The Mission Planning Graphical Tool (MPGT) computer program provides a mouse-driven graphical representation of data on a spacecraft and its environment, for use in planning a space flight. MPGT is designed to be a generic software tool that can be configured to analyze any specified Earth-orbiting spacecraft mission.
The data are presented as a series of overlays on top of a two- or three-dimensional projection of the Earth. As many as six spacecraft orbital tracks can be drawn at one time. Position data can be obtained by either an analytical process or by use of ephemeris files. If the user chooses to propagate a spacecraft orbit by use of an ephemeris file, then files in Goddard Trajectory Determination System (GTDS) format must be supplied. The MPGT user's guide provides a complete description of the GTDS format so that the user can create the files. Other overlays include ground-station antenna masks, solar and lunar ephemerides, coverage by the Tracking Data and Relay Satellite System (TDRSS), a field-of-view swath, and orbit number. From these graphical representations, an analyst can determine such spacecraft-related constraints as communication coverage, infringement of interference zones, availability of sunlight, and visibility of targets to instruments.
The presentation of time and geographical data as graphical overlays on a world map makes possible quick analyses of trends and of parameters related to time. For instance, MPGT can display the propagation of the positions of the Sun and Moon over time, shadowing of sunrise and sunset terminators to indicate day and night for spacecraft and the Earth, and color coding of spacecraft-orbit tracks to indicate day and night for spacecraft. In the case of the three-dimensional display, the user specifies a vector that represents a position in the universe from which the Earth is to be viewed. From the "viewpoint," the user can zoom in on, or revolve about, the Earth. The zoom feature is also available with the two-dimensional display.
MPGT also provides alphanumeric data on spacecraft orbit tracks, celestial bodies, and TDRS positions. The user can scroll through the spacecraft and celestial data; that is, can propagate data into the future or past. The program contains data files of world-map continent coordinates, contour information, antenna-mask coordinates, and a sample star catalogue.
Since the overlays are designed to be mission-independent, it is not necessary to modify the software in order to satisfy requirements for various spacecraft. All overlays are generic, with communication-zone contours and spacecraft terminators generated analytically on the basis of spacecraft-altitude data. Interference-zone contours are specified by the user through text-edited data files. Spacecraft-orbit tracks are specified via Keplerian, Cartesian, or Definitive Orbit Determination System (DODS) orbit vectors. Finally, all overlays related to time are based on an epoch supplied by the user.
A user-interface subsystem enables the user to alter any system parameter through a series of pull-down menus and pop-up data-entry panels. The user can specify, load, and save profile data files; control graphical presentation formats; enter a DOS shell; and terminate the operation of the system. MPGT includes a menu option for printing all graphical images by use of any printer compatible with the HALO Professional software. The user-interface subsystem automatically checks for errors in, and validates, all input data from either a file or keyboard entry. A help facility is also provided.
MPGT includes a utility subprogram, called "ShowMPGT," which displays screen images that were generated and saved by previous use of MPGT. Specific sequences of images can be recalled without having to reset profile-related parameters.
MPGT is written in FORTRAN, C, and Macro Assembler for use on IBM-PC-compatible computers running MS-DOS version 3.3 or higher. Necessary hardware includes 620KB of core (random-access) memory; Enhanced Graphics Adapter or Video Graphics Array; 1.5MB of either floppy- or fixed-disk storage capacity; a 1.44MB, 3.5-in. (8.89-cm) floppy-disk drive, and an 8087, 80287, 80387, or compatible processor. The software supports the use of a mouse, which is optional.
This program was written by Lisa Mazzuca, James Jeletic, and Stan Watson of Goddard Space Flight Center. GSC-13669