Some of the most important parts of any launch vehicle are its engines. Both its efficiency and power among other factors can have a massive influence on a rocket’s payload capability, production time, and even reuse properties. For a while now we have been receiving the occasional update on the next generation of Raptor engines powering Starship.
Earlier today however Musk shared some significant information on both upcoming production and the removal of heat shields and fire suppression in Super Heavy thanks to engine upgrades. Here I will go more in-depth into why Raptor 3 is such a big deal, some of the various improvements, the engine’s timeline, and more.
No More Heat Shield
Over time the Raptor engines have progressed from what was described by Musk as a Christmas tree of plumbing and components to both a cleaner and more capable Raptor 2. Despite the success of this engine so far, SpaceX is not done upgrading it yet. This morning Elon replied to a tweet talking about the impressive number of Raptor engines currently in production and being built. Here he was quoted saying, “We could build a lot more, but the next version of Raptor is really the one to scale up production. We begin testing it in McGregor within a week or so. Regenerative cooling and secondary flow paths have been made integral to the whole engine, thus no heat shield is required. Nothing quite like this has ever been done before. Taking away the engine heat shields also removes the need for 10+ tons of fire suppression behind the engine heat shield, as any gas leaks simply enter the already super-heated plasma surrounding the engines, rendering the leaks irrelevant. Raptor 3 also has higher thrust and Isp” he said.
There is quite a lot to unpack in just this one statement. For one he mentioned that testing of the new engine is set to officially begin within the next week or so. Here we can expect some consistent firings at McGregor as they start putting these new engines to the test. Its worth noting that around this time last year, SpaceX was conducting some of the first Raptor V3 fires ever. For example in May 2023, Musk tweeted saying, “Raptor V3 just achieved 350 bar chamber pressure (269 tons of thrust). Congrats to the SpaceX propulsion team! Starship Super Heavy Booster has 33 Raptors, so total thrust of 8877 tons or 19.5 million pounds.” This also included a graph of the chamber pressure relative to the time. While this test did occur around 1 year ago, it had very different goals from upcoming testing, not to mention it was basically an experimental Raptor V3. For example, at the time Musk mentioned, “Yeah. To be frank, we did not expect the engine to survive a full duration run at that pressure. It is uncharted territory” he said. Now after a year of time they have a much more developed engine and are preparing to mass-produce it.
This also brings up his comment about being able to build a lot more but waiting for Raptor 3 to be ready. In other words, they are hesitant to significantly increase Raptor 2 production when they know a much better engine variant is right around the corner. The plan would then be to start pumping out Raptor 3s at a rapid and consistent pace.
Focusing back on this morning’s comment, he also talked about the removal of the heat shield which also removes the need for 10+ tons of fire suppression behind the engine. Months ago when it was originally mentioned that these engines wouldn’t require a heat shield, some estimated that would help remove at least a tone or two of mass. This 10+ figure from Musk helps put in perspective the importance of these upgrades. Currently, the combustion chamber and the bell nozzle are already regen-cooled. With this new Raptor, they have found a way to continue that pattern for practically the rest of the engine. Keeping it cool and making an entire heat shield and fire suppression system not necessary.
So far all of the integrated flight tests that have occurred have used the Raptor 2 engine. From the first flight to the fourth, there has been consistent improvement both with engine performance and the vehicle itself. Even still, we are seeing the occasional engine issue such as an early shutdown around liftoff or during the Booster’s landing burn. More time and testing along with a new upgraded engine should help SpaceX solve any of these issues. It will be interesting to see what Raptor V3 looks like on a full-flight test. Fortunately, we should expect to see this testing begin in only a few weeks if not days based on this morning’s comment from Musk. Something to look forward to in the near future.
Improving Raptor
Raptor V3 has some ambitious goals regarding power and propulsion. Looking more closely at a chart provided by SpaceX, you can see the difference between Raptor V1, 2, and 3. Raptor’s thrust first went from 185tf to 230tf and the next goal is 280. That power increase would help facilitate an even bigger Starship variant and increased payload capacity. In theory, Starship 3, which is quite a bit taller than Starship 2, would be able to place more than 200 metric tons into orbit in a fully reusable mode.
