The Reusability Flight Experiment – ReFEx: Details of the Proto-flight-model Integration Campaign and a Final Update Prior to Flight

Kurzfassung

The Reusability Flight Experiment (ReFEx), developed by the German Aerospace Center (DLR), is a technology demonstration mission aimed at validating key technologies for aerodynamically controlled reusable launch vehicle (RLV) stages. Scheduled for launch in 2027 from the Koonibba Test Range (KTR) in South Australia, ReFEx will be carried by a VSB-30 sounding rocket to a trajectory representative of a returning RLV first-stage. The experiment seeks to autonomously guide the vehicle as far back as possible toward the launch site using only aerodynamic control surfaces, demonstrating fully autonomous flight control capable of critical heading changes and energy-efficient returns. ReFEx features a compact design, measuring 2.7 meters in length with foldable wings and a mass of approximately 450 kg. The mission will test advanced guidance, navigation and control (GNC) systems, aerodynamic control strategies, structural resilience under hypersonic and subsonic conditions. By collecting flight data to validate aerodynamic models and control algorithms, ReFEx aims to enhance the development of future European reusable launch vehicles, contributing to more sustainable and cost-effective space access.

As was described in previous papers, a key aspect of the project is a rigorous pre-flight verification campaign, including structural integrity tests, avionics integration and environmental simulations. This paper in particular, will describe the trimming process and verification of system functions prior to shipment of the flight vehicle to its launch site. Trimming is a critical and challenging process as two not necessarily compatible sets of requirements need to be satisfied. One, the payload which is aerodynamically active has to be trimmed so that it can safely be launched on a sounding rocket and two, the trimming must be compatible with the deployed flight configuration. In both cases stringent requirements in terms of centre of gravity location as well as moments of inertia have to be satisfied. In addition, the flight vehicle, also known as the re-entry segment, will have to be functionally checked out prior to flight. The key here is to verify proper system responses to flight conditions, while only being able to simulate very limited parts of the flight environment in the lab. As such a combination of subsystem HiL (Hardware in the Loop) tests and specific complete system tests were devised and will be described in this paper.