Showing papers presented at "IEEE Aerospace Conference in 1998"

Design of the Remote Agent experiment for spacecraft autonomy

Abstract: This paper describes the Remote Agent flight experiment for spacecraft commanding and control. In the Remote Agent approach, the operational rules and constraints are encoded in the flight software. The software may be considered to be an autonomous "remote agent" of the spacecraft operators in the sense that the operators rely on the agent to achieve particular goals. The experiment will be executed during the flight of NASA's Deep Space One technology validation mission. During the experiment, the spacecraft will not be given the usual detailed sequence of commands to execute. Instead, the spacecraft will be given a list of goals to achieve during the experiment. In flight, the Remote Agent flight software will generate a plan to accomplish the goals and then execute the plan in a robust manner while keeping track of how well the plan is being accomplished. During plan execution, the Remote Agent stays on the lookout for any hardware faults that might require recovery actions or replanning. In addition to describing the design of the remote agent, this paper discusses technology-insertion challenges and the approach used in the Remote Agent approach to address these challenges. The experiment integrates several spacecraft autonomy technologies developed at NASA Ames and the Jet Propulsion Laboratory: on-board planning, a robust multi threaded executive, and model-based failure diagnosis and recovery.

Experiences with operations and autonomy of the Mars Pathfinder Microrover

Abstract: The Microrover Flight Experiment (MFEX) is a NASA OACT (Office of Advanced Concepts and Technology) flight experiment which, integrated with the Mars Pathfinder (MPF) lander and spacecraft system, landed on Mars on July 4, 1997. In the succeeding 30 sols (1 sol=1 Martian day), the Sojourner microrover accomplished all of its primary and extended mission objectives. After completion of the originally planned extended mission, MFEX continued to conduct a series of technology experiments, deploy its alpha proton X-ray spectrometer (APXS) on rocks and soil, and image both terrain features and the lander. This mission was conducted under the constraints of a once-per-sol opportunity for command and telemetry transmissions between the lander and Earth operators. As such, the MFEX rover was required to carry out its mission, including terrain navigation and contingency response, under supervised autonomous control. For example, goal locations were specified daily by human operators; the rover then safely traversed to these locations. During traverses, the rover autonomously detected and avoided rock, slope, and drop-off hazards, changing its path as needed before turning back towards its goal. This capability to operate in an unmodeled environment, choosing actions in response to sensor input to accomplish requested objectives, is unique among robotic space missions to date.

MEMS pressure sensors for aerospace applications

Abstract: MEMS (microelectromechanical systems) pressure sensors have been designed, fabricated and characterized. The fabrication process is fully compatible with IC (integrated circuit) fabrication such that multifunctional microelectronics can be directly integrated on the same chip for advanced aerospace applications. These pressure sensors are designed based on the piezoresistive sensing principle on surface micromachined polysilicon thin diaphragms. Both square- and circular-shape diaphragms with thickness of 2 /spl mu/m and width (diameter) of 100 /spl mu/m have been designed and fabricated. Prototype pressure sensors with 100 Psi in full scale have a measured sensitivity of 0.15 mV/V/Psi and a maximum linearity error of /spl plusmn/0.1% FSS (full scale span).

Active pixel sensor (APS) based star tracker

Abstract: Charge-Coupled Device (CCD) based star trackers provide reliable attitude estimation onboard most 3 axis stabilized spacecraft. The spacecraft attitude is calculated based on observed positions of stars, which are located and identified in a CCD image of the sky. A new photon sensitive imaging array, active pixel sensor (APS), has emerged as a potential replacement to CCDs. The APS chips utilize existing Complementary Metal Oxide Semiconductor (CMOS) production facilities, and the technology has several advantages over CCD technology. These include: lower power consumption, higher dynamic range, higher blooming threshold, individual pixel readout, single 3.3 or 5 Volt operation, the capability to integrate on-chip timing, control, windowing, analog to digital (A/D) conversion and centroiding operations. However, because the photosensitivity of an APS pixel is non-homogeneous, its suitability as a star tracker imager has been unknown. This paper reports test results of a 256/spl times/256-pixel APS chip for star tracker applications. Using photon transfer curves, a system read-out noise of 7 electrons, under laboratory conditions, has been determined (photogate type). The full well of an APS pixel is determined to be around 450,000 electrons. Utilizing astronomical observations, the sensitivity of APS was measured to 13600 e/sup -/(second.mm/sup 2/) for a 0/sup th/ magnitude star. Centroiding accuracy of the APS was in the order of 1/10 pixel. The dynamic range of the APS was better than 9 magnitudes. These measurements allow us to conclude that the APS is a potential replacement for CCD star trackers.

