FR3117458A1 - Protective device for a satellite optical instrument - Google Patents

Abstract

The invention relates to a device (10) for protecting an optical instrument (11) of a satellite (100), the optical instrument (11) being intended to point along a pointing axis (12), said device for protection (10) being characterized in that it comprises: a support (13), the optical instrument (11) being arranged on the support (13) and oriented along a first axis (14), a sunscreen (15) comprising walls (16) and an opening (17), the walls (16) forming a cavity (18); in that the optical instrument (11) is arranged in the cavity (18) of the sunscreen (15), and in that the support (13) is rotatable about a second axis (24) distinct from the first axis (14), so as to move the optical instrument (11) from a pointing position in which the first axis (14) is substantially coincident with the pointing axis (12) at a protection position in which the first axis (14) and the pointing axis (12) are distinct, and/or from the position of protection at the pointing position. Figure for the abstract: Fig. 1

Description

Protective device for a satellite optical instrument

The present invention lies in the field of space optics and relates to a solar protection device for an optical instrument of a satellite.

During observation missions in geostationary orbit, it happens that the observation payload, called optical instrument in the following, cohabits with another payload, in particular for telecommunications. During such missions, it is imperative to prevent solar radiation from penetrating inside the optical instrument, otherwise it will be damaged, during all phases of the mission: positioning, survival mode (this is i.e. when an anomaly is detected during an operational phase) and Earth observation day and night.

In the known prior art, there are several solutions aimed at protecting the optical instrument from solar radiation. A first solution consists in the installation of anti-solar baffle. A baffle is a hollow cylinder or flared cone that extends from the end of the optical instrument for some length. Thanks to the length of the baffle, the optical instrument is protected from the sun's rays that hit the baffle. This is to form a barrier to solar radiation. Such a solution requires a very long baffle. This baffle length is problematic for compatibility with the fairing of the launcher and/or the ground test means. Indeed, for ground tests, the vacuum chambers used have a predefined ceiling height which imposes strict dimensions. During launch, the volume available under the fairing of the launcher is limited and it is generally not possible to insert additional large parts. In addition, the implementation of an operational constraint of 180° rotation of the satellite around the Earth axis combined with the presence of a beveled baffle implies additional constraints on a telecommunications satellite, since it requires interruptions of the mission.

Another known solution from the prior art is the installation of a deployable baffle or a deployable cap. This solution solves the problem of onboard volume under the fairing of the launcher. But the cost of development and the reliability of this solution represent its major flaw.

Finally, an alternative solution of the prior art consists in placing a shutter device at the entrance of the optical instrument. This solution is expensive and requires a mechanism with daily movement closing a large opening.

The invention aims to overcome all or part of the problems mentioned above by proposing a device for protecting the optical instrument that is operational in all mission phases where the instrument could be damaged by solar glare. This device is simple, inexpensive, compact, robust and relies on tilting the instrument to protect it from solar radiation. This results in the possibility of being able to use, for observation missions in geostationary orbit, an instrument developed for missions in low Earth orbit.

• un support, l’instrument optique étant disposé sur le support et orienté selon un premier axe,
• un écran solaire comprenant des parois et une ouverture, les parois formant une cavité ;

l’instrument optique étant disposé dans la cavité de l’écran solaire,
et le support étant mobile en rotation autour d’un deuxième axe distinct du premier axe, de sorte à faire passer l’instrument optique d’une position de pointage dans laquelle le premier axe est sensiblement confondu avec l’axe de pointage à une position de protection dans laquelle le premier axe et l’axe de pointage sont distincts, et/ou de la position de protection à la position de pointage.To this end, the subject of the invention is a device for protecting an optical instrument of a satellite, the optical instrument being intended to point along a pointing axis, said protection device comprising:

• a support, the optical instrument being placed on the support and oriented along a first axis,
• a sunscreen comprising walls and an opening, the walls forming a cavity;

the optical instrument being disposed in the cavity of the sunscreen,
and the support being rotatable about a second axis distinct from the first axis, so as to move the optical instrument from a pointing position in which the first axis is substantially coincident with the pointing axis to a position protection in which the first axis and the pointing axis are distinct, and/or from the protection position to the pointing position.

Advantageously, the support is mobile around a third axis separate from the first and second axes.

In one embodiment of the protection device according to the invention, the first axis passes through the opening of the sunscreen in the pointing position, and the first axis is oriented towards the walls of the sunscreen in the position of protection.

