1. NAME AND TITLE

 SIGMA II: Space Radiation Dose Analysis Within Complex Configurations.

SIGMA II is a substantially extended and revised version (1974) of the original SIGMA code (1967) which makes it applicable to a more general class of space radiation dose problems.

2. CONTRIBUTORS

 McDonnell Douglas Astronautics Company, Western Division, Huntington Beach, California.

 McDonnell Douglas Missile & Space Systems Division, Santa Monica, California.

 Oak Ridge National Laboratory, Oak Ridge, Tennessee.
 
 

3. CODING LANGUAGE AND COMPUTER

 FORTRAN IV; CDC 6600 (C00118/C6000/00).

 FORTRAN 77; PC 486 (C00118/PC486/00).
 
 

4. NATURE OF PROBLEM SOLVED

 SIGMA II calculates space radiation doses at arbitrary points inside a space vehicle by performing a numerical angular integration of dose attenuation kernels about the dose points. The kernels are curve-fit functions constructed from input data. The geometry of the vehicle, equipment and supplies, and man models are described by quadric surfaces. Simultaneous dose calculations for multiple vehicle trajectories, each involving several radiation sources, may be performed for each specified dose point. The calculation may be a parametric study of dose as a function of shield thickness or an analysis of the dose received through designated outer sectors of the vehicle.

5. METHOD OF SOLUTION

 SIGMA may be used in conjunction with other codes such as CCC-70/CHARGE. The latter code computes basic dose transmission data through materials for idealized spherical or slab geometries of various thicknesses and for various types of radiations. The space vehicle dose calculation is performed by angular integration accomplished numerically by means of Simpson's rule. The polar and azimuthal angles about a dose point are divided into intervals, the endpoints of which define directions for which ray tracing analysis through the space vehicle is performed. This analysis yields material thicknesses between dose point and vehicle exterior for each ray. From the source angular description, which may be anisotropic, the material thicknesses, and the basic dose transmission versus shield thickness (calculated, for example, by CHARGE) input, the dose at a given point is calculated. The source strength for a given ray direction is approximated by linear interpolation between source input value cosines and strengths. The dose transmissions for a given ray thickness is approximated by exponential interpolation between the basic dose transmission and shield thickness values.

 SIGMA II adds the following capabilities: random selection of ray directions, time-dependent dose point position and orientation, built-in geometric man model, calculation of mass distribution, selection of ray lengths from mass distribution, and variable dimensioning of data storage.

 Results are presented as either a printout of dose as a function of shield thickness or a printout of the dose received through designated outer sections of the vehicle.

6. RESTRICTIONS OR LIMITATIONS

 None noted.

7. TYPICAL RUNNING TIME

 No study was performed by RSICC.

8. COMPUTER HARDWARE REQUIREMENTS

 The code was originally designed for the IBM 7094 and was converted to run on the CDC 6600.  The PC version was run on a Micron Pentium Pro.

9. COMPUTER SOFTWARE REQUIREMENTS

 A FORTRAN IV compiler is required for the CDC version.
 
 The PC version was converted from the CDC 6600 release of October 1974.  The only changes made to the code were those required to create an executable using the Lahey F77/L3-EM32 Version 5.2 compiler.
 

 
10. REFERENCES

 a. Included in package:

 T. M. Jordan, ``SIGMA, A Computer Program for Space Radiation Dose Analysis Within Complex Configurations,'' DAC-60878 (November 1967).

 W. R. Yucker, ``Extended Capabilities of the SIGMA Program,'' DAC Memo A3-830-BBFO-121 (April 1971).

b. Background information (Packaged in CCC-157/MEVDP):

 P. G. Kase, ``Computerized Anatomical Model Man,'' AFWL-TR-69-161 (1970).

 B. Liley and S. C. Hamilton, ``Modified Elemental Volume Dose Program (MEVDP),'' AFWL-TR-69-68 (1969).

11. CONTENTS OF CODE PACKAGE

 Included are the referenced documents (10.a) and a DOS-formatted diskette which contains the source code and input for a sample problem for the CDC version.   Output for the sample problem is included in the printed documentation.

 The PC package includes Fortran source, executable, and test cases transmitted on one DS/HD (1.44 MB) 3.5-in. diskette in DOS format.
 
 

12. DATE OF ABSTRACT

 August 1971; updated July 1981, March 1998.

KEYWORDS: SPACE RADIATION; COMPLEX GEOMETRY; MICROCOMPUTER