The unique scenario SpaceX is in related to engine production also needs to be mentioned. Around 1 year ago Musk was quoted saying, we even “Slowed down Raptor engine production “because we’ve got more Raptors than we know what to do with.” This helps put in perspective the amount of work going into this hardware.
As for design, on Raptor V1 you can see a labyrinth of plumbing and parts surrounding the entire engine in a very complex design. Musk mentioned that V1 looks kinda like a “Christmas tree, spaghetti pile”, “while V2 is greatly simplified, while also increasing thrust at the same time.” In this side-by-side comparison, it becomes very clear the major improvements made. This simplification not only improves the efficiency of the engine, but also helps SpaceX with the cost and time to produce Raptor V2. Elon even pointed out that V2 costs about half as much as V1 even though it’s much more powerful. V3 manages to continue this pattern with an even simpler-looking engine.
By early 2016, SpaceX had constructed a new engine test stand at their McGregor test site in central Texas for Raptor testing. In 2021 SpaceX announced that they would be building a second production facility for Raptor engines, this one in south Texas near the existing rocket engine test facility. At the time it was reported in that SpaceX would “break ground soon” and that the facility will concentrate on the serial production of Raptor 2, while the California facility will produce Raptor Vacuum and new/experimental Raptor designs. In 2019 the (marginal) cost of the engine was stated to be approaching $1 million. SpaceX plans to mass-produce up to 500 Raptor engines per year, each costing less than $250,000.
Moving on to late 2021, SpaceX said that scaling Raptor production to support the frequent Starship test program planned for 2022 was “currently the biggest constraint on how many vehicles they could make” and that failing to achieve a flight rate of at least once every two weeks by late 2022 would open up the possibility of bankruptcy for SpaceX. The reason given was that Starship’s orbital launch capability is necessary to deliver the next-generation Starlink satellites needed to operationalize the massively capital-intensive Starlink broadband internet constellation. They since have begun making quite a bit of progress.
Not only are these new Raptor engines crucial for the first stage of Starship but also the upper stage. Right now the Starship upper stage features 3 Sea Level Raptor engines and 3 Vacuum optimized Raptor engines. Raptor Vacuum (RVac) is a similar design to the Raptor engine, but features a larger exhaust section and a larger expansion nozzle to maximize the engine’s efficiency in space. Specifically, Raptor Vacuum (RVac) is a variant of Raptor with an extended, regeneratively-cooled nozzle for higher specific impulse in the vacuum of space.
In terms of design, the Raptor engine is powered by subcooled liquid methane, and subcooled liquid oxygen in a full-flow staged combustion cycle. This is a departure from the simpler “open-cycle” gas generator system and LOX/kerosene propellants that the current Merlin engines use. Also, the RS-25 engines (which were first used on the Space Shuttle) use a simpler form of a staged combustion cycle, as do several Russian rocket engines, including the RD-180 and the RD-191. The Raptor engine is designed for the use of deep cryogenic propellants—fluids cooled to near their freezing points, rather than using the cryo-propellants at their boiling points as it is more typical for cryogenic rocket engines. The use of subcooled propellants increases propellant density to allow more propellant mass to be stored within the vehicle’s tanks. Engine performance is also increased with subcooled propellants. Specific impulse is increased, and the risk of cavitation at inputs to the turbopumps is reduced due to the higher propellant fuel mass flow rate per unit of power generated. All of which important factors in this new engine’s performance and future. If SpaceX can complete Raptor V3 testing with promising results, a ramp-up in production could be right around the corner. From there the actual use of these engines on future Starship variants would begin.
Conclusion
This morning Elon revealed some new information about the next generation of Raptor engines. Specifically, V3 is going to remove the need for a heat shield and with it, over 10 tons of fire suppression. They also arent even manufacturing the current Raptor engine as fast as they could because they know it won’t be necessary once V3 is up and running. We will have to wait and see how it progresses and the impact it has on the space industry.