How Project FENRIR and Xometry Developed a Modular Free-Fall Experiment Platform for Microgravity Research

Making Space Exploration More Accessible

Project FENRIR was founded at Luleå University of Technology (LTU) in Sweden, as part of the REXUS/BEXUS program, a joint initiative between the German Aerospace Center (DLR) and the Swedish National Space Agency (SNSA), with support from European Space Agency (ESA). The program provides students across Europe with the opportunity to design, build, and launch experiments on suborbital sounding rockets, enabling hands-on experience in aerospace research.

The project is driven by a diverse group of LTU students, working across five specialised departments: mechanical, electrical, software, science & payload, and management. Since its inception, 25 contributors have been involved, with 16 currently working on-site in Kiruna, Sweden. Their collaborative effort focuses on overcoming complex engineering challenges while ensuring the platform remains reusable for future missions.

The FENRIR team’s mission is to create a cost-effective and adaptable platform for microgravity experiments, building on LTU’s earlier successes. The Free-Falling Unit (FFU) is designed to be ejected from the rocket at its apogee (~80 km), providing approximately 70 seconds of reduced gravity for scientific experiments. This feature allows future researchers to focus solely on their experiments without the need to design an entirely new experimental platform from scratch.

To ensure a successful experiment, the FFU features a controlled parachute deployment system for safe recovery. Its modular structure, combined with an Attitude Stabilisation System (ATSS) and Phase Change Material (PCM) payload, provides an adaptable research platform for future microgravity studies.

FENRIR follows in the footsteps of earlier LTU projects, particularly the ASTER project, which was part of the REXUS/BEXUS program, a European student initiative for suborbital research. ASTER aimed to develop precision attitude control for Free-Falling Units. While ASTER focused on highly controlled attitude stabilisation, FENRIR prioritises modularity, enabling researchers to integrate and adapt different scientific payloads without redesigning the entire platform.

The FENRIR team working on the Free-Falling Unit (FFU), performing electronic diagnostics and system integration. The unit’s CNC-machined aluminum structure and internal electronics are being tested to ensure optimal performance before launch.©

The Free-Falling Unit (FFU) housed within its cylindrical module, featuring CNC-machined aluminium components that provide structural integrity and precision for deployment from the REXUS 34 rocket.©

ATSS: Stabilising Microgravity Conditions

One of FENRIR’s key innovations is the Attitude Stabilisation System (ATSS), designed to minimise angular velocity during descent, ensuring a stable microgravity environment for experiments. The ATSS features three reaction wheels mounted perpendicular to each other, which store and redistribute angular momentum, effectively slowing the FFU’s rotation.

By reducing the rotational motion of the FFU, the ATSS improves experimental conditions, making it possible to conduct more precise microgravity studies. Unlike previous systems that required complex attitude control, FENRIR’s approach ensures stability while maintaining an adaptable design that can be used for future research.

PCM: Investigating Phase Change Materials in Space

The FFU also houses a Phase Change Material (PCM) payload, designed to investigate how materials transition between solid and liquid states in microgravity. PCM technology is widely used in thermal control systems for spacecraft due to its ability to store and release heat, but its behavior in microgravity remains poorly understood.

To address this knowledge gap, the FENRIR team developed a dedicated PCM experiment module, consisting of:

• A transparent observation window, allowing onboard cameras to record the phase transition process.
• A copper roof and a heating pad, which induce phase transitions in a controlled manner.
• Four internal temperature sensors, tracking heat distribution and phase change behavior in real time.

The PCM experiment, combined with the ATSS stabilisation system, will provide valuable insights into heat regulation in space environments, contributing to future advancements in spacecraft thermal control and microgravity research.

By integrating the ATSS and PCM payloads, FENRIR provides a versatile platform for future microgravity studies. Its modular architecture supports ongoing advancements in space research, allowing scientists to conduct experiments without needing to design entirely new systems.

