing rapid exhaustion of that supply. Filling an army of these things (as would be needed to produce a significant amount of power) would use massive amounts of helium and would need to be re-filled regularly.

    You could look into using hydrogen instead, but then you’d have all of the safety concerns of manufacturing and handling massive quantities of highly flammable hydrogen. Also, hydrogen is so small that is leaks through the walls of, pretty much, anything it is stored in (even thick steel tanks) over time. That’s one of the many problems also faced by hydrogen powered cars.

    1. Copypaste much?

      Helium was probably used due to its reluctance to react with other elements. Hydrogen would be completely unacceptable in its place, though perhaps nitrogen would be? Not sure.

      I really loved seeing the Mythbusters almost blow up their shop with the liquid Nitrous Oxide and paraffin wax rocket they made for the Civil War Rocket episode.

    2. leftthehypnotistearly: I don’t think anyone claims that party balloons are causing helium to be exhausted, only that it is a wasteful use of helium and a higher price would stop such use.

      This is a rocket engine. Sustainable fuel is not high on the requirement list for those and hardly not anything that causes it to be considered DOA. Compared to most other rocket engines, this one uses rather nice fuel. Not the usual leathal stuff.

      Regarding leakage; helium atoms are smaller than hydrogen molecules.

    3. I guess going into hippie-dippie environmentalist histrionics is easier than watching the video where they say they plan to switch to Nitrogen, isn’t it? It must feel good, like a drug, being able to act alarmist and grab at attention whenever someone does something you yourself could never hope to do, desperately trying to detract in whatever way you can in order to sleep peacefully at night by telling yourself that you’re so much smarter than them, right?

  2. We need the helium for MRI scanners and other vital equipment, wasting it for rockets is insane! Once certain natural gas fields are empty there is no more helium on this planet accessible!

    1. Maybe you do have a point don’t outway the benifits of rocket science, mabey we’ll discove some better replacement for this gas surrounding some other planet in space. Don’t rule your side as the only side, all sciences are important not just your.

      HaD if you feel the need to remove this comment because it can be taken offensive in any way feel free and you have my consent!

    1. You got it. This IS really sweet. These guys are kicking ass. Frankly, it’s a legitimate use of helium in the name of science.

      Perhaps we can throw a party for ourselves (in the name of self-indulgence and feeling good) with all the helium we save by not building rockets. Great idea, no?

    2. Thank you Steve. Nice to try to keep the SN ratio reasonable.

      That video was an excellent introduction to this class of engine. I wish these guys the best of luck although it sounds like they’ve really done their homework. Does anyone know what engine they were showing being test fired?

  3. Lots of whining on both sides of this issue, eh?

    Watching the video, I’m struck by the concise and eloquent explanation from the spokesperson/engineer. However, I wonder why they use the propellent for cooling, and a separate gas for pumping; when the oxidizer itself is under a great deal of pressure, at a very low temperature. It seems to this absolute layman, that lox would make an efficient and powerful coolant/pump; while simplifying the plumbing by perhaps a third.

    Surely this is so obvious that it has previously been tried and rejected; so the question is more for my own edification than any criticism of the engineering of this awesome device.

    1. Not to mention LOX is an oxidizer. Typically you want to minimize contact with the oxidizer because… well, it oxidizes. For example, cleanliness is extremely important in these systems. In an aluminum line, a small particle creating a scratch in an oxidizer line would cause the oxygen to react with the aluminum (burn). Other materials can react similarly.

      Besides that though, your idea is spot on. A lot of engines use regenerative cooling with fuel instead of the oxidizer. The SSME is a good example.

    2. Perhaps :
      If you have a coolant failure and it’s inert, no big bang.
      If the coolant heats up too much and the coolant is also fuel then the bang could be quite large.
      Although if anything goes wrong with this sort of thing, it’s time to run away really quickly and laminate yourself on the scenery. Maybe this would make a slightly wider debris spread.

  4. What a impressive undertaking. I will gladly give up party balloons for life to see this thing fire.

    I’ve not yet watched the video but from the description it sounds like this design uses features developed for the V2. I wonder if the use of fuel as coolant is a feature of modern liquid fuel engines? Have there been fundamental changes in liquid fuel engine design since the V2?

  5. Its not the cost of the helium, they could as well use nitrogen, no problem. The real problem is that the tanks must be thick walled, thus heavy to withstand the pressure needed to feed the fuel to the engine. So alot of rocket mass is wasted on the tanks.

