Unfurlable reflector telescope

Abstract

The invention relates to an unfurlable reflector telescope (2), in particular for a satellite (1), preferably a small / miniaturised satellite or CubeSat, at least comprising: - a folding segmented main reflector (3), formed by a number of separate planar reflector segments (3a) which are connected via first hinge devices (4) to an unfolding support structure (5); - the unfolding support structure (5), which is intended for receiving the reflector elements (3a) of the main reflector (3) and is formed by a plurality of first rod-shaped connection elements (5a) which are interconnected via second hinge devices (5b); and - an unfolding secondary reflector (6).

Description

[0001] Deployable reflecting telescope

[0002] This application claims priority from German patent application No. 10 2023 115 899.6, the contents of which are incorporated herein by reference.

[0003] The invention relates to a deployable reflecting telescope. The invention also relates to a satellite, in particular a small / micro satellite or CubeSat, with a deployable reflecting telescope, as well as a method for deploying a reflecting telescope.

[0004] In recent years, visual Earth observation has undergone significant changes, from complex and expensive satellites in geostationary orbit (GEO) and LEO (Low Earth Orbit) (approximately 500 km - 1000 km) to small satellites or micro-satellites, particularly CubeSats, deployed in larger numbers in lower Earth orbits. These offer the advantage of enabling rapid revisits (repeated observations of the same point on Earth) due to their high number, thus allowing each point below their trajectories to be observed more frequently. Currently, constellations of optical CubeSats with more than 150 satellites are known. This allows up to twelve revisits of a specific location on the ground per day.

[0005] Currently, the majority of CubeSat systems for Earth observation are based on CubeSats of the 3U format (dimensions approx. 10 x 10 x 30 cm 3, weight approx. 5 kg). However, these limit the available optical aperture to approximately 90 mm. This results in a ground resolution of approximately 3 m at an altitude of 400 km. However, the altitude and the low mass also result in a very limited lifetime of one to two years in orbit. Furthermore, the resolution of 3 m is still below the target value of better than 1 m. This resolution is achieved by satellites such as SkySat, which, however, have dimensions of approximately 60 x 60 x 95 cm. 3 and weighing 120 kg, they are significantly larger and more expensive. The optically clear aperture of such satellites is approximately 450 mm.

[0006] The next generation of CubeSats will therefore also rely on a larger base structure to increase resolution while remaining significantly below the cost of SkySat-class satellites. Such satellites will achieve an aperture size of 180 mm in a 12U CubeSat (20 x 20 x 30 cm). 3). However, even these systems only achieve a resolution of 1 m from very low orbits and thus have a very short lifetime.

[0007] One way to increase the optical aperture—and thus the resolving power—of an optical Earth observation telescope without increasing its launch volume is to use deployable telescope mirrors, or telescope mirrors that are only deployed into their final configuration in orbit. The most prominent example of this is currently NASA's James Webb Space Telescope (JWST).

[0008] For some time now, efforts have been underway to develop foldable optical telescopes that enable a larger optical aperture than the dimensions of the satellite in its launch configuration. These can be used in both CubeSats and larger satellites. Reference is made to the following publications: "A Deployable Telescope for Sub-Meter Resolutions from MicroSatellite Platforms, Dennis Dolkens, Delft University of Technology, October 2014," "Primary Mirror Fine Positioning Mechanism for a Deployable Space Telescope, S.M. Pepper, Delft University of Technology, November 27, 2018," and "Design of deployment systems for high-resolution deployable telescope based on CubeSat, Daim Haobin et al., Xi'an Institute of Optics and Precision Mechanics, November 24, 2021."

[0009] However, previous publications on folding reflecting telescopes have only described systems with simple folding mechanisms, where the side walls fold outward, thus creating a larger optical diameter. Such telescopes are also called "pedal-style" telescopes.

[0010] A foldable CubeSat mirror is also described in "High-resolution deployable CubeSat prototype, Noah Schwartz et al., AI, UK Astronomy Technology Centre, December 13, 2020." This configuration demonstrates a significant directional dependence of the resolving power, as the diameter of the entrance aperture is not constant. In the areas where the mirrors are deployed, this diameter can be adjusted by changing the length of the mirror segments. This results in "adjustable" resolving power along these axes. However, in the areas between the mirrors, there is no clear aperture. This results in an image with significant imaging artifacts. The described configuration is also not easily scalable or applicable to different configurations.While it is possible to extend the mirror segments or even add a second folding mechanism to further extend the segments, this only further contributes to the aforementioned problem of not having sufficient resolution in all spatial directions. Furthermore, the configuration does not efficiently utilize the available volume in the initial configuration. The space within the mirror segments is virtually empty.

