The present invention generally relates to space optic systems and more specifically to an autonomously assembled space telescope.
The progress in large aperture telescopes has been quite remarkable over the last two decades. In space, the Hubble Space Telescope with a 2.4-meter monolithic primary mirror has been operating since 1993. Work on the James Webb Space Telescope (JWST) with a 6.5-meter deployable, segmented primary mirror has recently begun, and is scheduled for launch in 2011. In the ground-based optics arena, the 10-meter diameter Keck I and Keck II telescopes and 9.2-meter diameter Hobby Eberly telescopes became operational between 1992 and 1996.
In the past, considerable effort has been spent attempting to design reflective telescopes having larger and larger optics, but two basic difficulties have arisen: achieving and maintaining sub-wavelength tolerances over the large apertures, and designing telescopes which are light and compactly packaged for launch and eventual deployment into orbit. The telescope must be launchable (i.e., light weight and folded-up at launch) yet deploy to optical precision tolerances (fractional wavelengths). This has not yet been accomplished.
Realization of a large diameter space-based astronomical observatory would involve overcoming these difficulties. Launching such an instrument into orbit means that the payload mass of the observatory must be maintained as low as feasible. In some lightweight designs, optical or other components are not self-supporting in an earth gravity environment and thus cannot be fully or easily tested on earth prior to launch.
The payload mass capacity and fairing size of the launch vehicle limits the optics size. For example, the diameter of the largest commercial launch vehicle, the modified Delta Heavy, is approximately 4.5 m, and as such imposes a fundamental restriction on aperture size of the space telescopes. The deployable optical telescope, JWST, aims to overcome the fairing size limitation by launching a stowed telescope and deploying upon reaching orbit. Still, the size and mass constraints of the launch vehicle limit the primary diameter to 6.5 meters with the current state of technologies in segment, telescope structure and deployment.
It is highly desirable to design a telescope having significantly larger apertures without the need to redesign launch vehicles with larger payloads. It is also highly desirable that such telescopes be testable on the ground and easily reassembled in space.
The present invention discloses a method for autonomously assembling a segmented filled aperture telescope (“AAST”) in space using components that are launched into orbit using multiple launches. Autonomous assembly will overcome the current limitations regarding the size of space optics, which is currently limited by the size of the launch vehicle.
The present invention will also enable significantly higher resolution astronomy through the use of larger apertures having a filled aperture design. The filled aperture design of the AAST gives better optical performance as compared with sparse aperture optics and multi-telescope systems due to the lack of side lobes and also due to the least post-processing of image data.
Further, the present invention may be potentially more cost effective because the components of the AAST can be robotically assembled in space to a high precision, and robotic assembly reduces the risk of requiring astronauts for assembly of large space optics.
Other objects and advantages of the present invention will become apparent upon considering the following detailed description and appended claims, and upon reference to the accompanying drawings.
Referring now to
Alternatively, the secondary mirror 24 may be coupled to a separate satellite (not shown) which hovers near the satellite containing the primary mirror 22. In addition, diagnostics systems (which check the alignment of the space telescope in real time), computer control systems, and other operational systems may be housed on a separate satellite. Operation of the space telescope 20 is thus coordinated between the two satellites.
The primary mirror 22 is formed of a plurality of modular segmented optics 40 spaced circumferentially around the central hole 28. Each of the segmented optics 40 have a precisely shaped front reflecting surface 44 made of ultra-low expansion glass. The front reflecting surface 44 is coated with a very thin layer of pure aluminum 46 and optionally protected by an even thinner layer of magnesium fluoride 48, which makes the mirrors 22 more reflective to ultraviolet light if desired.
Each of the segmented optics 40 is supported by a mirror backing structure that is coupled to the orbiting satellite 21. The mirror backing structure is also formed of modular components. The modular concept for the primary mirror may be formed in two fundamental ways.
In one concept, the mirror backing structure 42 is first formed from a plurality of mirror backing structure segments 66. Next, modular segmented optics 40 are introduced one at a time to the coupled mirror backing structure 42.
In another concept, as shown in
The concept for forming the modular primary mirror 22 addresses many of the issues found in prior art optics systems. First, because the primary mirror 22 is formed sequentially by coupling together plurality of smaller segmented optics 40 to a modular mirror backing structure 42, new optics systems can be designed in space without size limitation. As one of ordinary skill recognizes, larger optics will enable higher resolution astronomy and ground imaging, and will provide better efficiency of a space-based laser missile defense system.
Further, because the smaller modular segmented optics 40 and modular mirror backing segments are sized smaller than traditional telescopes, they can be more easily loaded onto a single launch vehicle or may be alternatively loaded onto multiple launch vehicles. By contrast, the size of monolithic telescopes (such as the Hubble Telescope) or deployable telescopes (such as the James Webb Space Telescope) is fundamentally limited by the storage compartment size of a single launch vehicle.
