The aerospike engine holds great promise for spaceflight, but for various reasons, has remained slightly out of reach for decades. But thanks to Leap 71, the technology has moved one step closer to a spacecraft near you with the test fire of their generatively-designed, 3D printed aerospike.
We reported on the original design process of the engine, but at the time it hadn’t been given a chance to burn its liquid oxygen and kerosene fuel. The special sauce was the application of a computational physics model to tackle the complex issue of keeping the engine components cool enough to function while directing 3,500˚C exhaust around the eponymous spike.
Printed via a powder bed process out of CuCrZr, cleaned, heat treated, and then prepped by the University of Sheffield’s Race 2 Space Team, the rocket produced 5,000 Newtons (1,100 lbf) of thrust during its test fire. For comparison, VentureStar, the ill-fated aerospike single stage to orbit project from the 1990s, was projected to produce more than 1,917 kilonewtons (431,000 lbf) from each of its seven RS-2200 engines. Leap 71 obviously has some scaling up to do before this can propel any crewed spacecraft.
If you want to build your own aerospike or 3D printed rocket nozzles we encourage you to read, understand, and follow all relevant safety guidelines when handling your rockets. It is rocket science, after all!
please include the weight differential of the engines, not just hteir thrust differential. How can we judge them otherwise?
Yes. This.
What the heck is meant by “weight differential” or “thrust differential”? Differential with respect to what?
Is that related to the thrust:mass ratio? or specific impulse? or variation in specific impulse with respect to ambient pressure?
With respect to each other. How much thrust does one have vs the other, how much mass does one have vs the other. If one has more thrust but it’s a lot heavier, it might negate any advantage. Isp would be good to know too, both sea level and vacuum
It’s called thrust-to-weight ratio. Maker didn’t specify weight. But if they did, someone would ask “what about other hardware, what about full weight of engine with support machinery”? They didn’t specify it either.
ok…….but did it melt itself?
Don’t think so. Regenerative cooling; since it’s 3d-printed, you can have channels and cavities all through the thing, so the whole engine is the styrofoam cup filled with water that won’t melt… or in this case, filled with cryofuel. The aeroplug included. Looks like it is covered in frost even while running, a common occurrence with regenerative cooling.
They won’t melt. But thermal stress can cause the material to fail.
The alloy melts at 1070-1080°C (1958-1976°F). The only reason it doesnt melt itself is the design succeeded and the liquid oxygen being routed through the spike before combustion is keeping things cool despite the 3,500˚C exhaust.
I don’t think aerospike engines will have a large increase in efficiency. It will be an incremental improvement.
The advantage of an aerospike is that the delivered specific impulse increases with altitude. A conventional bell nozzle delivers maximum impulse at one particular external pressure. Of course this means that the primary use will be for space shots or sounding rockets, where there is a dramatic change in external pressure during the flight.
Every pound increase of thrust efficiency is an increase of payload
How does “pound” quantify “thrust efficiency”?
Cost of development?
Get a bit more efficient, get a “free” pound of thrust
(Free to the Tsiolkovsky equation, not to your bank account)
I am waiting for metal 3D printers to make their way into homes so that I can finally print my whackjob ideas in all their metal glory. Or just print benchy.
The maximum temperature of an extruder could go up to is possibly 380 degrees Celsius, or 720 degrees Fahrenheit.
You could nearly print a benchy today with zinc (419.5°C ; 787.1°F melting point), you could probably print with lead (327.5 °C ; 621.5 °F melting point), bismuth (271.4 °C ; 520 °F), tin (232 °C ; 450 °F), electrical solder (180°C to 230°C ; 356°F to 446°F) or even Wood’s metal ( 70°C ; 158°F). But floating is probably not an option.
I wonder if metal would conduct heat too well, so laying down a second layer might melt the layer below, especially on small features.
You can extrude solder through a 3d printer, but I’ve only seen it used in two dimensions: https://hackaday.com/2024/10/27/a-brand-new-additive-pcb-fab-technique/
In order to get adhesion, you have to at least somewhat melt the metal in the lower layer, if you’re in an oxygen rich environment. In vacuum, though, it’s possible that metal-metal contact would be sufficient to get bonding. (Spacecraft design has a lot of time spent trying to make sure metals that are in pivot contact don’t weld together.)
It’s also easier to use metals with really lousy thermal conductivity like titanium and stainless steel.
Metal 3D printers are mature and commercially available. You can arrange for one to make its way into you home the same way you get a plastic squirting printer there: Exchange some money for it. You may also need to upgrade your home a bit for the supporting infrastructure needed.
He may also need to downgrade his home in order to create funds to purchase said expensive machine.
Pretty much every metal printer out there is running $100k-1M
The EOS m280 uses a 200w fiber laser when it came out in 2014 it would set you back ~$700k, they still fetch around $140K on the used equipment market.
Meanwhile, you can buy a fiber laser engraver with a 200W raycus fiber laser on ebay for $4-6K.
And a Laser welder with a 2000W raycus fiber laser for about the same.
If no patents stood in the way, Im pretty sure someone could cook up a sub $10k metal printer
Unfortunately we will be waiting at least another decade before we see.
Maybe with some aluminum?
https://www.engineering.com/one-drop-at-a-time-xerox-3d-prints-with-liquid-metal/
Companies like JLCPCB will print or machine your whackjob ideas for you right now for not very much, you’d likely have to do a LOT of prints before it became cheaper to buy your own, although iterating is slower when you have to wait for the postman to bring it from China.
There are numerous companies doing contract metal printing in the US, Canada, across the EU, and Austrailia. Unlike traditionally manufactured goods the expense of these parts lie more in the base material cost, and the machine time your design consumes than the labor employed significantly diminishing if not negating the principal advantage of dealing with China and other such options.
For the US Sculpteo, Stratasys Direct, Xometry, and Jawstec are all good resources for SLM. If DMLS meets your needs there are even more options to consider.
Dont kid yourself though DMLS and SLM parts are EXPENSIVE. All3DP did an article comparing batches of several different parts and finishes from a number of services last July. Google it if youve curiosity.
More energetic propellants should be the path:
https://phys.org/news/2025-06-scientists-stable-neutral-nitrogen-allotrope.amp
An N6 rocket needs no oxidizer…being closer to Sprint HIBEX it can perhaps be made more rugged like the Flying Crowbar of Pluto/SLAM.
Steel SRBs whose grain is about to burn out would be strong enough for injection of cryogenic N6.
Steel solids can support the weight of an entire stack, so if they soften a tad in flight no biggie.
The svelte shuttle design at the end of this video:
https://m.youtube.com/watch?v=2c-kXHJ_qEo
-made me wonder if this concept could be a whole stack:
https://spaceflighthistory.blogspot.com/2017/02/?m=1
Spaceplane on top—tankage in shape of Lifting Body (good for Mars?)
Raptors and TPS under lifting body—orbiter with ablative TPS if in emergency.
Of course, if N6 is a wonder propellant—perhaps it could tow a Blackhorse to space via tether—the latter skyhooked DOWN with no TPS—or just that single use ablative.
On aircraft design
https://www.spacedaily.com/m/reports/AI_system_accelerates_aircraft_concept_design_using_language_models_999.html
Get real: “* N6, upon decomposition, releases an exceptional amount of energy—2.2 times more per unit mass than the known explosive TNT *” Or about one fifth that of H2-O2 bipropellant, and slightly more than hydrogen peroxide.
Which would give it a Isp around 200s — worse than any rocket currently flying.
Sorry for the misplacement: Meant to be a reply to Jeff Wright above.