Showing papers presented at "IEEE Aerospace Conference in 1997"

Phase-only adaptive nulling with a genetic algorithm

Abstract: This paper describes a new approach to adaptive phase-only nulling with phased arrays. A genetic algorithm adjusts some of the least significant bits of the beam steering phase shifters to minimize the total output power. Using small adaptive phase values results in minor deviations in the beam steering direction and small perturbations in the sidelobe level in addition to constraining the search space of the genetic algorithm. Various results are presented to show the advantages and limitations of this approach, in general, the genetic algorithm proves to be better than previous phase-only adaptive algorithms.

Beowulf: harnessing the power of parallelism in a pile-of-PCs

Abstract: The rapid increase in performance of mass market commodity microprocessors and significant disparity in pricing between PCs and scientific workstations has provided an opportunity for substantial gains in performance to cost by harnessing PC technology in parallel ensembles to provide high end capability for scientific and engineering applications. The Beowulf project is a NASA initiative sponsored by the HPCC program to explore the potential of Pile-of-PCs and to develop the necessary methodologies to apply these low cost system configurations to NASA computational requirements in the Earth and space sciences. This paper describes the technologies and methodologies employed to achieve the increased performance of PCs. Both opportunities afforded by this approach and the challenges confronting its application to real-world problems are discussed in the framework of hardware and software systems as well as the results from benchmarking experiments. Finally, near term technology trends and future directions of the Pile-of-PCs concept are considered.

ESL: a language for supporting robust plan execution in embedded autonomous agents

Abstract: ESL (Execution Support Language) is a language for encoding execution knowledge in embedded autonomous agents. It is similar in spirit to RAPs (1989), RS (1983), and RPL Reactive Plan Language, and its design owes much to these systems. Unlike its predecessors, ESL aims for a more utilitarian point in the design space. ESL was designed primarily to be a powerful and easy-to-use tool, not to serve as a representation for automated reasoning or formal analysis (although nothing precludes its use for these purposes). ESL consists of several sets of loosely coupled features that can be composed in arbitrary ways. It is currently implemented as a set of extensions to Common Lisp, and is being used to build the executive component of a control architecture for an autonomous spacecraft.

Towards an application framework for automated planning and scheduling

Abstract: A number of successful applications of automated planning and scheduling applications to spacecraft operations have recently been reported in the literature. However, these applications have been one-of-a-kind applications that required a substantial amount of development effort. In this paper, we describe ASPEN (Automated Planning/Scheduling Environment), a modular, reconfigurable application framework which is capable of supporting a wide variety of planning and scheduling applications. We describe the architecture of ASPEN, as well as a number of current spacecraft control/operations applications in progress.

Microelectromechanical systems (MEMS)

Abstract: The following topics are dealt with: MEMS fundamentals; MEMS fabrication technology; MEMS market and industry structure; defense applications; investment assessment; inertial measurement devices; multiple device chips; optical MEMS components; monolithic free-space optical disk pickup head; digital micromirror display; optomechanical displays; environmental monitoring sensors; wireless integrated microsensors; tactical remote sensors; mass spectrograph; miniature analytical instrumentation; microdisk arrays for data storage; multi-user MEMS projects; electronic design aids; fluid flow analysis; and MEMS technology trends.

On-board planning for New Millennium Deep Space One autonomy

Abstract: The Deep Space One (DS1) mission, scheduled to fly in 1998, will be the first NASA spacecraft to feature an on-board planner. The planner is part of an artificial intelligence based control architecture that comprises the planner/scheduler, a plan execution engine, and a model-based fault diagnosis and reconfiguration engine. This autonomy architecture reduces mission costs and increases mission quality by enabling high-level commanding, robust fault responses, and opportunistic responses to serendipitous events. This paper describes the on-board planning and scheduling component of the DS1 autonomy architecture.

Mars Global Surveyor mission

Abstract: The Mars Global Surveyor (MGS) Spacecraft was successfully launched on November 7, 1996 to the planet Mars for an extended study of the planet's surface, atmosphere, gravitational field and magnetic field. In order to achieve the scientific objectives of the mission, the spacecraft will be inserted into a low-altitude, near-polar, sun-synchronous orbit. Data will be collected and returned from six prime experiments on the spacecraft for over one Martian year (687 Earth days) and will provide for a better understanding of the geology, geophysics, and climatology of Mars.

