Skybreaker Rocket Engine

After discovering techniques to make ablative rocket engine combustion chambers, I decided I would make the largest possible amateur liquid rocket engine, and I was going to do it correctly. So now armed with calculus and a whole vault of things I learned from the first engine, I began a from-scratch design of a 25kN 5600lbf methalox rocket engine called Skybreaker. Some preliminary CFD was done on the chamber and is shown below:

Image: Skybreaker Startup CFD at 0.03 seconds, Jan 5, 2022

Extensive research of various ablative materials and composite structures led me to use a somewhat available phenolic resin called phenol resorcinol formaldehyde and 98% pure silica weave as my ablative liner. This liner will be overwrapped with an initial unidirectional 4k carbon fiber twill to handle the radial loads pushing out from chamber pressure, then another unidirectional 4k twill layer running tangentially to the chamber to take the tangential shear loads on the flange that will be woven into the chamber and act as the injector mounting point. The final layers will be a uniform 4x4 2k carbon fiber weave that will serve as a binding and cosmetic layer. These will be wrapped onto a mold release coated 3D printed mandrel split in two and bolted together to act as a single piece.

Image: Skybreaker Mandrel January 12, 2022

I designed the central chamber flange to be machined out of aluminum and be insulated from exposure to the main chamber with a layer of ablative material. The flange went through around six iterations before being made. Most of the changes to each iteration were to reduce cost and increase the bonding area.

Image: Skybreaker Final flange CAD, January 18, 2022, Skybreaker Mandrel with milled Flange for fit checks, February 18, 2022

Skybreaker layup started with laying the silica fabric down with a layer of the phenol resorcinol ablative resin. Then after that was cured with a wrap of carbon fiber around the throat, the injector flange was mounted using RTV sealant, a liquid rubber solution. Then the final step was to overwrap the chamber with carbon fiber and epoxy and then vacuum bag it to ensure quality lamination of the chamber.

Ultimately this is yet another project that would go on hold and act as a pathfinder, which taught me important things about working with ablatives that came in very useful later in another project.

Image: Skybreaker ablative layer layup, March 6, 2022, Skybreaker ablative liner with flange mount, March 7, 2022

Images: Skybreaker being vacuum laminated and the final part being freed, March 11, 2022

Image: Skybreaker Pathfinder v1 vs Asteris, March 12, 2022

GUI Overhaul

Skybreaker brings a new and improved graphical user interface I designed to enable complete control and visual of the test stand that will carry out firings of Asteris 1A SN2, Skybreaker, and future engines. It's still being developed but is coming along nicely. In this GUI, there will be visualized sensor data for every pressure transducer, thermocouple, and force sensor on the stand, along with tank level monitoring at all times. I can also run the desired feedback loops with that much sensor data to operate an engine like Skybreaker safely. One such feedback loop is continuously checking chamber pressure and ensuring it doesn't exceed a certain margin set by the test sequence file. A scaled-back P&ID diagram on the GUI lets me monitor valve states anywhere on the stand. The array of controls also lets me open or close any valve. It also has extensive data recording abilities to allow for post-test inspection of large amounts of data.

Image: Test stand GUI overhaul, February 12, 2022

Injector Design

I juggled multiple injector designs for quite some time, trying to balance performance, price, and simplicity from unlike impinging stream injectors to coaxial swirler injectors similar to Asteris 1A. I ultimately decided on a pintle injector for its moderate simplicity and ability to throttle through a hydraulic or pneumatic sleeve. This approach would also allow for a safe state of the engine called “face shut-off.” My pintle design deals with a lox-centered fixed pintle structure with a concentric fuel orifice and a piston sleeve that, with high tolerances, slides to cover the pintle orifices and seal the fuel ring. This piston is then actuated via hydraulic pressure and set to return position through a spring. The main body is designed to be milled in 3 pieces, the fuel manifold, the hydraulic head plate, and the pintle body itself.