When NASA was looking to go back to the moon, it did look at resurrecting the Saturn V rocket, after all, it had delivered men to the moon from 1969 to 1972 with no failures of the rocket itself, barring apollo 13 which was a failure of an oxygen tank in the command service module.
But to do that, both NASA and the contractors who built it would have had to go back to decades-old technology and working methods using highly skilled engineers all of whom are either retired or no longer here.
I did a video 5 years ago looking at why we could not re-make the F1 engine today but in those 5 years additive manufacturing has come on in leaps and bounds and now represents an alternative future of not only rocket engine design and manufacture but also of the whole rocket itself.
So let’s see if NASA could re-make a new modern F-1 engine today.
The Rocketdyne F-1 engine was a miracle of engineering which made it not only the most powerful single-chamber engine ever built but also one of the most reliable with no major failures on all of its flights to the moon and later to place Skylab, the first US space station into orbit.
Each F-1 was more powerful than the combined output of 3 space shuttle main engines but making the F-1 was a major undertaking with each one hand built with no two exactly the same as improvements from mission to mission took place.
Back in the day manufacturing techniques included the machining of thousands of parts which made up each engine and the assembly by bolting, welding, and brazing.
To give one example would be the regenerative cooling of the thrust chamber. The most obvious thing about the F-1 engine was the large bell-shaped nozzle which accelerates the hot exhaust to produce thrust.
There are two parts to the nozzle, the upper part or thrust chamber and the lower nozzle extension. The problem was that the burned gases were up to 3,200 °C, easily enough to melt the metal of the nozzle. The solution was to cool the upper thrust chamber with some of the RP-1 kerosene fuel before it was mixed and burned with the liquid oxygen.
This was done by making the thrust chamber out of 178 primary down tubes, each then split into two parallel tubes and 178 alternate up tubes. These were brazed together in the shape of the nozzle and held in place by a series of lateral bands which gave the nozzle its strength. The tubes themselves were heavily jacketed to give some direct protection from the hot gas inside the thrust chamber.
Approximately 70% of the RP-1 fuel was diverted into the down tubes before returning in the up tubes and into the manifold to be sent to the injector plate to be burned.
A separate gas generator drove a turbine at 5500 rpm producing 55,000 hp or 41MW which drove both the fuel and liquid oxygen pumps. The fuel pump delivered 976 litres of RP-1 per second, of which about 680 litres per second were pumped through the tubing that made up the thrust chamber walls. This was enough to keep the metal from melting.
The material the tubes were made from was Inconel X-750, a high-temperature, heat-treatable, nickel base alloy. But because it was made from nickel it wasn’t very ductile and it was difficult to work.
Now this is where a huge amount of skill and metal working knowledge had to come in. With all these separate tubes, joins, and supporting bands, the F-1 had over 900 meters or 3,000 feet of joints between the tubes that had to be brazed together and everyone had to be inspected to make sure there were no leaks or bad joins.
This very complex build operation was repeated for each engine making them both slow to produce and very expensive, and this is just one part of the F-1 engine.
The way they were built was a product of the times and the technology available, since then there have been major changes in not only engine design but the build techniques and materials used, all of which required different skills to that used on the F-1.
One particular technology that wasn’t even thought of in the late 1960s was 3D printing, yes the same thing that we can now do in our home with a few hundred dollar 3D printer, to make almost any small shaped object out of tiny layers of extruded molten plastic.
3D printing takes a virtual computer-generated object and then digitally slices it into very thin layers which are “printed” layer by layer to build up the complete computer-generated object in real life.
This is almost the polar opposite of conventional manufacturing where you start off with a block of raw material like steel for example, then process it in various ways to shape it, drill it and mill it into a new component, building up complex machines and shapes from smaller simple ones. Even casting into a mold still requires machine work to produce a finished item and is only suitable for certain components.
It was in 1981 when Dr. Hideo Kodama invented one of the first rapid prototyping machines that created parts layer by layer, using a resin that could be polymerized by UV light.
In 1988, Carl Deckard, a student at the University of Texas, licensed selective laser sintering (SLS) technology – another type of 3D printing that uses a laser to sinter powdered material like metals into solid structures.
Since then there have been many advances in this technology which offers ways to make components out of metal that would be impossible to do with traditional machine work.
