DARPA’s Gambit Program: Revolutionizing Rocket Engines with Rotating Detonation Engines (RDEs)

Introduction:

Rocket engines are critical to space exploration, but they consume vast amounts of fuel and pose challenges in terms of efficiency and complexity. However, DARPA’s Gambit program, launched in August 2022, is set to change the game. It focuses on developing Rotating Detonation Engines (RDEs) that have the potential to make rockets more fuel-efficient, lightweight, and cost-effective, while also enhancing their capabilities for time-critical target strikes from fourth-generation fighters. This groundbreaking technology could pave the way for a new generation of air-to-ground missiles and long-range hypersonic weapons.

The Basics of Rocket Engines:

Rocket engines are a type of reaction engine designed to expel mass and generate thrust, propelling rockets and spacecraft into space. Thrust, measured in pounds, kilograms, or Newtons, results from the pressure exerted on the combustion chamber walls. Rockets carry their own working fluid, or propellant, which sets them apart from air-breathing engines. The term “rocket” applies when gas dynamic expansion accelerates the propellant. This is in contrast to other propulsion methods like electric thrusters that rely on body forces such as the Coulomb electrostatic force.

Fuel Efficiency: A Major Challenge:

Launching objects into space requires massive quantities of fuel. For instance, sending NASA’s Space Shuttle into orbit demanded over 3.5 million pounds of fuel, making it 15 times heavier than a blue whale. These conventional rocket engines are highly fuel-intensive and complex to manufacture, driving the need for more efficient propulsion technologies.

Enter Rotating Detonation Engines (RDEs):

DARPA’s Gambit program is focused on harnessing the potential of Rotating Detonation Engines (RDEs). RDEs represent a new class of propulsion systems that promise to revolutionize rocket engines.

Current propulsion technologies (e.g. conventional rockets, ramjets, and gas-turbine engines) have limitations in maximum range, speed, and/or affordability that hinders their ability to meet the Gambit program objectives. RDEs are more compact than conventional ramjets, which allows them to carry more fuel. Additionally, RDEs are less complex than gas turbine engines. The combination of these two factors enable RDEs to affordably meet the Gambit program objectives.

An RDE is a type of internal combustion engine that uses detonation waves to propel the engine. Detonation waves are self-sustaining supersonic shock waves that travel through a combustible mixture at a speed of up to five times the speed of sound. RDEs use a rotating detonation wave to create a continuous thrust.

Unlike conventional rocket engines, ramjets, and gas-turbine engines, RDEs offer a compact design that enables them to carry more fuel. Furthermore, RDEs are less complex than traditional gas turbine engines. The synergy of these two factors positions RDEs as a cost-effective solution that aligns with the Gambit program’s objectives.

The Gambit Program’s Objectives:

The primary aim of the Gambit program is to develop and showcase a groundbreaking Rotating Detonation Engine propulsion system. This system will facilitate the creation of mass-producible, cost-efficient, high-supersonic, long-range weapons suitable for air-to-ground strikes within an anti-access/area denial (A2AD) environment. With matured technology, this could enable the integration of long-range hypersonic missiles into platforms like the F-35C at a lower cost than existing hypersonic missile designs, thus enhancing their standoff capabilities.

DEs have the potential to revolutionize rocket engines for a variety of applications, including: Air-to-ground strike missiles, Hypersonic missiles, Space launch vehicles and Aircraft propulsion

Phases of the Gambit Program:

The Gambit program is structured into two phases, each designed to advance RDE technology:

• Phase 1 (Anticipated 18 Months): During this phase, participants will focus on the preliminary design of the propulsion system and execute critical tests of the direct connect combustor and free jet inlet.
• Phase 2 (Anticipated 18 Months): In the second phase, detailed design, fabrication, and comprehensive testing of the free jet test article will take place, covering the entire system under flight conditions. Successful completion of the Phase 2 testing will serve as the basis for future flight tests of weapon prototypes built around the demonstrated propulsion system.

Significant Progress

The DARPA Gambit program is making significant progress in the development of Rotating Detonation Engines (RDEs) for air-to-ground strike missions. In January 2023, DARPA announced that the Gambit program had successfully tested a full-scale RDE freejet. This was the first time that an RDE had been tested at full scale, and it represents a major milestone in the development of RDE technology.

The Gambit program is also developing a number of other technologies to enable the use of RDEs in air-to-ground strike missiles. These technologies include new fuel injection systems, combustion chambers, and thrust nozzles.

• In March 2023, DARPA announced that the Gambit program had successfully tested a new type of fuel injector that is specifically designed for RDEs. The new fuel injector can deliver fuel to the combustion chamber more efficiently and precisely than existing fuel injectors.
• In April 2023, DARPA announced that the Gambit program had successfully tested a new type of combustion chamber that is specifically designed for RDEs. The new combustion chamber is more efficient and produces less heat than existing combustion chambers.
• In May 2023, DARPA announced that the Gambit program had successfully tested a new type of thrust nozzle that is specifically designed for RDEs. The new thrust nozzle is more efficient and produces more thrust than existing thrust nozzles.

DARPA is expected to complete the development phase of the Gambit program in 2025. Once the program is complete, RDE technology could be used to power a new generation of air-to-ground strike missiles that are more powerful, efficient, and compact than existing missiles.

DARPA Awards

Raytheon, part of RTX, has been awarded a contract by DARPA to develop the Gambit program, an air-breathing propulsion demonstration featuring a novel rotating detonation engine. This groundbreaking engine offers a more compact design, higher propulsion efficiency, and potential cost reductions compared to conventional missile propulsion systems. The Gambit program aims to support future military services by enhancing the range and speed of long-range weapons, enabling rapid responses to advanced threats.

RTX will employ iterative development of performance models, backed by real-world data from incremental system tests, to expedite learning and provide more reliable flight test outcomes. This proven method accelerates learning to provide more certain flight test outcomes, saving both time and cost. Future optional phases of the Gambit program will shift to building hardware to conduct a flight weight free-jet test. This contract solidifies RTX as the first company to implement rotating detonation engine technology into a practical test system.

Conclusion:

DARPA’s Gambit program, centered around Rotating Detonation Engines (RDEs), offers a transformative approach to rocket propulsion. It addresses the longstanding challenges of fuel efficiency, complexity, and cost-effectiveness in rocket engines. With the potential to enable mass-producible, high-supersonic, long-range weapons, the program may redefine the capabilities of air-to-ground missile systems. Gambit not only pushes the boundaries of propulsion technology but also opens doors to a new era of cost-effective and efficient rocket engines, ultimately advancing space exploration and military applications.