A sub-reflector deployment mechanism

Abstract

A Cassegrain, Gregorian or axially displaced satellite reflector system and a mechanism sub-reflector deployment mechanism that allows the system to stow in a minimum height configuration for launch. This mechanism uses pushers, guy wires and a metrology system to deploy and accurately position the sub-reflector on orbit. This minimum height configuration in turn allows many satellites to be stacked and launched together on a single launch vehicle for better economics.

Description

[0001] A SUB-REFLECTOR DEPLOYMENT MECHANISM

[0002] BACKGROUND OF THE INVENTION

[0003] Pat. App. No. 63 / 561 ,499 filed 5 March 2024 is incorporated herein by reference.

[0004] FIELD OF THE INVENTION

[0005] The present invention relates to apparatus and methods for deploying a satellite sub-reflector after launch.

[0006] DISCUSSION OF RELATED ART

[0007] Conventional communications satellites frequently use reflector antenna systems. In some cases these use fixed reflectors mounted on an earth deck, body mounted reflectors, where main reflector is cantilevered out from the body of the satellite, or unfurlable reflectors, which fold up like an umbrella are deployed away from the body of the satellite on a boom. Fixed and cantilevered antennas are limited in their size and unfurlable reflectors are expensive and failure prone.

[0008] SUMMARY OF THE INVENTION

[0009] A satellite design is based around a large Cassegrain, Gregorian, or axially- displaced reflector or the like where the sub-reflector stows for launch, minimizing the stowed height of the satellite. This allows many satellites to be stacked for launch. The sub-reflector is deployed on orbit with a set of pushers, guy wires and a metrology system that provides fine positioning control for the sub-reflector.

[0010] BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a schematic diagram of a communications satellite with a Cassegrain reflector system in the deployed in orbit configuration.

[0012] Figure 2 is a schematic diagram of a communications satellite with a cassegrain reflector system in the stowed for launch configuration.

[0013] Figure 3 is a schematic diagram of communications satellites with a cassegrain reflector system in the stowed configuration stacked for launch. Figure 4A is an isometric schematic diagram of a sub-reflector deployment mechanism in the stowed configuration. Figure 4B is a sideview of the sub-reflector deployment mechanism of Figure 4A in the stowed position.

[0014] Figure 5A is an isometric schematic diagram of a sub-reflector deployment mechanism in the deployed configuration. Figure 5B is sideview of the sub-reflector deployment mechanism of Figure 5A in the deployed configuration.

[0015] Figures 6, 7, and 8 are schematic diagrams of pusher mechanisms.

[0016] Figure 9 is a schematic diagram showing the operation of a satellite deployment.

[0017] DETAILED DESCRIPTION OF THE INVENTION

[0018] Figure 1 shows a communications satellite 102 with a Cassegrain reflector system in a deployed configuration for operation on orbit. The sub-reflector 114 is deployed away from the primary reflector 103 generally on the center axis of the system. In this embodiment, two pushers 408 are used to deploy 106 the sub-reflector (see Figures 4A-5B) 114 but any number of pushers of two or greater can be used. A similar system can be constructed for a Gregorian or axially displaced reflector system. Note that there is an opening 116 at the vertex of the primary reflector 103 for the satellite body / bus 112 and feed array 110. Deployment mechanism 106 is anchored, for example, on rim 118 of opening 116 or on the payload deck (not shown).

[0019] A reflector 103 is the primary reflector in a center feed Cassegrain, Gregorian, or axially displaced system as shown in Figure 1 . This reflector 103 can be made of any radio reflective material such as metal or carbon fiber. The reflector 103 has an opening 116 around the vertex to allow a feed array 110 to project signals onto a sub-reflector 114. Solar array 108 is deployed as well.

[0020] Figure 2 shows a communications satellite 102 with for example a Cassegrain reflector system in a stowed for launch configuration. The sub-reflector 114 is stowed in or above the opening 116 in the vertex of the main reflector 103. A similar system can be constructed with a Gregorian or axially displaced reflector system. This stowed configuration allows the sub-reflector 114 to be securely held during launch and it minimizes the height of the stowed satellite. In this example solar array 108 folds under main reflector 103 in the stowed configuration.

[0021] A sub-reflector 114 forms the secondary reference in the Cassegrain, Gregorian, or axially displaced system. This sub-reflector 114 is stowed for launch in or just above the opening 116 at the vertex of the primary reflector 103, as shown in Figure 2.

[0022] Figure 3 shows several of the same satellites 102 stacked for launch. The ability to stow the sub-reflector 114 minimizes the height of the satellite in the stowed configuration and allows many satellites 102 to be stacked together for launch in the payload fairing 104 of a launch vehicle. In this example embodiment up to 30 satellites are stacked on one launch vehicle. This greatly reduces the launch cost per satellite.

[0023] Figure 4A is an isometric schematic diagram of a sub-reflector deployment mechanism 106 in the stowed configuration. Figure 4B is a sideview of sub-reflector deployment mechanism 106 in the stowed position.