[0011] Other telescopes, primarily the JWST, have significantly reduced the problem of direction-dependent resolution by using hexagonal mirror segments. This significantly reduces the aperture deviation from the ideal circular shape.

[0012] However, a folding system like the one used in the JWST also requires a very limited packing density of the mirror segments in the launch configuration and, due to the massive mechanical structure, is only suitable for use in CubeSats to a limited extent. None of the aforementioned concepts has yet been realized in a "flightable" form. Implementations are limited to prototypes, some of which deviate quite significantly from the proposed designs and only achieve significantly smaller clear apertures than intended.

[0013] A similar concept to the JWST was already documented in US 5,898,529 A and later in US 2005088734 A1. A more complex but more compact folding was discussed in US 8,179,598 B1.

[0014] For pedal-style telescopes, please refer to US 2013 / 229709 A1 and WO 2022 / 109747 A1.

[0015] DE 20 2005 020 683 U1 describes a device for the space-saving deployment of a deployable optical system for use in space.

[0016] Proceeding from this, the present invention is based on the object of creating a deployable reflecting telescope of the type mentioned at the outset, which avoids the disadvantages of the prior art, in particular requires little installation space when folded and provides a large aperture when unfolded.

[0017] This object is achieved according to the invention by a deployable mirror telescope having the features mentioned in claim 1.

[0018] According to the invention, a deployable telescope or reflecting telescope, in particular for a satellite, preferably a small satellite or CubeSat, is proposed, which comprises at least:

[0019] - a hinged segmented main mirror formed by a number of separate flat mirror segments which are connected to a foldable support structure via first joint devices;

[0020] - the foldable support structure for receiving the mirror segments of the main mirror, which is formed by a plurality of first rod-shaped connecting elements which are connected to one another via second joint devices; and

[0021] - a fold-out secondary mirror.

[0022] The "foldable" telescope according to the invention is particularly suitable for use on small satellites or micro-satellites (e.g., in the 12U format), but can also be used on larger satellites with the necessary modifications. A segmented primary mirror and a foldable arm for the secondary mirror significantly reduce the space required during launch, while creating a telescope with a large aperture in flight configuration. The invention allows for the combination of cost-effective individual mirror segments to create a mirror of high optical quality. When folded, the telescope according to the invention can have a format of 12U and, when unfolded, an aperture of approximately 600 mm, which corresponds to approximately twice the length of the longest edge of a 12U system. The mirror segments can, for example, have a diameter of 20 cm.The invention also allows an increase in the packing density for optical telescopes during the launch phase and thus the use of cost-effective launch systems (especially for mirrors larger than 1 m in diameter in geostationary orbit).

[0023] A first joint device may comprise at least: - a rotary bearing, the shaft of which is connected to one of the mirror segments and which allows rotation of the connected mirror segment from a starting position to a folded-out end position; and / or

[0024] - a spring mechanism which is designed to cause a rotation of the connected mirror segment from the starting position to the unfolded end position and which is preferably activated by means of a releasable locking device, for example a removable pin, meltable nylon cords or the like; and / or

[0025] - at least one damping device designed to dampen the rotational movement caused by the spring mechanism; and / or

[0026] - at least two, preferably three V-shaped ball bearings, which in the unfolded end position of the connected mirror segment are formed by V-shaped grooves and balls accommodated therein, adapted to the V-shaped grooves; and / or

[0027] - one or more adjustment devices or actuators, preferably piezo actuators, which are designed to enable fine adjustment of the alignment of the connected mirror segment, in particular about two tilt axes and in the focus position and are preferably arranged below the balls of the V-ball bearings.

[0028] The position of the individual mirror segments and their supporting structures can be determined with high precision (e.g., in the pm range) and play-free via three V-shaped ball bearings in the first joints. This allows for defined and stable positioning. The special feature here is that the segments are not referenced to a higher-level mechanical structure, but are positioned relative to each other. The V-shaped ball bearings and their arrangement allow for static determinacy in six degrees of freedom, thus creating a clear, reproducible position.

