Sensor generates interference fringes varying in number (horizontally and vertically) as a function of the total angular deviation relative to the line-of-sight axis. Device eliminates errors from zero or null shift due to lack of electrical circuitry stability

Walsh, T. M.

English

NASA Technical Reports Server

July 1972	 B72-10274 
NASA TECH BRIEF 
Ames Research Center
	 -4r 
NASA Tech Briefs announce now technology derived from the U.S. space program. They are issued to encourage 
commercial application. Teci Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Interferometric Rotation Sensor 
The problem: 
To detect rotation relative to the line-of-sight axis 
of a sensor that is pointed to a star. 
The solution: 
Generate interference fringes which vary in number 
(horizontally and vertically) as a function of the total 
angular deviation relative to the line-of-sight. 
How it's done: 
The sensor is constructed of glass for use with the 
visible spectrum, quartz for the ultraviolet regions, or 
calcium fluoride for the infrared, and is constructed 
as indicated in the diagram. The interfaces of the 
beamsplitter and the trihedral prism are cemented 
together to form one component; the three outer sur-
faces of the component are coated with high reflec-
tance materials. 
When a collimated beam of starlight is brought to 
the sensor by a suitable optical system, a fringe pat-
tern is formed and can be examined at the exit pupil 
of the sensor. The pattern is projected onto an image 
dissector tube and the fringes are counted by hor-
izontal and vertical sweeps of the tube face. The 
horizontal and vertical counts of the number of fringes 
are the basic data for error-signal generation. 
When the optical axis of the sensor is in theoretically 
exact alignment with the beam of starlight, there will 
be no fringes either horizontally or vertically on the 
tube face. Pitch and yaw counts are zero and rotation 
deviations from the star beam are zero in pitch and 
yaw. The sensor is insensitive to roll about the star 
beam. Motion in pitch only will result in generation 
of horizontal fringes. Motion in yaw only will result 
in generation of vertical fringes. Any combination of 
pitch and yaw will cause apparent rotation of the 
fringes on the face of the tube. Vertical and horizontal
scan counts will reveal the components of pitch and 
yaw leading to the number and inclination of the 
fringes which could be computed if total deviation 
and plane of deviation were desired as computed 
M 
Beamsplitter 
	
Surface I 	 Corner 
	
I	 Cube 
data. Otherwise, the V and H scan counts serve as 
raw error signals for null tracking or pointing. 
The sensor minimizes errors due to translations 
relative to the line-of-sight such as may occur because 
of vibration, thermal expansion or contraction of 
components, and creep due to mechanical distortion of 
components. It also eliminates errors from zero or null 
shift due to lack of stability of electrical circuitry 
from causes such as voltage variations, temperature 
changes, etc. The fringe counting operation is not as 
dependent on these parameters as are other techniques 
used to detect rotation.
(continued overleaf) 
Thisdocumentwas prepared underthe 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=19720000273 2020-03-17T03:28:52+00:00Z
Note:	 Patent status: 
No additional documentation is available. Specific	 Inquiries about obtaining rights for the commercial 
questions, however, may be directed to: 	 use of this invention may be made to: 
Technology Utilization Officer	 Patent Counsel 
Ames Research Center 	 Mail Code 200-1A 
Moffett Field, California 94035 	 Ames Research Center 
Reference: B72-10274 	 Moffett Field, California 94035 
Source: Thomas M. Walsh
Ames Research Center
(ARC-10278) 
B72-10274	 Category 03


Interferometric rotation sensor

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