Spaceborne GPS current status and future visions

Abstract: The Global Positioning System (GPS), developed by the Department of Defense, is quickly revolutionizing the architecture of future spacecraft and spacecraft systems. Significant savings in spacecraft life cycle cost, in power, and in mass can be realized by exploiting Global Positioning System (GPS) technology in spaceborne vehicles. These savings are realized because GPS is a systems sensor-it combines the ability to sense space vehicle trajectory, attitude, time, and relative ranging between vehicles into one package. As a result, a reduced spacecraft sensor complement can be employed on spacecraft and significant reductions in space vehicle operations cost can be realized through enhanced onboard autonomy. This paper provides an overview of the current status of spaceborne GPS, a description of spaceborne GPS receivers available now and in the near future, a description of the 1997-1999 GPS flight experiments and the spaceborne GPS team's vision for the future.

Frequency-selective MEMS for miniaturized communication devices

Abstract: With Q's in the tens to hundreds of thousands, micromachined vibrating resonators are proposed as IC-compatible tanks for use in the low phase noise oscillators and highly selective filters of communications subsystems. To date, LF oscillators have been fully integrated using merged CMOS+microstructure technologies, and bandpass filters consisting of spring-coupled micromechanical resonators have been demonstrated in the HF range. In particular, two-resonator micromechanical bandpass filters have been demonstrated with frequencies up to 14.5 MHz, percent bandwidths on the order of 0.2%, and insertion losses less than 1 dB. Higher-order three-resonator filters with frequencies near 455 kHz have also been achieved, with equally impressive insertion losses for 0.09% bandwidths, and with more than 64 dB of passband rejection. Evidence suggests that the ultimate frequency range of this high-Q tank technology depends upon material limitations, as well as design constraints-in particular, to the degree of electromechanical coupling achievable in micro-scale resonators.

Using ASPEN to automate EO-1 activity planning

Abstract: This paper describes the application of an automated planning and scheduling system to the NASA Earth Orbiting 1 (EO-1) mission. The planning system, ASPEN, is used to autonomously schedule the daily activities of the satellite. The satellite and operations constraints are encoded within a software model used by the planner. This paper includes a description of the planning system and the associated modeling language. We then discuss how we encoded the EO-1 spacecraft operations with the modeling language. We conclude with a description of the end-to-end planning system as we envision it for EO-1.

A dual polarized dual band microstrip antenna for wireless communications

Abstract: The demand for antennas for mobile wireless applications has increased dramatically over the last 10 years. Today we have a number of land and satellite based systems for wireless communications using a wide range of frequency bands. Not only do we see an increase in the number of subscribers in the different systems but also a demand for dual or multi band equipment capable of handling two or more frequency bands. Our paper describes a dual polarized, dual band antenna element suited for use in a base station antenna. The antenna element is an aperture coupled, stacked patch, maintaining the symmetry needed for dual polarization operation. The total height is less than 0.15 /spl lambda/ at the lowest frequency and the element provides broadside radiation. Whereas most previously presented dual band elements are linearly polarized microstrip antennas which utilize a number of narrow-band resonators, our design has all the broadband and dual-polarized characteristics of traditional aperture coupled patch antennas. The bandwidth for return loss>10 dB of the element covers both the 880-960 MHz GSM (Global System for Mobile Communication) band and the 1710-1880 MHz DCS (Digital Cellular System) frequency band. The measured isolation between the ports corresponding to the two orthogonal polarizations is greater than 32 dB in both bands.

