U.S. patent application number 10/948353 was filed with the patent office on 2006-03-30 for compact-depth spiral telescope and method of making and using the same.
This patent application is currently assigned to General Dynamics Advanced Information Systems, Inc.. Invention is credited to Thomas Zaugg.
Application Number | 20060066965 10/948353 |
Document ID | / |
Family ID | 36098754 |
Filed Date | 2006-03-30 |
United States Patent
Application |
20060066965 |
Kind Code |
A1 |
Zaugg; Thomas |
March 30, 2006 |
COMPACT-DEPTH SPIRAL TELESCOPE AND METHOD OF MAKING AND USING THE
SAME
Abstract
The invention according to a first aspect may include an optical
system. The optical system may have an axial axis. This optical
system may have a number of primary mirror segments. A number of
reflectors may be arranged about the axial axis. The primary mirror
segments may be configured to reflect a number of principal rays
along a first set of chords to corresponding reflectors. These
reflectors may be configured to reflect the corresponding principal
rays along a second set of chords. Both the first set of chords and
the second set of chords may have an angle in excess of 45 degrees
with respect to the direction of the axial axis. The invention
according to a first aspect may also include a second set of
reflectors. The second set of reflectors may be configured to
direct the light to an image plane. Other aspects of the invention
may include a method of receiving light using an optical system
configured to spiral light though the system and a method of making
such a system.
Inventors: |
Zaugg; Thomas; (Ypsilanti,
MI) |
Correspondence
Address: |
HOWREY LLP
C/O IP DOCKETING DEPARTMENT
2941 FAIRVIEW PARK DR, SUITE 200
FALLS CHURCH
VA
22042-2924
US
|
Assignee: |
General Dynamics Advanced
Information Systems, Inc.
Arlington
VA
|
Family ID: |
36098754 |
Appl. No.: |
10/948353 |
Filed: |
September 24, 2004 |
Current U.S.
Class: |
359/861 ;
359/857 |
Current CPC
Class: |
G02B 17/06 20130101;
G02B 23/00 20130101 |
Class at
Publication: |
359/861 ;
359/857 |
International
Class: |
G02B 5/08 20060101
G02B005/08 |
Claims
1. An optical system having an axial axis, comprising: a first
primary mirror segment, a second primary mirror segment and a third
primary mirror segment, each of the first primary mirror segment,
the second primary mirror segment, and the third primary mirror
segment being radially disposed about the axial axis of the optical
system; a first reflector, a second reflector, and a third
reflector arranged around the axial axis, the first, second, and
third primary mirror segments being configured to reflect a
corresponding plurality of principal rays along a first plurality
of chords to the firsts, second, and third reflectors, the first,
second, and third reflectors being configured to reflect the
corresponding plurality of principal rays along a second plurality
of chords, the first plurality of chords and the second plurality
of chords having an angle in excess of 45 degrees with respect to
the direction of the axial axis, and such that the reflected
principal rays do not pass through the axial axis of the optical
system, the principal rays being reflected such that a path of the
reflected principal rays represents a piecewise linear spiral about
the axial axis; and a plurality of secondary reflectors configured
to receive a respective one of the plurality of principal rays and
direct the plurality of principal rays to an image plane.
2. The optical system of claim 1, wherein the first, second, and
third reflectors and the plurality of secondary reflectors are
configured to reduce the depth of the optical system.
3. The optical system of claim 1, wherein an image of the source is
formed upon the image plane.
4. The optical system of claim 1, wherein the first, second, and
third reflectors includes secondary mirror segments.
5. The optical system of claim 1, wherein the light is received at
a first end of the optical system and the plurality of secondary
reflectors is located at a second end of the optical system.
6. The optical system of claim 5, wherein the image plane is
located substantially at the first end.
7. The optical system of claim 5, wherein the image plane is
located at a plane beyond the second end.
8. The optical system of claim 1, each of the primary mirror
segments defining an input aperture, wherein the input aperture is
substantially circular and at least one of the first primary mirror
segment, the second primary mirror segment and the third primary
mirror segment is an elliptical reflector.
9. The optical system of claim 1, wherein at least one of the
first, second and third reflectors are fold mirrors.
10. (canceled)
11. The optical system of claim 1, wherein the first primary mirror
segment has a cross section that has a parabolic component.
12. The optical system of claim 1, wherein the optical system
functions as a beam expander.
