Air Force-funded Ursa Major successfully tests Draper engine designed to power future spacecraft
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Air Force-funded Ursa Major successfully tests Draper engine designed to power future spacecraft

Colorado-based space and defense company Ursa Major has announced the first successful “hot fire” test of its Draper liquid-fuel engine. Funded by Air Force Research Labs (AFRL), Ursa Major first launched a 4,000-pound, closed-cycle engine in May 2023, with the ultimate goal of having a fully operational engine capable of operating in the atmosphere or space by the end of 2024.

According to a company statement, the successful test in May put Draper ahead of schedule and “ahead of industry standards.”

“We are excited about how quickly the development program is progressing and look forward to deploying the engine for hypersonic and space applications in the coming years,” said Brad Appel, Chief Technology Officer, Ursa Major.

Non-cryogenic fuel makes Draper ideal for hypersonic and space applications

In a company statement, the Draper engine’s creators say its ability to create a powerful thrust profile without using cryogenic fuels offers spacecraft engineers unprecedented versatility. The fuels, which don’t need to be stored at subzero temperatures, save significant space compared to liquid oxygen engines, allowing for significantly more fuel to be carried into space.

Draper's Fire TestAir Force-funded Ursa Major successfully tests Draper engine designed to power future spacecraft
Image Source: Ursa Major

“Thanks to its thrust profile, the engine is not only able to maneuver objects in orbit, but it does so without completely depleting its fuel supply, potentially enabling additional mission functions,” the company explains.

Ursa Major says this level of versatility is becoming increasingly important as adversaries develop a range of weapons platforms designed to disable or destroy U.S. space assets. As the space race progresses, the company says, “the need for defensive technologies will continue to grow.” That means engines like the Draper, which can give spacecraft multiple in-space launches before running out of fuel, will become increasingly critical to protecting those space assets.

Draper's Fire TestDraper's Fire Test
Ursa Major Test fires Ripley rocket in development. Image source: Ursa Major.

In promotional materials for the engine in development, the company notes that the Draper is an evolution of its production Hadley rocket engine. However, unlike the Hadley, which is fueled by a combination of liquid oxygen and kerosene, the Draper runs on a combination of hydrogen peroxide and kerosene. According to the company, this change means that the Draper “combines the storage attributes of a solid rocket motor with the active throttle control and throttle range of a liquid engine.” This combination, they explain, also gives the Draper “the maneuverability and flexibility that are essential for hypersonic defense.”

Air Force Research Labs Praise Engine’s Power and Versatility

While Ursa Major has several engines in development, including the 50,000 lb of Ripley thrust and the 200,000 lb of Arroway heavy-lift thrust, the non-cryogenic Draper liquid-fuel engine was specifically funded by Air Force Research Labs. This funding included the design and construction of a specialized test stand at the Ursa Major Test Facility in Berthoud, Colorado, where these test firings took place. According to the company, this specialized test stand “has enabled and will continue to enable greater testing capabilities and, as a result, faster iteration and development of the Draper engine.”


While there is no exact timeline for the Draper engine to be deployed in real-world conditions, AFRL says it is impressed with recent testing and the rapid pace of engine development over the past twelve months.

“Perhaps the most impressive aspect of this program is delivering a versatile, storable rocket engine in such an incredibly short time frame,” said Dr. Shawn Phillips, AFRL’s chief of rocket propulsion. “AFRL and industry are taking on the challenge that USAF and USSF leadership asked us to… deliver faster capabilities, create closer ties with industry, and leverage what already exists to enable asymmetric advances.”

“Fortunately, this is just the tip of the iceberg in terms of what we do as One Team,” Dr. Phillips added.

Christopher Plain is a science fiction and fantasy novelist and the lead science writer at The Debrief. Follow and connect with him on X, You can find more information about his books at or email him directly at [email protected].