The fully programmable spacecraft: procedural sequencing for JPL deep space missions using VML (Virtual Machine Language)

VML (Virtual Machine Language) has been used as the sequencing flight software on over a dozen JPL deep-space missions, most recently flying on GRAIL and JUNO. In conjunction with the NASA SBIR entitled Reactive Rendezvous and Docking Sequencer, VML version 3.0 has been enhanced to include object-oriented element organization, built-in queuing operations, and sophisticated matrix / vector operations. These improvements allow VML scripts to easily perform much of the work that formerly would have required a great deal of expensive flight software development to realize. Autonomous turning and tracking makes considerable use of new VML features. Profiles generated by flight software are managed using object-oriented VML data constructs executed in discrete time by the VML flight software. VML vector and matrix operations provide the ability to calculate and supply quaternions to the attitude controller flight software which produces torque requests. Using VML-based attitude planning components eliminates flight software development effort, and reduces corresponding costs. In addition, the direct management of the quaternions allows turning and tracking to be tied in with sophisticated high-level VML state machines. These state machines provide autonomous management of spacecraft operations during critical tasks like a hypothetic Mars sample return rendezvous and docking. State machines created for autonomous science observations can also use this sort of attitude planning system, allowing heightened autonomy levels to reduce operations costs. VML state machines cannot be considered merely sequences - they are reactive logic constructs capable of autonomous decision making within a well-defined domain. The state machine approach enabled by VML 3.0 is progressing toward flight capability with a wide array of applicable mission activities.

Advanced Pointing Imaging Camera (APIC) for planetary science and mission opportunities

The General Mission Analysis Tool (GMAT) is an open-source space mission design, analysis and trajectory optimization tool. GMAT is developed by a team of NASA, private industry, public and private contributors. GMAT is designed to model, optimize and estimate spacecraft trajectories in flight regimes ranging from low Earth orbit to lunar applications, interplanetary trajectories and other deep space missions. GMAT has also been flight qualified to support operational maneuver planning for the Advanced Composition Explorer (ACE) mission. ACE was launched in August, 1997 and is orbiting the Sun-Earth L1 libration point. The primary science objective of ACE is to study the composition of both the solar wind and the galactic cosmic rays. Operational orbit determination, maneuver operations and product generation for ACE are conducted by NASA Goddard Space Flight Center (GSFC) Flight Dynamics Facility (FDF). This paper discusses the entire engineering lifecycle and major operational certification milestones that GMAT successfully completed to obtain operational certification for the ACE mission. Operational certification milestones such as gathering of the requirements for ACE operational maneuver planning, gap analysis, test plans and procedures development, system design, pre-shadow operations, training to FDF ACE maneuver planners, shadow operations, Test Readiness Review (TRR) and finally Operational Readiness Review (ORR) are discussed. These efforts have demonstrated that GMAT is flight quality software ready to support ACE mission operations in the FDF.

Program comprehension is an essential activity to perform software maintenance and evolution. Comprehensibility often encompasses the analysis of individual logical units, called features, which are often scattered through many program modules. Understanding how the feature code is implemented along the software evolution history is essential, for instance, to perform refactoring activities. However, existing tools do not provide means to comprehend the feature code evolution. To overcome this shortcoming, this paper presents a tool called Source Miner Evolution (SME) that provides multiple interactive and coordinated views to comprehend feature code evolution. SME implements a feature-sensitive comparison of multiple program versions. Our usability assessment with experienced developers indicated that SME allows them to efficiently perform recurring comprehension tasks on evolving feature code. The developers' performance was influenced by the combination of visual SME mechanisms, such as colors, tool tips and menu-popup interactions over the features' code elements.

Reducing bugs in software is a key issue in software development. Many techniques and tools have been developed to automatically identify bugs. These techniques vary in their complexity, accuracy and cost. In this paper we empirically investigate the language constructs which frequently contribute to bugs. Revision histories of eight open source projects developed in multiple languages are processed to extract bug-inducing language constructs. Twenty six different language constructs and syntax elements are identified. We find that most frequent bug-inducing language constructs are function calls, assignments, conditions, pointers, use of NULL, variable declaration, function declaration and return statement. These language constructs account for more than 70 percent of bug-inducing hunks. Different projects are statistically correlated in terms of frequencies of bug-inducing language constructs. Developers within a project and between different projects also have similar frequencies of bug-inducing language constructs. Quality assurance developers can focus code reviews on these frequent bug-inducing language constructs before committing changes.

The paper investigates the impact of high level distributed programming language constructs on the engineering of realistic software components. Based on reengineering two non-trivial telecoms components, we compare two high-level distributed functional languages, Erlang and GdH, with conventional distributed technologies C++/CORBA and C++/UDP. We investigate several aspects of high-level distributed languages including the impact on code size of high-level constructs. We identify three language constructs that primarily contribute to the reduction in application size and quantify their impact. We provide the first evidence based on analysis of a substantial system to support the widely-held supposition that high-level constructs reduce programming effort associated with specifying distributed coordination. We investigate whether a language with sophisticated high-level fault tolerance can produce suitably robust components, and both measure and analyse the additional programming effort needed to introduce robustness. Finally, we investigate some implications of a range of type systems for engineering distributed software.

An overview of the flight software development for the Ionospheric Observation Nanosatellite Formation (ION-F) is presented. ION-F, a constellation of three 15 kg satellites to be launched from the Space Shuttle in mid-2002, is designed as an experiment in formation flying technologies. The satellites will utilize micro-pulsed plasma thrusters and an integrated GPS/cross-link system to allow fast and accurate update of relative satellite positions. This paper describes the ION-F formation flying mission, flight software development to date, and simulation results. A nonlinear simulation environment (hardware in the loop) has been developed that includes the full nonlinear orbital dynamics in FreeFlyer/sup TM/, and nonlinear attitude dynamics in MATLAB/sup TM/. The simulation allows extensive flight software development to take place by integrating modules developed in C/C++ within the MATLAB environment.