[0029] Piezo fine adjusters or piezo actuators on the V-shaped ball bearings, especially below the balls, enable adjustment of the individual mirror segments in tilt around two axes, as well as in the focus position. Appropriate flexure joints can also be used for this purpose.

[0030] The spring mechanism can be activated, for example, by means of a removable pin or bolt. The at least one damping device can, for example, comprise a tube filled with silicone oil or the like.

[0031] The second joint devices can also be provided with damping devices to avoid high rotational speeds.

[0032] In a very advantageous embodiment of the invention, the mirror segments can be hexagonal.

[0033] The use of hexagonal segments achieves a high entrance pupil fill factor and virtually homogeneous resolving power in all spatial directions. The mirror segments can have a curved surface, particularly an off-axis hyperbolic or parabolic one. The unfoldable reflector telescope according to the invention can preferably be a Ritchey-Chretien-Cassegrain telescope.

[0034] The mirror segments can be arranged in a ring-like manner when unfolded.

[0035] When the reflecting telescope is folded, the mirror segments can be braced against each other and secured by launch locks. Furthermore, when the reflecting telescope is folded, the support structure can form a magazine in which the mirror segments are arranged one behind the other.

[0036] In the launch configuration, the segments can be braced against each other and secured by launch locks. Furthermore, the individual mirror segments can be arranged one behind the other in a magazine in the launch configuration. These measures increase the natural frequencies of the arrangement and reduce unwanted movements under launch load (e.g., 20 g). The launch locks can, for example, comprise nylon cords, which are melted before deployment by means of appropriately designed and arranged electrical resistors. For this purpose, the resistors are appropriately energized.

[0037] The secondary mirror can be unfolded by a plurality of second rod-shaped connecting elements, which are connected to one another via third joint devices, and can be connected to the unfoldable support structure or a reference structure of the satellite.

[0038] The segmented primary mirror may be formed by six mirror segments. In addition, six first joint devices and / or six second joint devices may be present.

[0039] Claim 9 specifies a satellite, in particular a small / micro satellite or CubeSat with a deployable mirror telescope according to the invention.

[0040] Claim 10 relates to a method for deploying a mirror telescope according to the invention which is arranged on a satellite, wherein:

[0041] - in a first step, several or all, in particular six, second joint devices for unfolding the support structure each perform a rotation, in particular by approximately 120°, after which

[0042] - in a second step, the mirror segments are rotated from the starting position to the unfolded end position by means of the first joint devices, and after which

[0043] - In a third step, one or more, in particular three, second joint devices each perform a further rotation, in particular by approximately 120°, in order to at least approximately completely or entirely close the foldable support structure and form the segmented primary mirror. After completion of the second step, the rotation bearings of the first joint devices can be decoupled to prevent the formation of a statically overdetermined system.

[0044] Before the first step, the secondary mirror can be unfolded.

[0045] In the third step, every second of the second joint devices can perform the further rotation, in particular by approximately 120°, in order to close the foldable support structure at least approximately completely or entirely and to form the segmented primary mirror.

[0046] In the third step, the components arranged at both opposite ends of the support structure (i.e., rod-shaped connecting elements or second joint devices) can be firmly connected to one another, in particular, to at least approximately or completely close the foldable support structure. Thus, in the third step, the rearmost of the first rod-shaped connecting elements can be firmly connected to the frontmost second joint device, preferably to at least approximately or completely close the foldable support structure. This measure allows a rigid and reproducible arrangement to be created.

[0047] The process of deploying a reflecting telescope can be started after reaching the orbit, whereby the tension of the mirror segments and the launch locks are released.

[0048] After the third step, a fine adjustment of the alignment of the mirror segments around two tilt axes and in the focus position can be carried out by means of actuators, preferably piezo actuators.

[0049] In the process of unfolding a reflecting telescope, the mirror segments can be positioned relative to each other.

[0050] Advantageous embodiments and further developments of the invention emerge from the subclaims.

[0051] In the following, exemplary embodiments of the invention are described in principle with reference to the drawing.

[0052] They show:

[0053] Figure 1 is a simplified perspective view of a deployable reflecting telescope according to the invention;

[0054] Figure 2 is a simplified perspective view of a deployable reflecting telescope according to the invention mounted on a satellite;

[0055] Figure 3 shows a simplified perspective view of a first joint device of the reflecting telescope according to the invention in a starting position; Figure 4 shows a simplified perspective view of a first joint device of the reflecting telescope according to the invention in an end position;

[0056] Figure 5 is a simplified perspective view of the reflecting telescope according to the invention in the folded state;

[0057] Figure 6 shows a first simplified perspective view of the primary mirror of the reflecting telescope according to the invention when unfolded;

[0058] Figure 7 shows a second simplified perspective view of the primary mirror of the reflecting telescope according to the invention when unfolded; and

[0059] Figure 8 is a simplified perspective view of the unfolded or unfolded primary mirror of the reflecting telescope according to the invention.

[0060] Functionally identical elements are provided with the same reference numerals in the figures.

[0061] Figure 1 shows a deployable telescope or mirror telescope 2 according to the invention, in particular for a satellite 1 (see Figure 2), preferably a small / micro satellite or CubeSat, which comprises at least:

[0062] - a hinged segmented main mirror 3, which is formed by a number of separate flat mirror segments 3a, which are connected via first joint devices 4 to a foldable support structure 5;

[0063] - the foldable support structure 5 for receiving the mirror segments 3a of the main mirror 3, which is formed by a plurality of first rod-shaped connecting elements 5a, which are connected to one another via second joint devices 5b; and

[0064] - a fold-out secondary mirror 6.

[0065] As further shown in Figure 1, the secondary mirror 6 can be unfolded by a plurality of second rod-shaped connecting elements 6a, which are interconnected via third joint devices 6b, and connected to the unfoldable support structure 5 or a reference structure of the satellite 1 (not shown in detail). The unfolding of the secondary mirror 6 can be achieved, for example, via spring mechanisms (not shown in detail).

[0066] Figure 2 shows a simplified representation of satellite 1, in particular a small / micro satellite or CubeSat, with the deployable reflecting telescope 2 according to the invention. As can be seen from Figure 2, satellite 1 further comprises at least one camera or an optical, electronic, or optoelectronic sensor 1a, upstream of which reflecting telescope 2, in particular also other optical elements not shown, is connected, as well as at least one data communication device 1b. Of course, satellite 1 can also comprise other optical or electronic components not shown, as well as a housing.

[0067] The mirror segments 3a can have a curved surface, particularly an off-axis hyperbolic or parabolic one. The unfoldable mirror telescope 2 according to the invention can preferably be a Ritchey-Chretien-Cassegrain telescope. As can be seen, the mirror segments 3a can be hexagonal. Furthermore, the mirror segments 3a can be arranged in a ring-like manner when unfolded.

[0068] As can also be seen, the segmented primary mirror 3 can be formed by six mirror segments 3a. Furthermore, six first joint devices 4 can be provided. Furthermore, six second joint devices 5b can be provided.

[0069] Figure 3 shows a first joint device 4 of the reflecting telescope 2 according to the invention in a starting position. Figure 4 shows the first joint device 4 of the reflecting telescope 2 according to the invention in an end position.

[0070] As can be seen from Figures 3 and 4, the first joint device 4 can comprise at least:

[0071] - a rotation bearing 4a, the shaft of which is connected to one of the mirror segments 3a (not shown in detail) and which allows rotation of the connected mirror segment 3a from the starting position to the unfolded end position (see also Figures 6 and 7); and / or

[0072] - a spring mechanism (not shown in detail) which is designed to cause a rotation of the connected mirror segment 3a from the starting position to the unfolded end position and which is preferably activated by means of a releasable locking device 4f, for example a removable pin, meltable nylon cords or the like; and / or

[0073] - at least one damping device 4b, which is designed to dampen the rotational movement caused by the spring mechanism; and / or

[0074] - at least two, preferably three V-shaped ball bearings 4c, which in the unfolded end position of the connected mirror segment 3a are formed by V-shaped grooves 4d and balls 4e accommodated therein and adapted to the V-shaped grooves 4d; and / or

[0075] - one or more actuators (not shown), preferably piezo actuators, which are designed to enable fine adjustment of the alignment of the connected mirror segment 3a, in particular about two tilt axes and in the focus position and are preferably arranged below the balls 4e of the V-ball bearings 4c.