Advanced grid stiffened structures for the next generation of launch vehicles

Abstract: Although the necessity of using composite materials in the next generation of launch vehicles has become widely accepted, the specific structural type (monocoque, sandwich, skin-stringer, etc.) has yet to be determined. One possible candidate is the Advanced Grid Stiffened (AGS) structure, a rib-skin configuration evolved from early isogrid stiffening concepts. AGS structures show great promise for satisfying increased reliability and reduced cost requirements due to their adaptability to automated manufacturing. They also lend themselves to use in operational environments, due to their high strength, resistance to moisture absorption, and damage tolerance. Recent research has focused on the manufacture and design of AGS structures, specifically focusing on the potential for automated manufacture. In early 1997, the first composite AGS launch vehicle component, a payload shroud fabricated using fully automated techniques, will be flown on a suborbital flight. The manufacturing and tooling techniques developed as part of this program represent a significant step toward the goal of affordable launch-vehicle structures. An overview of AGS structures is presented along with a description of their current manufacturing 'state of the art'. A synopsis of the AGS payload shroud program is also presented.

Automating the process of optimization in spacecraft design

Abstract: Spacecraft design optimization is a difficult problem, due to the complexity of optimization cost surfaces and the human expertise in optimization that is necessary in order to achieve good results. In this paper, we propose the use of a set of generic, metaheuristic optimization algorithms (e.g., genetic algorithms, simulated annealing), which is configured for a particular optimization problem by an adaptive problem solver based on artificial intelligence and machine learning techniques. We describe work in progress on OASIS, a system for adaptive problem solving based on these principles.

Array-based vapor sensing using chemically sensitive, polymer composite resistors

Abstract: We describe herein the construction of simple, low-power, broadly responsive vapor sensors. Insulating polymer-conductor composites have been shown to swell reversibly upon exposure to vapors. Thin films of polymer composites have been deposited across two metallic leads, with swelling-induced resistance changes of the films signaling the presence of vapors. To identify and classify vapors, arrays of such vapor-sensing elements have been constructed, with each element containing either carbon black or poly(pyrrole) as the conducting phase mixed with one of several different organic polymers as the insulating phase. A convenient chemical polymerization of poly(pyrrole) which allows a high degree of processibility is also described. The differing gas-solid partition coefficients for the various polymers of the sensor array produce a pattern of resistance changes that can be used to classify vapors and vapor mixtures. This type of sensor array has been shown to resolve common organic solvents, including molecules of different classes (such as aromatics from alcohols) as well as those within a particular class (such as benzene from toluene and methanol from ethanol). The response of an individual composite to varying concentrations of solvent is shown to be consistent with the predictions of percolation theory. Accordingly, significant increases in the signals of array elements have been observed for carbon black-polymer composites that were operated near their percolation thresholds.

Space-based bistatic GMTI using low resolution SAR

Abstract: A new approach for matched filtering of moving targets using long dwell time Synthetic Aperture Radar, SAR, is presented. The approach eliminates the need for the matched filter to track the envelope of a target as it moves through different range bins. The process uses a keystone format mapping of the raw radar data which eliminates the effects of linear range migration. After keystoning, multiple two dimensional quadratic phase references are used to match all possible target accelerations. This matched filter approach is applied to a strawman spaced-based bistatic surveillance system for detecting targets in ground clutter with velocities up to 50 mph (22 m/sec). Matched filter performance is simulated and estimates are made of the processing resource requirements showing that onboard processing is feasible.

Microwave and mechanical considerations in the design of MEM switches for aerospace applications

Abstract: Microelectromechanical Systems (MEMS) technology is expected to have tremendous impact on aerospace systems. Indeed, phased array antennas, frequency multiplexers, spacecraft GN&C, on-board communications, autonomous health monitoring and safety, space structures, thermal control, and on-board system reconfigurability will favorably and decisively impacted MEMS technology. One of the most fundamental and ubiquitous components in these functions, enabled by MEMS technology, will be the electrostatic microelectromechanical (MEM) switch. The MEM switch, due to its simplicity and high performance potential, is poised to become the pioneering MEMS component, particularly, for microwave signal processing-related applications in space-based communications systems. This paper will discuss the impact of microwave performance specifications of the MEM switch on its mechanical structure and design. In particular, quantitative discussion of switch parameters including actuation voltage, actuation frequency, loss, and isolation will be presented.