In another embodiment, the opening of the sunscreen forming an open surface, the protection device further comprises a baffle extending from the periphery of the open surface of the sunscreen, preferably substantially perpendicular to the open surface of the sunscreen.

Advantageously, the protection device according to the invention comprises a ring placed on the periphery of the open surface of the sunscreen.

In another embodiment of the protection device according to the invention, the sunscreen is rotatable integrally with the support.

The invention also relates to a satellite comprising such a protection device.

The satellite comprising a body, said satellite according to the invention advantageously comprises a fixed shutter arranged to obscure the opening of the sunscreen in a parking position in which a wall of the sunscreen of the protection device is close to the box.

Advantageously, the satellite further comprises an orientation device able to move the support in rotation according to an angle calculated as a function of an angular position of an incident radiation.

The satellite comprising a pointing mechanism intended to point the optical instrument towards a previously defined zone, the support of the protection device is advantageously the pointing mechanism.

The satellite comprising a body comprising an Earth face oriented towards the Earth, the protection device can be placed on the Earth face.

The satellite comprising a body, the protection device can be placed in the body of the satellite.

The invention will be better understood and other advantages will appear on reading the detailed description of an embodiment given by way of example, description illustrated by the attached drawing in which:

There schematically represents the principle of a device for protecting an optical instrument according to the invention;

There schematically represents a first embodiment of a device for protecting an optical instrument according to the invention;

There schematically represents a second embodiment of a device for protecting an optical instrument according to the invention;

There schematically represents the geometric parameters of the protection device according to the invention;

There schematically represents a first configuration of the second embodiment of a device for protecting an optical instrument according to the invention;

There schematically represents a second configuration of the second embodiment of a device for protecting an optical instrument according to the invention;

There schematically represents a third configuration of the second embodiment of a device for protecting an optical instrument according to the invention;

There schematically represents a fourth configuration of the second embodiment of a device for protecting an optical instrument according to the invention;

There schematically represents a fifth configuration of the second embodiment of a device for protecting an optical instrument according to the invention;

There schematically represents a parking position of the first embodiment of a device for protecting an optical instrument according to the invention;

There schematically represents a pointing position of the first embodiment of a device for protecting an optical instrument according to the invention.

For the sake of clarity, the same elements will bear the same references in the various figures. For better visibility and for the sake of increased understanding, the elements are not always represented to scale.

There schematically represents the principle of a protection device 10 of an optical instrument 11 according to the invention. The optical instrument 11 can by way of non-limiting example be a telescope having a main mirror 9, also called primary mirror. The primary mirror 9 concentrates the light rays towards a secondary mirror fixed on a support frame 8 which sends them back to detectors placed at the focus of the telescope. Depending on the operational phases, the optical instrument 11 can be exposed to solar radiation. Such a situation may damage the optical instrument. It is therefore imperative to protect it from these harmful radiations. There represents the protection device 10 of the optical instrument 11 of a satellite 100. The optical instrument 11 is intended to point along a pointing axis 12. This pointing axis 12 can correspond to a pointing direction for a mission of 'observation. According to the invention, the protection device 10 comprises a support 13. The optical instrument 11 is arranged on the support 13 and oriented along a first axis 14. The first axis 14 is thus associated with the real orientation of the instrument optical 11. During the pointing mission, in operational mode, the first axis 14 is therefore substantially coincident with the pointing axis 12. The protection device 10 comprises a sunscreen 15 comprising walls 16 and an opening 17, the walls 16 forming a cavity 18. The optical instrument 11 is arranged in the cavity 18 of the sunscreen 15. The support 13 is rotatable around a second axis 24 distinct from the first axis 14 (substantially perpendicular for example, but not necessarily), so as to move the optical instrument 11 from a pointing position in which the first axis 14 is substantially coincident with the pointing axis 12 to a protective position in which the first axis 14 and the point axis age 12 are distinct, and/or from the protection position to the pointing position. In other words, the support 13 is capable of tilting the first axis 14 (and therefore the optical instrument 11) from the pointing position to the protection position and from the protection position to the pointing position. As a result, depending on the mission phases of the satellite 100, the protection device 10 of the invention makes it possible to position the support and therefore the optical instrument 11 in its operational pointing position (figure on the left of the ) or to position the support and therefore the optical instrument 11 so that it is not impacted by solar radiation (figure on the right of the ).

