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SSC Users Guide - Table of Contents

1.0 INTRODUCTION

1.1 Satellite Situation Center (SSC)

This center is an operational unit of the Space Physics Data Facility (SPDF), and previously the National Space Science Data Center's international counterpart, World Data Center A for Rockets and Satellites (WDC-A-R&S). SSC personnel and software systems support NASA and international space physics activities by maintaining an ephemeris database for scientific satellites in geocentric or heliocentric orbits which can be used to plan and support analysis of coordinated science observations by multiple satellites. The Space Physics Data Facility (SPDF), which now provide software development and operational support for SSC, are part of the Heliophysics Science Division at NASA Goddard Space Flight Center with primary contractor support from ADNET Systems.

The SSC was established in the mid-1970's to support and coordinate multi-mission planning for the International Magnetospheric Study (IMS) [Teague et al., 1982]. SSC software resources developed during the IMS era continued to be used in mission and science planning for missions such as Dynamics Explorer 1 and 2 (DE 1/2), the International Sun-Earth Explorer series (ISEE 1, 2, and 3), and the Interplanetary Monitoring Platform series (IMP 7 and 8). The SSC supported the on-going series of Coordinated Data Analysis Workshop studies that began in 1978. In 1986 SSC played a major planning and coordination role during the multi-mission Polar Region and Outer Magnetospheric International Studies (PROMIS) program. Later SSC similarly supported the Solar Terrestrial Energy Program (STEP) during 1990-1994. SSC was also supported by NASA's Global Geospace Science (GGS) program, the International Solar Terrestrial Physics (ISTP) program, and the International Heliospheric Study (IHS).

Updated orbital elements for many active satellites are routinely received electronically by SSC from the United States Space Command (USSPACECOM/USSTRATCOM), previously known as NORAD. Elements for active satellites of interest to NASA-supported missions and international programs are processed by SSC staff into time-ordered Cartesian (X-Y-Z) coordinates, and stored in a database within the SSC Software System in SPDF/NSSDC's Common Data Format (CDF) [Treinish and Gough, 1987]. The Cartesian data points are stored at maximum time resolution of one minute in Geocentric Equatorial Inertial True of Date (GEI TOD) coordinates. SSC originally used software maintained at NASA Goddard's Flight Dynamics Division, and now uses open source software for processing Two-Line Elements (TLE) from Space-Track.org, and the NASA NIAF SPICE library for processing the orbit kernels from many active missions. SSC also pulls orbit data directly from other active missions.

The software and hardware capabilities of SSC have evolved over many years since the first generation of SSC programs was written in FORTRAN to run on a MODCOMP IV/25 computer for production of simple reports and data listings. In 1975, an interactive graphics system was added for preconfigured plots of key orbital parameters. In 1985, the software was ported to a MODCOMP Classic II/45 computer after previous updates and additions in 1980 in support of the Dynamics Explorer mission. Upgrades have included ports to more powerful computers in the SUN/UNIX environments and most recently (September, 2011) the operational system was ported to the Linux environment. In addition, upgrades have been made to the magnetic field models [Peredo et al., 1992] and the definitions for magnetospheric regions. Whereas user queries were exclusively handled by SSC staff prior to spring 1993, the emergence of the SSC Software System into the NSI network environment now makes possible direct access to SSC software and data by the space science community. The latest development in this area has been the creation of a World Wide Web interface to the SSC. Now anyone with access to the internet and a browser can utilize the user friendly Graphical User Interface of their browser to access the SSC database.

REFERENCES

Teague, M. J., D. M. Sawyer, and J. I. Vette, The Satellite Situation Center, in The IMS Source Book. Guide to the International Magnetospheric Study Data Analysis, edited by C.T. Russell and D. J. Southwood, pp. 112-116, American Geophysical Union, Washington, D. C., 1982.

Treinish, L., and M. Gough, A software package for the data-independent management of multidimensional data, EOS, 68, 633-635, 1987.

1.2 SSCWeb Software System

The SSC Software System is based on models of the Earth's magnetospheric regions and magnetic field, and programs generate information listings and trajectory plots for purposes of planning spacecraft instrument operations and/or data analysis. These programs identify the time periods during which a specified spacecraft is in a particular magnetospheric region or is in magnetic conjunction with other spacecraft or ground stations; allow a choice of internal and external magnetic field models for field-line tracing options (Internal, IGRF; External, Tsyganenko); plot spacecraft trajectories, illustrating spacecraft position relative to various magnetospheric regions; and perform conversions among geocentric and magnetic coordinate systems.

An easy-to-use World Wide Web interface allows the user to quickly move from one part of the system to another, and to easily specify input parameters and options. The SSC software provides the user three (3) options for querying and viewing data available in an extensive database. These options, Query, Locator, and the database itself are described in the following sections.

The main section of this User's Guide is organized to match the items presented to the user by the SSCWeb interface. Technical descriptions of the magnetic field models, magnetospheric region definitions, and coordinate systems used, as well as a list of usable ground stations, are given in Appendices A, B, C and D, respectively. Appendix E contains a glossary of terms used throughout the system itself and the documentation.

User comments, suggestions and problem reports would be greatly appreciated. Please forward them to:

gsfc-spdf-support@lists.nasa.gov

1.3 Locator

The Locator component of the SSC system allows the user to obtain location data in a tabular format. The user may request the spacecraft's location converted into a variety of coordinate systems (see section 5.0), as well as the following coordinate related items:

1.4 Query

The Query processor provides two query matching options, magnetospheric region occupancy and magnetic field line tracing. The region setup option provides magnetospheric region occupancy by listing the entry and exit times in which specified satellite(s) were in particular magnetospheric regions. The trace setup option provides the means to perform field line tracing queries to identify either periods when one or more spacecraft are on the same magnetic flux tube of force as a specified lead spacecraft, or periods when one or more spacecraft occupy a field line which traces down to a specified ground station.

At intervals equal to the time between successive ephemeris data points, the ephemeris information of each spacecraft is used to evaluate the magnetic field vector at the position of the spacecraft. Next, the sampling point is moved in the direction of the vector to reach a neighboring point along the tube where the local field vector specifies the direction of the next step. This process is then iterated until finally the footpoint of the tube is reached. The magnetospheric models available for field line tracing are listed in Appendix A.

To facilitate complex queries, the user can specify up to nine conditions under which a single query may be made. A condition consists of satellite selections, region specifications, and field line tracing options. PLEASE NOTE that the condition number is located at the top of the screen. The trace model selection, as well as the start and stop times, are used throughout all conditions.

The main screen of the Query Interface requires selection of at least one satellite for processing from a scrolling list of available satellites, and entry of the start and stop times for satellite processing.

Query also contains fields for specifying whether the satellites, time ranges and setups will apply to the current condition, to all of the conditions, or to any of the conditions. These conditions may be queried independently, or together.

Several models are available to independently specify the terrestrial (internal) magnetic field and the magnetospheric (external) magnetic field. The size of the magnetic flux tube can also be specified as either a bin of x-deg latitude by y-deg longitude or a circular tube of a specified radius.

1.5 Extensive Database

Updated predictive and definitive ephemeris for over 150 satellites are maintained at the Satellite Situation Center. Time and position over specific time periods at varying resolutions are stored for each satellite. The orbital elements themselves are not currently stored in the database. This database is updated periodically with ephemeris for new satellites or revised ephemeris for existing satellites.

1.6 Navigation Help for SSCWeb

What follows below are some hints for using you're browser effectively to navigate through the SSCWeb.

SSC Users Guide - Table of Contents

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