[0076] Furthermore, the first joint device 4 has clamping devices 4g and a mechanism 4h for disengaging the rotary bearing 4a.

[0077] Figure 5 shows the primary mirror 3, or its mirror segments 3a, and the secondary mirror 6 in the folded state of the mirror telescope 2. The mirror segments 3a can be braced against each other and secured by launch locks (not shown in detail). The support structure 5 can form a magazine 7 in which the mirror segments 3a are arranged one behind the other.

[0078] Furthermore, a method for unfolding the reflecting telescope 2 arranged on the satellite 1 is proposed, wherein:

[0079] - in a first step, several or all, in particular six, second joint devices 5b for unfolding the support structure 5 each perform a rotation, in particular by approximately 120° (see Figure 6), after which

[0080] - in a second step, the mirror segments 3a are rotated from the starting position to the unfolded end position by means of the first joint devices 4 (see Figure 7), and after which

[0081] - in a third step, one or more, in particular three, second joint devices 5b each carry out a further rotation, in particular by approximately 120°, in order to at least approximately completely close the foldable support structure 5 and to form the segmented main mirror 3.

[0082] Before the first step, the secondary mirror 6 can be unfolded (not shown).

[0083] The second joint devices 5b can—analogously to the first joint devices 4—also be provided with damping devices (not shown) that dampen the rotational movements. The rotational movements of the second joint devices 5b can also be effected by spring mechanisms or the like (not shown in detail).

[0084] In the third step, every second of the second joint devices 5b can perform the further rotation, in particular by approximately 120°, in order to at least approximately completely close the foldable support structure 5 and to form the segmented main mirror 3.

[0085] In the third step, the components 5a', 5b' arranged at both opposite ends of the support structure 5 can be connected, in particular firmly to one another, to at least approximately or completely close the foldable support structure 5. Thus, in the third step, the rearmost of the first rod-shaped connecting elements 5a' can be preferably firmly connected to the frontmost second joint device 5b' to at least approximately or completely close the foldable support structure 5. For this purpose, the respective second joint devices 5b' can be adapted accordingly (see Figures 6 and 7).

[0086] The process for unfolding the mirror telescope 2 can be started after reaching the orbit, whereby the tension of the mirror segments 3a and the launch locks are released.

[0087] After the third step, a fine adjustment of the alignment of the mirror segments 3a around two tilt axes and in the focus position can be performed using actuators, in particular piezo actuators. During the process for unfolding the reflecting telescope 2, the mirror segments 3a can thus be positioned relative to one another.

[0088] Figure 8 shows the fully unfolded or unfolded primary mirror 3 of the reflecting telescope 2 according to the invention with the support structure 5 but without the secondary mirror 6.

[0089] List of reference symbols

[0090] 1 satellite

[0091] 1a optical sensor

[0092] 1 b Data communication device

[0093] 2 reflecting telescopes

[0094] 3 primary mirrors

[0095] 3a Mirror segments

[0096] 4 First joint devices

[0097] 4a Rotation bearing

[0098] 4b Damping device

[0099] 4c V-ball bearings

[0100] 4d V-shaped groove

[0101] 4 balls

[0102] 4f releasable locking

[0103] 4g clamping device

[0104] 4h Mechanism for disengaging the rotary bearing

[0105] 5 Supporting structure

[0106] 5a,5a' First rod-shaped connecting elements

[0107] 5b,5b' Second joint devices

[0108] 6 secondary mirrors

[0109] 6a Second rod-shaped connecting elements

[0110] 6b Third joint devices

[0111] 7 Magazine

Claims

Patent claims:

1. Deployable reflecting telescope (2), in particular for a satellite (1), preferably a small satellite or CubeSat, comprising at least: - a hinged segmented main mirror (3) which is formed by a number of separate flat mirror segments (3a) which are connected to a hinged support structure (5) via first joint devices (4); - the foldable support structure (5) for receiving the mirror segments (3a) of the main mirror (3), which is formed by a plurality of first rod-shaped connecting elements (5a) which are connected to one another via second joint devices (5b); and - a fold-out secondary mirror (6).