The angle represented by the reference 7 corresponds to the access zone of the optical instrument 11 in the pointing position. The instantaneous field of view of the instrument can be +/- 2°, with a misalignment cone of +/- 4°. This results in an access zone 7 of 6°, which corresponds to an access zone on Earth in a 12° cone. The angle represented by the reference 6 corresponds to the angle below which the sun is likely to enter the optical instrument 11. This angle is known by the English expression "Sun Exclusion Angle", angle of solar exclusion.

To prevent the sun's rays from coming into contact with the optical instrument 11, the device of the invention 10 enables the protection of the optical instrument by tilting it from its pointing position to its protective position. A rotation around the second axis 24 is carried out to allow passage from the pointing position to the protection position in which the first axis 14 forms an angle 5 with the pointing axis.

Advantageously, the support 13 is mobile around a third axis 34 distinct from the first and second axes 14, 24. The third axis 34 can be perpendicular to the first and second axes 14, 24 for example, but this is not compulsory. This configuration makes it possible, from the pointing position, to tilt the instrument into its protective position no longer in the same plane but in a three-dimensional space.

The invention also relates to a satellite 100 comprising a body 110 and the protection device which is the subject of the invention. The satellite 100 includes a pointing mechanism intended to point the optical instrument 11 towards a previously defined zone. In the invention, the support 13 of the protection device 10 is the pointing mechanism. The fact of using the pointing mechanism of the satellite allows savings in terms of costs and mass, size. Thus, the invention combines the pointing function and the sun protection function cleverly with the same mechanism by moving the optical instrument.

Advantageously, the walls of the solar screen 15 comprise a coating of emissive surfaces with high emissivity. Such walls make it possible to evacuate the solar fluxes entering during the exposure phases and are suitable for the radiative cooling of the dissipative elements located inside the solar screen, the detection focal plane and the focusing motor(s). in movement of the support 13.

There schematically represents a first embodiment of a device 20 for protecting an optical instrument 11 according to the invention. In this first embodiment, the sunscreen 15 is rotatable integrally with the support 13. In other words, when the optical instrument 11 passes into the protective position, the entire sunscreen 15 which undergoes rotation about the second axis 24 (and possibly the third 34). This embodiment makes it possible to orient the assembly formed by the optical instrument 11 and the sunscreen 15. The optical instrument 11 remains surrounded by the walls 16 and faces the opening 17. The optical instrument 11 is then immobile with respect to the walls 16 since it is the whole of the sunscreen that moves.

There schematically represents a second embodiment of a device 10 for protecting an optical instrument 11 according to the invention. In this embodiment, the first axis 14 passes through the opening 17 of the sunscreen 15 in the pointing position (references (1) and (2) of the ), and the first axis 14 is oriented towards the walls 16 of the sunscreen 15 in the protection position (references (3) and (4) of the ). Unlike the first embodiment, in this second embodiment, the optical instrument 11 is movable relative to the walls 16. In other words, the optical instrument 11 is set in motion by means of the support 13 in the cavity 18 of the sunscreen 15. The sunscreen 15 is immobile, and it is the optical instrument 11 which tilts inside the cavity 18. Thus, the support 13 serves on the one hand to depointing of the optical instrument 11 in the image acquisition phase (reference (1)), and on the other hand to position the optical instrument in order to avoid any solar entry (references (3) and (4)) .

Advantageously, the opening 17 of the sunscreen 15 forming an open surface 18, the protection device 10 further comprises a baffle 19 extending from the periphery of the open surface 18 of the sunscreen 15, preferably substantially perpendicularly to the open surface 18 of the sunscreen 15. The baffle 19 may be a hollow cylinder or a hollow flared cone. It aims to limit the access of the sun's rays to the optical instrument 11.

The height of baffle 19 defines the Sun Angle Exclusion. As already explained, below this angle, the sun is likely to enter the optical instrument 11. The support 13 is then activated to protect the instrument, the optical instrument passes from the pointing position (2) to the protection position (3).

Advantageously, the protection device 10 comprises a ring 29 placed on the periphery of the open surface 18 of the sunscreen 15. This ring limits the angle of solar entry.

There schematically represents the geometric parameters of the protection device 10 according to the invention. The height h of the baffle 19 is limited by the maximum authorized volume. This can be determined by limiting the ground test means: dimension of the box during the satellite thermal vacuum test, for example, or limiting the volume allocated under the fairing of the launcher.