Microfluidic MEMS

Abstract: The advent of MEMS (micro-electro-mechanical systems) has enabled dramatic changes in diverse technological areas. In terms of control and distribution of liquids and gases (microfluidics), MEMS-based devices offer opportunities to achieve increased performance, and higher levels of functional integration, at lower cost, with decreased size and increased reliability. Microfluidic actuators include distribution microchannels and orifices, microvalves, micropumps, and microcompressors. Related microsensors are required to measure temperature, flow, pressure, viscosity, and density. This work focuses on the application of microfabricated valves based on the principles of thermopneumatic actuation. A brief comparison to other actuation techniques is made. The science and technology of silicon-based thermopneumatic microvalves is then detailed. The dynamics of the controlled fluid, and thermal and mechanical behavior of structures, necessary to understand the relationships between flow, pressure, and temperature are presented. The power required for actuation, the response speed, and the effect of shrinking size on these parameters are also derived. In terms of applications, previous research and product development efforts have demonstrated the application of thermopneumatic microvalves to problems of industrial gas and liquid control. Wide ranges of pressure, temperature, and flow rate have been achieved. Expansion valves for refrigeration control have also been produced. Most recently, the integration of microfluidic components using advanced packaging techniques has been used to create devices with higher levels of functionality. Specifically, high-precision pressure regulators, and pressure-based mass flow controllers, have been devised, based upon both normally-open and normally-closed microvalves. Also, low leak-rate shut-off valves, appropriate for use in vacuum system applications, have been developed successfully. At the highest level of integration, these modules have been themselves integrated into mesoscale gas sticks, and gas distribution panels, for use in distribution and control of electronics specialty gases.

The advancing state-of-the-art in second generation star trackers

Abstract: Until recently, only first-generation charge coupled device (CCD) spacecraft star trackers have been available. These track a small number of bright stars and are dependent on external processing for acquisition, calculation of corrections and transformation from CCD referenced to inertial referenced coordinates. Now, powerful microprocessors (>10 million instructions per second (MIPS)) with a few Mbytes of memory have become available in space qualified grades and have enabled the next step in star tracker concepts: second-generation fully autonomous designs. These second-generation units are equipped with star catalogs covering the entire sky. Their microprocessors instantly perform acquisition by pattern recognition of the entire image, thus relating the output from the star tracker directly to the celestial sphere. Their output data can be used in the attitude control system of a spacecraft without intermediate data processing. This saves central processor load, memory capacity and integratation of thousands of line of source code. The use of a large number of stars in each data frame makes the attitude estimates more accurate and operation both smoother and more robust in comparison to first-generation star trackers.

Spacecraft design using a genetic algorithm optimization approach

Abstract: Spacecraft design is a highly coupled problem. The design of the spacecraft must balance payload objectives and orbital design against cost and schedule guidelines. Currently spacecraft are 'optimized' manually through a tool-assisted evaluation of a limited set of design alternatives. With this approach there is no guarantee that a system-level focus will be taken and 'feasibility' rather than 'optimality' is commonly all that is achieved. With support from NASA, the author has investigated better methods for performing the earliest stage of spacecraft design (including cost analysis) to ensure that a systems perspective is taken. This paper describes a tool for conceptual spacecraft design, SCOUT (Spacecraft Concept Optimization and Utility Tool), that uses a set of design estimating relationships (DERs) and cost relationships (CERs) coupled with genetic optimization. A retrospective comparison between SCOUT results and the actual design of the Near Earth Asteroid Rendezvous (NEAR) spacecraft is made.