2. Reflecting telescope (2) according to claim 1, wherein a first joint device (4) comprises at least: - a rotary bearing (4a), the shaft of which is connected to one of the mirror segments (3a) and which allows rotation of the connected mirror segment (3a) from a starting position to a folded-out end position; and / or - a spring mechanism which is designed to cause a rotation of the connected mirror segment (3a) from the starting position to the unfolded end position and which is preferably activated by means of a releasable locking device (4f); and / or - at least one damping device (4b) which is designed to dampen the rotational movement caused by the spring mechanism; and / or - at least two, preferably three V-shaped ball bearings (4c), which in the unfolded end position of the connected mirror segment (3a) are formed by V-shaped grooves (4d) and balls (4e) accommodated therein and adapted to the V-shaped grooves (4d); and / or - one or more actuators, preferably piezo actuators, which are designed to enable fine adjustment of the alignment of the connected mirror segment (3a) about two tilt axes and in the focus position and are preferably arranged below the balls (4e) of the V-ball bearings (4c).

3. Reflecting telescope (2) according to claim 1 or 2, wherein the mirror segments (3a) are hexagonal.

4. Reflecting telescope (2) according to claim 1, 2 or 3, wherein the mirror segments (3a) have a, in particular off-axis, hyperbolic or parabolic curved surface.

5. Reflecting telescope (2) according to one of claims 1 to 4, wherein the mirror segments (3a) are arranged in a ring-like manner in the unfolded state.

6. Reflecting telescope (2) according to one of claims 1 to 5, wherein in the folded state of the reflecting telescope (2): - the mirror segments (3a) are braced against each other and secured by launch locks; and / or - the support structure (5) forms a magazine (7) in which the mirror segments (3a) are arranged one behind the other.

7. Reflecting telescope (2) according to one of claims 1 to 6, wherein the secondary mirror (6) is foldable by a plurality of second rod-shaped connecting elements (6a) which are connected to one another via third joint devices (6b), and is connected to the foldable support structure (5) or a reference structure of the satellite (1).

8. Reflecting telescope (2) according to one of claims 1 to 7, wherein the segmented primary mirror (3) is formed by six mirror segments (3a), and / or wherein six first joint devices (4) are present, and / or wherein six second joint devices (5b) are present.

9. Satellite (1), in particular a small / micro satellite or CubeSat with a deployable reflecting telescope (2) according to one of claims 1 to 8, at least one electronic or optoelectronic sensor (1 a) upstream of which the reflecting telescope (2) is connected, and at least one data communication device (1 b).

10. A method for deploying a reflecting telescope (2) according to one of claims 1 to 8, which is arranged on a satellite (1) according to claim 9, wherein: - in a first step, several or all, in particular six, second joint devices (5b) for unfolding the support structure (5) each carry out a rotation, in particular by approximately 120°, after which - in a second step, the mirror segments (3a) are rotated from the starting position to the unfolded end position by means of the first joint devices (4), and after which - in a third step, one or more, in particular three second joint devices (5b) each carry out a further rotation, in particular by approximately 120°, in order to at least approximately completely close the foldable support structure (5) and to form the segmented main mirror (3).

11. A method for unfolding a reflecting telescope (2) according to claim 10, wherein the secondary mirror (6) is unfolded before the first step.

12. Method for unfolding a reflecting telescope (2) according to claim 10 or 11, wherein in the third step every second of the second joint devices (5b) carries out the further rotation, in particular by approximately 120°, in order to at least approximately completely close the foldable support structure (5) and to form the segmented main mirror (3).

13. Method for unfolding a reflecting telescope (2) according to claim 10, 11 or 12, wherein in the third step for at least approximately closing the foldable support structure (5) the rearmost of the first rod-shaped connecting elements (5a') is preferably firmly connected to the frontmost second joint device (5b').

14. A method for deploying a reflecting telescope (2) according to one of claims 10 to 13, which is launched after reaching the orbit, wherein the bracing of the mirror segments (3a) and the launch locks are released.

15. A method for deploying a reflecting telescope (2) according to one of claims 10 to 14, wherein, after the third step, a fine adjustment of the alignment of the mirror segments (3a) about two tilt axes and in the focus position is performed using the actuators.

16. Method for unfolding a mirror telescope (2) according to one of claims 10 to 15, wherein the mirror segments (3a) are positioned relative to one another.

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