Referring now to
On the backside 54 of each of the segmented optics 40, as best shown in
A guide 62 is also preferably added to the backside 54 that ensures that each of the segmented optics 40 is gently brought to the backing structure 42 without disturbing the neighboring segments 66 during assembly. The guide 62 is coarse-aligned before being fastened to the backing structure 42 through one or more fastening steps.
The backing structure 42 may have a corresponding guide (not shown) so that the segmented optics 40 are guided in the direction normal to the plane of the optics 40 and the backing structure 42 when the optics 40 are brought towards the backing structure 42 for assembly. The optics 40 are therefore constrained from translation in the plane of the optics and rotation. This facilitates the assembly process and aids in preventing damage to neighboring optics elements.
Also shown on the backside 54 of the segmented optics 40 is an optional rear grapple fixture 64 that may be used to aid in positioning the segmented optics 40 during assembly.
Each segmented optic 40 formed in
As best shown in
To form the mirror backing structure 42 of
The side slots 74 may be formed such that the trusses 66 extend substantially planar with respect to each other, or alternatively, so that the trusses 66 extend slightly upwardly or downwardly (i.e. each truss is not coplanar with respect to all other trusses 66 extending from the same interlocking structure) with respect to one another, therein allowing the segments 40 to be attached slightly non-planar with respect to each other to properly focus and reflect light towards the secondary mirror 24. The process of adding segments 66 is repeated until the mirror backing structure 42 has the desired number and arrangement of modular segments 66. Additional unused side slots 74 along the outer periphery of the formed mirror backing structure 42 may then be used as attachment points for a respective support connector 32 used to couple the secondary mirror 24 at a location distant from the primary mirror 22.
Referring now to
To form the mirror backing structure of
The side slots 74 may be formed such that the trusses 66 extend substantially planar with respect to each other, or alternatively, so that the trusses 66 extend slightly upwardly or downwardly (i.e. each truss is not coplanar with respect to all other trusses 66 extending from the same interlocking structure) with respect to one another, therein allowing the segments 40 to be attached slightly non-planar with respect to each other to properly focus and reflect light towards the secondary mirror 24. The process of adding segments 66 is repeated until the mirror backing structure 42 has the desired number and arrangement of modular segments 66.
Next, as shown in
Next, as shown in
First, the segments 40 are moved into position adjacent to the mirror backing structure 42. To accomplish this movement in space, a robot (one preferred embodiment is shown as 101 in
Next, the flexible center attachment 58 of one of the segmented optics 40 is coupled around (i.e. snapped onto) a respective top coupling 75 by moving the arm 103 and coupled respective segmented optic 40 further downward onto the top coupling 75.
Next, the respective actuator attachment 60 is coupled around an adjacent and corresponding adjacent top coupling 75 by continuing to move arm 103 further downward towards the mirror backing structure 42, therein snapping the actuator around the respective adjacent top coupling 75. The robot 101 continues to move the segmented optics 40 downward until the guide 62 is properly seated onto one or more of the trusses 66 or onto the respective guides 77. This ensures that each of the respective segmented optics 40 may be gently brought to the backing structure 42 without disturbing the previously coupled neighboring optics 40.
The process as described above is repeated to couple each additional segmented optic 40 to the mirror backing structure 42. Each additional segment 40 is coupled such that the nearest side edges 43 substantially abut one another such that the front reflective surfaces 44 are substantially coplanar with respect to each other. The optional edge sensors ensure that adjacent segmented optics 40 are properly aligned with the next adjacent segmented optics along each respective side surface 43.
Of course, in alternative preferred embodiments, the attachment between each respective segmented optic 40 and the mirror backing structure may be accomplished in a wide variety of different ways. For example, while
Further, while the shape of the attachments 58, 60 and respective top coupling 75 is shown as circular and rod-like, respectively, the attachments may in fact be any number of shapes. For example, the attachments could be triangularly shaped and the top coupling could have a triangular rod shape that is inserted within the inner regions of the attachments 58, 60.
In addition, alternative and/or additional attachment structures may be added to the attachments. For example, screws or an adhesive may be introduced to fasten the center attachment 58 or actuator attachments 60 to the respective top coupling 75. In addition, external couplers (not shown) may be used to attach the center attachment or actuator attachments to the respective top coupling.
While one preferred embodiment of a robot 101 is shown in
In another alternative embodiment as shown in
In this preferred embodiment, the center attachment 58 of the segmented optic 40 is coupled within an inlet region 88 of a multi-arm guide 87. Of course, the center attachment 58 could alternatively be coupled around the inlet region 88. The inlet region 88 is contained within one side of a central hub 89. The central hub 89 also has a protruding region 93 located on the opposite side of the inlet region 88 that couples within the hollow portion 90 of the top coupling 75. Extending radially outward from the central hub 89 are arms 91 that are coupled over each respective actuator attachment 60. Again, in alternative preferred embodiments, it is equally likely that the actuator attachment could be coupled around the lower portion of the arms and achieve the same effect. The outer surfaces 95 of the arms 91 are then seated onto the respective trusses 66 to ensure that the mirror segment 40 is properly aligned on the trusses 66. Edge sensors contained on the edge regions 43 ensure that each respective segment 40 is properly aligned.
