Design study of a device to simulate the dynamic environment encountered under condi- tions of reduced or zero gravity final report

Design study of reduced or zero gravity environment simulation devic

First and second simulator evaluations of advanced integrated display and control systems

Advanced integrated visual and control systems simulator evaluations for post-Apollo manned spacecraf

Digital flight control research

The results of studies which were undertaken to contribute to the design of digital flight control systems, particularly for transport aircraft are presented. In addition to the overall design considerations for a digital flight control system, the following topics are discussed in detail: (1) aircraft attitude reference system design, (2) the digital computer configuration, (3) the design of a typical digital autopilot for transport aircraft, and (4) a hybrid flight simulator

Adaptive Estimation and Heuristic Optimization of Nonlinear Spacecraft Attitude Dynamics

For spacecraft conducting on-orbit operations, changes to the structure of the spacecraft are not uncommon. These planned or unanticipated changes in inertia properties couple with the spacecraft\u27s attitude dynamics and typically require estimation. For systems with time-varying inertia parameters, multiple model adaptive estimation (MMAE) routines can be utilized for parameter and state estimates. MMAE algorithms involve constructing a bank of recursive estimators, each assuming a different hypothesis for the systems dynamics. This research has three distinct, but related, contributions to satellite attitude dynamics and estimation. In the first part of this research, MMAE routines employing parallel banks of unscented attitude filters are applied to analytical models of spacecraft with time-varying mass moments of inertia (MOI), with the objective of estimating the MOI and classifying the spacecraft\u27s behavior. New adaptive estimation techniques were either modified or developed that can detect discontinuities in MOI up to 98 of the time in the specific problem scenario.Second, heuristic optimization techniques and numerical methods are applied to Wahba\u27s single-frame attitude estimation problem,decreasing computation time by an average of nearly 67 . Finally, this research poses MOI estimation as an ODE parameter identification problem, achieving successful numerical estimates through shooting methods and exploiting the polhodes of rigid body motion with results, on average, to be within 1 to 5 of the true MOI values

Hexapod Design For All-Sky Sidereal Tracking

In this paper we describe a hexapod-based telescope mount system intended to provide sidereal tracking for the Fly's Eye Camera project -- an upcoming moderate, 21"/pixel resolution all-sky survey. By exploiting such a kind of meter-sized telescope mount, we get a device which is both capable of compensating for the apparent rotation of the celestial sphere and the same design can be used independently from the actual geographical location. Our construction is the sole currently operating hexapod telescope mount performing dedicated optical imaging survey with a sub-arcsecond tracking precision.Comment: Accepted for publication in PASP, 10 page

Analysis of a Near Real-Time Optimal Attitude Control for Satellite Simulators

Dynamic optimization of spacecraft attitude reorientation maneuvers can result in significant savings in attitude determination and control system size, mass, and power. Optimal control theory is generally applied using an open loop trajectory which is vulnerable to disturbances. A closed loop implementation of optimal control has been difficult to achieve due to the computational requirements needed to quickly compute solutions to the optimal control problem. This research focuses on evaluating a near real-time optimal control (RTOC) system for large angle slew maneuvers on the Air Force Institute of Technology\u27s spacecraft simulator called SimSat. A near RTOC algorithm computes optimal control solutions at a rate of 0.4 Hz using a pseudospectral-based solver. The solutions or trajectories are then resampled at a fixed time step of 100 Hz and fed forward to a closed loop on SimSat. This algorithm is developed and tested on the hardware and compared to simulated and hardware results of a proportional-integral-derivative (PID) controller and an open loop optimal control controller for 90 degree and 180 degree Z-axis rotations. The benefits of decreased time to complete the maneuver and increased accuracy at the end of the optimal maneuver are shown to be improvements over traditional over PID control and open loop optimal control

Tähtede identifitseerimisalgoritmide kasutamine ESTCube-2 tähejälgimiskaameral

This thesis estimates the feasibility and determines the expected performance characteristics of a star tracker for ESTCube-2 student satellite. It measures limiting magnitude for the ESTCube- 2 star tracker hardware and estimates the decrease in signal-to-noise ratio due to the spacecraft’s rotational motion using geometric modelling. The acquired limiting magnitude is used to determine the optimal parameters to use with the pattern recognition algorithms for star identification purposes. The work also develops a way of creating and structuring a reference database in an effective way. Test results indicate that using the acquired parameters, the star tracker will be able to determine spacecraft’s attitude for cases of slow rotation up to 5 degrees per second. Results also indicate capability of attitude determination up to 10 times per second. The spacecraft’s mission also contains a phase of fast rotation, during which the star tracker will no longer be able to produce accurate attitude estimates at all times. With the algorithm configurations recommended in the thesis the ESTCube-2 star tracker could still provide a valuable contribution to the attitude and orbital control subsystem while experiencing angular velocities greater than 5 degrees per second. Thus it may outperform state-of-the-art commercial nanosatellite star trackers in that particular situation

Universality in D-brane Inflation

We study the six-field dynamics of D3-brane inflation for a general scalar potential on the conifold, finding simple, universal behavior. We numerically evolve the equations of motion for an ensemble of more than 7 \times 10^7 realizations, drawing the coefficients in the scalar potential from statistical distributions whose detailed properties have demonstrably small effects on our results. When prolonged inflation occurs, it has a characteristic form: the D3-brane initially moves rapidly in the angular directions, spirals down to an inflection point in the potential, and settles into single-field inflation. The probability of N_{e} e-folds of inflation is a power law, P(N_{e}) \propto N_{e}^{-3}, and we derive the same exponent from a simple analytical model. The success of inflation is relatively insensitive to the initial conditions: we find attractor behavior in the angular directions, and the D3-brane can begin far above the inflection point without overshooting. In favorable regions of the parameter space, models yielding 60 e-folds of expansion arise approximately once in 10^3 trials. Realizations that are effectively single-field and give rise to a primordial spectrum of fluctuations consistent with WMAP, for which at least 120 e-folds are required, arise approximately once in 10^5 trials. The emergence of robust predictions from a six-field potential with hundreds of terms invites an analytic approach to multifield inflation.Comment: 28 pages, 9 figure

Advanced flight control system study

The architecture, requirements, and system elements of an ultrareliable, advanced flight control system are described. The basic criteria are functional reliability of 10 to the minus 10 power/hour of flight and only 6 month scheduled maintenance. A distributed system architecture is described, including a multiplexed communication system, reliable bus controller, the use of skewed sensor arrays, and actuator interfaces. Test bed and flight evaluation program are proposed