Two transparent plates are mounted at equal and opposite angles in secondary optical-system housing, angles being set for optimum astigmatism correction. Rotation of secondary housing assembly and translation of detector are proportional to angular position of secondary image. Combined movement of two retains image within sagittal foci of secondary system

Amon, M.

Rosin, S.

English

NASA Technical Reports Server

March 1974
	 B73-10468 
NASA TECH BRIEF	 4I 
•i *,2i1 Goddard Space Flight 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. 
Fine Guidance for a Spaceborne Telescope 
The problem: 
Ritchey.Chretien telescopes are designed for the 
simultaneous observation of two optical images, one of 
which is located on the primary axis and the second 
off-axis. The problem with these telescopes involves an 
increasing astigmatism as the off-axis angle of the 
secondary image increases. Secondary images, as a result, 
become large blurs at large angles, which of course 
cannot be tolerated for spacecraft tracking or observatory 
sightings. 
The solution: 
This astigmatism is corrected substantially by em-
ploying a pair of transparent flat plates before the 
secondary image detector and by moving the secondary 
image detector and by moving the secondary optical 
system, to maintain the detector in focus.
astigmatism correction. The rotation of the secondary 
housing assembly and the translation of the detector 
are proportional to the angular position of the secondary 
image. The combined movement of the two retains the 
image within the sagittal (secondary) foci of the 
secondary system.
Servo Control 
Manual or 
Automatic 
Housing
Flat Detector 
How it's done: 
Basically, two transparent plates are mounted at 
equal and opposite angles in the secondary optical-
system housing, the angles being set for optimum
Servo-

Controlled
Plate 
Primary Image Beam 
Source 
Primary.	 Secondary Mirror 
Primary Optical - 
Axis
a- 
Primary Image Beam 
Secondary 
- - 
Source	 Secondary Image Beam
Transparent 
Plates (2) 
Field Flattener 
Lens 
'
Focal-Plane 
Detector 
Annular Plane 
Mirror 
Primary 
Mirror 
Ritchey-Chretien Telescope
(continued overleaf) 
This documentwas 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.
r
https://ntrs.nasa.gov/search.jsp?R=19730000468 2020-03-17T07:32:13+00:00Z
The telescope as shown in the figure is divided into 
two systems. The first system is responsive to optical 
energy from an on-axis (primary) source, and the second 
is responsive to the off-axis (secondary) source. Both 
systems obtain their images from the primary and 
secondary hyperbolic mirrors that are centered about the 
primary optical axis. The primary optical system includes 
a focal-plane detector for monitoring the primary 
on-axis source. 
The secondary optical system is centered about the 
secondary optical axis. This axis is orthogonal to the 
primary axis, as projected through the center of an 
annular-plane mirror. Light from the secondary image 
is reflected from this mirror and is transmitted through 
a field-flattener lens to the two transparent flat plates. 
Each of these plates is identical in thickness and has the 
same index of refraction. Light transmitted through 
these plates is directed to a flat detector. 
Both the detector and the plates are mounted on a 
servo-controlled plate. This plate is translated horizon-
tally with servo M 1 and is rotated by M 2 about the axis 
that is perpendicular to the secondary optical axis. The 
extent of the translation and rotation is directly 
proportional to the field angle, p, i.e., the field angle 
formed between the primary optical axis and the 
secondary image. In addition, servo M 3 rotates the 
entire secondary system housing by an angle 0, which is 
the angular position of the secondary image on the plane 
perpendicular to the primary axis. All three servos can 
be controlled either manually or automatically.
The combined motion of all of these components 
maintains the position of the secondary image detector 
on the sagittal (secondary) foci of the telescope. The 
result is that the secondary image is maintained in 
focus at all times, with the astigmatism being corrected 
by the two transparent plates. 
Note: 
Requests for further information may be directed to: 
Technology Utilization Officer 
Goddard Space Flight Center 
Code 207.1 
Greenbelt, Maryland 20771 
Reference: TSP73-10468 
Patent status: 
This invention has been patented by NASA (U.S. 
Patent No. 3,752,559); Inquiries concerning nonexclusive 
or exclusive license for its commercial development 
should be addressed to: 
Patent Counsel 
\ Goddard Space Flight Center 
' Code 204 
Greenbelt, Maryland 20771 
Source: Seymour Rosin and
Max Amon of
Kollsman Instruments Corp.
under contract to
Goddard Space Flight Center
(GSC. 1 1487) 
B73-10468	 Category 03


Fine guidance for a spaceborne telescope

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