The entry diameter D of the baffle 19 is sized by the desired land cover angle (6° in our example). In the survival or positioning configuration (reference (4)), no solar ray enters the optical instrument 11.

If we take the non-limiting example mentioned above, the instantaneous field of view of the instrument can be +/- 2°, with a misalignment cone of +/- 4°. This results in an access zone 7 of 6°, which corresponds to an access zone on Earth in a cone of 12°. The solar exclusion angle (SEA = 42° in the example of the ) results from the maximum height accepted. We then have the following relations:

Tangent SEA = (d ₁ -(Dd ₁ )/2)/h

Tangent α = (Dd ₂ )/2 /H

This results, for example, in the following data:

α =6°; d₁ = 1200mm; d₂=1000mm; h=1500mm; H=2500mm; D=1526mm; SEA = 42°

The solar exclusion angle SEA defines the time during which the optical instrument 11 is in the protection position, and therefore unavailable.

It can be noted when without such a protection device which allows the tilting of the optical instrument in the protection position, if we nevertheless wished to avoid any solar entry by adapting the length of the baffle, this length should then be, in our example, 5.5m (D/tan (8.7°)).

There schematically represents a first configuration of the second embodiment of a protection device 10 of an optical instrument 11 according to the invention. The box 110 comprises an Earth face oriented towards the Earth, the protection device 10 is placed on the Earth face. In this configuration, the sunscreen 15 of the protection device 10 is symmetrical about the pointing axis. This configuration makes it possible to have a protective position all around the pointing axis.

In figures 5 to 9, the arrows represent the solar rays which have access to the open surface 18 of the opening 17.

There schematically represents a second configuration of the second embodiment of a protection device 10 of an optical instrument 11 according to the invention. In this configuration, the protection device 10 is arranged on the Earth side and the sunscreen 15 of the protection device 10 is asymmetrical around the pointing axis. This configuration is less cumbersome than the first configuration, but only makes it possible to have a protective position in a zone around the pointing axis (and no longer all around).

There schematically represents a third configuration of the second embodiment of a device for protecting an optical instrument according to the invention. In this configuration, the protection device 10 is arranged in the body 110 of the satellite 100, and the sunscreen 15 of the protection device 10 is symmetrical about the pointing axis. This configuration makes it possible to have a protective position all around the pointing axis, without cluttering the outer faces of the box 110.

There schematically represents a fourth configuration of the second embodiment of a protection device 10 of an optical instrument 11 according to the invention. In this configuration, the protection device 10 is arranged in the body 110 of the satellite 100, and the sunscreen 15 of the protection device 10 is asymmetrical around the pointing axis. This configuration is less cumbersome than the third configuration, but only makes it possible to have a protection position in an area around the pointing axis (and no longer all around), without cluttering the outer faces of the box 110.

In such a configuration where the device for protecting the optical instrument is arranged in the body of the satellite, it can also be the protection device 20 for which the sunscreen 15 is movable in rotation integrally with the support 13. In In this specific case, if an anomaly appears, this configuration in the body ensures solar avoidance without returning to the so-called parking position, which is a position adopted to protect the instrument from solar inputs.

There schematically represents a fifth configuration of the second embodiment of a protection device 10 of an optical instrument 11 according to the invention. In this configuration, the protection device is arranged on a side face of the body 110 of the satellite 100.

There schematically represents a parking position of the first embodiment of a device 20 for protecting an optical instrument 11 according to the invention. As presented previously, in this embodiment, it is the assembly formed by the sunscreen 15 and the optical instrument 11 which switches between the pointing position and the protective position.

The satellite 100 comprises a fixed shutter 21 arranged to obscure the opening 17 of the sunscreen 15 in a parking position in which a wall 16 of the sunscreen 15 of the protection device 20 is close to the body 110. The wall 16 can for example be pressed against the body 110 or else the wall 16 can form a slight angle with the body 110, of the order of a few degrees, for example 5°, 10°, and even up to 30° . This parking position can be adopted to protect the instrument from solar inputs when being put in position and when going into survival mode, that is to say when the optical instrument 11 was in operational mode and that an anomaly has been detected. It is then necessary to place the optical instrument in a safe position. The shutter 21 acts as a barrier. Advantageously, the shutter has a shutter surface substantially parallel to the surface 18 formed by the opening 17 of the sunscreen 15.

There schematically represents a pointing position of the first embodiment of a protection device 20 of an optical instrument 11 according to the invention.

