Development of a Numeric Predictor-Corrector Aerocapture Guidance for Direct Force Control

Direct force control, where the angle of attack and sideslip angle are modulated, has been proposed as an alternative to bank angle control for aero-assist maneuvers. This paper reimplements the current state-of-the-art aerocapture guidance for bank angle control, Fully Numeric Predictor-corrector Aerocapture Guidance (FNPAG), for direct force control. The optimal control theory underlying the structure of FNPAG is shown to not be applicable to the direct force control approach. Several solution structures for the longitudinal channel are compared by simulating dispersed three-degree-of-freedom trajectories for a reference mission consisting of a low lift-to-drag vehicle and a highly elliptical, 1-sol target orbit around Mars. The equations of motion for the lateral channel are derived, and a controller is designed to target a specified orbital plane. Finally, a Monte Carlo is used to demonstrate the performance of the new guidance

In Mild Defiance of Rectangular Stability

This Artist\u27s Statement is concerned with the awareness of one\u27s environment, and the pursuit and evolution of an idea based on this awareness

Comparison of Aerocapture Performance Using Bank Control and Direct Force Control with Two Human-Scale Vehicles at Mars

Recent studies of human-scale missions to Mars have included a wide trade space of vehicle configurations and control schemes. Some configurations fly at a low angle of attack with a low L/D,while others fly at a high angle of attack with a mid L/D. Some use bank angle control, while others use direct force control, where the angle of attack and sideslip angle are independently modulated. This paper compares the performance of three vehicle configurations: a low-L/D vehicle using direct force control, a low-L/D vehicle using bank control, and a mid-L/D vehicle using bank control. The reference mission is aerocapture at Mars into a highly elliptical, 1-sol orbit. The trajectories are integrated in three degrees of freedom. All three cases utilize numeric predictor-corrector guidances and emulate control system responses with rate and acceleration limits. The configurations are compared using a Monte Carlo analysis. The robustness of each configuration to increased dispersions is also compared

Modal Analysis of a Two-Parachute System

The Orion capsule is designed to land under a nominal configuration of three main parachutes; however, the system is required to be fault tolerant and land successfully if one of the main parachutes fails to open. The Capsule Parachute Assembly System (CPAS) Team performed a series of drop tests in order to characterize the performance of the system with two main parachutes. During the series of drop tests, several distinct dynamical modes were observed. The most consequential of these is the pendulum mode. Three other modes are benign: flyout (scissors), maypole, and breathing. The actual multi-body system is nonlinear, flexible, and possesses significant cross-coupling. Rather than perform analysis of this highly complex system directly, we conduct analysis of each dynamical mode observed during flight, based on first principles. This approach is analogous to traditional aircraft flight dynamics analysis in which the full nonlinear behavior of the airframe is decomposed into longitudinal dynamics (phugoid and short-period modes) and lateral dynamics (spiral, roll-subsidence, and dutch-roll modes). This analysis is intended to supplement multi-body nonlinear simulations in order to provide further insight into the system

Linear Analysis of a Two-Parachute System Undergoing Pendulum Motion

Motion resembling that of a pendulum undergoing large-amplitude oscillation was ob- served during a series of flight tests of an unoccupied Orion Capsule Parachute Assembly System (CPAS) drop-test vehicle. Large excursions away from vertical by the capsule could cause it to strike the ground or ocean at a large angle with respect to vertical, with an undesirable attitude with respect to heading, or with a large horizontal or vertical speed. These conditions are to be avoided because they would endanger the occupants of the capsule in an actual mission. Pendulum motion is intimately related to a parachutes aerodynamic normal force coefficient, which is a nonlinear function of angle of attack. An analytical investigation of the dynamics of pendulum motion is undertaken with the aid of a simplified model of the physical system and the assumption that the normal force coefficient is a linear function of angle of attack in the neighborhood of a value corresponding to stable equilibrium. The analysis leads to a simple relationship for the location of a pivot point, which provides insights that are consistent with previous studies

A Comparison of Three Algorithms for Orion Drogue Parachute Release

The Orion Multi-Purpose Crew Vehicle is susceptible to ipping apex forward between drogue parachute release and main parachute in ation. A smart drogue release algorithm is required to select a drogue release condition that will not result in an apex forward main parachute deployment. The baseline algorithm is simple and elegant, but does not perform as well as desired in drogue failure cases. A simple modi cation to the baseline algorithm can improve performance, but can also sometimes fail to identify a good release condition. A new algorithm employing simpli ed rotational dynamics and a numeric predictor to minimize a rotational energy metric is proposed. A Monte Carlo analysis of a drogue failure scenario is used to compare the performance of the algorithms. The numeric predictor prevents more of the cases from ipping apex forward, and also results in an improvement in the capsule attitude at main bag extraction. The sensitivity of the numeric predictor to aerodynamic dispersions, errors in the navigated state, and execution rate is investigated, showing little degradation in performance

MMSE Estimation of Time-Varying Channels for DVB-T Systems with Strong Co-Channel Interference ∗

We present a minimum mean-square error (MMSE) channel estimator for a multi-antenna DVB-T receiver in the presence of strong co-channel interference. Based on the scattered pilot symbols contained in the DVB-T transmit signal, our method estimates the timevarying vector channel in an off-line, blockwise fashion. An implementation in the time-delay domain is used to reduce computations and enhance estimation performance. We also propose algorithms for estimating the channel statistics required for the design of the channel estimator. Simulation results show that in the case of strong co-channel interference, the proposed channel estimator achieves a significant performance improvement over a reference method.

Multipliers for p-Bessel sequences in Banach spaces

Multipliers have been recently introduced as operators for Bessel sequences and frames in Hilbert spaces. These operators are defined by a fixed multiplication pattern (the symbol) which is inserted between the analysis and synthesis operators. In this paper, we will generalize the concept of Bessel multipliers for p-Bessel and p-Riesz sequences in Banach spaces. It will be shown that bounded symbols lead to bounded operators. Symbols converging to zero induce compact operators. Furthermore, we will give sufficient conditions for multipliers to be nuclear operators. Finally, we will show the continuous dependency of the multipliers on their parameters.Comment: 17 page