Mojave Sphinx is a high-power amateur rocket with a liquid bipropellant propulsion system powered by nitrous oxide and any number of solvent or hydrocarbon fuels. It is designed to be as simple and economical as possible so that an individual or team with high-power or experimental rocketry experience can build and launch it within a reasonable timeline and budget.
Mojave Sphinx is a design optimized for low cost and high cadence. All parts and materials can be purchased for an amount well within most university teams’ budgets, and fabrication requires only a modest amount of machining which can be accomplished in a few days if divided among multiple team members.
Essentially, Mojave Sphinx was sized so that an individual or small team can build a liquid propulsion system cheaply, learn basic machine work, and come away with a large, unique-looking rocket that is fun to launch.
Diameter: 4 in.
Length: 96 in.
Oxidizer: Nitrous Oxide
Fuel: Alcohol
Mixture Ratio: 2.1
Apogee: 5,000-10,000 ft
Thrust: 250 lbf
Impulse: 5000 Ns
Burn Time: 5 s
Cost (in-house machining):
Rocket: $1130
Consumables: $184 (3 Launches)
GSE: $529
Machine time: 15-20 hours
This guidebook covers:
Background and fundamentals of Half Cat Rocketry's propulsion architecture, standards, and safety
Design, analysis, test history, parts list, and assembly instructions of Mojave Sphinx
Design, parts list, and assembly instructions for ground support equipment
Preparation, launch, and recovery procedures
Design and manufacturing reference materials
This publication is intended to be a practical guide to building an amateur liquid bipropellant rocket which can be launched repeatedly and reliably.
The guidebook is available for purchase so that teams can have a physical copy to reference. We do not make any money from this service, it is provided purely for the benefit of those who wish to have one.
All files needed for Mojave Sphinx are available for download through our official Google Drive repository. Half Cat Rocketry provides the following:
Build, Integration and Launch Guidebook - HCR-5100 (PDF)
SolidWorks CAD files (.sldprt)
SolidWorks drawing files (.slddrw)
Drawing package (PDF)
3D models of machined, printed, and flat-cut components (.step and .stl)
Vector files of flat-cut components (.dxf)
HalfCatSim v1.3.8 motor simulation (.xlsx)
Sample thrust curve file (.eng)
OpenRocket simulation file (.ork)
Please note that the SolidWorks CAD was created in the version 2022 student edition and is for educational purposes. All files will eventually move to GitHub for version and release control.
Half Cat Rocketry is not liable for the usage of this content, and the authors bear no responsibility for the usage of its content. Read the README and License files before viewing or downloading.
Mojave Sphinx is not one specific rocket but a design of liquid rocket, to be replicated and modified. Although the first vehicle bears the name of the design, readers are encouraged to give their builds fun or unique names (and paint jobs). Half Cat Rocketry maintains a list of constructed Mojave Sphinx rockets, each assigned a serial number. To avoid a 'Ship of Theseus' situation – where all parts are gradually replaced over time until nothing original is left – the serial number is attached to the propellant tank casing tube, the single largest and most costly component.
Teams may submit a build form to register their serial number, and are encouraged to mark or engrave it on the tank casing. (This tool or similar is recommended)
Owner: Half Cat Rocketry
Status: Retired
Mojave Sphinx was the first of its kind, and HCR-5100 was written based on its design. The name is derived from a cat species and the landscape in which this rocket typically resides.
This rocket was retired after 38 firings (19 launches / 19 static tests), making it perhaps the most heavily used amateur liquid rocket up to that point.
Owner: Half Cat Rocketry
Status: Destroyed
Half Cat Walking II was built as a test of HCR-5100's assembly procedures. It is named in homage to Half Cat Rocketry's first liquid rocket.
On 07 September 2024, SN02 made its third launch, stacked with SN01's heavily used airframe and recovery system. As a result of overuse and suboptimal recovery packing, the shock cord broke and the propulsion system was destroyed on impact.
Owner: Wildcat Rocket Engineering Club
Status: Active
Sonoran Wildcat is a build in progress by students at the University of Arizona. It is named for the local desert and the school's mascot, which is itself named for local species of cats.
Owner: Half Cat Rocketry
Status: Active
Schmuserkadser was built for demonstration at Tripoli Rocketry's BALLS 32 event, where it performed one static fire and multiple launches. It is named after the Sad Cat meme, paying tribute to the untimely loss of SN02.
Status: Active
Sinnoh Sphinx+ is an upgraded build of Mojave Sphinx using a fiberglass airframe, anodized aluminum parts. and other "premium" components.
