Aerodynamic Decelerators, The Year in Review,

Aerospace America, December 1996

Copyright c 1996 by the American Institute of Aeronautics and Astronautics, Inc, all rights reserved

From the exotic to the mundane, 1996 has been a year of stark contrasts in the field of aerodynamic decelerator systems. At once, high-performance parachutes are flying sophisticated payloads into extraterrestrial atmospheres while, here on earth, the US Army is preparing to replace that venerable mainstay of the airborne, the T-10 parachute system.

The Jet Propulsion Laboratory's Pathfinder lifted off on December 4 and is now on its way to Mars. This mission follows the astonishing success of the Galileo probe's descent on parachute into the crushing atmosphere of Jupiter. During the probe's flight, the main four-meter-diameter conical ribbon parachute saw winds of 125 meters per second. This latest planetary adventure is the second in NASA's Discovery Program. On the Fourth of July 1997, Pioneer Aerospace's thirteen-meter-diameter disk-gap band-parachute will decelerate the Pathfinder lander to between ten and thirty meters per second, developing deceleration forces of 25 g's. Once below an altitude of just 25 meters, the parachute bridle will be released and the lander will fall to the Martian surface, cocooned by an envelope of airbags.

At the same time, the US Army has solicited industry bids to replace its 1950's technology T-10 paratrooper parachute system. The last forty years have seen quantum leaps in materials technology and extraordinary advances in parachute design and performance modeling. The Army is sure to get a cost-effective workhorse system with higher reliability and greater performance.

Personnel parachutes are not all that the Army's Soldier Systems Command develops. In 1996, the Natick Research, Development and Engineering Center concluded a highly successful "Advanced Airdrop for Land Combat" technology demonstration. A cornerstone of this program is the Guided Parafoil Air Delivery System, a family of Pioneer Aerospace high-glide parafoils autonomously controlled by SSE, Inc.'s, GPS-based onboard controller. Flying a parafoil with a wingspan of 45 meters (more than a C-130 Hercules) the controller steered a 16 metric ton payload -- the heaviest parafoil payload in history -- to a soft, precise landing. GPADS' of different scales have now delivered a number of operational payloads including a HMMWV. The commercially available GPADS-Light (fourteen-meter-wingspan) successfully completed Type Qualification testing with the US Army, verifying performance of the militarized guidance, navigation and control system. GPADS-Heavy (wingspans up to 53 meters) is in continuing development by NASA Johnson Space Center for the controlled, precise recovery of the International Space Station X-38 Crew Return Vehicle. The X-38 is an implementation of the US Air Force/Martin X-24A lifting body research vehicle.

Today's designers face even more sophisticated mission requirements. In addition, modern materials exhibit extraordinary tensile strength characteristics, capable of handling hundreds of g's of aerodynamic loading. That's why engineers are devoting so much of their energy to developing reliable and practical computer-based structural design models and dynamic simulators. Most of these efforts involve the numerical coupling of 3-D computational fluid dynamics codes to structural dynamics models to predict the performance of many types of parachutes. Some of the most exciting work is being performed by collaborating investigators from Soldier Systems Command, the Army High Performance Computing Research Center, the Army Research Laboratory and the Universities of Connecticut and Minnesota. Staff at Parks College, St. Louis University, have embarked upon an ambitious experimental program using instrumented skydivers to gather data on the dispersion of ram-air parachute inflation. This unique database will allow investigators to validate existing parachute inflation models and numerical simulations.

Reductions in defense and space exploration budgets have brought stiffened competition and merger-mania to the American parachute industry. Para-Flite, purchased by GQ Parachutes of the UK, now joins Irvin Industries and Pioneer Aerospace as a foreign-owned subsidiary company. The AIAA's committee on Aerodynamic Decelerator Systems Technology, the National Parachute Technology Council and the Parachute Industry Association have formed a strategic alliance. They have banded together to ensure increased educational opportunities for the next generation of parachute technologists, adequate funding for fundamental research, and properly maintained commercial specs in the post-MIL-spec era.

by Dean S. Jorgensen