In another preferred embodiment, as shown in
A plurality of integrated modular segments 109 are then coupled together in space in the desired shape such that the edges 43 of each modular segmented optic 40 abut an adjacent edge 43 of the next adjacent modular segment 109 and such that the top reflective surfaces 44 are formed with a continuous surface at a proper angle with respect to the secondary mirror 24 and the optical beam path 26 to ensure minimum wavefront distortion upon reflection from the primary mirror 22. An external coupler or internal coupler (not shown) attached to the reaction structure 105 is utilized to fasten each integrated modular segment 109 to the next adjacent integrated modular segment in the desired pattern. In addition, the integrated segments 109 are preferably formed with coupling regions (not shown) on its outer periphery that can be used to attach to the support connectors 32 of the secondary mirror 24.
Next, in Step 310, the power, command, and control units are assembled. These assembled units are subsequently used to assemble the space robotics, as shown in Step 320. As multiple robotics may be needed (one for the primary mirror, one for the sensors etc.), it may be necessary to assemble a guide and support structure, through which the multiple space robots are tethered at various parts of the telescope. The space robotics are activated in Step 330.
In Step 340, the telescope spacecraft bus is assembled including power, thermal, computer, orbital, attitude adjustment subsystems, command units, and control units. Next, in Step 350, the telescope foundation is assembled and integrated with the telescope spacecraft bus.
Next, the primary mirror and mirror backing structure are assembled, aligned, and attached to the telescope foundation to act as a single unit. Steps 360 and 370 describe these methods with respect to the embodiments as described
In Step 360, the primary mirror backing structures 42 are assembled, aligned, and attached to the telescope foundation to act as a single unit. In Step 370, each primary mirror segment 40 or a subassembly with multiple mirror segments are aligned and fastened onto the primary mirror support structure as described above in
For
In Step 390, the primary mirror segments are sensed and aligned with respect to each other to meet a coarse piston/tilt error budget. Next, in Step 400, the telescope metering structure is assembled. In Step 410, the secondary mirror is assembled onto the telescope metering structure.
In Step 420, the remainder of the optical train is assembled. This includes optical beam path 29, optional tertiary mirror 27, and relay optics. In Step 430, the cameras and sensors are assembled at one or more imaging locations. In Step 440, other optical sources such as inertial reference units and calibration lasers are assembled and coupled to the telescope structure.
Next, in Step 450, connections are made to the power, thermal, computer, command and control units between the telescope subsystem and telescope spacecraft bus. In Step 460, the secondary optics, optical beam train, and sensor suites are coarse aligned and positioned with respect to the primary mirror and the telescope. Next, in Step 470, the robotics are removed and stowed if necessary.
In Step 480, the actuators and sensors will make initial alignments that will be used during the design mission by the telescope spacecraft. The alignment mode will transition from coarse alignment to fine optical alignment requiring tens of nanometer distance and milli-arcsecond levels of angular resolution. Finally, in Step 490, the optical telescope 21 is made operable.
The present invention thus addresses many of the issues found in prior art optics systems. First, new optics systems can be designed in space without size limitation. These larger optics will enable higher resolution astronomy and ground imaging, and will provide better efficiency of a space-based laser missile defense system.
Further, because the segmented optics and mirror backing structure are modular components, the size of the optics systems is not limited fundamentally by the space constraints of a single launch vehicle, as is the case with monolithic telescopes (such as the Hubble Telescope) or deployable telescopes (such as the James Webb Space Telescope). Instead, the components may be launched on multiple launch vehicles, therein allowing the size of the primary mirror to be increased incrementally over time.
In addition, because the smaller segments 40, 66 may be packed more efficiently within a single launch vehicle, other non-related space components (not shown) may be added to the saved space within the payload area of the launch vehicle. This adds increased flexibility and cost savings associated with a single vehicle launch.
Also, the components of the present invention may be autonomously assembled in space using a simple robotic device 101. This is desirable for a number of reasons. First, because the mirror will operate in space (i.e. in zero gravity), additional support structures, such as the whiffletree structures added to the mirror backing structure of Keck Telescope (which is operated on earth) to prevent sagging of the backing structure under the weight of the primary mirror structure, are not necessary. Also, by assembling the components using robotic devices, astronaut lives will not have to be put at risk for the purpose of building larger telescopes in space.
Finally, while not shown, one or more additional satellites may be used in conjunction with the primary central satellite to further improve the performance of the space telescope. These additional satellites can be fitted with additional modular segmented optics and associated backing structures as described above in
While the invention has been described in terms of preferred embodiments, it will be understood, of course, that the invention is not limited thereto since modifications may be made by those skilled in the art, particularly in light of the foregoing teachings.