Star/horizon simulator is used for alignment and optical plus photoelectric tests of the sextant for the Apollo guidance and navigation system optical unit assembly. The unit is basically a refractive collimator with a two inch objective lens system and a twenty-four inch focal length

Schmidt, W. C.

English

NASA Technical Reports Server

May 1967	 Brief 67-10110 
NASA TECH BRIEF	 1 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Star/Horizon Simulator Used to Test Space Guidance System 
A star/horizon simulator, basically a refractive col-
limator with a 2-inch objective lens system and a 24-
inch focal length, capable of simulating stars and the 
earth's horizon, is described. The unit is used for 
alignment and optical plus photoelectric tests of the 
Apollo guidance and navigation system Optical Unit 
Assembly (OUA). The OUA consists of a scanning 
telescope and sextant, however, since the simulator 
is used only for testing the sextant, the scanning tele-
scope is not discussed here. 
The sextant consists of a fixed visual line of sight 
(fixed with respect to the OUA), an articulating visual 
line of sight, a fixed photosensitive line of sight, and 
an articulating photosensitive line of sight. The sextant 
is used during the Apollo mission for angular meas-
urements between stars, stars and landmarks, and 
stars and the earth's horizon in a manner similar to 
the use of a navigational sextant on seagoing vessels. 
The star/horizon simulator lens system, consisting 
of a doublet lens, transmits electromagnetic energy in 
the 3000 to 8000 A range and is color corrected for 
focusing at 3500 A and 5760 A. The collimator is 
focused at infinity and can project circles of 5 arc 
seconds, 30 arc seconds, and 30 arc minutes. The 5 and 
30 arc second circles are used to simulate stars while 
the 30 arc minute circle is used to simulate the earth's 
horizon. The 30 arc minute horizon is formed by pro-
jecting condensed diffused light through a circular 
aperture and reflecting it from a front-silvered mirror 
located at the focal point of the collimator. The 5 and 
30 arc second stars are etched on the same front-
silvered mirror and are formed by projecting con-
densed diffused light from the rear of the mirror 
through the etched areas. Spectral content of the stars 
and horizon is matched to the sextant photosensor 
range by suitable filters. Super micrometers (accurate
to 0.000050 inch) permit limited, calibrated movement 
of the stars in two directions mutually perpendicular 
to the optical axis. 
To gain collimated light greater than the 2-inch 
aperture would normally exhibit, two mirror arrayas-
semblies provide lines of sight separated by approxi-
mately 6 inches, or the equivalent performance of an 
8-inch collimator. Each mirror array assembly consists 
of two front-silvered mirrors set at a discrete distance 
apart and with reflective surfaces parallel within 3 arc 
seconds. One mirror in each assembly is pierced with a 
circular aperture to allow a portion of a light beam 
directed at that mirror to pass through it to the second 
mirror. The mirror reflective surfaces are set at 45° 
with respect to the collimator axis and the original 
2-inch collimated bundle is divided at the first mirror 
(part reflected and part passing through the aperture 
to the second mirror) and two collimated beams ob-
tained. Parallelism of the mirror array assemblies is 
checked by standard autocollimation technique. Abso-
lute calibration of star magnitude and horizon inten-
sity is accomplished by comparison of the star/ 
horizon simulator output with the output of a lumi-
nescent radioactive substance. 
Notes: 
1. Incorporation of the two mirror array assemblies 
to obtain the effect of an 8-inch collimator from a 
2-inch aperture should have definite application in 
other optical areas. 
2. Inquiries concerning this invention may be di-
rected to: 
Technology Utilization Officer 
Manned Spacecraft Center 
Houston, Texas 77058 
Reference: B67-101 10 
_!S
	
(continued overleaf) 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19670000110 2020-03-11T20:46:33+00:00Z
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA, Code 
GP, Washington, D.C. 20546. 
Source: William C. Schmidt

of Massachusetts Institute of Technology 
under contract to

Manned Spacecraft Center 
(MSC-407) 
Brief 67-10110	 Category 02


Star/horizon simulator used to test space guidance system

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