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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - ReDSHIFT (Revolutionary Design of Spacecraft through Holistic Integration of Future Technologies)

Teaser

Summary

\"The overall ReDSHIFT objective was to push for improved debris mitigation measures with the use of theoretical results on spacecraft orbital dynamics coupled with new technologies, such as solar and drag sails. The new paradigm of 3D printing was applied to enhance aspects of the spacecraft design and manufacturing concurring to the mitigation efforts, such as sail storage, shielding and design for demise (D4D). First, an analysis of the current mitigation measures was performed, to highlight their benefits and deficiencies. While it is well known that the fundamental step to preserve the space environment is the disposal of the spacecraft at end-of-life (EOL), the maneuvers needed to achieve this goal might not be practicable for energetic or technical reasons. A thorough understanding of the orbital dynamics allowed us to identify stability and instability region in space, and to exploit them to find preferential routes (dubbed \"\"deorbiting highways\"\") minimizing the energetic requirements for the operators, improving the applicability of the disposal maneuvers. Once identified, the maneuvers needed to reach the \"\"entrances\"\" to the highways or the graveyards were computed and the technical means to be used were identified. The project focused on a few passive technologies such as solar and drag sails. The theoretical aspects of the sail dynamics and the technological aspects of sail manufacturing were tackled. The focus was also on spacecraft designed for demise, to minimize the chances that chunks of the spacecraft might reach the ground. To make the solutions easier and more attractive to produce and implement in future spacecraft design, ReDSHIFT explored the possibility to use additive manufacturing (3D printing), to realize and test specific parts related to the debris mitigation, such as shielding, sail canisteris, joints, etc. and a model spacecraft.
The mapping, from Low Earth Orbit (LEO) to Geostationary Orbit (GEO), is currently the most detailed available. Based on it, deorbiting strategies from every orbital regime were studied and implemented in the ReDSHIFT software. The effectiveness of the the deorbiting highways were demonstrated with long term simulations. The 3D printed spacecraft showed the advantages of the additive manufacturing in producing small satellites and will represent a viable solution for future space efforts. The samples performed well in the tests and proved to be ready for space qualification. The results were applied to the analysis of the regulations related to space debris and improved mitigation practices and rules were proposed.
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Work performed

To quantify the effectiveness of the current mitigation measures, long term simulations were performed. A mapping of the phase space in the circum-terrestrial space, from LEO to GEO, was performed with more than 100 millions of orbits propagated for 120 years. The output of the propagations was stored in terms of maps displaying, e.g., the lifetime or the maximum eccentricity growth for the orbits, identifying the stable and unstable regions. The reasons for the noted behaviors was traced back to the resonances between effects of the geopotential, lunisolar attraction and solar radiation pressure. Resonant inclinations shortening the orbital lifetime were identified (deorbiting highways). The maps were assembled in an atlas (accessible from the project web site) to be used to identify the best deorbiting options. The manoeuvres to reach the highway entrances were computed. The dynamics of the solar sail was studied showing that it can be a viable option for small to medium satellites in LEO and MEO. Both deorbiting and long term stable graveyard solutions were found for orbits of the Global Navigation Satellite Systems (GNSS) and for equatorial and inclined GEO. The improvements on the evolution of the debris environment obtained by the exploitation of the resonant corridors were highlighted again with simulations.
In the design topic the initial work was devoted to the definition of the system requirements and the review of the aspects of spacecraft design relevant to the debris mitigation. A first design of an 8U-cubesat structure was performed and spacecraft bus were produced in aluminium and in plastic material (Ultem) with a traditional design, mixing 3D printed with CNC milled parts. Later, the detailed design of the spacecraft was completed after a design retrofit based on the lessons from the 3D printing sessions and from the environmental tests analysis. The satellite was re-designed to exploit the advantages offered by the 3D printing and was converted into a structural model for manufacturing and testing. Many spacecraft parts were 3D printed and tested too. The innovative shielding was defined, printed and tested with hypervelocity impacts showing enhanced protection capabilities. Vibration, thermal vacuum and radiation tests were performed on the samples and prototypes showing that the 3D printed spacecraft were apt for actual launches. The printed samples and other parts used in the space missions underwent a D4D test campaign. For the first time, a demise test of a complete CubeSat and of a reaction wheel were performed showing that the observed demise process is different from models, with many small parts surviving the heat flux.
A software suite was produced exploiting the findings of the project. It allows the design of a debris compliant mission giving indication of the available disposal options for different orbital regimes, according to the dynamical mapping. The modules allow the computation of the impact flux on the chosen disposal orbit, the shielding needed to protect from with this flux and the demisability of the spacecraft upon reentry. A web version of the software is accessible from the project site.
Based on the technical findings, possible improvements for the mitigation guidelines were identified and proposed.

Final results

\"The dynamical map of the circumterrestrial space produced an atlas with an unprecedented level of detail, showing the most promising regions where the \"\"deorbiting highways\"\" or the stable graveyards can be found. The atlas was made available on the project web site paving the way to a wider use of the concept of dynamics disposal. Easing the energetic requirements for deorbiting can increase the general compliance to the EOL practices, reducing the proliferation of the debris. The web version of the software shall help to exploit the findings of the project, including the mapping, the flux modelling, the sail dynamics, the D4D and the shielding results.
The 3D printed samples represent a significant advancement with respect to the state of the art in terms of structural design, reduced weight and increased shielding, all embedded in the same satellite structure. These properties were achieved with an innovative diamond-like internal texture of the aluminium mesh. These achievements integrates in the developing industrial paradigm of additive manufacturing and will contribute to the advancement of the European competitiveness.
Proposals for improved mitigation guidelines were drafted and disseminated to a wide interested audience.
In addition to an extensive activity in specialized fora, two meetings with universities and high schools were organized to inform the students about the importance of the space debris issues. Papers and presentations produced during the project are available from the project web site.\"