Student team uses simulation to design, manufacture, test and prepare a satellite launch

Innovation in space applications

SpaceDot is a nonprofit, interdisciplinary student team supported by the Aristotle University of Thessaloniki (AUTh). The team was founded in December 2020 with one goal in mind: to pave the way for innovative research of space applications. The team aims to make space more accessible for the broad scientific and academic community as well as the general public. The SpaceDot team makes themselves available to the community by being an opensource resource so nearly all research work, results and implementation details are available as-is for everyone to explore.

The team consists of more than 80 student members from AUTh and other universities across Greece and Europe from various scientific disciplines including electrical engineering, mechanical engineering, physics, biology, medicine and many more.

The SpaceDot team has been working on a multidisciplinary project for several years that requires advanced simulation.

The SpaceDot team started using Simcenter™ 3D software, which is part of the Siemens Xcelerator business platform of software, hardware and services, to help them execute this project.

They used Simcenter 3D software modeling tools and Simcenter NASTRAN software to address some of their structural simulation challenges. Using Simcenter 3D helped them reduce the time required to prepare a simulation. Using Simcenter NASTRAN solver helped them minimize the required run time compared to the software they used prior to Simcenter.

CubeSats and education

CubeSats are small satellites used to fulfill space experiments or payloads on an affordable and accessible platform. A CubeSat can consist of one or more 100x100x100 millimeters (mm) cubic modules (units). Due to their low cost, universities frequently use these for educational purposes and academic experiments. The first CubeSat was launched in 2003 and more than 1,600 have been launched since then. About three out of four CubeSat missions are successful with the percentage getting higher as the total number of missions increases. With the success of CubeSat, SpaceDot decided to take things to the next level.

AcubeSAT

SpaceDot developed AcubeSAT, a three-unit (U) CubeSat with external dimensions of 340.5x100x100mm. AcubeSAT is being used to study the effects of microgravity and cosmic radiation on brewer’s yeast (Saccharomyces cerevisiae) cells in low earth orbits. The team set out to perform large-scale biology-centered research in outer space outside of the International Space Station (ISS). However, they wanted to achieve this in a low-cost, scalable and easily reproducible way. They set out to do this by becoming part of the Fly your Satellite! program.

Although more than 565 humans have been sent into space, we only possess systemic (at a physiological level) knowledge instead of a more analytical view at a cellular or even molecular level.

The Fly your Satellite! program

Fly your satellite! (FYS!) is a program organized by the Educational office of the European Space Agency intended for student teams from the ESA member states, also with the inclusion of Canada, Latvia, Lithuania, Slovakia and Slovenia. The goal of FYS! is for the selected teams to experience a real space mission by designing, manufacturing, testing and eventually launching their own satellite. The Educational office of the European Space Agency contributes to this goal by providing the teams with lectures and workshops, technical guidance and consultation from experts and testing facilities as well as the opportunity to launch their own satellite.

SpaceDot submitted a technical proposal document for AcubeSAT, consisting of 160 pages of preliminary design for the third iteration of the program. The project was selected as one of the three teams to be part of the program in early 2020.

The project passed the critical design review in the summer of 2021, which consists of more than 1,150 pages of technical documentation and is now entering the manufacturing and testing phase of its lifecycle. Adding an intricate payload, like the lab-on-a-chip instrumentation of AcubeSAT, to an already challenging initiative only increases the complexity of the project.

The AcubeSAT nanosatellite consists of a combination of commercial off-the-shelf, custom or completely in-house subsystems. The entire system is divided into 10 subsystems including the science unit, systems engineering, on board data handling and software, attitude determination and control, communications, electrical power supply, structural, thermal, trajectory and operations.

The SpaceDot team had frequent design sessions between multiple subsystem teams to achieve a layout that met the needs of each subsystem. This led to constant design modifications and iterations to achieve a functional system.

The team faced a lot of critical issues but the most important constraint was the spatial one. Initially, the team found it nearly impossible to fit an entire microbiology lab that can function remotely without human interaction in a 200x100x100 mm space.

