A historical summary of the design, development, and analysis of the disk-gap-band parachute

The Disk-Gap-Band (DGB) parachute was originally developed in the late 1960's by Clint Eckstrom for high-altitude meteorological rocket applications. It was designed as a balance between drag and stability with a relatively simplistic design and low packing volume. Due to its demonstrated high-altitude performance and design features, the DGB was selected as a candidate for Viking precursor test programs such as the Planetary Entry Parachute Program (PEPP) and the Supersonic Planetary Entry Decelerator (SPED), in which the parachute was tested at high altitude supersonic conditions similar to those that would be experienced during an entry at Mars. The DGB was eventually selected for the Viking mission and qualified using a series of low-altitude drop tests and high-altitude balloon-launched decelerator tests (BLDT). Based on the success of the DGB on the Viking I and II missions, as well as the wealth of data generated during the PEPP, SPED, and BLDT test programs, the DGB parachute has been used on all subsequent U.S. missions to the surface of Mars with great success. Recently, an effort was undertaken to further improve the structural capability of the DGB parachutes used at Mars. An early activity was undertaken to better understand the breadth of designs, design modifications, and general evolution of the DGB canopy to better inform future designs. This paper collates historical DGB designs and structural performance. A key design shift includes the switch from low-tenacity Dacron skeletal components used in the Viking era to high-tenacity Kevlar skeletal components used in the Pathfinder era, which fundamentally changes the load sharing and energy absorption characteristics of the parachute. The paper also scrutinizes the analysis methods and flight limit load policies used throughout history. Of note is that the analysis methods have become “smarter,” transitioning from hand calculations to finite element analyses, but the use of more advanced methods have likely been eroding design conservatism leading to more aggressively designed parachute systems. Reflection upon previous DGB design and flight practices has shown that modern design practices may be driving large DGB designs outside the traditionally successful margin limits.