13. The optical system of claim 1, wherein the optical system
functions as a telescope.
14-21. (canceled)
22. The optical system of claim 1, the optical system being a first
optical system, wherein a second optical system is disposed within
a volume formed by the first, second and third primary mirror
segments and the first, second and third reflectors disposed about
the axial axis of the optical system, such that an axial axis of
the second optical system is proximate to the axial axis of the
first optical system.
23. (canceled)
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a compact-depth spiral
telescope and a method of making and using the same. More
particularly, the present invention relates to a telescope having a
reduced depth compared to conventional telescope designs of
comparable performance.
BACKGROUND OF THE INVENTION
[0002] Telescopes have been used for hundreds of years to magnify
the images of distant objects. In 1672, Sir Isaac Newton developed
what was believed to be the first reflective telescope. This type
of telescope has become known as a Newtonian telescope. One
specific type of a Newtonian telescope is a Gregorian telescope.
Gregorian telescopes may be used in applications where upright
images are required and in applications that cannot tolerate strong
optical aberration. Traditional Gregorian telescopes have a primary
mirror and a secondary mirror, where the distance between the
primary mirror and the secondary mirror is greater than the focal
length of the primary mirror. Other types of telescopes may
include, for example, those employing refractive, reflective or
catadioptic systems.
[0003] One problem of such systems is encountered when large
optical telescopes are deployed, for example, extra-terrestrially.
A limiting factor in telescope design is the launch-vehicle
capacity. Such large telescopes quickly meet the payload capacities
of launch-vehicles. One solution to this problem was the use of
sparse aperture telescopes. Alternatively, or in conjunction with a
sparse aperture telescope, telescope arrays have also been used.
These telescopes have just recently been realized and may be able
to reduce the weight and size of the system below that for a
fully-filled aperture system. Sparse aperture telescopes may be
able to increase the effective diameter of an optical system while
reducing the overall weight and stowable size of the system.
Generally speaking, a sparse aperture system synthesizes the light
received from a number of smaller apertures, known as sub-apertures
that are phased to form a common image field. This configuration
enables the increase of the effective aperture size, while avoiding
the difficulties associated with manufacturing and transporting a
large monolithic mirror.
[0004] An additional solution to the problems associated with large
telescope designs is to segment the primary mirror of the
telescope. Segmenting the primary mirror of the telescope permits
telescopes with larger aperture dimensions. Sparse apertures can be
used to maximize resolving power given a mass constraint. However,
for such systems, a significant fraction of the mass budget is
typically devoted to the superstructure necessary to achieve the
required levels of stability and rigidity. This is due to the axial
extent of the system, or "depth". This depth is usually much larger
than the aperture extent. A reduction in the depth of a sparse
aperture system may be achieved by employing an array of
telescopes, but the optics required to optically combine the
telescopes to image at a single image plane is very complex and may
result in field-of-regard and throughput limitations.
[0005] What is needed is a telescope with a reduced depth to permit
higher-powered telescopes to be carried by traditional
launch-vehicles. Additionally, what is needed is a telescope that
has a length measured in an axial direction that is substantially
reduced as compared with traditional telescopes, while being
configured with the same aperture size. Also, what is needed is a
telescope that does not require complex optical systems for the
combination of outputs from a number of telescopic systems.
SUMMARY OF THE INVENTION
[0006] Thus, the present invention seeks to address at least some
of the foregoing problems identified in prior art telescopic
systems. Thus, the present invention may be configured such that
the length of the telescope measured along an axial axis is
substantially reduced as compared with traditional telescopic
systems. Furthermore, the superstructure of an optical system, such
as, for example, a telescope or a beam expander, may be
substantially reduced when compared to traditional optical
systems.
[0007] The invention according to a first aspect may include an
optical system. The optical system may have an axial axis. This
optical system may have a number of primary mirror segments. A
number of reflectors may be arranged about the axial axis. The
primary mirror segments may be configured to reflect a number of
principal rays along a first set of chords to corresponding
reflectors. These reflectors may be configured to reflect the
corresponding principal rays along a second set of chords. Both the
first set of chords and the second set of chords may have an angle
of in excess of 45 degrees with respect to the direction of the
axial axis. The invention according to a first aspect may also
include a second set of reflectors. The second set of reflectors
may be configured to direct the light to an image plane.
