Reefing the Mars Science Laboratory parachute

The Mars Science Laboratory (MSL) mission will utilize a 21.5 m reference diameter Viking-Type Disk-Gap-Band (DGB) parachute to decelerate the MSL entry vehicle from supersonic to low subsonic speeds during entry into the Martian atmosphere in 2012. This canopy is larger than any DGB parachute tested or flown in a high Mach, low dynamic pressure environment that is representative of a Mars surface mission. Empirical observations of prior deployments of parachutes, in similar environments, indicates that the DGB parachute will experience a series of partial inflations and collapses, termed Area Oscillations (AO), during flight above Mach 1.5. Early in the MSL development process it was decided that structural qualification of the parachute via high altitude, high Mach testing would be cost prohibitive. Instead, the JPL team utilized the National Full-Scale Aerodynamics Complex (NFAC) at NASA Ames to perform the canopy structural qualification under subsonic conditions. Reefing of the canopy was initially selected as a means of exposing a single parachute to the multiple load spikes associated with the expected number of Area Oscillations. This paper describes the conventional and non-standard reefing methods used, as well as the corresponding aerodynamic performance of the reefed canopy. Unfortunately, releasing the canopy from a reefed configuration in this test specific application proved unreliable. Ultimately, a unique "sleeve deployment" technique (SD) was developed and successfully used to complete structural qualification. The sleeve deployment technique and corresponding parachute inflation process are also discussed in this paper.