ALBERT

Description: GMAS was designed as a general control framework to satisfy multiple applications in a core-limited and optionally interactive environment. During execution, the system uses and releases memory as needed to provide the user with a system that is only as large or small as the problem demands. Although GMAS was designed for trajectory-related spacecraft mission analysis specifications, the organization of the system software makes GMAS applicable to many computational functions. Any large computer program that can be separated into independent functional areas (load modules) can probably be implemented under GMAS. Because of the program's modular nature, the GMAS system offers software development time savings, core savings and efficiency, stability, and flexibility. The major components of GMAS are the executive module, the dynamic load modules, the dynamic arrays, and the automatic sequence. The GMAS executive module is primarily responsible for interpretation of user control directives and data management. The executive passes control to user-designated dynamic load modules after having prepared user-specified and default data for the utilities. The executive also controls the dynamic assignment and release of core-space for user-specified modules and data areas. The dynamic load modules contain the applications software to be used in specific problem solutions. These load modules may consist of the GMAS library of standard routines along with user developed libraries of routines. Each dynamic load module is a separate group of subroutines which, when loading during GMAS execution, can be executed to solve part of the user problem then deleted from core. Dynamic load module input and output can be transferred through out-of-core files or through user-specified dynamic arrays located in a core area separate from the executive and any dynamic load modules. The dynamic arrays are the primary communications link between load modules. The GMAS automatic sequence allows the user to control the other 3 components. The user creates the automatic sequence, or application program, by using a simple control language which has been created especially for GMAS. The automatic sequence contains the names of executive modules and utility load modules; data for these modules; and logical operation directives. GMAS capabilities include simulation of satellite orbits, shadow and station coverage studies, targeting and optimization capability, a Monte Carlo error analysis package, and a graphing capability that can be used to generate comparison graphs of selected orbital parameters of two satellites. Interactive graphics are provided for in the form of tabular, plot, and message display capabilities for the IBM 3250 and 2250 display devices. GMAS includes a very comprehensive set of over 600 orbital calculation routines which handle a variety of functions, including: performing impulsive maneuvers while controlling the altitude of the spacecraft; providing acquisition tables for ground station and tracking and data relay satellite coverage; estimating the effects of spacecraft thrust on the orbit; developing maneuver commands by modeling the hydrazine propulsion system of the spacecraft; sequentially summing the gravitational effects for each perturbing body using an independent two body model; generating plots of combinations of dynamic arrays on a Cartesian grid; and determining visibility status and pointing angles from the view of the spacecraft. GMAS is written in FORTRAN (75%), JCL (17%), and Assembler (8%) for implementation on the IBM 370 series under the IBM 370 MVS Operating System running under VM and under the IBM VM/SP CMS Operating System. The executive component, which is always resident in core, has a central memory requirement of approximately 220K. GMAS was developed in 1977 and last updated in 1988.