[0008] According to one embodiment of the present invention, the
telescope may be configured to reduce the depth of the optical
system. This depth reduction may be along the axial axis of the
optical system. The optical system may be configured to form an
image of the source in the image plane. Furthermore, the reflectors
may be mirror segments arranged around the axial axis of the
optical system. These mirror segments may be secondary mirror
segments in the optical system. The optical system may be
configured to receive light at a first end of the optical system
and the second set of reflectors may be disposed at the second end
of the optical system. Depending on the overall system
configuration and particularly, the orientation of the second set
of mirrors, the image plane may be located substantially at the
second end of the system. According to another embodiment of the
present invention, the image plane may be located at a plane beyond
the second end of the system. Alternatively, the image plane may be
arranged at the first end of the system. According to yet another
aspect of the invention, the system may include a substantially
circular input aperture, which may be defined by a substantially
elliptical reflector. According to another aspect of the invention,
the reflectors may be fold mirrors. According to another embodiment
of the invention, the input aperture may include a first mirror and
a second mirror. Additionally, the first mirror may be configured
to have a cross section that has a parabolic component. The optical
system may be configured to function, for example, as a telescope
or a beam expander.
[0009] A method according to a second aspect of the present
invention may include, for example, receiving light from a source.
This source may be, for example, a distant source of light such as
a star or other celestial body. The method according to a second
aspect of the present invention may also include reflecting a
principal ray associated with the received light along a number of
chords. These chords may have an angle of at least 45 degrees with
respect to the direction of the axial axis. The method according to
the second aspect of the present invention may also include
directing the light received from the source to an image plane.
[0010] The method according to a second aspect of the present
invention may also include receiving the light using a plurality of
reflectors disposed about the axial axis of an optical system. This
optical system may have a first end and a second end. The first end
may be disposed closer to the source than the second end.
Additionally, the step of reflecting may be performed by a
reflector. This reflector may be located proximate to the second
end, for example.
[0011] A method of making a compact-depth telescope may include,
for example, segmenting a primary reflector. Additionally, the
method of making a compact-depth telescope may include determining
a reflector pitch. The reflector pitch may be determined such that
the first set of chords and the second set of chords have an angle
in excess of 45 degrees with respect to the direction of the axial
axis so as to reflect the light a number of times from an
associated set of reflectors located within an interior volume of
the compact-depth telescope. Furthermore, the method may include,
for example, segmenting a second reflector.
[0012] The method of making a compact-depth telescope according to
another aspect of the present invention may include, for example,
disposing a number of mirrors within an interior volume of the
compact-depth telescope. Additionally, the step of segmenting the
primary reflector may include segmenting a primary reflector such
that the primary reflector includes a number of elliptically-spaced
reflector sections. According to yet another aspect of the present
invention, a method of making a compact-depth telescope may include
disposing the mirrors within the volume of the compact-depth
telescope, where the mirrors are fold mirrors.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] While the specification concludes with claims particularly
pointing out and distinctly claiming the present invention, it is
believed the same will be better understood from the following
description taken in conjunction with the accompanying drawings,
which illustrate, in a non-limiting fashion, the best mode
presently contemplated for carrying out the present invention, and
in which like reference numerals designate like parts throughout
the Figures, wherein:
[0014] FIG. 1 shows an example of how light received from a source
"spirals" through an optical system according to one aspect of the
present invention;
[0015] FIGS. 2A and 2B show examples of reflector geometry
according to an aspect of the present invention;
[0016] FIG. 3 shows an example of a compact optical system
according to one embodiment of the present invention;
[0017] FIG. 4 shows another example of a compact optical system
according to another embodiment of the present invention;
[0018] FIG. 5 shows yet another example of a compact optical system
according to yet another embodiment of the present invention;
[0019] FIGS. 6A-6D show various reflector configurations and chord
spans according to various embodiments of the present invention;
and
[0020] FIG. 7 shows an optical system having three segments
according to an exemplary embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0021] The present disclosure will now be described more fully with
reference the to the Figures in which various embodiments of the
present invention are shown. The subject matter of this disclosure
may, however, be embodied in many different forms and should not be
construed as being limited to the embodiments set forth herein.
[0022] FIG. 1 shows an example of how light received from a source
"spirals" through an optical system according to one aspect of the
present invention. One or more primary reflectors 110, 120 that
form the input aperture of the optical system 100 may receive
light. While FIG. 1 shows two primary reflectors 110, 120
configured to act as input apertures, one of ordinary skill in the
art will realize that more than two primary reflectors may be used.
