Question for the space nerds: how impressive is this?
* Uses liquid methane and oxygen for fuel, which is far easier to work with than the current Vulcain hydrogen/oxygen fueled engine and burns cleaner than kerosene/oxygen engines, which is better for reusability.
* This is an engine that might work well on a small to medium reusable launcher, which ESA no longer has access to after their Vega rocket repeatedly failed and they lost access to Russia's Soyuz rockets[0].
* ESA is at least trying to do reusability after dismissing the idea for years.
Negatives:
* "100-tonne thrust class" is half the thrust of either SpaceX's Raptor or Blue Origin's BE-4 engines, which will be similarly reusable and using the same fuels.
* Additive layer manufacturing sounds cool but I'm not sure it has any real benefits over conventional engine manufacturing techniques. SpaceX is reportedly close to building one Raptor engine _per day_ without 3D printing.
* They are undecided on the fuel ("A version using liquid hydrogen-liquid oxygen is also being developed."). That is an entirely different engine and ground support infrastructure, but they are presumably doing it so it could be used directly in the Ariane 6 rocket?
* Arianespace/ESA is at least a decade[1] behind SpaceX in reusability and due to rocket failures and retirements, and the delays with Ariane 6, won't have _any_ flying rockets until 2024. So they are far behind and do not have a good track record with speedy development.
[0] https://spacenews.com/europe-grappling-with-space-access-cha...
[1] https://www.space.com/europe-no-reusable-rocket-until-2030s
Raptor is by far the best engine ever built according to that measure.
Prometheus doesn't seem that impressive but we don't have all the information on it as far as I can find.
What? I am a casual observer but I believe specific impulse is most important - how much thrust do you get per unit of fuel. The amount of fuel you have to carry has a huge impact on how much. Of course things like ion thrusters have high ISP but not enough thrust for launch - but once you get enough thrust to launch a rocket, you want a high ISP. High ISP means way less fuel required which means even with less thrust you will be okay. So thrust per nozzle area isn't strictly that important if the engine is so inefficient you need to carry twice as much fuel.
Weight/thrust is important; thrust/area is important; ISP is important; thrust/dollar is important...
something more like that is probably the most important variable.
all the rest of them impress space nerds, the ones ending in per-dollar are the ones that impress accountants and finance people.
If you can not get enough thrust under your rocket sectional area, your capsule will simply not leave the ground and your astronauts won't make it to the Moon, independently on the accountants opinion on the matter.
All of those things are important.
High thrust to weight ratio is important for a rocket. The higher your TWR the less gravity loses your rocket suffers.
There is a reason most rockets main liftoff comes from lowers ISP RP-1 engines or solids rocket. High ISP hydrogen engines just result in losses.
SpaceX Raptor actually deliberately reduced its ISP to increase its thrust.
Also I think what they meant is that the engine's thrust dictates the height above it that it can lift. So lots of larger low thrust engines = short and stubby rocket, which adds all sorts of limitations (construction, transportation, aerodynamics).
When it comes to mass production, 3d printing isn't that problematic, as you can just have several printers.
> 3d printing isn't that problematic, as you can just have several printers.
The faster you want to manufacture the more printers you need. Its ok for most engine plant but for SpaceX Raptor manufacturing line, it would be challenging.
SpaceX does use 3d printing in Raptor in some form. Although it might just be for one off parts for prototyping before changing the production line.
(But that is of course hard, to get the same results)
We know that SpaceX has its own material science team developing its own alloys specifically for their use case. This material doesn't seem to be designed for 3D printing (as far as we know).
What if SpaceX had instead invested that money in superior material for 3D printing instead?
Maybe somebody who is doing their PhD on material science in rocketry can comment.
I would also consider that engine likely has other places that would be more likely to put a limiting factor on durability so maybe it doesn't matter so much.
It's a methalox/methane-oxygen engine, like SpaceX's Raptor, as opposed to RP-1 kerosene, like Merlin. One nice aspect of this is that methalox doesn't deposit so much soot on the inside of the engine, so reuse should be simpler (this is one of the reasons for SpaceX's newer Raptor engines also using methalox).
It's got an open gas generator cycle, which means that it's likely less efficient than SpaceX's full-flow staged combustion Raptors, since it means it loses a few percent of its fuel to just running the turbopumps and the exhaust spitting off the side, rather than than heading down into the combustion chamber.
It sounds like it's much cheaper to build vs. their last generation of engine, but we'll see how it ends up in practice.
Getting something like this working is impressive, but who knows if it will end up being competitive, SpaceX is still iterating really quickly. Not an expert, but the design feels a little dated already, in comparison in comparison to Raptor, and Raptor is already flying.
Typo there :)
It's not "never been done before" impressive, they're a few years behind e.g. SpaceX's Raptor engine, which uses the same propellants, and is also reusable. But still, a new rocket engine is no small feat - the engine is probably the hardest part of a rocket. This is quite literally rocket science.
By 2019, they'd tested their full size Raptor at 1.5 meganewtons (172Tf) of thrust.[3] The current production version of Raptor produces 2 meganewtons (225Tf)[4]. SpaceX has successfully tested a newer version of Raptor that produced 2.4MN (269Tf) for 45 seconds.[5]
1. https://twitter.com/elonmusk/status/780275236922994688
2. "With a thrust of 1MN (225klbf) at sea level, this was to be the first methane full flow engine to ever reach a test stand." https://www.nasaspaceflight.com/2016/10/its-propulsion-evolu...
3. https://twitter.com/elonmusk/status/1093424663269523456