Primary mirror for an optical payload and an optical payload with such a primary mirror

Abstract

A primary mirror (1) for an optical payload (2) for terrestrial observation comprises a support base (20), wherein the mirror (1) is connectable to the support base and comprises an aspherical reflecting surface (10) and a counter surface (11) facing the support base (20) with a plurality of protruding reinforcing ribs (12).

Description

Technical area

[0001] The present invention is generally applicable in the technical field of Earth observation from space and, in particular, relates to a primary mirror for an optical payload for Earth observation and to an optical payload for Earth observation comprising such a primary mirror. Definitions

[0002] In this document, the term ‘optical payload’ and its derivatives refer to the set of equipment, instruments, media and sensors on board a satellite designed to collect information about the Earth’s surface and atmosphere by interacting with electromagnetic radiation, predominantly in the visible, infrared and sometimes ultraviolet spectrum. State of the art

[0003] In the field of space-based Earth observation, optical payloads are known to collect data that helps predict weather conditions, monitor biodiversity, manage natural resources, and respond to natural disasters.

[0004] Such optical payloads enable the monitoring of details of the Earth with a resolution typically less than one meter.

[0005] These payloads include instruments with a light-gathering primary mirror and a secondary mirror, as well as their mounts and corresponding sensors.

[0006] Known primary mirrors have a typical “capital” design, meaning they have a conical reflecting surface with a diameter typically not exceeding 350 mm and a central crown as support.

[0007] However, this type of mirror is not suitable for obtaining larger primary mirrors that allow resolutions even below one meter.

[0008] In fact, primary mirrors manufactured using state-of-the-art technology are too heavy and have low vibration resistance, leading to a risk of breakage under stress, for example during launch, and negatively impacting the optical performance required in space. Description of the invention

[0009] The aim of the present invention is to at least partially overcome the disadvantages outlined above by providing a primary mirror for a scalable optical payload for Earth observation.

[0010] Another goal is to provide a primary mirror that meets the environmental requirements of space, such as temperature, vacuum, radiation, and mass.

[0011] Another goal is to provide a shatter-proof primary mirror.

[0012] Another goal is to provide a vibration-resistant primary mirror.

[0013] Another goal is to provide an optical payload for Earth observation with a resolution of less than one meter.

[0014] These and other purposes, which will become more apparent hereinafter, are achieved by a primary mirror for an optical payload and / or an optical payload according to what is described, illustrated and / or claimed herein.

[0015] The dependent claims define advantageous embodiments of the invention. Short description of the drawings

[0016] Further features and advantages of the invention will become clearer from the detailed description of a preferred, but not exclusive, embodiment of the invention, illustrated by way of non-limiting example with the aid of the attached drawings. FIG. 1A is a schematic front view of a payload 2, of which Fig. Figure 1B is a schematic plan view; FIG. 2 is a schematic cross-sectional view along a frontal plane of a payload 2; FIGS. 3A and 3B are schematic axonometric views of a mirror 1; FIG. 4 is a schematic axonometric view of a mirror 1 on a base 20; FIG. 5 is an exploded axonometric schematic view of a base 20. Detailed description of some popular implementation examples

[0017] With reference to the attached figures, a primary mirror 1 for an optical payload 2 for Earth observation from space, for example from satellites in low Earth orbit (LEO), is described.

[0018] The payload 2 may, as described in more detail below, comprise a support base 20 which may rest on other elements of the payload 2 by means of suitable bipods 200.

[0019] The primary mirror 1 may comprise an aspherical reflecting surface 10 and an opposite surface 11 facing the support base 20.

[0020] For example, the reflective surface 10 may have a diameter of 500 mm or more.

[0021] Preferably, the surface 11 may comprise a plurality of protruding reinforcing ribs 12.

[0022] These ribs 12 may preferably have a substantially polygonal shape in plan view and may contribute to reducing the weight of the mirror 1 while at the same time imparting rigidity to it.

[0023] This makes it possible to reduce the mass of mirror 1 while maintaining the optomechanical specifications.

[0024] To ensure high stability, the mirror can be conveniently made entirely of glass-ceramic with an extremely low coefficient of thermal expansion (CTE) of less than (0 ± 0.100) × 10 -6 / K in the range from 0 °C to 50 °C. For example, Clearceram ® or Zerodur ® in question .

[0025] Choosing this type of material prevents deformation and the resulting loss of optical quality, especially in a space environment without gravity.

[0026] A further aspect of the invention relates to the optical payload 2 for terrestrial observation, which, in addition to the above-mentioned support base 20, also comprises the described primary mirror 1 and at least three bipods. 21 carrier, which is connected to both the mirror 1 and the support base 20.

[0027] This configuration ensures stability and reduces the total mass of the payload 2

[0028] Advantageously, the bipods 21 may consist of a pair of legs 22 with an end portion 22' connected to the support base 20 and a second end portion 22".

[0029] The end sections 22" of the two legs 22 converge in a connecting section 23 which is connected to the surface 11 of the mirror 1.

[0030] For example, the connection could be made with a flexible two-component epoxy adhesive.

[0031] To ensure maximum thermal stability and resistance to shocks and vibrations, bipods 21 can be made of a nickel-iron alloy, for example Invar ® , consist.

[0032] This choice allows the precision in positioning of mirror 1 to be maintained and any thermal deformation and vibration to be compensated.

[0033] Suitably, the support base 20 may comprise a plurality of interconnected layers 24 made of different, compatible materials.

[0034] For example, the support base 20 may be in the form of a composite plate having at least one pair of carbon end layers 240, 241 and at least one aluminum core layer 242 with additional titanium inserts 243.

[0035] The plurality of layers 24 may also include adhesive layers 244 suitable for bonding the end layers 240, 241 and the middle layer 242.

[0036] This multi-layer structure, connected by 244 adhesive layers, ensures high resistance to permanent deformation and low mass.

[0037] Preferably, the payload 2 may comprise a secondary mirror 27, an image sensor 25 and a focus adjustment system 26 connected to the support base 20 and supporting the image sensor 25.

[0038] In particular, the primary mirror 1 and secondary mirror 27 may define a direction for the light along an optical axis, and the focus adjustment system 26 may be configured to shift the position of the image sensor 25 along the optical axis to correct the focus within a predetermined range of allowable values.

[0039] This will allow for the temperature fluctuations that Payload 2 will be exposed to during its mission to be compensated.

[0040] The architecture of the focus adjustment system 26 may include a main body 261, a focal plane interface, a motor 263, a harmonic reducer 264, an anti-rotation flange 265, and an outer cover 266.

[0041] The main body 261 may be made of titanium to provide structural strength while limiting mass.

[0042] The focal plane interface can enable a translation of the sensor 25 of, for example, 2-4 mm in both directions.

[0043] This movement can be driven by the motor 263 , for example of the stepper motor type, which is connected to a harmonic reduction gear 264 and bevel gears that can amplify the torque and rotate the direction of movement.

[0044] 265- Anti-rotation flange and disc springs ensure precise, backlash-free axial movement and withstand starting loads.

[0045] The outer cover 266 may be equipped with seals to prevent the leakage of lubricants.

[0046] Suitably, the payload 2 may comprise a substantially tubular structure 28 for supporting the secondary mirror 27, which structure is made of composite material.

[0047] In order to achieve this supporting effect, the mirror 27 can be connected to the tube 28 by means of a suitable supporting spider 30.

[0048] Preferably, the tube 28 is made of carbon to minimize deformation and vibration and to provide a stable environment for the internal optical elements.

[0049] The tubular structure 28 may include embedded titanium inserts 29 for fixed anchorage to the support base 20 and the spider 30.

[0050] 2 could conveniently be of the Ritchey-Chrétien type, with two hyperbolic mirrors 1 and 27 and a three-lens corrector, for example made of quartz glass.

[0051] The present invention may comprise various similar or identical parts and / or elements. Unless otherwise stated, similar or identical parts and / or elements are designated by a single reference numeral. The described technical features apply to all similar or identical parts and / or elements.

[0052] The invention is capable of numerous modifications and may fall within the scope of the appended claims. All details may be replaced by other technically equivalent elements, and the materials may be varied as needed, without departing from the scope of the invention as defined in the appended claims.

Claims

[1] A primary mirror (1) for an optical payload (2) for terrestrial observation comprises a support base (20), the mirror (1) being connectable thereto and comprising an aspherical reflecting surface (10) and a counter surface (11) facing the support base (20) with a plurality of protruding reinforcing ribs (12). [2] A mirror according to the preceding claim, wherein the plurality of ribs (12) have a substantially polygonal shape in plan view. [3] A mirror according to any one of the preceding claims, wherein it is made entirely of glass-ceramic material having a thermal expansion coefficient of less than (0 ± 0.100) × 10 -6 / K in the range of 0 °C to 50 °C, the same material preferably being made of Clearceram ® or Zerodur ® is selected . [4] Optical payload for Earth observation, including: - a support base (20); - a primary mirror (1) according to one of the preceding claims; - at least three support bipods (21) connected to each other with the mirror (1) and the support base (20). [5] Payload according to the preceding claim, wherein the bipods (21) each comprise a pair of legs (22) with a respective first end portion (22') connected to the support base (20) and a second end portion (22"), wherein the second end portions (22") of the legs (22) are connected to each other in a connecting portion (23) which in turn is connected to the opposite surface (11) of the mirror (1). [6] Payload according to the preceding or one of the preceding claims, wherein the at least three bipods (21) consist of a nickel-iron alloy, preferably Invar ® is. [7] Payload according to one of claims 4 to 6, wherein the support base (20) comprises a plurality of interconnected layers (24) of different, compatible materials. [8] Payload according to the preceding claim, wherein the plurality of layers (24) comprises at least one pair of end layers (240, 241) made of carbon and at least one middle layer (242) made of aluminum, the support base (20) having at least one titanium insert (243). [9] A payload according to any one of claims 4 to 8, further comprising a secondary mirror (27), an image sensor (25) and a focus adjustment system (26) connected to the support base (20) and supporting the image sensor (25), wherein the primary mirror (1) and the secondary mirror (27) define a direction for the light along an optical axis and the focus adjustment system (26) is configured to shift the position of the image sensor (25) along the optical axis to correct the focus within a predetermined range of allowable values. [10] Payload according to one of claims 4 to 9, further comprising a substantially tubular structure (28) supporting the secondary mirror (27), the structure being made of a composite material, which is preferably carbon.

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