Autonomous failure detection, identification and fault-tolerant estimation with aerospace applications

Abstract: In this paper, we propose a novel approach for Failure Detection and Identification (FDI) in nonlinear systems based on the Interacting Multiple Model (IMM) Extended Kalman Filter (EKF) approach. In the nonlinear system FDI application, the main idea consists of representing each failure mode by a model and combining the outputs of EKF's based on different models in a near-optimal way. This IMM-FDI filter provides not only failure detection and identification but also a near-optimal estimate of the system state (even during a failure). The approach has been applied successfully to a problem of spacecraft autonomy for the detection and identification of sensor (gyro, star tracker) and actuator failures. The results of this application show that IMM-EKF detects and identifies failures much more rapidly and reliably than the multi-hypothesis EKF. Furthermore, it handles satisfactorily both permanent and transient failures. Current efforts are underway to perform extensive validation testing on high-fidelity simulation models of representative spacecraft.

Tracking ground targets with road constraints using an IMM estimator

Abstract: This paper presents the development of a tracker based on the Interacting Multiple Model (IMM) estimation algorithm for tracking groups of ground targets using Moving Target Indicator (MTI) reports obtained from an airborne sensor. The targets are moving along a constrained path, for example, a highway, with varying obscuration due to changing terrain conditions. In addition, the roads on which the targets travel can branch, merge, or cross. This constrained motion estimation problem is handled using an IMM estimator with varying mode sets depending on the topography. The design and implementation of the topography based Variable Structure IMM (VS-IMM) estimator is described. Simulation results are also presented.

An overview of smart antenna technology: the next wave in wireless communications

Abstract: Space is truly one of the "final frontiers" when it comes to next generation wireless communication systems. Large-scale penetration of such such systems into our daily lives will require the significant reductions in cost and increases in capacity that only the spatial dimension can hope to offer. That this is certainly the case is attested to by the significant number of companies that have been recently formed to bring products based on such concepts to the wireless marketplace. The approaches range from switched-beam to fully-adaptive with the benefits provided by the various approaches differing accordingly. At one end of the spectrum is Spatial Division Multiple Access (SDMA) technology, a technology with roots in various defense-related development programs, and which ArrayComm is currently developing in its IntelliCell(TM) line of products. SDMA technology employs antenna arrays and multi-dimensional nonlinear signal processing techniques to provide significant increases in capacity and quality of many wireless communication systems. Antenna arrays coupled with adaptive signal processing techniques employed at base stations improve coverage, capacity and trunking efficiency allowing lower cost deployments with cells of moderate to large size. The basic principles and architecture of SDMA wireless communication systems are outlined. Experimental results obtained from systems built to these new architectural specifications are presented demonstrating the efficacy of SDMA technology.

On the suitability of fiber optic data links in the space radiation environment: a historical and scaling technology perspective

Abstract: As NASA, DoD, industry, and others propagate the current spacecraft trends for increasing science data throughput and on-board processing, the use of fiber optic data links between spacecraft subsystems has gained heightened interest. With this is mind, we present a perspective of the use of these fiber optic systems in the space radiation environment that encompasses both the historical past and scaleable future space systems and their requirements.

Linear quaternion equations with application to spacecraft attitude propagation

Abstract: The kinematic relationship between body rates and rate of change of Euler parameters is an instance of linear quaternion differential equations. This paper presents solutions for general linear quaternion equations in terms of state transition quaternions, in parallel to similar results for matrix/vector linear differential equations. Series expansions of these transition quaternions are presented. For constant coefficient quaternion differential equations, the transition quaternion is shown to be the quaternion exponential, which is described in this paper. These results are used to derive algorithms for the solution of the kinematic relationship between spacecraft body rates and Euler parameters. First, it is demonstrated mathematically, that the quaternion exponential gives the exact rotation quaternion for slews about inertially fixed rotation axis, with no coning. Secondly, a popular third-order attitude propagation algorithm is derived using this approach. Variants of this algorithm for accuracy enhancements of attitude propagation algorithms are discussed.