Space-Based Infrared System (SBIRS) system of systems

Abstract: The Space-Based Infrared System (SBIRS) is the modern, cost effective follow-on to the Defense Support Program (DSP). SBIRS will support four broad mission areas: missile warning, missile defense, technical intelligence, and battlespace characterization. Like DSP, SBIRS will provide missile launch warning and attack assessment to the strategic and theater command centers. SBIRS additionally supports national and theater missile defense as well as technical intelligence and battlespace characterization. The SBIRS architecture includes constellation of satellites in high and low altitude orbits. Four satellites in geosynchronous (GEO) orbit and two sensors on multi-mission satellites in Molniya orbit (HEO, Highly Elliptical Orbit) comprise the high altitude component of the constellation. The Low Earth Orbit (LEO) configuration has not yet been selected, but it will likely include from eighteen to forty satellites. The SBIRS processing and reporting will be consolidated at a Mission Control Station (MCS) in the Continental United States (CONUS). The MCS will be developed first and go on-line in 1999 to support the DSP system; the high altitude satellites will be developed and launched next, starting in 2002; and the low altitude satellites will be launched last, starting in 2006. Lockheed-Martin will develop the SBIRS System of Systems and High Component. The SBIRS system Of systems architecture is referred to as "High now, Low later".

STARDUST: Discovery's InterStellar dust and cometary sample return mission

Abstract: The STARDUST Discovery mission will collect samples of cometary coma and interstellar dust and return them to Earth. Five years after launch in February 1999, coma dust will be captured by impact into ultra-low-density silica aerogel during a 6 km/s flyby of Comet Wild 2. The returned samples will be investigated at laboratories where the most critical information on these primitive materials is retained. The Jet Propulsion Laboratory provides project management with Lockheed Martin Astronautics as the spacecraft industrial partner. STARDUST management is aggressively pursuing cost control through the use of Total Quality Management principles, specifically operating in a Project Engineering and Integration Team that "flattens" the traditional hierarchical structure by including all project elements from the beginning, in a concurrent engineering framework focusing on evolving Integrated Mission Capability.

TIER II Plus airborne EO sensor LOS control and image geolocation

Abstract: TIER II Plus is a high altitude unmanned reconnaissance aircraft carrying a synthetic aperture radar (SAR) and electro-optical/infrared (EOIR) sensor that will provide all-weather, day and night, high resolution imagery of ground targets for joint armed forces users. Its high area coverage rate is achieved in near real-time by transmitting the collected imagery while the vehicle is airborne and relaying that imagery via satellite to ground stations for processing and dissemination. The electro-optical sensor assembly consists of a mid-wave infra-red (MWIR) staring array built by Hughes Aircraft Company and a CCD visible staring array from Kodak that share common reflective optics. The telescope/sensor subassembly is mounted on the inner gimbal of a two axis gimbal set that directs the sensor line-of-sight (LOS) to designated earth-fixed locations. An on-gimbal inertial rate sensor provides the 2-degree-of-freedom (2DOF) inertial reference to stabilize the sensor LOS. An off-gimbal GPS-aided inertial navigation system (INS) provides aircraft navigation data to the control system for inertial position stabilization and for determining the target image geolocation. Fine stabilization and step/stare requirement is jointly achieved with two-axis image motion compensation (IMC) mirror mechanisms mounted internally in the telescope optical train. This paper describes the salient features of the TIER II Plus control system design with emphasis on the algorithms used for LOS control, command generation, and target image geolocation. Computer simulation results will be presented to support the design.