The team needed to integrate both electronic, mechanical and fluidic components to fulfill the systems’ requirements and make the experiment feasible. The need for interaction between parts of such different nature and working conditions, while in a very compact space, posed great challenges during the design phase.

Combining a stack of printed circuit boards with different weight of components (like batteries, cables and connectors) and a heavy payload with a variety of components like valves and pumps, camera and other electronics, make it so that the static as much as the dynamic response to the launch sequence plays an important role on the architecture of this satellite.

Simulation-driven structures

The launch environment of a rocket can be dangerous for the team’s delicate system and payload. To ensure it will stay safe, intact, operational and ready to fulfill its mission after launch, the structural subsystem team had to run a plethora of analyses to simulate the effects of the loading environment of a launching rocket in a CubeSat.

The types of the analyses included quasi-static acceleration simulations, eigenfrequencies and modes extraction, frequency response and random base excitations. For that purpose, the team generated a digital twin finite element model while considering the required accuracy for the calculations. As a result, the team generated big models with hundreds of thousands of degrees-of-freedom (DOF) that would normally require many hours of run time.

That’s when the SpaceDot team used Simcenter 3D software modeling capabilities and the state-of-the-art Simcenter NASTRAN software for solving the structural simulation. Simcenter 3D, with an easy-to-use graphical interface, helped the team reduce the time required to set up and prepare a simulation, the Simcenter NASTRAN solver minimized the required run time compared to similar software.

Specifically for the dynamic solutions, the random base excitation solver only required a couple of minutes to output the requested results, which came as a surprise that sped up the design process of the structural subsystem.

According to the results, the team modified the satellite’s components to increase the stiffness and strength where required, or to reduce the total weight of the system as much as possible. This reduced the mass of the payload’s primary structure by 30 percent while still maintaining sufficient stiffness and strength to protect the experiment in the launch environment.

The SpaceDot team also had to make a few modifications during the design phase to achieve an optimal layout and a functional system. During the various design iterations, it was important for the team to rerun the analyses on the fly without compromising accuracy. The user-friendly environment of Simcenter 3D, combined with the fast computation times of Simcenter NASTRAN and the convenient postprocessing capabilities allowed the team to run simulations for more than one design version in less than one evening and easily manage strict deadlines and detailed technical documentation.

The future of simulation for SpaceDot

The design phase of the project might have ended, but there is still a long way ahead for the AcubeSAT project. Currently, the team is planning and preparing testing campaigns to qualify all in-house developed components and subsystems. That includes campaigns to qualify the antenna deployment mechanism, the on-board computer board, which will also accommodate the attitude determination and control functionalities and the payload instrumentation. The acceptance campaign for the entire system will take place following the qualification at the subsystem level.

Throughout the rest of the campaign, the team will have the opportunity to test the design and the accuracy of the simulations. The campaigns will include excessive vibration testing in electrodynamic shakers and thermal vacuum testing, including balance and cycling, functional tests in software and hardware, leak detection and leak rate measurements.

During this process, rapid prototyping will take place. There is a chance for flaws or impracticalities in designing the components to become apparent, which may lead to minor redesigns and development. At the same time, engineering models and commercial components required in the system are being manufactured and procured.

But, as is normal, manufacturing and procurement issues arise, which leads to choosing different components or performing geometry optimizations. These types of changes might seem minor at first glance, but they may add up and lead to heavier loads or excitations around components that are particularly sensitive, such as the imaging system. All of these changes need to be analyzed and tested using Simcenter to assess their impact.

There is also a need for constant documentation of every detail of the satellite system, such as its dynamic response to vibrations. This is needed for passing tests and becoming verified to pass on to the next phases of making a fully functional satellite model and then getting it into orbit.

The team expects to deliver its manufacturing readiness review at the end of 2022 and finalize the qualification and acceptance tests in 2023. AcubeSAT is expected to launch in mid-2024. Provided the launch is successful, the team will continue to operate the satellite from its ground station located at AUTh and continue to use Simcenter 3D to complete all simulations and help the next generation explore space.