Nonlinear mechanics research for better space structures
Nasa, ESA, JPL
Novel spacecraft architectures will be paramount in addressing major societal issues, and fostering the next generation of robotic and human space exploration. In particular, these new space systems can play a pivotal role in the fight against climate change. For instance, radiometry satellites can dramatically augment our climate modelling capabilities, improve our forecasting of natural disasters, and enable a more accurate tracking of ecosystems and greenhouse gas emissions. In the energy sector, space solar power satellites can collect sunlight continuously throughout the day, convert it into microwaves and send it directly where it is needed on Earth, hence solving current issues in storing and transferring renewable energies across the globe. To be technically and economically viable, these applications require very large space structures. Similar large space architectures can be leveraged to enable deep-space electric power generation as well as large infrastructures and habitats on the Moon and on Mars. Besides very large space structures, lighter and larger apertures can be integrated in small satellites, paving the way for highly capable mega-constellations and new high impact applications on Earth.
Apollo 17, Nasa
Space structures often rely on thin shells to reduce mass and launch volume, fostered by the development of deployable booms which can be elastically deformed, flattened, and rolled. However, as lower spacecraft masses are sought, increasingly thinner structural components are required, and their use become limited by instabilities such as buckling. The decrease in thickness worsens the structures high imperfection sensitivity, exacerbating their chaotic behavior. Therefore, predicting buckling becomes extremely challenging, and operating structures close to their theoretical buckling load is avoided at all costs. The resulting design approach rely on very conservative safety factors, which dramatically limit the mass efficiency of space structures, and consequently their size. Our research leverages new computational and experimental approaches to unveil the physics behind thin shell instabilities, and enable the use of structures closer to and even beyond their buckling limit. It would result in dramatically lighter structures and has the potential to enable new applications, such as extremely large aperture satellites.
In-space manufacturing and assembly
Creating larger systems in space will require a dramatic paradigm shift in how structures are manufactured and deployed. In-space manufacturing and assembly offer the unique opportunity to go beyond the mass and volume limitations imposed by the launcher fairing, and enable designs that are specifically optimized for the space environment rather than for the stringent loads encountered during launch. These processes also allow for the design of more sustainable, flexible and cost-effective space missions. In-space manufacturing refers to the formation of raw feedstock materials into structures, while in-space assembly consists in joining structural members made on the ground. Today, most in-space manufacturing concepts rely on melt-based processing (metal additive manufacturing) and fiber composite extrusion, while in-space assembly rely on complex robotics. Our research focuses on developing thin shell structural elements which can be deployed, elastically deformed, and can self-assemble into complex structures in space. This hybrid approach between in-space manufacturing and assembly has the potential to dramatically decrease the power required to create structures in space, and to increase their structural efficiency, precision, and size.
As the size of structures increases, it becomes harder to guarantee their shape precision and accuracy when subjected to disturbances in space (thermal, vibration...). This issue is exacerbated in structures manufactured in space, for which the initial shape cannot be measured on the ground before launch. Shape morphing structures can mitigate this shortcoming, and applied for instance to large space antennas and reflectors, in which surface accuracy needs to be kept under a fraction of the signal’s wavelength. In addition, they can enable functionalities such as beam steering, wavefront correction and thermal distortion compensation. Today, such structures often have a large number of degrees of freedom, and therefore require many actuators to be powered continuously. This approach yields large masses and power consumption, which hinder their use in space. To overcome this limitation, our research leverages high strain thin-ply composites with embedded actuation, and instabilities in thin shells to create ultra-lightweight shape morphing structures. In addition, we are investigating the integration of functional materials into shell structures, to merge load-bearing and multiphysics capabilities into a single system.