Space technology and the discovery of the Lost City of Ubar

Abstract: The location of the legendary city of Ubar, a desert caravansary which supported the ancient and lucrative frankincense trade, has likely been found at the edge of the Arabian Peninsula's Empty Quarter in modern day Oman. Legend was that Ubar perished in a sandstorm as divine punishment for wicked living. Actually, much of the fortress collapsed into a sinkhole, perhaps undermined by extensive ground water withdrawal used to irrigate the surrounding oasis. The archaeological site was located by an unusual combination of historical research and the application of space technology in support of traditional archaeology.

Assessment of a large aperture telescope trade space and active opto-mechanical control architecture

Abstract: The Air Force's Phillips Laboratory has actively pursued component technology developments that support space based imaging and space-based laser weapon platforms. The components must be integrated successfully to field operational systems. The integration of many of these technology developments is tightly coupled and often themselves a technology barrier that must be overcome before a system can go ahead. As a result, the Phillips Laboratory initiated the UltraLITE program. The program has focused on the integration concerns of advanced sparse optical array systems. Sparse optical arrays offer significant benefits over the existing monolithic telescopes flown in space today; however, for a sparse optical array successful, the program technologies in the areas of advanced optical element fabrication, advanced lightweight actively controlled deployable structures, wavefront error sensing and compensation methods, and image post-processing algorithms. All these technologies must come to fruition and work together for such a program to succeed. The UltraLITE program concentrates on providing techniques for large precision deployable structures and wavefront sensing and control. The program will demonstrate these technologies in the laboratory with the long term goal of a space flight in a 0-g, micro-gravity environment.

The Poynting theorems and the potential for electrically small antennas

Abstract: Analyses of power in radiation fields are nearly universally based upon the complex Poynting theorem (CPT), yet the scientific basis for its use is not well established. The time dependent Poynting theorem (TDPT), is seldom used yet its scientific basis is well established. We use Hansen's method to obtain a generalized modal expansion for all possible electromagnetic fields that can originate within a confined volume and travel infinitely outward, combine the modal expansions and both Poynting theorems to determine the power expressions, and contrast results. The TDPT shows that the characterization of power in a sinusoidal field requires three numbers. Therefore it cannot be fully described by only real and reactive values. We conclude that the CPT is intrinsically an insufficient basis for a full description of power in a radiation field. We compare TDPT and CPT solutions for several idealized antenna designs. Comparative analyses show that the TDPT provides solutions that correspond to reality in all cases and the CPT does not. Proofs that electrically small antennas cannot be efficient are based upon the CPT; we re-examine these proofs using the TDPT and find that certain mixed modal configurations surpass the generally accepted small antenna rules.

Automated test methodology for Operational Flight Programs

Abstract: This paper describes how a new testing methodology was employed to evaluate the possibility of reducing the cost of systems testing and improving reliability of the F-16A/B Expanded Fire Control Computer (XFCC) Operational Flight Program (OFP). This new testing methodology was utilized to automatically generate tests which provide all of the stimuli and verification needed to fully drive and test the XFCC OFP in a simulated environment.

Resource scheduling for a network of communications antennas

Abstract: This paper describes the Demand Access Network Scheduler (DANS) system for automatically scheduling and rescheduling resources for a network of communications antennas. DANS accepts a baseline schedule and supports rescheduling of antenna and subsystem resources to satisfy tracking goals in the event of: changing track requests, equipment outages, and inclement weather.

Payload technologies and applications for uninhabited air vehicles (UAVs)

Abstract: After more than 50 years of limited niche applications in such roles as aerial targets, UAVs have recently emerged as major aerospace platforms for both military and civilian uses. This is due to three fundamental breakthroughs: (1) UAVs have begun to achieve reliability levels which allow routine operational use, (2) payload technologies have matured to the point where extremely useful functions can be accommodated within the weight, volume and power constraints of small airplanes, and (3) evidence is mounting that UAVs can do many tasks better and more affordably than manned aircraft. In many ways, UAVs compete with space systems for equivalent functions, often with the advantage of persistence over an area of interest at far closer range than a geostationary satellite. This paper surveys some of the major electronics developments which contribute to this resurgence. Among the topics covered are UAV architectures; imaging sensors, including synthetic aperture radar (SAR) and infrared/electro-optical (IR/EO) cameras; communications and data link systems; specialized sensors for such things as chemical detection and RF spectrum surveillance; and onboard processing. In all of these, recent system designs demonstrate levels of performance, e.g., SAR resolution and image processing time, comparable to or better than those achievable a few years ago only in systems costing one to two orders of magnitude more. The ways in which these payloads support military missions such as surveillance and commercial operations such as communications relay and earth resources sensing are reviewed. Finally, some projections are presented about important trends in both payload technologies and system applications.

