Tech Briefs

The Crew Exploration Vehicle Parachute Assembly System (CPAS) project conducts computer simulations to verify that requirements on flight performance, parachute loads, and terminal rate of descent are met. The objective of this work was to obtain a high-fidelity simulation of Orion crew capsule flight test vehicles during parachute flight.

Decelerator System Simulation (DSS) is a FORTRAN software tool used to predict the motion of a vehicle coupled to a parachute. Separate equations of motion for the parachute and vehicle are employed. DSS was modified from an existing NASA software program for the space shuttle solid rocket booster (SRB) recovery system, called UD233A. DSS was used to study performance of parachute descent of flight test vehicle versions of the NASA Orion spacecraft. DSS incorporates six degrees of translational and rotational motion for both the vehicle and attached parachute, and models the deployment and inflation of the parachute system. DSS has separate aerodynamic and mass properties for both the vehicle and parachute.

DSS propagates the motion of vehicle and parachute bodies given forces and moments acting upon them. The bodies are treated separately and coupled by an elastic riser. Forces and moments acting on the bodies are from gravity, the elastic riser, and aerodynamics. DSS has a smart parachute release algorithm that releases the parachute at minimal vehicle rotational rates to help prevent tumbling prior to the next parachute inflation. DSS has a model of a harness structure between the riser and the vehicle, which consists of a separate small confluence mass at the vehicle end of the riser. The motion of the mass is modeled separately from the vehicle and the parachute. This mass is coupled to the parachute by the riser, and is coupled to the vehicle by up to four elastic harness legs. The legs may be attached at different locations on the vehicle. The parachute inflation model uses empirical equations to model the growth of the parachute and the load buildup during inflation.

This work was done by Peter A. Cuthbert, Christopher M. Madsen, Daniel A. Matz, Robert S. Merriam, Sarah E. Rieger, and David A. Hoffman of Johnson Space Center. MSC-25936-1

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