Mass properties analysis and measurements of a high altitude Supersonic Decelerator Test Vehicle

The mass properties of the Low Density Supersonic Decelerator (LDSD) Supersonic Flight Dynamics Test Vehicle (SFDTV) were analyzed and measured to ensure a successful test flight and allow for accurate post-flight reconstruction. This paper covers the methods used for analytical estimates of the mass properties throughout the design process, balancing and ballasting design, mass trends, measurements performed to verify the analytical models, and issues found. The test vehicle analyzed and measured is a full scale 4.7 m diameter, 3085 kg, high altitude test vehicle. Brought to Mars-like test conditions in Earth´s atmosphere at 180,000 ft and Mach 4 by a balloon and solid rocket motor, the spin stabilized vehicle deploys a parachute and inflatable toroid for enhanced Mars landings in the future. Control of mass, center of mass, and products of inertia were critical for stable and predictable flight conditions. Accurate knowledge of mass, center of mass, and inertias throughout all the changing states of the test flight were required for post-flight reconstruction of the performance achieved by the inflatable decelerator and parachute. A component-level line item Monte Carlo method was used to predict the mass properties and associated uncertainties. Spin table measurements of two components of center of mass, one moment of inertia, and two products of inertia were used to reduce the uncertainties of the mass properties. Spin table measured values matched pre-measurement predictions closely, providing validation of the analytical model. Ultimately the center of mass was controlled to within 3 mm of the geometric center of the vehicle, and the spin axis products of inertia were zeroed out to within 4 kg-m² at launch. Uncertainties for mass properties throughout all phases of flight, balloon drop through motor burnout and parachute deployment, were 10.8 kg for mass, 25 mm for center of mass, 1.6% for moments of inertia, and 10 kg-m² for products o- inertia, satisfying requirements for post-flight reconstruction.