With ReFEx (the Reusability Flight Experiment), the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) is developing a technology demonstrator for the vertical take-off and horizontal landing (VTHL) of a rocket stage. The launcher will demonstrate various key technologies: an aerodynamic design that allows ReFEx to fly stably within the atmosphere over a wide range of speeds, an autonomous guidance, navigation and control system (GNC) designed to ensure an optimal flight path, and a status monitoring system employing the latest sensor technology. This includes strategically positioned pressure sensors integrated into the demonstrator body to measure speed and flight attitude, along with glass fibres that measure thermal and mechanical distortions in the ReFEx equipment.
ReFEx is 2.7 m long, has a wingspan of approximately 1.1 metres and a mass of approximately 375 kg. The technology demonstrator has no propulsion technology itself except for a cold gas system for attitude control in space. It forms the tip of a specially modified two-stage, Brazilian-made VSB-30 sounding rocket. To avoid stability problems during ascent, it is topped with a fairing that initially shields its folding wings. Its geometrical design allows for a steady ascent and a stable, controlled re-entry trajectory.
After liftoff, the VSB-30 will carry ReFEx up to an altitude of approximately 130 kilometres. At this point, the first stage separates, similar to conventional space transport systems. ReFEx then follows a return trajectory comparable to that of a winged first stage.
Outside Earth's atmosphere, ReFEx is controlled by cold gas engines. It will perform several manoeuvres to improve the accuracy of the navigation system after launch, before moving into position for atmospheric re-entry. This is where the aerodynamic control system, consisting of front wings (known as ‘canards’) and a rudder at the rear, comes into play.
The Reusability Flight Experiment (ReFEx) is a technology demonstrator for future winged, reusable stages. This animation shows ReFEx in its re-entry configuration after it has been launched from its carrier rocket. Instead of a vertical landing, the test focuses on the horizontal landing of a stage, with autonomous navigation and controlled flight during each phase of the vehicle's mission. The vehicle is stabilised using an active aerodynamic control system, which transforms inputs from the navigation system and the guidance into control commands for the individual actuators. A demonstration flight is planned for 2025 from Koonibba Test Range, Australia.
Video: Technologiedemonstrator ReFEx
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Video: Technologiedemonstrator ReFEx
The Reusability Flight Experiment (ReFEx) is a technology demonstrator for future winged, reusable stages. This animation shows ReFEx in its re-entry configuration after it has been launched from its carrier rocket. Instead of a vertical landing, the test focuses on the horizontal landing of a stage, with autonomous navigation and controlled flight during each phase of the vehicle's mission. The vehicle is stabilised using an active aerodynamic control system, which transforms inputs from the navigation system and the guidance into control commands for the individual actuators. A demonstration flight is planned for 2025 from Koonibba Test Range, Australia.
Re-entry is fraught with challenges: these include the wide range of speeds and angles of incidence, from hypersonic to subsonic. During the re-entry manoeuvre, maximum speeds can reach approximately Mach 5 – roughly 1.5 km per second, 5400 km per hour or five times the speed of sound.
During the initial phase of re-entry, the demonstrator flies upside down at high negative angles of incidence to reduce speed and maintain flight stability. At Mach 1.5, ReFEx performs a 180-degree roll manoeuvre around its longitudinal axis to align with an angle of incidence of up to ten degrees – the maximum lift-to-drag ratio.
In addition autonomously following an optimised flight path to minimise thermal and mechanical stresses, ReFEx will also demonstrate its manoeuverability by flying a turn of at least 30 degrees – simulating a stage returning to the launch pad. In the event of unforeseen incidents immediately after decoupling from the launch vehicle, ReFEx is able to automatically select predefined secondary landing sites and redirect to one of them if necessary.
According to current plans, the development and final assembly of ReFEx will be completed by 2025, followed by a final inspection for approval before transport to Australia. The demonstrator will be launched from the Koonibba Test Range (KTR) in South Australia. The launch site is operated by Southern Launch and the Koonibba Aboriginal Community, who work in partnership to enable suborbital launches – in which the rocket does not leave Earth’s gravitational field – and return flights from space.
DLR participation in the ReFEx project
A total of nine DLR institutes and facilities are contributing to the ReFEx project:
