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Hadaegh, Fred Y.

Publications and source records attributed to Hadaegh, Fred Y..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

An Overview of the Formation and Attitude Control System for the Terrestrial Planet Finder Formation Flying Interferometer

The Terrestrial Planet Finder formation flying Interferometer (TPF-I) will be a five-spacecraft, precision formation operating near the second Sun-Earth Lagrange point. As part of technology development for TPF-I, a formation and attitude control system (FACS) is being developed that achieves the precision and functionality needed for the TPF-I formation and that will be demonstrated in a distributed, real-time simulation environment. In this paper we present an overview of FACS and discuss in detail its formation estimation, guidance and control architectures and algorithms. Since FACS is currently being integrated into a high-fidelity simulation environment, component simulations demonstrating algorithm performance are presented.

Scharf, Daniel P.↗
NASA NTRS2004

On the Constrained Attitude Control Problem

In this paper, we consider various classes of constrained attitude control (CAC) problem in single and multiple spacecraft settings. After categorizing attitude constraints into four distinct types, we provide an overview of the existing approaches to this problem. We then proceed to further expand on a recent algorithmic approach to the CAC problem. The paper concludes with an example demonstrating the viability of the proposed algorithm for a multiple spacecraft constrained attitude reconfiguration scenario.

semidefinite programming↗
NASA NTRS2004

Guaranteed spatial initialization of distributed spacecraft formations

In a precious paper the authors developed a formation initialization (FI) algorithm for a deep space, N-spacecraft formation. It was demonstrated analytically that this FI contribution of this paper is to extend this planar guarantee to deep space formations with arbitrary initial conditions. As part of the guarantee of initialization, a bound on the time-to-initialize is obtained. The guaranteed FI algorithm is then demonstrated for a two-spacecraft formation with realistic deep space mission constraints (e.g. limited field-of-view relative sensors and attitude constraints). The two-spacecraft scenario is challenging in that it has the least relative sensor field-of-view overlap. Finally, for this scenario, the distribution of time-to-initialize is characterized through a 150,000-case Monte Carlo analysis.

initialization↗
NASA NTRS2004

Dynamics of Earth orbiting formations

In this paper the equations of motion of a formation consisting of n spacecraft in Earth orbit are derived via Lagrange's equations. The equations of motion of the formation are developed with respect to both (1) a bound Keplerian reference orbit, and (2) a specific spacecraft in the formation. The major orbital perturbations acting on a formation in low Earth orbit are also included in the analysis. In contrast to the traditional approach based on the balance of linear momentum, the use of Lagrange's equations leads to a high-level matrix derivation of the formation equations of motion. The matrix form of the nonlinear motion equations is then linearized about a bound Keplerian reference orbit. Next, it is demonstrated that under the assumption of a circular reference orbit, the linearized equations of motion reduce to the well-known Hill-Clohessy-Wiltshire equations. The resulting linear and nonlinear dynamic equations lead to maximal physical insight into the structure of formation dynamics, and are ideally suited for use in the design and validation of formation guidance and control laws.

formation flying↗
NASA NTRS2004

Control of systems with tiered actuators with application to interferometer optical delay line control

High accuracy feedback control systems might employ tiers of actuators with different properties. Such systems performance can be estimated in advance using Bode integrals. The systems can be made globally stable with good transient responses and close to the best possible disturbance rejection when controllers include high-order linear links and multiple nonlinear dynamic links. The design approach is exemplified by designing conb-ol system for an interferometer optical delay line.

delay line control↗
NASA NTRS2004

Formations of Tethered Spacecraft as Stable Platforms for Far IR and Sub-mm Astronomy

