Supersonic F-104 Starfighter aircraft flies GE Aerospace’s first captive-carry tests of solid-fuel ramjet
September 23, 2025
GE Aerospace has successfully completed captive-carry flight tests of its new solid-fuel ramjet, flown on a Lockheed F-104 Starfighter operated by Starfighters International at NASA’s Kennedy Space Center in Florida.
The experimental system, known as the Atmospheric Test of Launched Airbreathing System (ATLAS) Flight Test Vehicle, flew three missions and reached supersonic speeds, GE announced on 22 September. The campaign marks the company’s first in-flight demonstration of solid-fuel ramjet hardware.
“This marks a pivotal moment for GE Aerospace as we showcase our solid-fuel ramjet technology in flight for the first time,” says Mark Rettig, vice president and general manager of Edison Works Business & Technology Development at GE Aerospace. “Captive-carry testing of reusable hardware allows for more frequent trials in realistic atmospheric conditions to better understand system behaviour.”
What captive-carry testing means for new flight systems
In aerospace development, captive-carry is an early safety and integration step. A new payload, such as a missile, rocket, or experimental engine, is attached to a host aircraft but not released.
The approach allows engineers to measure aerodynamics, vibrations, loads, and heating at representative speeds without the risk of an uncontrolled free flight. It also validates that the carrier aircraft can safely handle the payload.
Notable historical examples include NASA’s Space Shuttle Enterprise, carried aloft on a modified Boeing 747, and Virgin Galactic’s SpaceShipTwo, which conducted multiple captive-carry campaigns before powered flight.
For GE Aerospace, this method provided a way to expose the solid-fuel ramjet to real supersonic conditions while keeping it safely secured to the F-104.
Starfighters International and the F-104 legacy
The supersonic carrier for the campaign was a Lockheed F-104 Starfighter operated by Starfighters International — the only commercial company in the world licensed to fly at Mach 2 while carrying experimental payloads.
Founded by former US Navy pilot Rick Svetkoff, the Florida-based operator began with a single privately owned F-104 and has since built a unique fleet supporting research, development, and aerospace testing. Its seven active aircraft are sourced from retired military operators, including Canada, Norway, and Italy, which flew the type until the early 2000s.
Originally designed in the 1950s as a supersonic superiority fighter, the F-104 set multiple world records and became a workhorse for NATO air forces. Today, Starfighters International’s fleet is the world’s only active civilian stable of F-104s, used for payload deployment, space-launch simulation, and advanced propulsion trials.
What is a solid-fuel ramjet?
GE’s test vehicle carries a solid-fuel ramjet (SFRJ). Unlike a rocket, which must carry both fuel and oxidiser, a ramjet only carries fuel and draws oxygen directly from the atmosphere.
That design delivers much higher efficiency: while rockets typically achieve a specific impulse of 200–240 seconds, SFRJs can reach 800–1,000 seconds. In the system, the fuel is a solid hydrocarbon formed into a hollow cylinder.
Incoming high-speed air flows through the chamber, igniting at the fuel surface to create continuous combustion and thrust. With no moving parts, pumps, or tanks, an SFRJ is one of the simplest and most robust high-speed propulsion systems.
Pentagon backing and strategic aims
The ATLAS program is funded under Title III of the Defense Production Act, which supports technologies deemed critical to national security. The Pentagon’s goal is to scale up air-breathing propulsion such as ramjets and scramjets to give future weapons greater speed, range, and responsiveness.
By extending how far and how fast munitions can travel, this technology could transform long-range strike capabilities while keeping production comparatively straightforward and cost-effective.
The ATLAS trials are part of GE Aerospace’s broader investment in advanced propulsion. In 2022, the company acquired hypersonic specialist Innoveering and has since expanded test infrastructure in Ohio and New York to replicate higher-Mach flight conditions on the ground.
These facilities are intended to accelerate progress on air-breathing engines that could underpin future missiles, unmanned aircraft, and even space-access vehicles.
For now, GE’s captive-carry sorties remain experimental, but they represent a critical step. Demonstrating that a solid-fuel ramjet can survive and operate in real supersonic flight clears a major hurdle between laboratory testing and operational weapons.
The next milestone will be free-flight testing, where the ramjet is released to ignite and sustain thrust on its own. If successful, the technology could underpin new classes of weapons capable of flying further, faster, and more efficiently — capabilities increasingly decisive in modern air combat and deterrence strategies.
