Extraction and Separation Modeling of Orion Test Vehicles with ADAMS Simulation

Abstract

The Capsule Parachute Assembly System (CPAS) project has increased efforts to demonstrate the performance of fully integrated parachute systems at both higher dynamic pressures and in the presence of wake fields using a Parachute Compartment Drop Test Vehicle (PCDTV) and a Parachute Test Vehicle (PTV), respectively. Modeling the extraction and separation events has proven challenging and an understanding of the physics is required to reduce the risk of separation malfunctions. The need for extraction and separation modeling is critical to a successful CPAS test campaign. Current PTV-alone simulations, such as Decelerator System Simulation (DSS), require accurate initial conditions (ICs) drawn from a separation model. Automatic Dynamic Analysis of Mechanical Systems (ADAMS), a Commercial off the Shelf (COTS) tool, was employed to provide insight into the multi-body six degree of freedom (DOF) interaction between parachute test hardware and external and internal forces. Components of the model include a composite extraction parachute, primary vehicle (PTV or PCDTV), platform cradle, a release mechanism, aircraft ramp, and a programmer parachute with attach points. Independent aerodynamic forces were applied to the mated test vehicle/platform cradle and the separated test vehicle and platform cradle. The aero coefficients were determined from real time lookup tables which were functions of both angle of attack (α) and sideslip (β). The atmospheric properties were also determined from a real time lookup table characteristic of the Yuma Proving Grounds (YPG) atmosphere relative to the planned test month. Representative geometries were constructed in ADAMS with measured mass properties generated for each independent vehicle. Derived smart separation parameters were included in ADAMS as sensors with defined pitch and pitch rate criteria used to refine inputs to analogous avionics systems for optimal separation conditions. Key design variables were dispersed in a Monte Carlo analysis to provide the maximum expected range of the state variables at programmer deployment to be used as ICs in DSS. Extensive comparisons were made with Decelerator System Simulation Application (DSSA) to validate the mated portion of the ADAMS extraction trajectory. Results of the comparisons improved the fidelity of ADAMS with a ramp pitch profile update from DSSA. Post-test reconstructions resulted in improvements to extraction parachute drag area knock-down factors, extraction line modeling, and the inclusion of ball-to-socket attachments used as a release mechanism on the PTV. Modeling of two Extraction parachutes was based on United States Air Force (USAF) tow test data and integrated into ADAMS for nominal and Monte Carlo trajectory assessments. Video overlay of ADAMS animations and actual C-12 chase plane test videos supported analysis and observation efforts of extraction and separation events. The COTS ADAMS simulation has been integrated with NASA based simulations to provide complete end to end trajectories with a focus on the extra...

An Efficient Contact Model for the Simulation of Cargo Airdrop Extraction Phase

“…For the convenience of code implementation, the derivative of state variables in (11), (13), and ( 14) are already arranged to the left-hand side, thus the complete state vector for a 6-DOF body is y…”

“…The motion of the aircraft in DSS is predetermined and does not result from forces and moments acting upon it. In order to model the aircraft-cargo contact dynamics with higher fidelity, Fraire et al [13,14] established an extraction and separation model for Orion Test Vehicles in the commercial multibody dynamics program ADAMS, which provides a more accurate contact load prediction than its predecessor DSS. However, the aircraft motion is predefined by a pitch rate profile and does not response to the contact loads.…”

Extraction-Separation Performance and Dynamic Modeling of Orion Test Vehicles with Adams Simulation: 2nd Edition

“…Modeling aircraft dynamics during the extraction phase requires analysis of pitch plane test data to gain an understanding of the possible test vehicle responses as it reaches the end of ramp. The first two PTV tests used heritage data and defined conservative dispersion ranges for the pitch rate (0˚/s to 5.33˚/s) and ramp angle (0˚ to 5˚) to bound possible aircraft dynamics scenarios and used for Monte Carlo assessments 4 . As the CPAS EDU test campaign progressed, the availability of test data increased and contributed to the refinement of aircraft ramp modeling during extraction.…”