1. NAME AND TITLE

TRECO: An Orbital Integration Estimation of Trapped Radiation.

TRECO is a version of an orbital integration code developed at Aerospace Corporation for use in conjunction with the generation of trapped radiation model environments. The model environment work is now being done at National Space Science Data Center (NSSDC), and the data is available from NSSDC. TRECO is retained by RSIC to preserve space technology developed in the 1960s.

2. CONTRIBUTOR

National Space Science Data Center, NASA Goddard Space Flight Center, Greenbelt, Maryland.

3. CODING LANGUAGE AND COMPUTER

FORTRAN IV; IBM 360/75 and 360/91 (A) or CDC 6600 (B).

4. NATURE OF PROBLEM SOLVED

TRECO computes elliptic or circular orbits for earth satellites; or, alternatively, it can read previously generated orbits stored on magnetic tape or punched cards. For each orbit, TRECO computes the daily fluence of geomagnetically trapped particles from model trapped radiation environments. Both the flux of electrons and protons can be computed by the code.

5. METHOD OF SOLUTION

To estimate the geomagnetically trapped radiation that a satellite would accumulate, the trajectory is computed as a function of time, given six initial conditions. These are (1) latitude of perigee (the point on an orbit of nearest approach to the earth), (2) initial longitude of perigee, (3) height of apogee (the point on an orbit farthest away from the earth), (4) height of perigee, (5) orbit inclination, (6) quadrant of initial longitude of perigee or a direction for equatorial orbits.

Kepler's Laws and Kepler's Equation are used to determine the position of the orbiting satellite as a function of time in terms of geographic coordinates. The position in geographic coordinates, which is a three-dimensional representation, is mapped into a two-dimensional geomagnetic coordinate or the (B,L) coordinate system. In this system, B is the geomagnetic field strength and L is a parameter that is the physical analog of the geomagnetic equatorial distance to a field line in a dipole field and it is approximately constant along lines of force. The model trapped radiation environment is expressed in (B,L) coordinates. As each orbit (B,L) is determined, the flux is computed for each energy requested. Then each of these fluxes is multiplied by the time-interval in seconds, and the results are summed for each energy.

6. RESTRICTIONS OR LIMITATIONS

Maximum number of energy groups, 30. This can be increased easily by the user.

7. TYPICAL RUNNING TIME

Estimated running time of the packaged sample problem on the IBM 360/91: 2 minutes.

8. COMPUTER HARDWARE REQUIREMENTS

Originally designed for the IBM 7094, the code is now operable on the CDC 6600, the IBM 360/75, and the 360/91.

9. COMPUTER SOFTWARE REQUIREMENTS

Originally programmed in FORTRAN II, TRECO has been converted to FORTRAN IV for the CDC 6600 and is also available on the IBM 360/75/91 Operating Systems, using OS-360 FORTRAN H Compiler.

Flux maps and spectrum data are required as input and a number of sets of these data are included in the code package. Updates are available from NSSDC.

Input variables are used to determine the number and mode of tapes that may be used as orbit packages from a previous calculation, or written by the current calculation.

10. REFERENCES

A. B. Lucero, "TRECO, An Orbital Integration Computer Program for Trapped Radiation," NSSDC 68-02 (January 1968).

J. I. Vette, "Models of the Trapped Radiation Environment, Vol. I: Inner Zone Protons and Electrons," NASA SP-3024 (1966).

J. I. Vette, A. B. Lucero, and J. A. Wright, "Models of the Trapped Radiation Environment, Vol. II: Inner and Outer Zone Electrons," NASA SP-3024 (1966).

J. I. Vette and Antonio B. Lucero, "Models of the Trapped Radiation Environment, Vol III: Electrons at Synchronous Altitudes," NASA SP-3024 (1967).

J. H. King, "Models of the Trapped Radiation Environment, Vol. IV: Low Energy Protons," NASA SP-3024 (1967).

J. P. Lavine and J. I. Vette, "Models of the Trapped Radiation Environment, Vol. V: Inner Belt Protons," NASA-SP-3024 (1969).

J. P. Lavine and J. I. Vette, "Models of the Trapped Radiation Environment, Vol. VI: High Energy Protons," NASA SP-3024 (1970).

W. L. Imhof, C. O. Bostrom, D. S. Beall, J. C. Armstrong, H. H. Heckman, P. J. Lindstrom, G. H. Nakano, G. A. Paulikas, and J. B. Blake, "Models of the Trapped Radiation Environment, Vol. VII: Long Term Time Variations," NASA SP-3024 (1971).

R. H. Hilberg, M. J. Teague, and J. I. Vette, "Comparison of the Trapped Electron Models, AE-4 and AE-5 with AE-2 and AE-3," NSSDC 74-13 (September 1974).

11. CONTENTS OF CODE PACKAGE

Included are the referenced documents and one (1.2MB) DOS diskette which contains for each version the source code and input and output for a sample problem, including flux and energy spectrum data.

12. DATE OF ABSTRACT

August 1971; updated July 1981, February 1985, September 1991.