Index Page SIMPLE User's Guide

## Table of Contents

       SIMPLE User's Guide
          Abstract
          Summary

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# SIMPLE User's Guide

Last revised on 2002 DEC 13 by E. D. Wright.

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## Abstract

SIMPLE is a cookbook program that demonstrates how to use Toolkit routines to obtain state vectors.

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## Summary

The SIMPLE `cookbook' program illustrates the use of SPICE SPK ephemeris files and CSPICE Toolkit software. The program demonstrates how CSPICE routines fit together to solve a typical geometrical problem involving state vectors extracted from an SPK file.

SIMPLE demonstrates the use of the following high-level subroutines:

furnsh_c
  Load SPICE kernels

spkezr_c
  SPK, easy reader

str2et_c
  Convert time string to ephemeris time

et2utc_c
  Convert ephemeris time to UTC string

vsep_c
  Calculate angular separation between vectors

To run SIMPLE, you need a binary SPK ephemeris file and knowledge of the bodies and the corresponding time intervals contained in that file. The utility program named BRIEF summarizes the contents and time coverage of a binary SPK file. Refer to NAIF IDs Required Reading (naif_ids.req) for a list of body names and integer codes. In addition to an SPK file, you also require access to a leapseconds kernel (LSK).

The user enters the string names or NAIF ID codes for two target bodies and an observing body, and the end-points (expressed in UTC) of a time interval. The bodies may be any objects in the solar system, as long as the SPK file loaded into SIMPLE contains data for them during the time interval requested.

The time interval consists of ten (10) equally spaced time steps. SIMPLE computes the angular separation, in degrees, between the target bodies as seen from the observing body at each time step then displays the output to the terminal screen. The application then prompts the user to continue with another set of parameters or quit.

Below, find an example of a SIMPLE run. The session calculates the angle of separation between the Sun and the Moon as seen from Earth.

Please note: FORTRAN and C versions of the program can output numerical values in slightly different formats.

It is assumed the kernel files used by SIMPLE exist in the current directory (i.e. the directory from which your execute SIMPLE). This particular session was run on an Intel box using the LINUX operating system.

First, create the binary SPK kernel "cook_01.bsp" by running the CSPICE Toolkit TOBIN application on the transfer format file "cook_01.tsp" located in the CSPICE data directory. The program also requires a leapseconds kernel to run; an example leapseconds kernel, 'cook_01.tls' exists within the same directory. Now, execute SIMPLE:

                           Welcome to SIMPLE

       This program calculates the angular separation of two
       target bodies as seen from an observing body.

       The angular separations are calculated for each of 10
       equally spaced times in a given time interval. A table
       of the results is presented.

       Enter the name of a leapseconds kernel file: cook_01.tls

       Enter the name of a binary SPK ephemeris file: cook_01.bsp

       Enter the name of the observing body: earth

       Enter the name of the first target body: moon

       Enter the name of the second target body: sun

       Enter the beginning UTC time: 1 jan 1990

       Enter the ending UTC time: 2 jan 1990

       Working ... Please wait.

       The angular separation between bodies moon and sun,
       as seen from body earth.

       From: 1990 JAN 01 00:00:00
       To  : 1990 JAN 02 00:00:00

              UTC Time                 Separation
       ----------------------------------------------
         1990 JAN 01 00:00:00         46.25929528 deg
         1990 JAN 01 02:40:00         47.63463504 deg
         1990 JAN 01 05:20:00         49.01248624 deg
         1990 JAN 01 08:00:00         50.39282527 deg
         1990 JAN 01 10:40:00         51.77563064 deg
         1990 JAN 01 13:20:00         53.16088282 deg
         1990 JAN 01 16:00:00         54.54856399 deg
         1990 JAN 01 18:40:00         55.93865792 deg
         1990 JAN 01 21:20:00         57.33114978 deg
         1990 JAN 02 00:00:00         58.72602606 deg

       Continue? (Enter Y or N): N