Low-cost gossamer systems for solar sailing and spacecraft deorbiting applications.

Doctoral thesis English OPEN
Fernandez, Juan M. (2015)

Nowadays, a technology demonstrator platform popular amongst the research community given their relatively low cost and short development time are cubesats. Nevertheless, cubesats are by definition nano-satellites of small volume and mass, and therefore, they traditionally only allowed very limited sizes of any expandable structure onboard with final deployed areas in the order of a few square meters. This conflicts with the large areas required for efficient solar sails, making the demonstration of this exotic concept bound to more expensive missions with a dedicated launch. The applications that will be discussed throughout the thesis will be: three-axis stabilised solar sailing with a "rigid" support structure; and drag assisted deorbiting of a large host craft using a solar sail. Both of these applications still need validation in space, especially for Earth-bound missions. The main goal of this research effort is thus to satisfy the need of available deployable booms for their use on systems of unprecedented mass per unit area with cubesat-like mission constraints that will ultimately place more trust in gossamer concepts. For this, two novel rollable booms and their deployment mechanisms have been developed, one based on metallic tape-springs and the other on bistable composite slit tubes. Analyses and tests confirmed that the former boom has scalability problems related to stowage-induced boom axial curvature, and coil blossoming management. Reliable sail deployments of a 4 x 4 m^2 sail were achieved with them. The latter boom design solves previous scalability problems of bistable composite booms. The ground demonstrator tested deploys reliably a 5 x 5 m^2 sail, with the current compact boom design shown to be efficiently scalable for 100 m^2 class sails. To enable even larger sails with the bistable booms developed, a novel architecture named the completely stripped solar sail has been proposed. A simple experiment demonstrated the beneficial effect that dividing the sail into sets of parallel strips and using a continuous sail-boom attachment suspension configuration has towards scalability of the concept. A new structural characterisation programme developed means by which to characterise the slender booms properties. In addition, the test results validated and/or updated the imperfection seeded finite element models produced. These models are ultimately utilised in high-fidelity predictions of the performance of the solar sail booms under the established operational loads, as well as in the scalability analyses of the sail concepts proposed with them. Lastly, the first gossamer sail-based deorbiting system in it class, developed for medium mass (< 1000 kg) objects in Low Earth Orbit under an ESA contract, is introduced. Mission requirements, designs, and the purposely developed qualification programme are shown for the final system that reached TRL 5-6. The challenges and lessons learned from the ground testing of such lightweight structures are also documented with the aim of assisting future design and development efforts of similar concepts.
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