Testing autonomous systems for deep space exploration

NASA is moving into an era of Increasing spacecraft autonomy. However, before autonomy can be routinely utilized, we must develop techniques for providing assurance that the system will perform correctly in flight. We describe why autonomous systems require advanced verification techniques, and offer some management and technical techniques for addressing the differences. Autonomous goal-driven spacecraft require advances in verification techniques because optimization (e.g., planning and scheduling) algorithms are at the core of much of autonomy. It Is the nature of such algorithms that over much of the input space an intuitively small change in the input results in a correspondingly small change in the output: This type of response typically leads one to conclude, quite reasonably, that if the two responses are correct, those responses between them will probably also be correct. However, there are certain regions in the input space where a small change in the input will result in a radically different output: One is not so inclined to conclude that all responses in these transition zones are likely to be correct. We believe, for two reasons, that these transition zones are one place where autonomous systems are likely to fail. First, boundary conditions, often a rich source of faults, are highly exercised in the transition zones, and so increase the likelihood of faults. Second, within the transition zone the algorithm outputs are likely to appear unusual, and, since the outputs of the algorithm become inputs to the remainder of the system, the whole system is probably pushed outside of its nominal usage profile: historically shown to be another good source of faults. We close with a discussion of risk management. Autonomous systems have many well-known management risk factors. Risk management and quality concerns must be pervasive, throughout all team members and the whole life-cycle of the project.     

New architectures for space power systems

Electric power generation and conditioning have experienced revolutionary development over the past two decades. Furthermore, new materials such as high energy magnets and high temperature superconductors are either available or on the horizon. Our work is based on the premise that new technologies are an important driver of new power system concepts and architectures. This observation is borne out by the historical evolution of power systems both in terrestrial and aerospace applications. This paper introduces new approaches to designing space power systems by using several new technologies. Two new architectures are introduced: the current source current intensive system and the articulate system. Basic characteristics of these systems have been investigated. Some aspects of the articulate system architecture, as discussed in this paper can be implemented in the short term. Flexible AC transmission systems which are now undergoing rapid development and implementation, can be regarded as a subset of the family of control methodologies which constitute the realm of articulate systems     

Power beaming providing a space power infrastructure

A study based on two levels of technology maturity, which applies to the power beaming concept to four planned satellite constellations, is described. The analysis shows that with currently available technology, power beaming can provide mass savings to constellations to orbits ranging from low-Earth orbit to geosynchronous orbit. Two constellations, a space surveillance and tracking system and space-based radar, can be supported with current technology. The other two constellations, a space-based laser array and a boost surveillance and tracking system, will require power and transmission system improvements before their break-even specific mass is achieved. A doubling of SP-100 conversion efficiency from 10 to 20% would meet or exceed break-even for these constellations     

Thermionic/AMTEC cascade converter concept for high-efficiencyspace power

This paper presents trade studies that address the use of the thermionic/AMTEC cell-a cascaded, high efficiency, static power conversion concept that appears well-suited to space power applications. Both the thermionic and AMTEC power conversion approaches have been shown to be promising candidates for space power. Thermionics offers system compactness via modest efficiency at high heat rejection temperatures, and AMTEC offers high efficiency at modest heat rejection temperature. From a thermal viewpoint, the two are ideally suited for cascaded power conversion: thermionic heat rejection and AMTEC heat source temperatures are essentially the same. In addition to realizing conversion efficiencies potentially as high as 35-40% such a cascade offers the following perceived benefits: Survivability-capable of operation in the Van Allen belts; Simplicity-static conversion, no moving parts; Long lifetime-no inherent life-limiting mechanisms identified; Technology readiness-Large thermionic database; AMTEC efficiencies of 18% currently being demonstrated, with more growth potential available; and Technology growth-applicable to both solar thermal and reactor-based nuclear space power systems. Mechanical approaches and thermal/electric matching criteria for integrating thermionics and AMTEC into a single conversion device are described. Focusing primarily on solar thermal space power applications, parametric trends are presented to show the performance and cost potential that should be achievable with present-day technology in cascaded thermionic/AMTEC systems     

High energy density capacitors for space power conditioning

Several advanced capacitor designs that might be used in high average power space applications are described. Each type is fundamentally limited by breakdown phenomena. All are intrinsically limited to maximum fields on the order of 1000 MV/m. None of these units has been space rated for energy storage applications. Several problems that must be solved before use in space are presented as well as the current state of the art and estimates of developmental potential     

