Design of Subscale Parachute Models for MSL Supersonic Wind Tunnel Testing

Abstract

Subscale models of the Mars Science Laboratory (MSL) parachute were tested under conditions representative of the MSL deployment envelope at the NASA Glenn Research Center’s 10ft x 10ft wind tunnel. Four percent (4%) scale (0.813 m) parachute models were used to examine parachute performance in the wake of a similarly scaled Viking-type entry vehicle at supersonic speeds spanning Mach 2 to 2.5. Design of subscale parachute models is typically a trade off between scaling accuracy and survivability in the expected test environment. High fidelity scaling of structural elements renders the models susceptible to damage during operation at supersonic speeds, especially in the presence of high frequency area oscillations. Deploying and inflating these models at relatively high dynamic pressures and speeds also posed challenges, as evidenced by the catastrophic failure of several parachutes during and shortly after deployment in the first scheduled entry. As a result, the equipment and procedures used to protect and deploy the model parachute system were revised over several generations until a reliable system was obtained and utilized in the second available entry. Additional trades and design changes were incorporated for the third available entry in the test program. Measures were also taken in regard to the test environment to enhance the life-span of parachute models against the high frequency forces associated with canopy area oscillations. This paper provides a detailed description of the parachute models as well as the evolution of the ancillary equipment and test procedures that ultimately resulted in a reliable test technique.