While there’s been a number of cars launched into space – a couple human-driven ones on the moon, a bunch of robotic ones on Mars, for example – no internal-combustion piston engine has ever left Earth. That makes sense since, you know, they don’t work outside the atmosphere. Until now. Currently in development is the first ICE designed to go into space, and it’s an old-school straight-6, built by people who make NASCAR engines.
Those people building the engine are the team at Roush Fenway Racing, and they’re building the engine as part of United Launch Alliance’s Integrated Vehicle Fluids (IVF) program. IVF is a very clever concept that would take a given rocket stage’s multiple fluids and systems and reduce them down so that just hydrogen and oxygen are needed.
Currently, rockets use a combination of heavy batteries and solar cells for electrical power, hydrazine for attitude control and tank settling thrusters, and helium for tank pressurization. It’s a lot of complex, separate systems that take up a lot of weight—often around 15-20% of total spacecraft mass. That’s a lot.
What IVF hopes to do in ULA’s Vulcan rocket upper stage is to eliminate the complexity and mass of the current way of doing things by limiting fluids to liquid hydrogen and oxygen, and using an internal combustion engine—like the ones used in cars for over a century—to provide electrical power, heat for vaporizing fluids to act as pressurants, and settling thrust from exhaust, all for much less weight than batteries and multiple fluid storage tanks.
Plus, the best part of all is that running the combustion engine is essentially free: the engine runs off the hydrogen and oxygen that normally is lost to boil-off, anyway. In fact, the flow rate of hydrogen through the engine is less than the boil-off rate of the hydrogen, meaning all the fuel would have just been wasted, anyway.
In addition to saving weight, the IVF program also accomplishes a few more very important things that have to do with how upper-stage rockets can be used beyond just the job of getting our asses (and our robot’s assed) off the Earth.
Once in space, an IVF rocket stage has a much, much longer operational lifespan (up to 10x conventional designs!) than a conventional rocket with hydrazine, helium, and batteries. Plus, by limiting the necessary fluids the rocket needs to just hydrogen and oxygen, in-space refueling becomes much easier, meaning IVF rocket stages, running those straight-6 engines, can be used for long-term in-space missions that require a lot more moving around.
That means exciting things like asteroid mining and other missions that require a lot of what space geeks call ‘delta-v,’ which is roughly translated as “moving around.”
We’re a car site primarily, so let’s take a deeper look at this fascinating engine. It’s probably the smallest (600cc) and least powerful (about 26 HP) engine that Roush has ever built, but I’d argue it’s among the most fascinating.
What makes it especially interesting is the conceptual contrast of the engine’s technology: it’s built to aerospace tolerances, with cutting-edge materials and methods, but fundamentally it’s a really old-school flathead inline-6 design. It’s essentially the astronaut version of an old flathead inline-6 like you’d have found in an early ‘60s Rambler.
Here’s how the United Launch Alliance explains their use of such an archaic-seeming engine:
The “retro” design of the I6 is reminiscent of a classic Ford flathead V-8 design of the 1930s. These engines, while being incredibly tough, had a reputation for requiring oversized radiators since exhaust gas passages were close to block cooling passages and more heat than typical was transferred to the coolant. This heat rejection feature is much desired in the IVF engine since we wish to scavenge heat for tank pressurization. This allows us to eliminate the extraction of heat from the thrusters, a feature of earlier IVF designs, and keep all heat exchange functions within the engine. The engine head, which bridges the length of the engine, contains the heat exchange surfaces for rejecting heat to incoming hydrogen combustion gas, as well as vaporizing both liquid hydrogen and oxygen for tank pressurization.
Initially, they were experimenting with air-cooled Wankel engines for this job. While those sound very cool and I’d love to stick one in an old Beetle, in the case of IVF applications, the production of more waste heat was actually a benefit, since that heat was going to be used. Hence the old-school straight-6.
As much as possible, they’re even trying to use off-the-shelf components in the engine. For example, the ignition system uses coilpacks from a regular old GM 5.3L V8, just like they use on their pickups. You could buy them at Pep Boys or wherever. Same goes for the piston rods and spark plugs: they’re just regular, off-the-shelf units.
Here’s more about the engine, from the same report:
The key engine requirement was to have a robust and simple design that would maximize use of commercial experience and off-the-shelf hardware. The design team traded high-performance configurations like the air-cooled Wankel, and decided that a liquid-cooled Inline 6 (I6) cylinder engine offered the best combination of weight, operating robustness, performance, heat rejection, redundancy and low vibration. Compared to the Wankel, it offered a well characterized lubrication system and had large areas for extracting waste heat via standard liquid cooling. Waste heat is used in IVF for propellant vaporization; the more available, the more robust the overall system design.
The multi-cylinder design also offered operational robustness since one or more cylinders could be disabled and the engine would continue to run. Because of the overlap of intake strokes in an I-6, the flow of gases through the intake system is more regular and can be more easily modulated with simple devices. This eases mixture ratio control and simplifies the electronic control system. Similarly, the power delivery is very smooth with minimal variation in output torque over 720°of crankshaft rotation. This meant that time-consistent power could be directed to pumps and generators. It also allowed the elimination of a heavy engine flywheel since the generator and other rotating devices were sufficient. The larger displacement allowed elevated power delivery even at moderate RPMs and also provided large margins to address any future loads or desired growth.
The basic design of the Generation 1 development engine is shown in Fig. 4 and Fig. 5. The IVF ICE only displaces 600cc with a compression ratio of 6.5 and a redline of 8000 RPM. Renderings and photographs of the engine are consistently misleading – the engine is amazingly small, at less than 700mm long, despite no effort to remove excess material. No effort was applied to shed mass from the Generation 1 engine but it is likely it will weigh less than 50kg in flight configuration.
Everything about this project seems exciting to me. They’re adapting an old-school combustion engine design for use in space, first off, (is this the first time an ICE has been developed with a pressurized, contained oxygen supply?) and that engine is running off waste gases. The result gives more stamina, for less weight, and a much longer design life for these potential in-space rocket tugs.
I’m not sure I’ve ever encountered such a technological win-win situation that didn’t involve a hidden perpetual motion machine in the design somewhere.
The first launch of a Vulcan rocket with this stage is still a couple years away. I’ll see if I can arrange a press drive on it, but I’m not holding my breath. Also, there is no breath up there, I’m told.