System Architecture for De-orbiting Spacecrafts as a Platform for Experimental Aerodynamics Studies

Space vehicles encountering the Earth’s atmosphere are enveloped in a shock layer comprising an intense bow shock, further trailing into a shallow oblique shock. Due to remarkably high flight speeds approaching near orbital velocities, the detached shock layer heats the air, resulting in immense velocity and temperature gradients. Between the shock and the vehicle, there are velocity, thermal, entropy, and chemical boundary layers that are not self-similar. The shock detachment distance is inversely proportional to the Mach number, and at hypersonic speeds, the boundary layer thickness and shock layer are in juxtaposition. The vastly dominant flow regime surrounding the bodies of arbitrary shapes like orbital debris, rogue deorbiting spacecraft, or meteoroids is a matter of great interest in accurately predicting their flight path. The forces derived from onboard inertial measurement units may not be accurate in predicting the flight path and ground footprint of disintegrating spacecraft. Predictions requiring accurate aerodynamic characterization mandate high-fidelity simulations, which in turn require prior experimental validations. More often than not, in dynamically evolving situations like the disintegrating spacecraft, the predictions are heavily reliant on reduced-order models that are incidentally successful. As for the existing ground test facilities, they are designed to respect only a small set of flow similarity parameters at a time. These are often short-duration test facilities, ranging from milliseconds to a few seconds per test, and the runtime costs limit the operational frequencies. More recently, small spacecraft have been proposed as an inexpensive alternative to ground test facilities. Although limited in their payload capacity to accommodate a vast number of sensors and limited in controllability and repeatability, these provide actual in-flight measurements.The current research is focused on exploring the viability of small spacecraft for obtaining aerodynamic characterization for atmospheric re-entry. This paper will provide a system architecture for a) direct aerodynamic load measurement from a de-orbiting spacecraft, b) scientific missions to characterize aerodynamic loads for bodies of arbitrary shapes, and c) small spacecraft as a viable alternative platform for experimental aerodynamics research. The study brings in perspectives on challenges and opportunities in utilizing the small spacecraft as a platform to investigate complex aerodynamic phenomena. This will be followed by the exploration of viable flight path envelopes for scientific missions carrying payloads for aerodynamic studies and the assessment of the impact on ground footprints of disintegrating rogue spacecraft due to uncertainty in aerodynamic and geometric parameters. Lastly, the study proposes the use of an array of micro-electromechanical pressure sensors to directly measure unsteady aerodynamic forces from bodies of arbitrary shapes subjected to arbitrary flight attitudes. Such a measurement system integrated into small spacecraft would provide better insights into dynamically evolving flow characteristics than the integrated forces deduced from inertial measurement systems. The scope is limited to the integration of a pressure sensor array using open-source embedded systems, followed by assessing system performance and limitations.