One such of these is the thrust chamber of a rocket. Instead of all the tubes and bands associated metalwork we saw in the F-1, a far better thrust chamber could be made in one piece, built up layer by layer with all the cooling channels fabricated within the nozzle walls and with the optimum flow requirements built in. This could be made in a fraction of the time and with much less material than it would take by traditional methods.
Almost anything can be made in this way using a variety of metals like 316 stainless steel, Inconel, titanium, and other alloys and now dual metal prints can be done in one process.
In 2015, NASA successfully tested a 3D printed version of the gas generator that powered the fuel and LOX pumps used in F-1 engine and continues to compare the strengths and weaknesses of additive manufacturing to that of traditional forging and welding.
One company that has taken the lead in metal 3D printing is Relativity Space. This was co-founded by Ex Blue Origin engineer Tim Ellis who started Blue Origins 3D metal printing division.
Relativity Space’s goal is to build not only 3D metal-printed rocket engines but the entire rocket body itself.
Even though the company is only 7 years old it has already launched the world’s first 3D-printed rocket into space, the Terran 1.
The company has also worked with NASA to help produce the copper alloy GRCop-42 or Glenn Research Copper-42 for use in combustion chambers of high-performance rocket engines.
The GRCop family of alloys was developed by Dr. David Ellis when he was a NASA-supported graduate student during the space shuttle era.
At the time, the Space Shuttle Main Engine combustion chamber liners were typically replaced after one to five missions, but with the use of the then GRCop-84 this could be easily increased to 100 missions between maintenance services and 500 missions of engine life.
GRCop is a combination of copper, chromium, and niobium and is optimized for high strength, high thermal conductivity, high creep resistance and will tolerate temperatures up to 40% higher than traditional copper alloys. GRCop was used to 3D print the Aeon 1 engines which powered the Terran 1.
GRCop pairs well with the Laser Powder Directed Energy Deposition, a method of additive manufacturing. Here a Laser creates a melt pool and the powdered GRCop is blown into the melt pool creating a solid material.
A robot produces the 3D motion to direct the building process to create the entire part with the laser and blown powder. This is just one of a variety of additive manufacturing methods used today but it allows much larger parts to be produced but with fewer fine details.
Relativity Space has also created the world’s largest 3D metal printer called the Stargate which is used to make the main rocket body. Using existing wire welding technology, it builds up the structure including the fuel tanks out of aluminum which virtually eliminates welding and fixings and only requires minimal machining for the joint flanges.
This advanced technique even makes the shape slightly wrong to allow for the pressure of the fuel inside to correct it at launch. This allows the thickness of the walls of the rocket to be thinner in comparison to that of a can of coke and makes the whole rocket lighter and stronger which uses less fuel or carries a bigger payload.
Relativity Space says that they can make a complete rocket from raw materials in just 60 days, allowing the same fast fail prototyping method as used by SpaceX to greatly speed up development, namely make it, break it, then make it better.
The main aim of the Terran 1 launch was to prove the viability of additive-manufactured structural parts on a real launch which made up 90% of the vehicle by mass.
The Terran 1 which was 35 meters tall by 2.3 meters wide used 9 Aeon 1 rocket engines and was launched on the 23rd March 2023.
Although it passed max-Q successfully, that’s the point where the maximum stress on the rocket’s structure occurs, the second stage failed to ignite due to a slower than expected valve opening and vapor getting into the LOX turbopump causing the mission to fail before it could get to orbit.
Relativity Space has subsequently dropped development of the Terran 1 in favour of the Terran R, a much larger and partially reusable rocket and the much larger Aeon R engine, again both 3D printed.
Ellis has said that is to be a Falcon 9-sized 3D printed rocket with aims to launch an even larger payload due to the efficiencies gained by the additive manufacturing process.
So what about Aerojet Rocketdyne making a modern-day 3D-printed F-1, with all the advantages that have been learned over the past 50+ years?
Well, if you had asked that question 10 years ago it would probably have been a no, but with the rapid progress of additive manufacturing and companies like Relativity Space and materials like GRCop-24, it seems now far easier to accomplish.
Whether such a large rocket engine would be used compared to the Starship method of lots of smaller engines is another matter and although it would be nothing like the original F-1, its 3D-printed spiritual successor, should it be built, could well go on to do for future space missions that the F-1 did for the moon missions.