Autonomous nucleus tracking for comet/asteroid encounters: the Stardust example

Abstract: Stardust is a mission to fly by Comet Wild-2 in early 2004 and return samples of the coma to Earth. During its 120-150 km flyby of the comet nucleus, a secondary science goal is to obtain images of the nucleus using the onboard navigation camera. Due to the 40 minute round-trip light time, ground processing of navigation data to update pointing information to maintain the nucleus in the camera field-of-view is impractical. Thus, a simple, reliable, and fast algorithm was developed to close the navigation loop onboard during encounter. The algorithm uses images of the nucleus during approach to update target relative state information. This involves centroiding on the image to obtain nucleus center-of-figure data and then processing the data through a Kalman filter to update the spacecraft, position and attitude. Monte Carlo simulations were then performed to test the algorithm. These simulations incorporated errors in spacecraft initial position and in attitude knowledge to provide a "truth" model which the filter must recover from. The results of the simulations proved that the algorithm was successful in maintaining the nucleus in the camera field-of-view assuming nominal values for the error sources. Even with worst case errors, the algorithm performed successfully in over 90% of the cases.

Microtechnology for space systems

Abstract: Microelectromechanical systems (MEMS) are micron-to-millimeter size electromechanical devices that are fabricated using modified semiconductor batch-fabrication techniques We believe that MEMS technology will have a significant impact on future space systems by (1) reducing the size, mass, power, and cost of individual sensors and actuators used throughout spacecraft and launch vehicles and (2) ultimately reducing overall spacecraft size At the Aerospace Corporation, we are focusing on near and far-term applications of MEMS in space systems for reduced mass, improved performance, higher reliability, increased health and status awareness, and reduced life cycle costs Specific tasks include the development of micro-propulsion technology for microsatellites (1-to-100 kg mass) and nanosatellites (1-to-1000 gram mass), the development of a flight-qualifiable GN&C (guidance, navigation, and control) unit using a GPS receiver and MEMS inertial sensors, and the development of a MEMS-based wireless multiparameter sensor

Proposed U.S. Global satellite systems operating at Ka-Band

Abstract: In May 1997, the U.S. Federal Communications Commission (FCC) licensed 13 proposed new Ka-band (20-to 30-GHz) satellite systems. Twelve of these systems intend to use geostationary orbits, and the FCC has allocated 49 orbital locations for the 55 satellites proposed for these systems. The 13th system, known as Teledesic, was to employ 840 low earth orbit (LEG) satellites. Subsequently, Teledesic announced a redesign of its system to use 288 satellites, and Motorola filed for a LEO system to be known as Celestri, having 63 satellites. The proposals from the larger players (e.g., Hughes, Loral, Lockheed Martin, and Motorola) are all for global, or nearly global, systems. This paper summarizes these global systems and discusses some of the technical challenges that the designers of these systems must overcome, as well as the markets the new systems might be expected to serve. All of the Ka-band systems plan to use the 500-MHz bandwidth allocated for fixed satellite services, in accordance with the 1995 World Radiocommunications Conference (WRC-95) guidelines (29.5 to 30.0 GHz for uplink and 19.7 to 20.2 GHz for downlink). A majority of the systems will also use the 28.35-28.6/18.55-18.8 GHz (250-MHz) frequency bands. In addition, some of the systems use part or all of the 29.0-29.5/19.2-19.7 GHz frequency bands. These bands require coordination with local multipoint distribution services (LMDS) and/or mobile satellite services (MSS) feeder links. All but two of the announced global systems employ satellites in geostationary Earth orbit (GEO). All the Ka-band systems except Teledesic and Celestri are designed to cover land masses only. Teledesic proposes to cover the entire globe, including polar regions and oceans, while Celestri will cover all latitudes between /spl plusmn/60/spl deg/. The Astrolink and Galaxy/Spaceway systems cover virtually all land masses. Loral's Cyberstar, along with GE*Star and Morning Star, cover most of the major population centers or areas where rapid traffic growth is expected early in the next century.

