Ripley HotfireRipley Hotfire

American Rocket Propulsion Leader Ursa Major Completes Hotfire Test Campaign of 50,000-Pound Thrust “Ripley” Engine

|Press Release

Ripley is the Highest-Performing American Kerosene Engine Ever Built

DENVER – March 9, 2023 - Ursa Major, America's leading privately funded company focused solely on rocket propulsion, today announced a milestone in the development of its redesigned “Ripley” rocket engine: successful hotfire tests. The test campaign showed the integrated Ripley engine—including turbomachinery, oxidizer-rich preburner, and additive-manufactured copper thrust chamber assembly—firing as a complete system in flight-like conditions.

Ripley has the highest “Specific Impulse,” or Isp, a measurement of fuel economy, of any American kerosene rocket engine in history. 

“This hotfire test campaign is a critical milestone for Ripley as we move into full-scale development and production,” said Brad Appel, Chief Technology Officer at Ursa Major. “The new 50,000-pound-thrust design is in response to growing market demand for this medium-lift thrust class.”

Customers using Ripley will save years of time and millions of dollars while benefitting from best-in-class performance and reliability. 

The first iteration of the Ripley engine hotfired in 2021 with 35,000 pounds of thrust. Ursa Major increased the thrust to 50,000 pounds to better suit medium-class launch vehicles.  

Ursa Major tests its engines at its one-of-a-kind facility in Berthoud, Colorado, which houses engine design, manufacturing, and testing all in one place. To date, Ursa Major engines have accumulated more than 60,000 seconds of run-time. 

Unlike other propulsion systems, Ursa Major engines are designed to be used on multiple vehicles and for various use cases, creating efficiencies that help customers get to launch faster without relying on foreign-made technology or incurring the high cost of building engines in-house. 

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About Ursa Major 

Ursa Major is America's leading privately funded company focusing solely on rocket propulsion, bringing high-performance, staged combustion engines to market for space launch and hypersonic applications. Ursa Major customers, ranging from "New Space" startups to enterprise-level aerospace leaders and the U.S. government, get to flight faster, more reliably, and cost-effectively. The company employs the most sought-after engineers from top space programs and universities. Headquartered in Berthoud, Colorado, Ursa Major was named one of the best places to work by Built in Colorado three years in a row. For more information, visit For downloadable images and videos, visit

Media Contact
Perch Partners for Ursa Major

A fully assembled Ripley engine on the test stand.
A fully assembled Ripley engine on the test stand.
US Air Force Expands Hypersonic Arsenal With Ursa Major Pick
US Air Force Expands Hypersonic Arsenal With Ursa Major Pick


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