The High-rate Delay Tolerant Networking (HDTN) project at the NASA Glenn Research Center (GRC) is developing a performance-optimized Delay Tolerant Networking (DTN) implementation using the Bundle Protocol (BP) both for infusion in modern, distributed spacecraft systems and for foundational network research purposes. While one purpose of networking is to enable a returns-to-scale with communicating assets, it is recognized that neither the protocol nor its implementations may impose a bottleneck on data delivery if expected to be implemented. With this in mind, this paper explores the current status of the HDTN software, including its capabilities and also various performance metrics at the bundle layer, the convergence layers (e.g. performance-optimized Licklider Transmission Protocol, or LTP), and bundle storage and retrieval. This includes goals of software implementations that support multi-gigabit per second communications regardless of payload size. A discussion on the current software architecture and internal scheduling and routing is included. Interoperability with such extant DTN implementations as Interplanetary Overlay Network (ION) and DTN Marshall Enterprise Implementation (DTNME) are included. The research goals of the project are also listed, including Software-Defined Networking (SDN) and the theory of DTNs. A table-based filtration system for the Bundle Protocol (BP), called BP Filter, is also explored: this addition enables table-based policies within the context of a DTN for management purposes. Infusion begins with systems testing in the Johnson Space Center (JSC) Software Development and Integration Laboratory (SDIL), which supports International Space Station (ISS) Flight Software development, integration, and verification. Observations made from the results of testing in the SDIL and in flight testing are also discussed, pointing to a path for infusion into high data return low-earth orbit (LEO) missions. The paper concludes with areas for future work.

Characterizing the impact of emergent technologies on earth communications reliance for crewed deep space missions

The high ionization level and nonzero metallicity (similar to 1% Z(.)) of the intergalactic gas at redshifts z less than or similar to 5 implies that nonlinear structure had started to form in the universe at earlier times than we currently probe. In cold dark matter (CDM) cosmologies, the first generation of baryonic objects emerges at redshifts z similar to 10-50. Here we examine the observable consequences of the possibility that an early generation of stars reionized the universe and resulted in the observed metallicity of the Ly alpha forest. Forthcoming microwave anisotropy experiments will be sensitive to the damping of anisotropies caused by scattering off free electrons from the reionization epoch. For a large range of CDM models with a Scalo stellar mass function, we find that reionization occurs at a redshift z greater than or similar to 10 and damps the amplitude of anisotropies on angular scales less than or similar to 10 degrees by a detectable amount, similar to 10%-25%. However, reionization is substantially delayed if the initial stellar mass function transformed most of the baryons Into low-mass stars. In this case, the mass fraction of pregalactic stars could be constrained from the statistics of microlensing events in galactic halos or along lines of sight to quasars. Deep infrared imaging with future space telescopes (such as the Space Infrared Telescope Facility or the Next Generation Space Telescope) will be able to detect bright star clusters at z greater than or similar to 5. The cumulative bremsstrahlung emission from these star clusters yields a measurable distortion to the spectrum of the microwave background.

The aerospace industry is undergoing unprecedented transformation. New players, new ventures, and new technologies drive the established business towards a transition from traditional models and strategies to automated production and innovative methods. Software architecture for space systems needs to become more agile while preserving a high standard of quality. To that end, the rigorous verification and validation process that yields high quality software products should embrace automation and take full advantage of COTS hardware and software products. In line with the industry transformation, SSL’s Flight Software Development and Validation Department uses a modular, layered architecture that has evolved over decades of orbital experience. This paper describes the SSL Flight Software Development and Validation Workflow Management System and the advantages of such a system/framework for development and verification of very complex spacecraft. This system/framework allows faster cyclical test-fix-test process and also provides a platform that can be extended for a multitude of applications.

Chapter 24 - Recent Geoeffective Space Weather Events and Technological System Impacts

CASDAL is a high level data language designed and implemented for the database machine CASSM. The language is used for the manipulation and maintenance of a database using an unnormalized (hierarchically structured) relational data model. It also has facilities to define, modify, and maintain the data model definition. The uniqueness of CASDAL lies in its power to specify complex operations in terms of several new language constructs and its concepts of tagging or marking tuples and of matching values when walking from relation to relation. The language is a result of a top-down design and development effort for a database machine in which high level language constructs are directly supported by the hardware. This paper (1) gives justifications for the use of an unnormalized relational model on which the language is based, (2) presents the CASDAL language constructs with examples, and (3) describes CASSM's architecture and hardware primitives which match closely with the high level language constructs and facilitate the translation process. This paper also attempts to show how the efficiency of the language and the translation task can be achieved and simplified in a system in which the language is the result of a top-down system design and development.

This paper describes an application of a programming system, K-NET to the development of control software for an automated guided vehicle system. K-NET is based on a high-level Petri net which makes it simple to express sequence controls. Procedural language can be also used for information processing. K-NET has an editor to input and edit control specifications expressed with Petri net ; a simulator to verify edited specifications ; a generator to convert the net to C source programs for a controller ; a reporter to print control specifications ; and a monitor to display controller status in real-time. K-NET can support all development stages including general design, detailed design, programming and testing. K-NET has been used in the development of control software for an automated guided vehicle system, and results show a 2/3 rds cost-saving over development with conventional methods in which only procedural language is used.

World's largest space arena to be developed