An assessment of Beowulf-class computing for NASA requirements: initial findings from the first NASA workshop on Beowulf-class clustered computing

Abstract: The Beowulf class of parallel computing machine started as a small research project at NASA Goddard Space Flight Center's Center of Excellence in Space Data and Information Sciences (CESDIS). From that work evolved a new class of scalable machine comprised of mass market common off-the-shelf components (M/sup 2/COTS) using a freely available operating system and industry-standard software packages. A Beowulf-class system provides extraordinary benefits in price-performance. Beowulf-class systems are in place and doing real work at several NASA research centers, are supporting NASA-funded academic research, and operating at DOE and NIH. The NASA user community conducted an intense two-day workshop in Pasadena, California on October 22-23, 1997. This paper provides an overview of the findings and conclusions of the workshop. The workshop determined that Beowulf-class systems can deliver multi-Gflops performance at unprecedented price-performance but that software environments were not fully functional or robust, especially for larger "dreadnought"-scale systems. It is recommended that the Beowulf community engage in an activity to integrate, port, or develop, where appropriate, necessary components of the software infrastructure to fully realize the potential of Beowulf class computing to meet NASA and other agency computing requirements.

Teledesic: a global broadband network

Abstract: The Teledesic Network (the Network) is a high-capacity broadband network that combines the global coverage and low latency of a LEO constellation of satellites with the flexibility of the Internet and "fiber-like" transmission quality It brings affordable access to interactive broadband communication to all areas of the Earth, including to those users that could not be served economically by other means It can serve as the access link between a user and a gateway into a terrestrial network, as the internetwork that links networks together, or as the communication link between users Although optimized for service to fixed-site Terminals, the Network is able to serve transportable Terminals and some mobile Terminals, such as for maritime and aviation applications Teledesic service will be provided in host countries through local service providers who administer and control the services offered to their end users

Inflatable space antennas-a brief overview

Abstract: The use of inflatable structures in space has both fascinated and challenged many in the space community for forty years or more. The authors present some history on the evolution of precision inflatable reflector design from simpler inflatable structures that have flown in space. Examples of reflectors that have been ground tested are presented and discussed, followed by a description of the Inflatable Antenna Experiment off the Shuttle in 1996. Results from the surface accuracy measurements of some of these reflectors are also presented, along with measured and calculated RF gain and beam patterns of the 3-meter L'Garde Demonstrator Program (LDP) reflector. Finally, the authors comment on the current status of space inflatable reflector technology at L'Garde.

Spacecraft solar array technology trends

Abstract: Photovoltaic solar array systems are the most common method for providing spacecraft power generation. The flexibility and variability of the many array types and configurations combine to accommodate a multitude of mission applications and space environments. Solar array technologies and their system configurations changed dramatically over the years as more aggressive and demanding requirements were imposed. This paper addresses the historical solar array technology trends. The evolution of solar array technologies and the key requirements responsible for driving this evolution are presented. Industry growth trends towards future systems are identified. Evolutionary technological improvements in photovoltaics, structural platforms and deployment systems are shown. Array selection criteria for a variety of requirements, applications, and environments are presented. Solar array technologies required to meet future mission trends are shown.

ADSL for high-speed broadband data service

Abstract: Asymmetrical Digital Subscriber Line (ADSL) service, with digital data rates of up to 8 Mbps over ordinary copper telephone lines, will enable major breakthroughs for Internet access and telecommuting. A new modulation technology, called Discrete Multitone (DMT), is the key that allows the transmission of such high speed data. This paper summarizes the concepts and applications of the several existing xDSL technologies and examines the ADSL technology, its uses and its limitations. Pertinent details are given on DMT modulation and its implementation on a microchip. The technology is further explored through the presentation of several system-level reference designs.

Micromechanical devices at JPL for space exploration

Abstract: Space exploration in the coming century will emphasize cost effectiveness and highly focused mission objectives, which will result in frequent multiple missions that broaden the scope of space science and to validate new technologies on a timely basis. Micro electromechanical systems (MEMS) is one of the key enabling technologies to create cost-effective, ultra-miniaturized, robust, and functionally focused spacecraft for both robotic and human exploration programs. Examples of MEMS devices at various stages of development include microgyroscope, microseismometer, microhygrometer, quadrupole mass spectrometer, and micropropulsion engine. These devices, when proven successful, will serve as models for developing components and systems for new-millennium spacecraft.