In another embodiment of the invention, the satellite 100 may further comprise an orientation device able to move the support 13 in rotation at an angle calculated as a function of an angular position of an incident radiation. In other words, following an anomaly, to avoid having to make a rotation of 90° (or almost) which allows the protection device to reach the parking position, such an orientation device makes it possible to carry out a command aimed at carrying out to the optical instrument 11 a rotation in order to reduce the probability of solar entry on the optical instrument 11. Thus, the angle of rotation that the optical instrument must realize, by means of the orientation device, depends of the angular position of incident solar radiation before the occurrence of the anomaly, so as to reduce the probability and/or duration of solar entry (i.e. incident solar radiation) into the cavity 18.

The transition from the pointing position to the protection position, and vice versa, can be managed from a deterministic control law. It is possible to program this law for the lifetime of the satellite. It is also possible to control the passage from one position to another according to the orientations of the satellite, the optical instrument and the positioning of the satellite.

Thanks to the device for protecting an optical instrument according to the invention, it is possible to propose recurrent optical payloads for missions in low orbit on board telecommunications satellites in geostationary orbit at a lower cost, while using existing elements ( pointing mechanism that serves as a mobile support for the instrument). The invention makes it possible to embark on a geostationary satellite optical instruments that do not accept prolonged solar input, in particular LEO instruments.

The invention provides autonomous protection of an optical payload during all phases of the life of the satellite (positioning, survival, operational).

Advantageously, the invention uses the pointing mechanism on which the instrument is based. In other words, the support 13 is used both to point the optical instrument at the terrestrial areas to be observed and to move it into a protective position as soon as necessary.

Claims (12)

Protection device (10, 20) of an optical instrument (11) of a satellite (100), the optical instrument (11) being intended to point along a pointing axis (12), said protection device (10 , 20) being characterized in that it comprises:

• a support (13), the optical instrument (11) being arranged on the support (13) and oriented along a first axis (14),
• a sunscreen (15) comprising walls (16) and an opening (17), the walls (16) forming a cavity (18);

in that the optical instrument (11) is arranged in the cavity (18) of the sunscreen (15),
and in that the support (13) is rotatable about a second axis (24) distinct from the first axis (14), so as to move the optical instrument (11) from a pointing position in which the first axis (14) is substantially coincident with the pointing axis (12) at a protection position in which the first axis (14) and the pointing axis (12) are distinct, and/or from the position of protection at the pointing position. Protective device (10, 20) according to claim 1, in which the support (13) is movable around a third axis (34) distinct from the first and second axes (14, 24). A protective device (10) according to claim 1 or 2, wherein the first axis (14) passes through the aperture (17) of the sunscreen (15) in the pointing position, and the first axis (14) is facing the walls (16) of the sunscreen (15) in the protection position. Protective device (10) according to one of claims 1 to 3, the opening (17) of the sunscreen (15) forming an open surface (18), further comprising a baffle (19) extending from the periphery of the open surface (18) of the sunscreen (15), preferably substantially perpendicular to the open surface (18) of the sunscreen (15). Protective device (10) according to claim 4, comprising a ring (29) disposed around the periphery of the open surface (18) of the sunscreen (15). Protective device (20) according to Claim 1 or 2, in which the sunscreen (15) is rotatable integrally with the support (13). Satellite (100) comprising the protection device (10, 20) according to one of Claims 1 to 5. Satellite (100) comprising the protection device (20) according to claim 6, the satellite (100) comprising a body (110), the said satellite comprising a fixed shutter (21) arranged to obscure the opening (17) of the sunscreen (15) in a parking position in which a wall (16) of the sunscreen (15) of the protection device (20) is close to the body (110). Satellite (100) according to claim 8, further comprising an orientation device able to move the support (13) in rotation through an angle calculated as a function of an angular position of an incident radiation. Satellite (100) according to any one of Claims 7 to 9, the satellite comprising a pointing mechanism intended to point the optical instrument (11) towards a previously defined zone, characterized in that the support (13) of the protection (10, 20) is the pointing mechanism. Satellite (100) according to any one of Claims 7 to 10, the satellite (100) comprising a body (110) comprising an Earth face oriented towards the Earth, the protection device being arranged on the Earth face. Satellite (100) according to any one of Claims 7 to 10, the satellite comprising a body (110), the protection device (10, 20) being arranged in the body (110) of the satellite (100).