1. NAME AND TITLE

CARSTEP: Trajectory and Environment CodeElectron and Proton Fluxes Impinging on Spacecraft in Orbit.

This code was developed by combining a two-body trajectory program with NASA Goddard's environment routine.

The state of the art dates to the 1960s. It was used by the contributors below and was distributed by RSIC six times between 1965-1969.

2. CONTRIBUTORS

Northrop Space Laboratory, Hawthorne, California.

Aerospace Medical Research Laboratory, Wright-Patterson Air Force Base, Ohio.

3. CODING LANGUAGE AND COMPUTER

FORTRAN II; IBM 7090.

4. NATURE OF PROBLEM SOLVED

The CARSTEP code determines the flux of particles from the Van Allen zones that strike a space vehicle which is executing a mission in that volume of space. Using latitude, longitude, altitude of perigee, inclination and eccentricity of orbits, and mission time as input, the following data is given: latitude, longitude, and altitude of the vehicle at points along the trajectory, the flux of particles at these points, and the time integrated flux for the total mission.

5. METHOD OF SOLUTION

The position of the vehicles as a function of time is determined by a two-body analysis. The program is divided into three parts: lunar transfer trajectories, lunar return trajectories, and geocentric orbits.

The environment portion of CARSTEP uses a coordinate system (B,L) for mapping the distribution of geomagnetically trapped particles which has been developed by C. E. McIlwain.

6. RESTRICTIONS OR LIMITATIONS

The earth is considered a perfect sphere and atmospheric drag is neglected. One energy spectrum for particles is valid throughout the volume of space.

7. TYPICAL RUNNING TIME

Estimated running time of sample problem is 5 minutes.

8. COMPUTER HARDWARE REQUIREMENTS

The code was designed for an IBM 7090 or 7094 computer. A 32,768 core memory and three tape units are required.

9. COMPUTER SOFTWARE REQUIREMENTS

The code was designed for, and is operable on the IBM FORTRAN II Monitor System. The only tape assignments necessary are for input, output and the system. It may easily be made compatible with other FORTRAN compilers.

10. REFERENCE

M. R. Morrison and A. E. Tate, "Determination of Particle Fluxes Impinging on a Spacecraft, Northrop Space Laboratories," NSL 63-63R-1 (September 1963).

11. CONTENTS OF CODE PACKAGE

The package contains the referenced document and one (1.2MB) DOS diskette on which is written in separate files: the source card deck, plus input and output data for a sample problem.

12. DATE OF ABSTRACT

January 1966; updated July 1981, February 1985.

KEYWORDS: SPACE RADIATION; TRAJECTORY; ELECTRON; PROTON