For example, eighteen or more reflectors may be used as the input
aperture of the optical system 100. In the embodiment illustrated
in FIG. 1, received by the primary reflectors 110, 120 may be
"spiraled" through the volume 150 of the optical system. The volume
150 of the optical system 100 may be defined by superstructure and
a number of reflectors (not shown) arranged about the axial axis
170 of the optical system 100. The light received by the primary
reflectors 110, 120 may be reflected to a secondary reflector
within the volume 150 of the optical system 100 along a chord. The
mirrors may be configured such that the chord is at an angle in
excess of 45 degrees with respect to the axial axis 170 of the
optical system 100. The chord angle may be, for example, between
45.degree. and 89.degree. with respect to the axial axis. According
to one embodiment of the present invention, the angle may be, for
example, between 65.degree. and 85.degree.. Any angles may be used
that may achieve depth compression of the telescope by effectively
spiraling the light about the axial axis. In one embodiment of the
invention, the mirrors may be configured such that the chord is at
an angle in excess of 45 degrees with respect to the axial axis of
the optical system.
[0023] In the example shown in FIG. 1, the light may be reflected
multiple times within the volume 150 of the optical system 100, so
that the light effectively spirals through the volume along a
number of chord spans as it descends through the optical system
100. The light may be received by a set of reflectors 130, 140.
This set of reflectors 130, 140 may be configured to receive light
that has been reflected along at least one chord span that has an
angle in excess of 45 degrees with respect to the axial axis, and
may direct that light to an image plane 160. Alternatively, the
light may be reflected along at least one chord span that has an
angle with respect to the axial axis of the optical system such
that the depth of the optical system is substantially compressed.
The depth may be, for example, the dimension of the telescope along
the axial axis of the telescope. Thus, the optical system 100 may
be configured as a telescope.
[0024] Although the term "spiral" may be used in connection with
the present invention, it is to be understood that the light does
not travel in an arcuate path as it descends through the volume 150
of the optical system, but rather that the light is reflected along
at least one chord within a volume 150 of the optical system 100 at
an angle in excess of 45 degrees with respect to the axial axis of
the optical system 100. Additionally, while the term "chord" is
traditionally used to identify a straight line linking two points
on a circle, it should be noted that the optical system need not be
circular in cross section in a geometrical sense, nor does the
volume need to be perfectly cylindrical. A chord as used herein may
be defined as the path length from one reflective surface and
another reflective surface such that the light propagates at an
angle in excess of 45 degrees with respect to an axial axis in a
three-dimensional optical system.
[0025] FIGS. 2A and 2B show examples of reflector geometry
according to an aspect of the present invention. For example, in
FIG. 2A, a reflector 210 may be disposed about an axial axis of an
optical system (not shown). As shown in FIG. 2A, the dashed line
220 is substantially parallel to the axial axis of the optical
system. Therefore, light, represented by the ray 230 received at
the reflector 210 may be directed at an angle .alpha. with respect
to the axial axis of the optical system, i.e., because line 220 is
substantially parallel to the axial axis of the optical system,
light ray 230 will form substantially the same angle with respect
to the line 220 as it would with respect to the axial axis of the
optical system.
[0026] FIG. 2B shows the same concept illustrated in FIG. 2A in
three dimensions. As described above, line 220 may be substantially
parallel to the axial axis of the optical system. A reflector 210
may be configured to receive light and reflect that light along a
chord at an angle .alpha. with respect to the axial axis of the
system. This angle .alpha. may be at an angle of at least 45
degrees with respect to the axial axis of the optical system. As
shown in FIG. 2B, the light ray 230 may be represented by a
three-dimensional vector having an x-component, a y-component, and
a z-component, such that the light ray 230 is directed to an
associated mirror along a chord. Thus, the light ray may
effectively "spiral" through the optical system prior to being
directed to the image plane. This folding of the optical path
permits a substantial reduction in the depth of the optical
system.
[0027] FIG. 3 shows an example of a compact optical system 300
according to one embodiment of the present invention. The compact
optical system 300 may be configured as, for example, a telescope.