Wide area surveillance concepts based on geosynchronous illumination and bistatic UAV or satellite reception

Abstract: The authors describe and evaluate in this paper the performance of a space-based radar surveillance concept employing geosynchronous illumination and bistatic reception-with either unmanned airborne vehicles (UAVs) or low-orbit satellites as reception platforms. Two classes of surveillance are considered: that of aircraft targets (generically designated as "airborne moving target indication" or AMTI) and that of slow-moving ground targets (generically designated as "ground moving target indication" or GMTI). While the bistatic concepts are hardly new, it is our conclusion, based on design examples presented here, that the emergence of high-speed processing to support large-scale beamforming for AMTI, and MTI-SAR for GMTI, have made these approaches feasible with the result of substantial cost and performance advantages over more conventional monostatic approaches when only limited regions (i.e. one or two theater-sized areas) need to be covered at any one time. MTI-SAR represents moving target indication achieved by matching an ensemble of possible target phase histories using radar processing techniques similar to those employed in synthetic aperture radar (SAR) for fixed targets. Continuing improvements in processing and space component technology, beyond the assumed implementation date of 2010, may increase this advantage of bistatic system surveillance.

Mars Pathfinder flight system integration and test

Abstract: This paper describes the system integration and test experiences, problems and lessons learned during the assembly, test and launch operations (ATLO) phase of the Mars Pathfinder flight system scheduled to land on the surface of Mars on July 4, 1997. The Mars Pathfinder spacecraft consists of three spacecraft systems: cruise stage, entry vehicle and lander. The cruise stage carries the entry and lander vehicles to Mars and is jettisoned prior to entry. The entry vehicle, including aeroshell, parachute and deceleration rockets, protects the lander during the direct entry and reduces its velocity from 7.6 to 0 km/s in stages during the 5 minute entry sequence. The lander's touchdown is softened by airbags which are retracted once stopped on the surface. The lander then uprights itself, opens up fully and begins surface operations including deploying its camera and rover. This paper overviews the system design and the results of the system integration and test activities, including the entry, descent and landing subsystem elements. System test experiences including science instruments, the microrover, Sojourner, and software are discussed. The final qualification of the entry, descent and landing (EDL) subsystems during this period is also discussed.

Design and evaluation of the power and data contactless transfer device

Abstract: The transmission of electrical power and data through rotating interfaces in spacecraft equipment is a common requirement which is frequently mission-critical. The use of slip-ring and roll-ring type units, especially for high rotational rates, presents many drawbacks such as friction torque, electrical noise, high contact resistance, wear, debris and criticality concerning reliability and lifetime. These difficulties may be eliminated by means of a Contactless Transfer Device (CTD). The design, development and testing of such a device is described. This space-compatible Breadboard Model (BM) is capable of transferring over 250 W and 5 Mbps bi-directional digital data. The design accommodates a central axle or pole of up to 55 mm diameter, and may be used in an in-side-in or an in-side-out configuration A modulated subcarrier capacitive technique is used for the transfer of multiplexed data, and a rotating transformer for power-transfer. A modular approach allows the design to be tailored to the needs of specific users, and to allow the option of a fully redundant implementation. The paper presents and discusses the results of an extensive evaluation program which covered functional, electromagnetic compatibility, thermal, torque and vibration testing.

Software fault injection: growing 'safer' systems

Abstract: This paper describes software fault injection and what types of anomalies fault injection should simulate. We highlight the benefits that software fault injection could have provided to several infamous software error-related incidents. And, we explain how fault injection can be used to "grow" safer systems.