Large area solar cells for future space power systems

Space silicon solar cell technology has matured to the extent that large-area planar silicon cells can be fabricated in sizes up to 8 cm×8 cm with efficiencies up to approximately 15%. In order to achieve substantially higher efficiencies, cells based on GaAs are required. It is shown that, subject to certain boundary conditions, the efficiency of GaAs/Ge cells can reach 24% when used in the dual-junction configuration or approximately 19.5% if the Ge substrate is passive. The electrooptical properties of these cells are reviewed, and prospects for achieving these efficiency goals are presented. Experimental performance data are given     

Parametric cost model for solar space power and DIPS systems

A detailed cost model has been developed to parametrically determine the program development and production cost of photovoltaic, solar dynamic, and dynamic isotope (DIPS) space power systems. The model is applicable in the net electrical power range of 3 to 300 kWe for solar power and 0.5 to 10 kWe for DIPS. Application of the cost model allows spacecraft or space-based power system architecture and design trade studies or budgetary forecasting and cost benefit analyses. The cost model considers all major power subsystems (i.e., power generation, power conversion, energy storage, thermal management, and power management/distribution/control). It also considers system cost effects such as integration, testing, and management. The cost breakdown structure, model assumptions, ground rules, bases, cost estimation relationship format, and rationale are presented, and the application of the cost model to 100-kWe solar space power plants and to a 1.0-kWe DIPS is demonstrated     

Haptic based teleoperation with master-slave motion mapping and haptic rendering for space exploration

This paper presents a new solution to haptic based teleoperation to control a large-sized slave robot for space exploration, which includes two specially designed haptic joysticks, a hybrid master-slave motion mapping method, and a haptic feedback model rendering the operating resistance and the interactive feedback on the slave side. Two devices using the 3 R and DELTA mechanisms respectively are developed to be manipulated to control the position and orientation of a large-sized slave robot by using both of a user's two hands respectively. The hybrid motion mapping method combines rate control and variable scaled position mapping to realize accurate and efficient master-slave control. Haptic feedback for these two mapping modes is designed with emphasis on ergonomics to improve the immersion of haptic based teleoperation. A stiffness estimation method is used to calculate the contact stiffness on the slave side and play the contact force rendered by using a traditional spring-damping model to a user on the master side stably. Experiments by using virtual environments to simulate the slave side are conducted to validate the effectiveness and efficiency of the proposed solution.     

A 20 kHz hybrid resonant power source for the space station

A hybrid resonant inverter system is presented that satisfies the steady-state operating requirements of a power source for the proposed International Space Station mobile servicing system. The steady-state behavior of the inverter was analyzed and a method is described for optimizing the design of the resonant network. The performance characteristics such as the total harmonic distortion of the output voltage, RMS output voltage, and the inverter efficiency are presented. The hybrid resonant inverter system maintains an excellent efficiency over varying output-load demand     

Synthetic vision: a prototype display concept for commercial aircraft

The synthetic vision implementation discussed in this paper comprises elements in the navigation display, the vertical profile display, and the primary flight display. The design rationale is provided based on an overview of the intended functions, options to implement these functions, and the justifications used in the selection of a specific option.     

Data communications concept for a SATS scenario

The small aircraft transportation system (SATS) concept envisions doorstop to destination transportation in a safe and timely manner. Data communications are a key component in achieving the aviation-related operational performance improvements that are sought. However, data communication doesn't start when you get into the aircraft; it starts back at the location where the flight is planned. In fact, data communications support the pilot in all phases of the flight: flight planning, pre-flight, departure, en route, transition, approach, landing, and rollout as well as for a missed approach. The Internet is being used to perform flight planning activities, and the mobile communications available today support Internet access en route to the departure airfield. On-board the aircraft, data communications provide surveillance and air traffic control (ATC) support to the pilot. The location of other aircraft is available to the pilot and ATC system through automatic dependent surveillance-broadcast (ADS-B) and traffic information service-broadcast (TIS-B) applications that transmit the location of other aircraft in the vicinity. Other aircraft locations are used to forecast potential conflicts and, thus, enhance flight safety. As the aircraft nears a SATS-equipped airfield, the pilot uses data link messages to request a landing sequence. The airport management module (AMM) provides a landing sequence assignment to the aircraft. As the pilot maneuvers the aircraft for a landing, he/she is using data-linked surveillance data to determine the location of other aircraft and maintain a safe separation distance between aircraft even in a low visibility environment.     