The optical system 300 may include a first primary reflector 310
and a second primary reflector 320. The first primary reflector 310
and the second primary reflector 320 may be, for example, a
segmented primary mirror. The first primary reflector 310 and the
second primary reflector 320 may be configured to receive light
from a remote source and reflect the received light into the
optical system. Thus, FIG. 3 shows two segments of a
sparse-aperture spiral optical system. In this embodiment of the
present invention, the first primary reflector segment 310 and the
second primary reflector segment 320 may be configured to reflect a
chief ray for each segment through the axial axis of the telescope.
A first flat mirror 330 and a second flat mirror 340 may be
configured to reflect the chief rays across the interior of the
telescope. A second set of reflectors 350, 360 may be configured to
direct the light from the first primary reflector segment 310 and
the second primary reflector segment 320 to the image plane
370.
[0028] This exemplary embodiment of the present invention
illustrates one concept of the invention: all light paths
corresponding to each sub-aperture of a sparse aperture imaging
system may be independently folded in an arbitrary fashion so long
as they are brought into register at the image plane 370. Thus, as
shown in FIG. 3, the light incident on the first primary mirror
segment 310 and the second primary mirror segment 320 may be
reflected back and forth between the first flat mirror 330 and the
second flat mirror 340 until a final set of mirrors 350 and 360
direct the light to the image plane 370. The first flat mirror 330
and the second flat mirror 340 may be configured to be
substantially parallel to one another. By configuring the optical
system 300 to fold the light paths in this manner, a
long-focal-length telescope may be significantly compressed in
depth, i.e., along the direction of the telescope axis.
[0029] FIG. 4 shows another example of a compact optical system
according to another embodiment of the present invention. FIG. 4 is
similar to FIG. 3 in that the optical system 400 may be configured
to include a first primary segmented reflector 410 and a second
primary segmented reflector 420 that are configured to receive
light from a remote source and to reflect the chief ray through the
telescope axis. After the light is reflected from the first primary
reflector segment 410 and the second primary reflector segment 420,
the light may be reflected back and forth between a first flat
mirror 430 and a second flat mirror 430. The first flat mirror 430
and the second flat mirror 440 may be configured so as to be
substantially parallel to one another. The light may be received by
a set of reflectors 450 and 460, which may be configured to direct
the light back through the optical system 400 to an image plane
470. The embodiment of the invention illustrated in FIG. 4 may be
configured to further reduce the depth of the optical system as
compared to the embodiment of the invention illustrated in FIG.
3.
[0030] FIG. 5 shows yet another example of a compact optical system
according to yet another embodiment of the present invention. FIG.
5 is similar to the embodiments of the present invention
illustrated in FIGS. 3 and 4, however, in the embodiment
illustrated in FIG. 5, the first primary reflector segment 510 and
the second primary reflector segment 520 are arranged at an end of
the optical system that is furthest from the source. In this
exemplary embodiment of the present invention, the light may be
spiraled upwards through the optical system 500. When the first
primary reflector segment 510 and the second primary reflector
segment receive the light from the source (not shown), a chief ray
may be directed through an axial axis of the optical system 500.
The first primary reflector segment 510 and the second primary
reflector segment 520 may be configured to direct the light
received from the source to one of a first flat mirror 530 and a
second flat mirror 540, such that the light is reflected back and
forth between the first flat mirror 530 and the second flat mirror
540. The light may be directed to an image plane 570 by a set of
reflectors 550 and 560. As with FIG. 4, the set of reflectors 550
and 560 may be configured to direct the light back through the
optical system to an image plane located proximate to the first
primary reflector segment 510 and the second primary reflector
segment 520. While specific embodiments of the invention have been
shown as telescopic systems, the present invention may also be
configured as a beam expander by reversing the direction of the
rays of light as they propagate through the optical system. Thus,
the term optical system may include both imaging systems and beam
expansion systems, for example.
[0031] The two segment systems described with respect to FIGS. 3-5
are degenerate examples of a spiral telescope according to various
embodiments of the present invention. In the general case, however,
the light incident on multiple segments may be reflected so as to
spiral around the telescope axis, traveling along the chords.
Several examples are shown in FIGS. 6A-6D for a twelve segment
system. The differences between these systems may be characterized
in that the fraction of the circle subtended by the chord varies.
This may be a function of the angle of the reflectors. The chord
span may be, for example, the fraction of the circle subtended by
each chord.
[0032] FIG. 6A shows an exemplary configuration of an optical
system having twelve segments. In the embodiment illustrated in
FIG. 6A, reflector segments 610 may be arranged about an axial axis
620 of the optical system 600. The embodiment shown in FIG. 6A may
be configured to have chord spans of 1/3. FIG. 6B shows another
exemplary configuration of an optical system having twelve segments
according to a second embodiment of the present invention.
