Computer program provides time history of sun aspect angles as seen from spacecraft and generates binary tape containing time history of position, velocity, and body attitude angles of vehicle in local horizontal, local vertical system. Program is written in FORTRAN 5 and SLEUTH 2 for Univac 1108 computer

Boyd, C. C.

English

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December 1970	 Brief 70-10602 
NASA TECH BRIEF H 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage commercial 
application. Tech Briefs are available on a subscription basis from the National Technical Information Service, Springfield, 
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nology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Expanded. Sun-Look Angle Program 
The problem: 
To devise a method of quickly and efficiently pro-
ducing a time history of the flight of a space vehicle 
relative to variables identifying the flight pattern. 
The solution: 
This program provides a time history of the sun 
aspect angles as seen from a vehicle. It can also gener-
ate a binary tape containing a time history of the 
position, velocity, and body attitude angles of the 
vehicle in the local horizontal, local vertical system. 
How it's done: 
Input is a vehicle ephemeris tape and the AFMTC 
Standardized Theoretical Trajectori Magnetic Tape. 
The output binary tape may be used as input to a post-
processor trajectory program. The main program 
reads-in the input to the Sun-Look Angle Program 
from cards and trajectory data tape. 
The data tape is positioned to the first requested file 
and processed, a record at a time, using NTRAN. 
Negative IBM 7094 floating point numbers are con- 
verted to negative UNIVAC 1108 floating point num-
bers. If longitude is measured positive west of Green-
wich on the data tape, the program will switch the sign 
to measure longitude positive east of Greenwich. If the 
altitude, position, and velocity of the vehicle are 
input in meters and meters per second, respectively, 
the program will correspondingly convert these to 
international feet and international feet per second. 
Computation of the sun-look angles requires the 
position of the sun with respect to the vehicle. The 
position of the sun with respect to the earth-fixed 
geocentric (EFG) system is computed by using ephem-
eris tape, the ephemeris routine, and a transformation 
matrix which carries a vector in the earth-centered 
inertial system into a vector in the EFG system. The
position of the vehicle with respect to the EFG system 
is given via output. The position of the sun with re-
spect to the vehicle can be found by a simple vector 
subtraction. 
If a binary tape is to be generated, the velocity and 
body attitude angles of the vehicle with respect to the 
earth are computed, and this information is stored on 
the binary tape. 
If the time on some record exceeds the input termi-
nation time for a file, or if the last record on a file 
is read, the data tape will be positioned to the next 
requested file and processing will continue. The pro-
gram will write a final record on the binary tape which 
indicates the end - of processing for this file. 
When the final file has been processed, the program 
will read a new set of data cards if no binary tape is 
generated. If a binary tape is generated, the program 
will list the data from the binary tape on the output 
printer and then read a new set of data cards. 
Notes: 
1. This program was written in FORTRAN V lan-
guage and SLEUTH II for use on the UNIVAC 
1108 computer. 
2. Inquiries may be directed to: 
COSMIC 
Barrow Hall 
University of Georgia 
Athens, Georgia 30601 
Reference: B70-10602 
Source: Constance C. Boyd of

Lockheed Electronics Company
under contract to
Manned Spacecraft Center 
(MSC-13 176) 
0	 Category 09 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights,
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Expanded sun-look angle program

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