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  • 1
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    Martian Aerocapture Terminal Point Guidance: A Reference Path Optimization Study (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: An effective method of terminal point guidance is to employ influence coefficients, which are solved from a set of differential equations adjoint to the linearized perturbations of the equations of motion about a reference trajectory. Hence, to optimize this type of guidance, one must first optimize the reference trajectory that the guidance is based upon. This study concentrates on various methods to optimize a reference trajectory for a Martian aerocapture maneuver, including a parametric analysis and first order gradient method. Resulting reference trajectories were tested in separate 2000 6-DOF Monte Carlo runs, using the Atmospheric Guidance Algorithm Testbed for the Mars Surveyor Program 2001 (MSP '01) Orbiter. These results were compared to an August 1998 study using the same terminal point control guidance algorithm and simulation testbed. Satisfactory improvements over the 1998 study are amply demonstrated.
    Keywords: Astrodynamics
    Type: 1999 Flight Mechanics Symposium; 85-99; NASA/CP-1999-209235
    Format: text
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  • 2
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    Variational Trajectory Optimization Tool Set: Technical description and user's manual (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The algorithms that comprise the Variational Trajectory Optimization Tool Set (VTOTS) package are briefly described. The VTOTS is a software package for solving nonlinear constrained optimal control problems from a wide range of engineering and scientific disciplines. The VTOTS package was specifically designed to minimize the amount of user programming; in fact, for problems that may be expressed in terms of analytical functions, the user needs only to define the problem in terms of symbolic variables. This version of the VTOTS does not support tabular data; thus, problems must be expressed in terms of analytical functions. The VTOTS package consists of two methods for solving nonlinear optimal control problems: a time-domain finite-element algorithm and a multiple shooting algorithm. These two algorithms, under the VTOTS package, may be run independently or jointly. The finite-element algorithm generates approximate solutions, whereas the shooting algorithm provides a more accurate solution to the optimization problem. A user's manual, some examples with results, and a brief description of the individual subroutines are included.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA-TM-4442 , L-17166 , NAS 1.15:4442
    Format: application/pdf
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  • 3
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    Comparison of effects of copropagated and precomputed atmosphere profiles on Monte Carlo trajectory simulation (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A realization of a stochastic atmosphere model for use in simulations is presented. The model provides pressure, density, temperature, and wind velocity as a function of latitude, longitude, and altitude, and is implemented in a three degree of freedom simulation package. This implementation is used in the Monte Carlo simulation of an aeroassisted orbital transfer maneuver and results are compared to those of a more traditional approach.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA-TM-102600 , NAS 1.15:102600
    Format: application/pdf
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  • 4
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    An Atmospheric Guidance Algorithm Testbed for the Mars Surveyor Program 2001 Orbiter and Lander (1998)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: An Atmospheric Flight Team was formed by the Mars Surveyor Program '01 mission office to develop aerocapture and precision landing testbed simulations and candidate guidance algorithms. Three- and six-degree-of-freedom Mars atmospheric flight simulations have been developed for testing, evaluation, and analysis of candidate guidance algorithms for the Mars Surveyor Program 2001 Orbiter and Lander. These simulations are built around the Program to Optimize Simulated Trajectories. Subroutines were supplied by Atmospheric Flight Team members for modeling the Mars atmosphere, spacecraft control system, aeroshell aerodynamic characteristics, and other Mars 2001 mission specific models. This paper describes these models and their perturbations applied during Monte Carlo analyses to develop, test, and characterize candidate guidance algorithms.
    Keywords: Aircraft Stability and Control
    Type: AIAA Paper 98-4569 , AIAA Atmospheric Flight Mechanics Conference; Aug 10, 1998 - Aug 12, 1998; Boston, MA; United States
    Format: application/pdf
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  • 5
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    Mars Smart Lander Parachute Simulation Model (2002)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A multi-body flight simulation for the Mars Smart Lander has been developed that includes six degree-of-freedom rigid-body models for both the supersonically-deployed and subsonically-deployed parachutes. This simulation is designed to be incorporated into a larger simulation of the entire entry, descent and landing (EDL) sequence. The complete end-to-end simulation will provide attitude history predictions of all bodies throughout the flight as well as loads on each of the connecting lines. Other issues such as recontact with jettisoned elements (heat shield, back shield, parachute mortar covers, etc.), design of parachute and attachment points, and desirable line properties can also be addressed readily using this simulation.