Reflector segments 610 may be arranged about an axis 620 of the
optical system. In the embodiment shown in FIG. 6B, the chord spans
may be 1/4. Likewise, FIG. 6C shows an exemplary embodiment of the
present invention including a twelve-segment system. The
twelve-segment system may be configured to reflect light along a
number of chords such that the chord span is 1/6. FIG. 6D shows an
exemplary embodiment of the present invention having twelve
segments according to another embodiment of the present invention.
The twelve-segment system may be configured to reflect light along
a number of chords such that the chord span is 5/12.
[0033] As shown in FIGS. 6A-6D, the primary mirror segments 610 are
tilted. Thus, the mirrors may have an elliptical shape in order to
have the circular projections shown in FIGS. 6A-6D. These mirror
shapes are merely exemplary, as any shape may be used. Thus, the
mirror segments may be, for example, trapezoidal, rectangular, or
triangular.
[0034] The pitch of the chords traversing an interior volume of the
optical system may be defined as the change in the z-coordinate
(along the telescope axis) of the chief ray as it traverses a
single chord. The pitch ratio may be defined as the ratio of the
pitch to optical path length along a single chord, and may be
inversely proportional to the depth compression achieved by the
spiral telescope compared to a corresponding conventional design.
Thus, the transverse chord length may be given by: c x = 2 .times.
( 1 - r ) .times. sin .function. ( .PHI. 2 ) , ##EQU1## where r is
the radius of the sub-aperture (assuming that an aperture radius
that is normalized to one) and .phi. is the chord span in radians.
The minimum pitch may be defined by: c z = 2 .times. r .times. c x
c x + 4 .times. r . ##EQU2## Additionally, the chord length is
given by: c = c x 2 + c z 2 . ##EQU3##
[0035] Thus, for example, in an embodiment in which the radius of
the sub-aperture ("r") is 0.14, the pitch ratio may be, for
example, 0.158. This pitch ratio may correspond to a depth
compression factor of 6.3. The depth compression factor may be
defined as the inverse of the ratio of the axial length of the
spiral telescope system to the axial length of a corresponding
conventional telescope system with the same focal length, or more
precisely, the axial distance between the primary and secondary
mirrors. In an embodiment of the present invention including 18
sub-apertures, this configuration may have a fill ratio of 35%. The
fill ratio may be defined as the ratio of the aperture area to the
area of a circle circumscribing the entire aperture. Reducing the
sub-aperture size may allow for better depth compression, but also
may reduce the fill factor. Circular apertures may not necessarily
be the optimal configuration for the sub-apertures and therefore,
alternative aperture configurations may be employed.
[0036] FIG. 7 shows an optical system having three segments
according to an exemplary embodiment of the present invention. The
embodiment of the present invention illustrated in FIG. 3 is merely
exemplary and one of ordinary skill in the art will realize that
additional segments may be added. For example, twelve, eighteen or
more segments may be used in connection with the present invention.
Rays of light may be received from a distant source by a first
primary mirror segment 710, a second primary mirror segment 720,
and a third primary mirror segment 730. These primary mirror
segments 710, 720 and 730 may be elliptical in shape, as shown in
FIG. 7. Alternatively, these mirrors may have any shape to define
the sub-aperture.
[0037] After the light has been received at the first, second, and
third primary mirror segments, 710, 720, and 730, respectively, the
light may be directed along a corresponding chord to another mirror
740. The chord may have an angle with respect to the axial axis of
the system. This angle may be, for example, an angle greater than
45 degrees with respect to the axial axis. According to one
embodiment of the present invention, primary mirrors 710, 720, and
730 may have a parabolic component.
[0038] As shown in FIG. 7, the light may be directed to associated
mirrors 740 located about the interior volume of the optical
system. These mirrors may be, for example, segmented secondary,
tertiary, quaternary, or other level-mirrors. These mirrors may be,
for example, fold mirrors. Alternatively, any type of mirror may be
used with mirrors 740. Each of these mirrors may be configured to
direct a principal ray of the beam of light received from one of
the primary mirrors, for example, at an angle that is greater than
45 degrees with respect to an axial axis of the optical system.