In this paper we describe current research in tethered formations for interferometry, and a roadmap to demonstrating the required key technologies via on-ground and in-orbit testing. We propose an integrated kilometer-size tethered spacecraft formation flying concept which enables Far IR and Sub-mm astronomy observations from space. A rather general model is used to predict the dynamics, control, and estimation performance of formations of spacecraft connected by tethers in LEO and deep space. These models include the orbital and tethered formation dynamics, environmental models, and models of the formation estimator/controller/commander. Both centralized and decentralized control/sensing/estimation schemes are possible, and dynamic ranges of interest for sensing/control are described. Key component/subsystem technologies are described which need both ground-based and in-orbit demonstration prior to their utilization in precision space interferometry missions using tethered formations. Defining an orbiting formation as an ensemble of orbiting spacecraft performing a cooperative task, recent work has demonstrated the validity of the tethering the spacecraft to provide both the required formation rigidity and satisfy the formation reconfiguration needs such as interferometer baseline control. In our concept, several vehicles are connected and move along the tether, so that to reposition them the connecting tether links must vary in length. This feature enables variable and precise baseline control while the system spins around the boresight. The control architecture features an interferometer configuration composed of one central combiner spacecraft and two aligned collector spacecraft. The combiner spacecraft acts as the formation leader and is also where the centralized sensing and estimation functions reside. Some of the issues analyzed with the model are: dynamic modes of deformation of the distributed structure, architecture of the formation sensor, and sources of dynamical perturbation that need to be mitigated for precision operation in space. Examples from numerical simulation of an envisioned scenario in heliocentric orbit demonstrate the potential of the concept for space interferometry.

Quadrelli, Marco B.↗
NASA NTRS2004

Reconfigurable topologies for decentralized control of spacecraft formations in Deep Space

This paper discusses control and communication topologies that asynchronously distribute the sensing, communication and computation tasks amongst the spacecraft in the formation. Our approach allows the dynamic reconfiguration of the measurement and communication topologies while maintaining the specified formation performance objectives. An illustrative simulation example is presented.

Hadaegh, Fred Y.↗
NASA NTRS2003

Self-organizing control for space-based sparse antennas

An integrated control and electromagnetic/antenna formulation is presented for evaluating the performance of a distributed antenna system as a function of formation geometry. A distributed and self-organizing control law for the control law for the control of multiple antennas in Low Earth Orbit (LEO) is presented. The control system provides collaborative commanding and performance optimization to configure and operate the distributed formation system. A large aperture antenna is thereby realized by a collection of miniature sparse antennas in formation. A case study consisting of a simulation of four antennas in Low Earth orbit (LEO)is presented to demonstrate the concept.

formation flying↗
NASA NTRS2003

Guaranteed initialization of distributed spacecraft formations

In this paper we present a solution to the formation initialization (FI) problem for N distributed spacecraft located in deep space. Our solution to the FI problem is based on a three-stage sky search procedure that reduces the FI problem for N spacecraft to the simpler problem of initializing a set of sub-formations.

initialization↗
NASA NTRS2003

Initialization of distributed spacecraft for precision formation flying

In this paper’we present a solution to the formation initialization (FI) problem for N distributed spacecraft located in deep space. Our solution to the FI problem is based on a three-stage sky search procedure that reduces the FI problem for N spacecraft to the simpler problem of initializing a set of sub-formations. We demonstrate our FI algorithm in simulation using NASA’s five spacecraft Terrestrial Planet Finder mission as an example.

Ploen, Scott R.↗
NASA NTRS2000

Autonomous Landing and Smart Anchoring for In-Situ Exploration of Small Bodies

Future NASA missions include in-situ scientific explorations of small interplanetary objects like comets and asteroids. Sample acquisition systems are envisioned to operate directly from the landers that are anchored to the surface. Landing and anchoring proves to be challenging in the absence of an attitude control system and in the presence of nearly zero-gravity environments with uncertain surface terrain and unknown mechanical properties. This paper presents recent advancements in developing a novel landing and anchoring control system for the exploration of small bodies.

Ghavimi, Ali R.↗
NASA NTRS2000

Autonomous Sample Acquisition for Planetary and Small Body Explorations

Robotic drilling and autonomous sample acquisition are considered as the key technology requirements in future planetary or small body exploration missions. Core sampling or subsurface drilling operation is envisioned to be off rovers or landers. These supporting platforms are inherently flexible, light, and can withstand only limited amount of reaction forces and torques. This, together with unknown properties of sampled materials, makes the sampling operation a tedious task and quite challenging. This paper highlights the recent advancements in the sample acquisition control system design and development for the in situ scientific exploration of planetary and small interplanetary missions.

Ghavimi, Ali R.↗
NASA NTRS1998

Reconfigurable Control for the Formation Flying of Multiple Spacecraft

Several results on the reconfigurable control architecture for the formation flying of multiple spacecraft are presented. In this direction, simple control laws are combined with logic-based switching to propose a hybrid control architecture for leader reassignment, leader-following capturing, and dealing with control saturations.

Mesbahi, Mehran↗