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The Real-Time Specification for Java (RTSJ) provides facilities for deterministic, real-time execution in a language that is otherwise subject to variable latencies in memory allocation and garbage collection. A major consequence of these facilities is that the normal Java practice of passing around references to objects in heap memory cannot be used in hard real-time activities. Instead, designers must think carefully about what type of non-heap memory to use and how to transfer data between components without violating RTSJ's memory-area assignment rules. This report explores the issues of programming with non-heap memory from a practitioner's view in designing and programming realtime control loops using a commercially available implementation of the RTSJ.

The Advanced Multi-Mission Operations Systems (AMMOS) is NASA's premier space mission operations product line offering for use in deep-space robotic and astrophysics missions. The general approach to AMMOS modernization over the course of its 29-year history exemplifies a continual, evolutionary approach with periods of sponsor investment peaks and valleys in between. Today, the Multimission Ground Systems and Services (MGSS) office-the program office that manages the AMMOS for NASA-actively pursues modernization initiatives and continues to evolve the AMMOS by incorporating enhanced capabilities and newer technologies into its end-user tool and service offerings. Despite the myriad of modernization investments that have been made over the evolutionary course of the AMMOS, pain points remain. These pain points, based on interviews with numerous flight project mission operations personnel, can be classified principally into two major categories: 1) information-related issues, and 2) process-related issues. By informationrelated issues, we mean pain points associated with the management and flow of MOS data across the various system interfaces. By process-related issues, we mean pain points associated with the MOS activities performed by mission operators (i.e., humans) and supporting software infrastructure used in support of those activities. In this paper, three foundational concepts-Timeline, Closed Loop Control, and Separation of Concernscollectively form the basis for expressing a set of core architectural tenets that provides a multifaceted approach to AMMOS system architecture modernization intended to address the information-and process-related issues. Each of these architectural tenets will be further explored in this paper. Ultimately, we envision the application of these core tenets resulting in a unified vision of a future-state architecture for the AMMOS-one that is intended to result in a highly adaptable, highly efficient, and highly cost-effective set of multimission MOS products and services. * An interesting new area of academic research related to this topic is the field of Software Architecture Evolution. 8,9

a contract with the National Aeronautics and Space Administration. This document contains pre-decisional information -for planning and discussion purposes only.