Once the light has been effectively reflected and spiraled through
the volume of the telescope, the light may be received by a
respective one of the mirrors 750, 760, or 770, and may be directed
by the mirrors 750, 760, or 770 to the image plane 780. An
exemplary path taken by rays though the system is shown in FIG. 7,
using a solid and two types of dashed lines indicating the optical
path that the light takes through the optical system 700.
[0039] A method of constructing a compact-depth optical system will
now be described. The first step that may be employed in design of
a spiral telescope using a traditional telescope configuration
includes choosing the number and the size of the sub-apertures.
After the number and size of the sub-apertures have been selected,
the primary mirrors may be segmented. Additionally, secondary
tertiary or even quaternary mirrors may be segmented as well.
Additional mirrors may be segmented as well as applicable. After
the mirrors have been segmented, a chord span may be determined.
This chord span may be determined based on, for example, a pitch
ratio that may be predetermined to be optimal by the system
designer.
[0040] After the chord span has been selected, tilt may be added to
the figure of the primary mirror segments. Note that this is quite
different from merely tilting the primary segments. The figure for
a mirror segment is an equation describing the surface as a
function of the aperture coordinates, e.g. z=f(x,y). Tilt in an
arbitrary direction can be described by z=t.sub.x+t.sub.yy, where
t.sub.x and t.sub.y are the amounts of tilt in the x and y
directions, respectively.) This tilting may configure the mirror to
direct the chief ray along the appropriate chord through the
optical system. After this has been completed, flat mirrors may be
added either below or above the primary mirror segments. These
mirrors may be parallel to and facing the axial axis of the optical
system. At the point where the optical path along a segment chief
ray is the same as the distance between the primary segments and
the secondary segment of the original design, secondary segments
may be added. The pitch ratio may be adjusted until the secondary
segments are located in the same plane as the flat mirrors.
[0041] Additionally, the method of designing a compact-depth
telescope may include selecting a second chord span and pitch ratio
for the next section of the telescope. Additional tilt to the
secondary mirror figures, which, to reiterate is not the same as
tilting the segments may be added so as to direct the chief ray
along the next chord.
[0042] These steps may be repeated for additional mirror surfaces
disposed within the optical system. When too little optical path
remains for the chief ray to traverse another chord a mirror may be
added to direct the chief ray towards the telescope axis. This ray
may be intercepted with another mirror at a distance from the axis
equal to where the ray in the original design would be after
traversing the same optical path and direct it towards the image
plane.
[0043] According to another embodiment of the present invention,
actuators may be added to the last set of mirrors to permit
aligning of the segments. These same actuators may be used to steer
the field of view of the telescope off axis while maximizing the
off-axis Strehl ratio and effect phase diversity for improved image
reconstruction. According to other aspects of the present
invention, actuators may be added to other mirror segments to aid
in alignment and aberration management.
[0044] This spiral telescope may be configured to have a modular
structure, with struts extending below the primary segments. These
struts may be configured to support the flat mirrors and secondary
segments. According to one embodiment of the present invention,
each strut may be identical to the others. There are many potential
embodiments of a mechanical structure that may be used in
connection with the present invention. Requirements of such a
structure are that the structure be rigid and capable of
maintaining the position of the mirrors with relatively tight
tolerances. Additionally, the superstructure associated with the
system may be collapsible, permitting an even more compact design
for deployment and consuming less space in a launch vehicle.
[0045] According to an embodiment of the present invention, and as
may be seen in, for example, FIGS. 6A-6D, the space at the middle
of the cavity of the optical system may be empty and light need not
pass through the center as it propagates along the individual chord
lengths throughout the system. In one embodiment of the invention,
an additional compact telescope may be positioned in this empty
space proximate to the axis of the optical system. In yet another
embodiment, imaging electronics or other optical or mechanical
structures may be located proximate to the axis of the optical
system.
[0046] Numerous other configurations of a compact-depth spiral
telescope may be implemented based on the present disclosure. While
the invention has been described with reference to specific
preferred embodiments, it is not limited to these embodiments. The
invention may be modified or varied in many ways and such
modifications and variations as would be obvious to one of skill in
the art are within the scope and spirit of the invention and are
included within the scope of the following claims. For example,
various aperture configurations may be employed. Additionally, the
present invention is not intended to be limited to any particular
superstructure or mechanical structure as long as the structure is
rigid and retains the mirror segment alignment within the
predetermined tolerances.
* * * * *