Mars Microprobe entry analysis

Abstract: The Mars Microprobe mission will provide the first opportunity for subsurface measurements, including water detection, near the south pole of Mars. In this paper, performance of the Microprobe aeroshell design is evaluated through development of a six-degree-of-freedom (6-DOF) aerodynamic database and flight dynamics simulation. Numerous mission uncertainties are quantified and a Monte-Carlo analysis is performed to statistically assess mission performance. Results from this 6-DOF Monte-Carlo simulation demonstrate that, in a majority of the cases (approximately 2-/spl sigma/), the penetrator impact conditions are within current design tolerances. Several trajectories are identified in which the current set of impact requirements are not satisfied. From these cases, critical design parameters are highlighted and additional system requirements are suggested. In particular, a relatively large angle-of-attack range near peak heating is identified.

Interactive, repair-based planning and scheduling for Shuttle payload operations

Abstract: This paper describes the DATA-CHASER Automated Planner/Scheduler (DCAPS) system for automatically generating low-level command sequences from high-level user goals. DCAPS uses Artificial Intelligence (AI)-based search techniques and an iterative repair framework in which the system selectively resolves conflicts with the resource and temporal constraints of the DATA-CHASER Shuttle payload activities.

PARAGON: a paradigm for the specification, verification and testing of real-time systems

Abstract: The PARAGON toolset provides an environment for the modular and hierarchical design of resource-bound, real-time systems. It offers well-integrated graphical and textual specification languages with formal semantics. Both languages are based on the Algebra of Communicating Shared Resources (ACSR), a process algebra with explicit notions of time, resources and priority. The integration of the three notions widens the applicability of the PARAGON formalisms to embedded systems, control systems, and fault-tolerant systems where run-time resource requirements must be considered during the design phase. To facilitate the design of complex systems, PARAGON allows a designer to describe a system incrementally through refinement steps that preserve system properties. To increase dependability of system models, PARAGON offers three types of analysis: automated verification of system requirements, interactive simulation, and testing. In this paper, we demonstrate the design methodology that PARAGON offers through examples.

Health monitoring of vibration signatures in rotorcraft wings

Abstract: We propose to design and to evaluate an on-board intelligent health assessment tool for rotorcraft machines, which is capable of detecting, identifying, and accommodating expected system degradations and unanticipated catastrophic failures in rotorcraft machines under an adverse operating environment. A fuzzy-based neural network paradigm with an on-line learning algorithm is developed to perform expert advising for the ground-based maintenance crew. A hierarchical fault diagnosis architecture is advocated to fulfil the time-critical and on-board needs in different levels of structural integrity over a global operating envelope. The research objective is to experimentally demonstrate the feasibility and flexibility of the proposed health monitoring procedure through numerical simulations of bearing faults in USAF MH-53J PAVE LOW helicopter transmissions. The proposed fault detection, identification and accommodation architecture is applicable to various generic rotorcraft machines. The proposed system will greatly reduce the operational and developmental costs and serve as an essential component in an autonomous control system.

Integrating autonomy technologies into an embedded spacecraft system-flight software system engineering for new millennium

Abstract: Deep Space 1 (DS1) is the first deep-space mission of NASA's New Millennium technology validation program The DS1 flight software will validate five autonomy technologies: 1) Planner/Scheduler, which receives ground or on-board requests for spacecraft activities and schedules them to resolve any resource conflicts or timing constraints; 2) Smart Executive, which expands planned activities into lower-level commands, deduces required hardware configurations or other actions, and provides detection and avoidance of constraint violations; 3) Mode Identification and Reconfiguration engine, which incorporates models of hardware and software behavior, detects discrepancies due to hardware or software failures, and requests recovery actions via the Smart Executive 4) Autonomous Navigation, which determines the spacecraft trajectory from images of asteroids against the celestial sphere, and autonomously adjusts the trajectory to reach the target asteroid or comet 5) Beacon Monitoring, which uses radio carrier modification and telemetry summarization to simplify ground monitoring of spacecraft health Integration of these technologies into the spacecraft flight software architecture has presented a number of system engineering challenges, Some of these technologies were developed in a research-oriented, non-real-time, artificial intelligence organizational culture while spacecraft software is typically developed in a strong real-time, algorithmically-oriented culture The Navigation technology has been developed in a ground-based environment Integration of these different cultures and mutual education of the software team has been achieved An early rapid prototype of an existing spacecraft design proved very valuable in educating the team members and in working out the development process