[0024] Figure 4A shows the sub-reflector deployment mechanism 106 in the stowed configuration. The mechanism 106 is positioned around or inside of the edges 118 of the feed array 110 opening 116 (see Figure 1 ). In this configuration the sub-reflector 114 is located in or just above the opening 116 in the vertex of the main reflector 103 (as shown in Figures 1 and 2), the pushers 408 are in a retracted configuration, and the guy wires 410 are reeled in on reels 412. Metrology cameras 416 are positioned around the feed array 110 to measure the position of the sub-reflector 114 during deployment. A hold down and release mechanism 414 may be used to hold the subreflector 114 in place during launch by attaching it to the main reflector 103.

[0025] The release mechanisms 414 may comprise Hold Down and Release Mechanisms (HDRMs) having an attachment 414A which would live on the sub-reflector side, while the larger outer cylinder 414B releases the attachment once it is fed a command signal and lives on the main antenna or structural side. Release mechanisms 414 may also be attached in the reverse configuration, with end 414A attached to the structural side and end 414B attached to sub-reflector 114. Alternatively release mechanisms 414 might comprise pin-pullers, wherein a pin moves a required distance to allow ends 414A and 414B to separate. Release mechanisms 414 are generally non-frangible devices that mechanically release their connection when given a command signal.

[0026] The mechanism 106 to deploy and position the sub-reflector 114 in this example includes five parts: release mechanisms 414, pushers 408, guide wires 410, reels 412, and a metrology system 416. This mechanism 106 typically fits in the space between the feed array and the sub-reflector.

[0027] The deployed configuration is shown in Figure 5A (isometric view) and Figure 5B (side view). After launch, the hold down and release mechanism 414 is triggered, for example by a command from the ground (see Figure 9). The sub-reflector 114 is then deployed outward along the axis of the reflector 103 by the pushers 408 to allow the reflector system to function. The positioning of the sub-reflector 114 is done precisely so the reflector system focuses properly on the focal plane of the system. The position of the sub-reflector is determined using the metrology cameras, and adjusted by controlling reels 412. See Figure 9.

[0028] Figures 5A and 5B show the sub-reflector deployment mechanism 106 in the deployed configuration. The hold down and release mechanism clamps 414 have been released allowing the sub-reflector to move. The release mechanisms may be triggered by a command from the ground (see Figure 9) or from a processor on the satellite or the launch vehicle. The pushers 408 have been deployed, pushing the sub-reflector 114 outward to an initial deployed position. The metrology cameras 416 then measure the position and orientation of the sub-reflector and the guy wires 410 reel 412 out to precisely position the sub-reflector 114. In one preferred embodiment, the pushers and guy wires are made of dielectric materials that minimize the scattering of radio frequency signals.

[0029] The pushers 408 provide the outward force to move the sub-reflector 114 apart from its stowed position adjacent to main reflector 103. A hold down and release mechanism 414 may be employed during launch to prevent the sub-reflector from moving. After release mechanism 414 has been released, the pusher mechanism 408 extends, pushing the sub-reflector 114 out from the primary reflector 103. Two or more pushers 408 attached around the edges of the sub-reflector are advised to provide balanced forces. The pushers 408 are mounted to the satellite at the main reflector 103 around the edge of the feed array, for example on the rim 118 of opening 116.

[0030] Fine positioning of the sub-reflector 114 is performed with guy wires 410, as shown in Figures 5A and 5B. Reels 412 may have fixed attachments to two connected guy wires 410, so that both connected guy wires may be fully reeled in for stowing, both connected guy wires may be reeled out for deployment, and one connected guy wire may be reeled in more relative to the other connected guy wire for fine-tuning. Or, separate reels 412 may be used for each guywire 410.

[0031] The guy wires 410 are held in tension by the outward force of the pusher 408. The lengths of the guy wires 410 can be changed by reel mechanism 412 according to control signals. As few as six guy wires 410 can be used to translate the subreflector in three dimensions or rotate the sub-reflector about three axes. This embodiment shows eight guy wires 410. Fewer guy wires 410 can be used in embodiments where the pusher length can also be adjusted, or more may be used to provide additional control and redundancy. It is desirable for the guy wires 410 to be made from dielectric materials that are less likely to reflect radio waves such as plastics or fiberglass.

[0032] Figures 6-8 show embodiments of the pusher 408. Figure 6 shows a pusher 408 configured as a bi-static rolled tube 600. Figure 7 shows an embodiment of the pusher 408 including a pantograph (scissors) mechanism 700. Figure 8 shows an embodiment of the pusher 408 including a telescoping tube 800. These mechanisms can stow in a short length and then be extended outwards providing the force to move the sub-reflector and hold the guy wires in tension. Pushers 408 are typically biased open so that when release mechanisms 414 are released, they automatically extend, positioning sub-reflector 114 away from main reflector 103. As an alternative (or in addition) pushers 408 may be independently controlled by control signals. The pushers 408 can be implemented as a bi-static rolled tube 600, which is unrolled by a mechanism to form a stiff column, a pantograph (scissor mechanism) 700, or a telescoping tube 800 that is driven by cables, springs or compressed gas. Depending on the version, the pusher 408 may have a fixed deployed length or have an adjustable length that helps with the positioning of the sub-reflector. It is desirable for the pusher to be made from dielectric materials that are less likely to reflect radio waves such as plastics or fiberglass with as few metal components that might scatter radio waves as possible.

[0033] The final element of the deployment mechanism is a metrology system 416, as shown at the bottom of Figures 4A-5B. The metrology system measures the initial deployed position of the sub-reflector 114 after release mechanism 414 are released and pushers 408 extend. These measurements allow sub-reflector 114 to be positioned precisely at a fine-tuned position and to f the position over time in response to factors such as thermal expansion that might perturb or change the finetuned position of the sub-reflector 114. Different realizations of the metrology system can use techniques including using cameras 416 for photogrammetry, where one or more cameras is used to measure the distance and position of the sub-reflector, or LIDAR, where the position of the sub-reflector is measured by laser rangefinders. The measured position is then used to adjust the guy wires 410 according to control signals until the sub-reflector 114 is in the desired fine-tuned position.

[0034] Figure 9 is a schematic diagram showing the operation of a satellite deployment mechanism 106. During deployment, pushers 408 move sub-reflector 114 away from main reflector 103, either automatically via biasing or under the control 908 of processor 900, or both. Processor 900 receives information 906 on the position of sub-reflector 114 from metrology system 416 after deployment, and finetunes the position of sub-reflector 114 by controlling 910 the relative lengths of guy wires 410 with reels 412. Processor 900 may be controlled by a signal 920 from the ground or elsewhere. For example, signal 920 may simply tell processor 900 to trigger 904 release mechanisms 414, and processor 900 may be programmed to control positioning without further input. Or, Control signal 920 may include further commands, such as modifying the desired position of sub-reflector 114. Pusher mechanism 408 may operate automatically once release mechanisms 414 are released, or may be controlled by processor 900 via control signal 908.

[0035] While the exemplary preferred embodiments of the present invention are described herein with particularity, those skilled in the art will appreciate various changes, additions, and applications other than those specifically mentioned, which are within the spirit of this invention. Variations on metrology include LIDAR. Variations on fine control include adjusting the length of the pusher mechanisms to change the position of the sub-reflector. Other pusher mechanism may be used.

[0036] What is claimed is:

Claims

CLAIMS1 . A system for deploying a satellite having a main reflector and a sub-reflector, the system comprising: pushers for moving the sub-reflector to an initial deployed position apart from the main reflector; a metrology system for measuring the initial deployed position of the sub-reflector; guy wires for fine-tuning the initial deployed position of the sub-reflector to a finetuned position; reels for adjusting lengths of the guy wires to achieve the fine-tuned position; and a processor for controlling the reels according to measurements from the metrology system.

2. The system of claim 1 wherein the metrology system includes metrology cameras.

3. The system of claim 1 wherein the pushers comprise bi-static rolled tubes.

4. The system of claim 1 wherein the pushers comprise pantograph mechanisms.

5. The system of claim 1 wherein the pushers comprise telescoping tubes.

6. The system of claim 1, further comprising a release mechanism configured to hold the sub-reflector adjacent to the main reflector until triggered by the processor.

7. The system of claim 6 wherein the pushers automatically extend after the release mechanism is triggered.

8. The system of claim 6 wherein the processor is further configured to receive a command from a ground position to trigger the release mechanism.

9. The system of claim 1 wherein positions of the pushers are controlled by the processor.

10. The system of claim 1 wherein the pushers automatically extend.11 . The system of claim 10 wherein positions of the pushers are further controlled by the processor.

12. The system of claim 1 wherein the processor is configured to further adjust the fine-tuned position of the sub-reflector.

13. The system of claim 1 wherein the pushers are controlled by the processor to position the sub-reflector.

14. The system of claim 1 wherein the pushers and the guy wires comprise dielectric material.

15. The method of deploying a satellite having a main reflector and a subreflector comprising the steps of: moving the sub-reflector to an initial deployed position apart from the main reflector using pushers; measuring the initial deployed position of the sub-reflector; and fine-tuning the initial deployed position of the sub-reflector to a fine-tuned position by adjusting lengths of guy wires attached between the main reflector and the subreflector.

16. The method of claim 15 further comprising the step of further fine-tuning the fine-tuned position of the sub-reflector.

17. The method of claim 16 wherein the step of further fine-tuning is in response to the deployed position changing over time.

18. The method of claim 16 wherein the step of further fine-tuning is in response to control signals external to the satellite.

19. The method of claim 15 further including the step of releasing a release mechanism before moving the sub-reflector to the initial deployed position.

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