A methodology for aircraft mission effectiveness evaluation and design space exploration based on virtual operational test

The early involvement of test and evaluation can significantly reduce the cost of modifying issues and errors found in the later stages of aircraft development and design process.This paper presents a methodology for aircraft mission effectiveness evaluation and design space exploration based on Virtual Operational Test (VOT),incorporating Virtual Open Scenario (VOS) and User in Scenarios (UIS) concepts.By employing modeling and simulation technologies in the early stages of aircraft development and design,a virtual environment can be constructed,allowing aircraft users to participate more closely and conveniently in the design process.Virtual tests conducted by users within the mission context provide data on mission effectiveness and critical user feedback.This paper outlines the main components of the virtual operational test process and related conceptual methods,and discusses an open support system framework that supports VOT.The effectiveness and adaptability of the method are demonstrated through two case studies:a beyond-visual-range air combat scenario and a helicopter ground attack scenario.These case studies demonstrate the evaluation of aircraft mission effectiveness and the sensitivity analysis and optimization of design and operational parameters based on VOT.     

Fiber lasers: a future space technology

The constraints of operation in space have largely precluded the use of conventional solid-state laser systems for applications including remote sensing, communication relays, and active laser radars. A new technology, fiber lasers, may offer all of the needed features at an affordable price. An appealing aspect of the fiber laser is that it does not need a rigid optical bench. Only the output end of the fiber need be held in rigid reference to the optical tracking system. Design, fabrication, and testing of the laser resonator is generally the most expensive and longest lead part of the effort for conventional solid-state lasers. Advances in Fiber Optic technology and devices mean that the fiber laser need not be a simple device but may be a complex system employing sophisticated technology such as wavelength selective Bragg reflectors and nonlinear optical frequency shifters. Three companies have recently obtained single-mode outputs of 3540 watts single mode at 1.03-1.1 microns.     

Micromission spacecraft: a low-cost, high-capability platform for space science missions

The Ball Micromission Spacecraft (MSC) is a multi-purpose platform capable of supporting science missions at distances from the Sun ranging from 0.7 to 1.7 AU. In the baseline scenario, MSC is launched as a secondary payload on an Ariane 5 rocket from Kourou, French Guiana, to GTO using the Ariane 5 structure for auxiliary payloads (ASAP5). The maximum launch wet mass is 242 Kg and can include up to 45 Kg of payload depending on AV needs. The on-board propulsion system is used for maneuvering in the Earth-Moon system and injecting the spacecraft into its final orbit or trajectory. For Mars missions, MSC enables orbiting Mars for science payloads and/or communications and navigation assets, or for precision Mars fly-bys to drop up to six probes. The micromissions spacecraft bus can be used for science targets other than Mars, including the Moon, Earth, Venus, Earth-Sun Lagrange points, or other small bodies. This paper summarizes the current spacecraft concept and describes the multimission spacecraft bus implementation in more detail.     

The flying object: a flight data management concept

The drive for greater cost-effectiveness and improved safety/security in an environment of increasing air movements calls for improved availability of accurate and consistent flight data to stakeholder systems. Studies conducted by EUROCONTROL in 2001-2003 indicate significant levels of inconsistency between flight data available to aircraft operators, air traffic control (ATC), air traffic flow management (ATFM), airports and military systems, causing unnecessary workload, inefficient use of resources, and unnecessary delays. Eurocontrol's new flight data interoperability concept is intended to resolve this problem. Having passed through the initial feasibility phase, this concept is now entering the development phase, in which it will become the basis for the development of a draft interoperability standard to be used in Europe for the specifications of new flight data processing systems deployed from 2007 onwards, and potentially to be proposed to the International Civil Aviation Organisation (ICAO) for global standardisation.     

Is the need for a new ATM operational concept a strategic necessity?

We must face the fact that conventional methods of air traffic management (ATM) that have served us well cannot continue to cope indefinitely. We need-therefore, to decide what the new operational concept should be and agree on the transition path. Air traffic management is the term we apply today to the totality of the activities involved in the handling of air traffic. The quest for a new concept led to what was first called "free flight," an idea that has, in the meantime, acquired some notoriety and is today more commonly referred to in Europe as "air/ground cooperative ATS." Simply put, the original free flight concept, stipulated that given the right on-board equipment (display of traffic information, conflict detection, and resolution tools) aircraft could navigate and avoid each other completely on their own, without the need for ATC. That a new ATM operational concept will be needed to take the industry further by the time traditional methods run out of potential is difficult to question. Equally clear is that the only new concept available is free flight a.k.a. air/ground cooperative ATS.     

Development of a driver board power supply for high power IGBTsused in three-phase inverters

High power IGBTs have been widely used for medium power inverters up to 200 kVA. Their driver circuits often require multiple-output, isolated power supplies. This paper presents a simple flyback power supply especially designed for the driver boards of three-phase IGBT inverters. The detailed circuit diagrams and typical waveforms are reported. Certain performance data are given. The power supplies have been used in 100 kVA inverters for an electric vehicle drive and for a wind turbine inverter