Precision-manufactured components supplied by Xometry, including CNC-machined aluminium plates and custom-designed motor housings, essential for the structural integrity and performance of Project FENRIR’s Free-Falling Unit (FFU).©

How Xometry Helped Bring FENRIR’s Vision to Life

Manufacturing space-ready components requires extreme precision, strict material tolerances, and rapid iteration—challenges the FENRIR team tackled by partnering with Xometry. Through CNC machining and advanced 3D printing, Xometry provided critical FFU components that met aerospace standards while significantly reducing lead times.

“The support we’ve received from our partners has been crucial in addressing the challenges of creating such a complex platform,” says Eric Almqvist, Mechanical Department Lead at Project FENRIR. The Instant Quoting Engine also provided real-time feedback, enabling the team to optimise designs for manufacturability.

The FENRIR team carefully selected component materials based on a tradeoff between strength and weight. The parts needed to withstand vibrational loads during the mission while keeping the experiment mass to a minimum. Additionally, the team required electromagnetic isolation for the PCBs, ensuring radiosilence to prevent interference with onboard electronics.

The FENRIR team initially prototyped the parts in-house, iterating on their designs to meet the project’s unique requirements. Xometry’s engineers then helped refine these designs, ensuring manufacturability and improving efficiency for production. The parts manufactured by Xometry are the actual components that will fly on the REXUS 34 sounding rocket, meeting the strict standards required for aerospace applications.

Xometry manufactured several key components for the Attitude Stabilisation System (ATSS) and other systems, including:

• CNC-machined aluminum wall plates that form the structural cube of the FFU and include an electromagnetically isolating PCB case to shield electronics from interference.
• A CNC-machined stainless steel retention bracket, capable of securing a 3 kg payload at 4 Hz rotation, ensuring stability during the FFU’s operation.
• A CNC-machined rotor wheel, vital for the reaction wheel system within the ATSS.
• A DMLS 3D-printed motor mount, optimised for high strength-to-weight performance in microgravity.

The combination of CNC machining and advanced 3D printing allowed the FENRIR team to source components tailored to their specific needs, ensuring both manufacturability and performance. By utilising Xometry’s services, they successfully addressed their design challenges while staying on schedule.

Precision Manufacturing for Aerospace Applications

The FENRIR team relied on Xometry’s Instant Quoting Engine to simplify the design process. By receiving real-time feedback and cost estimates, they were able to optimise their designs for manufacturability while staying within budget.

“The Instant Quoting Engine helped us compare manufacturing processes quickly and made it easier to finalise our designs,” said Almqvist, “For simpler parts, the instant quoting engine saved us a lot of time, while more complex components benefited from Xometry’s engineering reviews.”

The components supplied by Xometry integrated seamlessly into the final assemblies, meeting the rigorous standards required for aerospace applications. This precision significantly accelerated the team’s timeline, allowing them to begin testing and integration earlier than planned.

“We were impressed with how smoothly the process went, from quoting to delivery,” Almqvist shared. “Xometry’s ability to deliver high-quality parts on time was essential to our success.”

Final Countdown: Project FENRIR’s Next Steps

With the launch of REXUS 34 scheduled for March 2025, the FENRIR team is conducting final preparations and ensuring their platform is mission-ready. Post-launch, they plan to analyse their experimental results and publish their findings, contributing valuable insights to the fields of microgravity research and space technology.

Although Project FENRIR is nearing its conclusion, the team remains committed to recommending Xometry to future LTU projects. “Xometry’s support has been invaluable, and we’re confident that other teams at LTU will benefit from their services in the future,” Almqvist concludes.

About Project FENRIR: Project FENRIR is a student-led initiative at Luleå University of Technology (LTU) dedicated to advancing space research through innovative microgravity experiments. As part of the prestigious REXUS/BEXUS program, supported by the German Aerospace Center (DLR) and the Swedish National Space Agency (SNSA), the team designs and develops modular Free-Falling Units (FFUs) to facilitate accessible and cost-effective reduced gravity research. By collaborating with industry partners like Xometry, Project FENRIR combines precision manufacturing with cutting-edge engineering to push the boundaries of space exploration.

Website: https://project-fenrir.netlify.app/

Contact: fenrir.ltu@gmail.com