Catoptric optical scanning system provides relatively fast line-scan rate for two-dimensional coverage. Rapid scan rates require low focal ratios between components and smallest possible masses. System is relatively free from monochromatic defects and chromatic aberrations

Abel, I. R.

English

NASA Technical Reports Server

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August 1973	 B73-10279 
NASA TECH BRIEF 
Lyndon B. Johnson Space Center 
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, 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. 
- Wide-Field Reflective Scanning Optical Systems 
.
The problem: 
Purely reflective (catoptric), scanning optical systems 
are an important component in scanning radiometers 
and spectroradiometers. Used in earth-resource sur-
veillance satellites, these scanning systems must provide 
a relatively fast line-scan rate for a two-dimensional 
coverage of the Earth's surface below. Rapid scan rates 
in optical scanning systems, in general, require low 
focal ratios between components and the smallest 
possible masses. In addition, the systems must be 
relatively free from monochromatic defects and chro-
matic aberrations, and any obscuration must be inde-
pendent of the scan angle.
Housing
The solution: 
A catoptric optical scanning system was developed 
which satisfies the above requirements. 
How it's done: 
The system, as shown in the figure, comprises a set of 
mirrors arranged in a specific configuration and enclosed 
in a housing. The scanner assembly comprises a pair of 
plane mirrors mounted for unitary rotation about an 
optical axis. The larger of the two mirrors intersects the 
optical axis at an acute angle. Both mirrors are normal 
to a common plane containing an optical axis and form 
opposite faces of a rhomboidal polyhedron. Upon 
•
	
Scanning Optical System 
• 
(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=19730000279 2020-03-17T06:56:14+00:00Z
. 
rotation, the smaller mirror traces a section of conical 
surface coaxial with the optical axis. 
Light from the object being observed is reflected 
from a primary spherical mirror onto a plane secondary 
mirror. The secondary mirror reflects this light through 
an arcuate mask to the scanning assembly. The scanning 
assembly in turn reflects this light onto the relay optics. 
Light enters the relay optics and is reflected first by an 
aspherical mirror and then by a spherical mirror to 
focus on a detector. The two spherical mirrors and the 
aspherical mirror have central apertures to permit the 
passage of light. 
As the scanner assembly rotates about the optical 
axis, the line of sight of the instrument traces an arcuate 
linear sweep. Light enters the instrument in such a 
direction that its major component is aligned with the 
optical axis. It emerges from the scanning assembly as a 
diverging axial field. Thus, the only correction necessary 
for the spherical aberration is provided by the aspherical 
mirror. 
The system has the following features: 
1. Only reflective elements are used to cover a broad 
spectral region. 
2. The image plane scanning allows a high scan rate 
(about 6000 rpm). 
3. Rotational scanning is used rather than oscillatory 
scanning to produce this high scan rate. 
4. A very large scan angle permits the coverage of a 
large area. 
5. The system has a relatively simple configuration. 
6. Two small mirrors are the only movable optical 
elements.
Note: 
Requests for further information may be directed to: 
Technology Utilization Officer 
Lyndon B. Johnson Space Center 
Code JM7 
Houston, Texas 77058 
Reference: TSP73-10279 
Patent status: 
This invention is owned by NASA, and a patent 
application has been filed. Inquiries concerning non-
exclusive or exclusive license for its commercial develop-
ment should be addressed to: 
Patent Counsel 
Lyndon B. Johnson Space Center 
Code AM 
Houston, Texas 77058
Source: I. R. Abel of
Honeywell, Inc.
under contract to

Johnson Space Center

(MSC-14096)
. 
B73-10279	 Category 03


Wide-field reflective scanning optical systems

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