    Keywords: Lunar and Planetary Science and Exploration
    Type: AIAA Paper 2002-4617 , AIAA Atmospheric Flight Mechanics Conference and Exhibit; Aug 05, 2002 - Aug 08, 2002; Monterey, CA; United States
    Format: application/pdf
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  • 6
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    LDSD POST2 Modeling Enhancements in Support of SFDT-2 Flight Operations (2016)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Program to Optimize Simulated Trajectories II (POST2) was utilized to develop trajectory simulations characterizing all flight phases from drop to splashdown for the Low-Density Supersonic Decelerator (LDSD) project's first and second Supersonic Flight Dynamics Tests (SFDT-1 and SFDT-2) which took place June 28, 2014 and June 8, 2015, respectively. This paper describes the modeling improvements incorporated into the LDSD POST2 simulations since SFDT-1 and presents how these modeling updates affected the predicted SFDT-2 performance and sensitivity to the mission design. The POST2 simulation flight dynamics support during the SFDT-2 launch, operations, and recovery is also provided.
    Keywords: Spacecraft Design, Testing and Performance
    Type: AAS Paper 16-221 , NF1676L-22644 , AAS/AIAA Space Flight Mechanics Meeting; Feb 14, 2016 - Feb 18, 2016; Napa, CA; United States
    Format: application/pdf
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  • 7
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    Validation of Multibody Program to Optimize Simulated Trajectories II Parachute Simulation with Interacting Forces (2009)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: A capability to simulate trajectories of multiple interacting rigid bodies has been developed, tested and validated. This capability uses the Program to Optimize Simulated Trajectories II (POST 2). The standard version of POST 2 allows trajectory simulation of multiple bodies without force interaction. In the current implementation, the force interaction between the parachute and the suspended bodies has been modeled using flexible lines, allowing accurate trajectory simulation of the individual bodies in flight. The POST 2 multibody capability is intended to be general purpose and applicable to any parachute entry trajectory simulation. This research paper explains the motivation for multibody parachute simulation, discusses implementation methods, and presents validation of this capability.
    Keywords: Astrodynamics
    Type: NASA/TP-2009-215765 , L-19644 , LF99-8627
    Format: application/pdf
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  • 8
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    Partial Validation of Multibody Program to Optimize Simulated Trajectories II (POST II) Parachute Simulation With Interacting Forces (2002)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: A capability to simulate trajectories Of Multiple interacting rigid bodies has been developed. This capability uses the Program to Optimize Simulated Trajectories II (POST II). Previously, POST II had the ability to simulate multiple bodies without interacting forces. The current implementation is used for the Simulation of parachute trajectories, in which the parachute and suspended bodies can be treated as rigid bodies. An arbitrary set of connecting lines can be included in the model and are treated as massless spring-dampers. This paper discusses details of the connection line modeling and results of several test cases used to validate the capability.
    Keywords: Astronautics (General)
    Type: NASA/TM-2002-211634 , L-18166 , NAS 1.15:211634
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  • 9
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    An Approach to Simulation of Extreme Conditions for a Planetary Lander (2001)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: A "Monte Carlo-like" design analysis tool is developed and applied to an aeromaneuvering Mars entry vehicle. This tool provides realistic but challenging design cases using many fewer cases than a full Monte Carlo analysis. The problem of random input variables that are provided a priori (as opposed to being drawn from a given distribution) is addressed and a solution is found that shows prospects for future improvement.
    Keywords: Launch Vehicles and Launch Operations
    Type: NASA/TM-2001-211246 , L-18125 , NAS 1.15:211246
    Format: application/pdf
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  • 10
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    Entry Vehicle Control System Design for the Mars Smart Lander (2002)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The NASA Langley Research Center, in cooperation with the Jet Propulsion Laboratory, participated in a preliminary design study of the Entry, Descent and Landing phase for the Mars Smart Lander Project. This concept utilizes advances in Guidance, Navigation and Control technology to significantly reduce uncertainty in the vehicle landed location on the Mars surface. A candidate entry vehicle controller based on the Reaction Control System controller for the Apollo Lunar Excursion Module digital autopilot is proposed for use in the entry vehicle attitude control. A slight modification to the phase plane controller is used to reduce jet-firing chattering while maintaining good control response for the Martian entry probe application. The controller performance is demonstrated in a six-degree-of-freedom simulation with representative aerodynamics.
    Keywords: Space Communications, Spacecraft Communications, Command and Tracking
    Type: AIAA Paper 2002-4504 , AIAA Atmospheric Flight Mechanics Conference and Exhibit; Aug 05, 2002 - Aug 08, 2002; Monterey, CA; United States
    Format: application/pdf
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