    Even the Germans in WWII figured that out in their V2. The tanks in modern rockets are so light weight that these need to be pressurized to retain their structural integrity, as seen in the Centaur upper stage.
    The real difficult part of a liquid fueled rocket engine is the turbine driven fuel pump.

    1. While earlier Centaur tanks were “balloons” with extremely thin metal which had to be pressureized, the current ones on the Atlas V are rigid and will don’t need to be pressurized before they’re filled.

  6. you always need active cooling on first stage engines. they would melt and explode otherwise. even on the satrun v engines you had fuel circulating through the thrust bell prior to ignition. its more efficient than using a separate coolant. especially when cryogenic fuel is used. it also preheats the fuel so it burns more efficiently. this is actually very common in engine design.

    the difference here is that the fuel is non-cryogenic. likely conversion from liquid to high pressure vapor will result in the neccisary cooling, and is actually quite effective. if you apply rubbing alcohol to your skin it evaporates and gets very cold very fast, and this is applied to the engine.

    1. It is a very old idea, employed in the earliest of liquid fuel rockets. It is also how jetpacks force the H2O2 into the motor. So obvious, but probably not brilliant.

  7. This was a fascinating article, the engineering was impressive, however there seem to be a lot of “reinventing the wheel”. While film cooling is effective it wastes propellant and reduces the trust-to-weight ratio.

    Using an inert gas to replace the turbo-pump is clever but also kills the trust-to-weight ratio.

    If they switched the fuel to liquid methane they could combine pressurization and regenerative cooling into a single system. The phase change from liquid to gas would cool the engine bell while the increased pressure from a heated gas could be used to pressurize the system.

    1. Helium is a far better pressurant gas than nitrogen for a bunch of reasons. *EVERY* liquid rocket engine I’m aware of uses Helium to pressurize its tanks. The space shuttle used lots of Helium for pressurization.

      In terms of rocketry don’t worry about using up Helium, while it’s used a lot there aren’t that many rockets launched, it’s going to be a long time before anybody launches enough rockets to make a dent in the world’s Helium supply.

      As the uses for Helium increase and the supply decreases the price for Helium will go up and eventually become too costly for party balloons, but it’ll still be plenty for other applications for a long time.

      All that having been said, if you’re trying to design a rocket on a budget you could use Nitrogen or Argon instead of Helium. While less efficient it could save you enough money to justify its use.

  8. Speaking as an actual rocket scientist, The reasons for using helium are multiple

    1) nitrogen liquefies at LOX temperatures, IE your LOX is now LOX with some N2 in it, this is generally not a major issue if your quick about pressurizing then launching, but if your on the pad for any length of time (30 minutes or so?) it starts to become an issue.

    2) nitrogen dissolves in most fuels, like CO2 in water, it becomes “fizzy”. Fizzy is not something you want in your fuel, you get all sorts of bad things, combustion instability leading to explosive disassembly. Cavitation, leading to burn through and explosive disassembly. Noisy sensor data causing unequal fuel usage at burnout leading to the engine burning in place of the fuel (LOX + hot Al = Al fire, exciting to watch, from a safe distance)

    In short, lots of people in the field try to use nitrogen for pressurization then wind up going to He as it solves many many (expensive, and tricky to determine the cause of) problems.

    This particular group has allot of experience however and if they say they are going to try nitrogen, good luck and please publish, inquiring minds want to know.

    Oh whilst I’m a big fan of H2 as a lift gas for balloons, pressurizing LOX with it is going to be very exciting. Please let me know when your going to try that so I can set up the high speed cameras and portable bunker at a safe distance. I’m in Australia and on average your in the USA, I think that should just about do it. If your not in the USA please give us (Australia) a heads up when your planning this either way, just in case we all need to book a trip to Brazil or somewhere nice.

  9. My big question (okay, I haven’t asked the video so it might be in there) is what’s the sea level thrust, what’s the nozzle’s exit ratio, and what’s the specific impulse?

    Metric or English units. Or Furlongs per fortnight.

    1. Its not generally that clear cut, waters boiling point is 100C, but it’ll evaporate and condense at a wide range of temperatures.

      Also lox at its BP is regarded as “fluffy” its not very dense so they generally try to use the lox at temps much lower than that. Generally lox comes in dewars moderately pressurised and at >~90k they then dump the pressure and boil off some lox chilling it well below its bpt, load up some lox into the tank to chill it off, then dump that and reload with the chilled lox.

      The russians used to(might still?) refrigerate their fuel (kero basically, to ~10C or something as i recall), so they could pack an extra 4-7% fuel in, makes a big difference to the total deltaV of the rocket.

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