Microelectromechanical systems (MEMS): an overview of current state-of-the-art

Abstract: The applications and basics of microelectromechanical systems (MEMS) are discussed. The four main silicon micromachining techniques, i.e., bulk micromachining, surface micromachining, wafer-to-wafer bonding, and high aspect ratio micromachining are presented in detail. A microelectromechanical quartz rate sensor is also discussed. These techniques have been adapted to applications in the aerospace, military, industrial, medical, telecommunications and automotive industries to realize miniaturized highly integrated MEMS in a cost effective manner.

Mission operations with an autonomous agent

Abstract: The Remote Agent (RA) is an Artificial Intelligence (AI) system which automates some of the tasks normally reserved for human mission operators and performs these tasks autonomously on-board the spacecraft. These tasks include activity generation, sequencing, spacecraft analysis, and failure recovery. The RA will be demonstrated as a flight experiment on Deep Space One (DS1), the first deep space mission of the NASA's New Millennium Program (NMP). As we moved from prototyping into actual flight code development and teamed with ground operators, we made several major extensions to the RA architecture to address the broader operational context in which RA would be used. These extensions support ground operators and the RA sharing a long-range mission profile with facilities for asynchronous ground updates; support ground operators monitoring and commanding the spacecraft at multiple levels of detail simultaneously; and enable ground operators to provide additional knowledge to the RA, such as parameter updates, model updates, and diagnostic information, without interfering with the activities of the RA or leaving the system in an inconsistent state. The resulting architecture supports incremental autonomy, in which a basic agent can be delivered early and then used in an increasingly autonomous manner over the lifetime of the mission. It also supports variable autonomy, as it enables ground operators to benefit from autonomy when they want it, but does not inhibit them from obtaining a detailed understanding and exercising tighter control when necessary. These issues are critical to the successful development and operation of autonomous spacecraft.

Satellite threat warning and attack reporting

Abstract: The Air Force Research Laboratory's Satellite Threat Warning and Attack Reporting (STW/AR) program will provide technologies for advanced threat warning and reporting of radio frequency (RF) and laser threats. The STW/AR program objectives are: (1) Develop cost-effective technologies to detect, identify, locate, characterize, and report attacks or interference against U.S. and Allied satellites. (2) Demonstrate innovative, lightweight, low-power, RF and laser sensors. The program focuses on the demonstration of RF and laser sensors. The RF sensor effort includes the investigation of interferometric antenna arrays, multi-arm spiral and Butler matrix antennas, wideband receivers, adaptive processors, and improved processing algorithms. The laser sensor effort includes the investigation of alternative detectors, broadband grating, and optical designs, active pixel sensing, and improved processing algorithms. An objective for both sensors is to miniaturize the sensor packages to reduce the weight and power requirements.

Integration of small satellite cost and design models for improved conceptual design-to-cost

Abstract: In the late 1980's a new satellite paradigm, modern small satellites, arose and opened up a new class of space applications. Since 1991, the Aerospace Corporation has been studying small satellites. Two products of this on-going study are the Small Satellite Cost Model (SSCM) and the Small Satellite Design Model (SSDM). In an effort to better meet design-to-cost goals for conceptual design, The Aerospace Corporation has recently developed the Aerospace Small Satellite Evaluation Spreadsheet Suite (ASSESS). This tool integrates the SSCM and SSDM into a single design-to-cost tool for use by a systems engineer either working alone or in cooperation with a design team. Several versions of the ASSESS tool are being developed with varying levels of fidelity. Features of each version of ASSESS and the method for obtaining them are discussed in detail in this paper.

Suggestions for low cost multifunction sensing

Abstract: Modern aerospace vehicles must perform a large number of sensing functions, but to fit within modernization budgets they must do it at very low cost. A modular, multifunction, open architecture, sensing system required of electro-optic (EO) systems on a combat aircraft is discussed. Multiple aperture modules are used, and one or more systems modules encompass common components. Target acquisition is analyzed for a large forward looking aperture, while missile warning, situational awareness, IRCM, and other functions are considered through multiple situational awareness apertures. A low cost multifunction RF system that is divided into three areas defined by analog-to-digital converter state of the art is discussed.