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MOJAVE SPHINX: AN OPEN-SOURCE LIQUID-FUEL ROCKET

A fully open amateur liquid-bipropellant rocket with a free build guidebook — schools and university teams are actually launching it.

by Half Cat Rocketry

FULL CAD BOM FIRMWARE DOCS

RocketryAerospace

Built with3D printing

difficulty
●●●●●
time
a serious project
license
GPL-3.0
repo
repo ACTIVE27 stars

WHAT YOU’LL NEED

Videos
1
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COMPAREE VERDICT

We're presenting this one with real caution: Mojave Sphinx is a genuine open-source amateur liquid-bipropellant rocket, published by Half Cat Rocketry with a free, complete build-and-launch guidebook. The engineering openness is remarkable — SolidWorks CAD, STEP and STL, flat-cut DXF parts, a BOM, OpenRocket simulations, and 22 registered builds by Half Cat, university clubs, a high-school club and individual builders. But this is not a maker weekend: it uses a nitrous-oxide oxidizer and alcohol fuel under pressure, produces serious thrust, and Half Cat lists an apogee of 5,000–10,000 ft. It demands a proper launch range, the right permits and permissions, experienced mentorship, and strict safety procedure — Half Cat is explicit that you build and fly at your own risk. Admire it, learn from the guidebook, and only pursue it within an experienced, authorized rocketry context.

GOOD TO KNOW

  • —Full open-hardware package: SolidWorks CAD, STEP + STL, DXF flat-cut parts, OpenRocket simulation and a complete PDF guidebook
  • —Licensed GPL-3.0, with an added requirement to credit Half Cat Rocketry in anything you publish based on it
  • —Serious hazards: nitrous-oxide oxidizer and fuel under pressure, high thrust — this is advanced amateur rocketry
  • —22 registered builds so far — by Half Cat itself, university rocketry clubs, a high-school club and individual builders

Parts to buy

4 items

From our check of the build. Exact quantities and part numbers are in the creator’s BOM.

  • Airframe materialsFind
  • TanksFind
  • PlumbingFind
  • Oxidizer/fuel system per the guidebookFind

BUILDS OF THE WEEK

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Can I build this?

Printsome 3D-printed and flat-cut (DXF) parts; the CAD is SolidWorks + STEP/STL
Buyairframe materials, tanks, plumbing, an oxidizer/fuel system per the guidebook
Toolsmachining, careful plumbing, pressure-system experience
Skillsadvanced amateur rocketry, propulsion, high-pressure safety
Timea serious multi-week project plus range time
Costband $$ — per Half Cat: about 1,130 dollars for the rocket, 529 dollars for ground support equipment, 184 dollars of consumables for three launches (in-house machining)
SafetyHIGH: nitrous-oxide oxidizer + fuel under pressure, high thrust, thousands of feet apogee — requires a proper range, permits and experienced supervision

Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.

Videos

Half Cat Flies Mojave Sphinx liquid rocket at FAR

Launch footage: Half Cat flies Mojave Sphinx at the Friends of Amateur Rocketry (FAR) site, filmed by Rocket Vlogs. The free HCR-5100 guidebook remains the primary build reference.

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Gallery

Mojave Sphinx on the rangeHalf Cat Rocketry
The rocketHalf Cat Rocketry
The build-and-launch guidebook coverHalf Cat Rocketry

Start here

Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.

  1. 1.Read the project page (overview and the free guidebook)
  2. 2.Study the guidebook first (HCR-5100 build/integration/launch — read fully before anything)
  3. 3.Review the CAD and simulations (SolidWorks, STEP/STL, OpenRocket)
  4. 4.Find an experienced, authorized range (never launch without supervision and permits)

Resources

Documentation, files and community threads for this build — we link straight to the original sources and never rehost the creator’s files.

KNOWN ISSUES

  • This is advanced amateur rocketry — nitrous-oxide oxidizer and fuel under pressure, high thrust; it demands experience, permits and a proper range
  • Half Cat explicitly disclaims liability — you build and fly at your own risk
  • There is no official build video series — the free guidebook is the real reference, though you can watch launches filmed at FAR and by registered build teams.
  • Not a project to attempt solo or without experienced mentorship

Is this really a liquid-fuel rocket you can build?

Yes — it's a genuine open-source amateur liquid-bipropellant rocket with a complete free guidebook, and 22 builds are registered, including university clubs and a high-school club. But it requires high-power or experimental rocketry experience and authorization.

Why is it flagged so heavily?

It uses a nitrous-oxide oxidizer and fuel under pressure and produces high thrust, reaching thousands of feet. That's real hazard territory needing a proper range, permits and supervision.

What's actually published?

A full open-hardware package: SolidWorks CAD, STEP/STL, flat-cut DXF parts, OpenRocket simulations and the HCR-5100 guidebook, under GPL-3.0.

What does it cost?

Band $$ — Half Cat lists about 1,130 dollars for the rocket, 529 dollars for ground support equipment and 184 dollars of consumables for three launches, assuming you do the machining in-house.

Community builds

No community builds yet — be the first, we feature the best ones.

Discussion1

FROM THE COMPAREE TEAM

More than 22 registered teams — including schools — are building this liquid-bipropellant rocket from a free guidebook. Is open-sourcing a nitrous-fed engine a great equalizer or a liability nightmare?

CompareeTEAM2mo agoedited

Correction (4 October 2026): we re-checked this page line by line against the project's own repository, documentation and videos, and fixed errors in earlier versions.

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Half Cat Rocketry

Published a complete open-source amateur liquid rocket with a free build-and-launch guidebook, aiming to make liquid rocketry approachable for experienced, safety-minded teams — and schools are building it.

GitHub Web

Star the project on GitHub

DISCLAIMER

  • Comparee is not the author of the projects featured here. All rights to each project belong to its creator — every page links to the original source, and we never host creators’ files.
  • Information is provided without warranty and may become outdated as projects evolve. Prices are indicative bands only — always check the creator’s parts list for current costs.
  • Building and operating any project is at your own responsibility. Protective equipment, safe workshop practice and compliance with local regulations are the builder’s responsibility.
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