WO2011120981A1

WO2011120981A1 - Device for controlling the temperature of a tube having a radiating collector

Info

Publication number: WO2011120981A1
Application number: PCT/EP2011/054852
Authority: WO
Inventors: Christian Flemin; David Haddad
Original assignee: Astrium Sas
Priority date: 2010-03-30
Filing date: 2011-03-29
Publication date: 2011-10-06
Also published as: FR2958449A1; FR2958449B1

Abstract

The invention relates to a device for controlling the temperature of an apparatus for dissipating heat by means of radiation, comprising means for reversibly filtering a portion, included between two predetermined end values, of the radiation emitted or received by the dissipating apparatus in at least one wavelength range, and means for controlling said selective filtering means. The dissipating apparatus is typically a travelling-wave tube (5) including a radiating collector, said tube (5) comprising a collector (6) projecting outside of the walls (2, 3) of equipment placed in a high-vacuum environment, the collector (6) being rigidly connected to a cooler (7) radiating toward the outside of the vehicle, while the filtering means comprises a screen (13) arranged around at least a portion of the solid angle of radiation of the cooler (7) radiating toward the outside of the equipment. The invention also relates to a method for driving the device.

Description

Thermal control device of a tube with radiant collector

The invention relates to the field of thermal control. It relates more particularly to the active thermal control of a device in a space environment, and aims in particular at an application in the case of a telecommunications satellite stabilized on three axes, and equipped with traveling wave tubes with radiant collector.

Context of the invention and problem

It is known that one of the problems of electronic payloads embedded on satellites in a space environment is the dissipation of the heat produced by said payload.

Indeed, in the case, for example, of a telecommunications satellite, the payload often includes traveling wave tubes ("TOP" or "TWT" for Traveling-Wave Tube, in English), intended for amplification of the signal to be transmitted with a very low background noise. Now these traveling wave tubes release a large amount of heat, which must be dissipated to space, to avoid a rise in heat of the payload endangering its proper operation. The manifold of these traveling wave tubes with radiant collector operates frequently at a temperature of about 200 ° C, while the tube itself is increased to a few tens of degrees C. For information only, the heat released on a satellite The current telecommunications reach several kilowatts, and it is clear that the heat dissipation capacity is then a sizing element of the power of the payload.

We consider here the case of telecommunications satellites stabilized in attitude on three axes, that is to say pointing a fixed direction over time. This is typically the case of geostationary satellites. It is then conventional to define for these satellites so-called Earth and anti-Earth faces, oriented towards the Earth or opposite to it, and East and West faces, perpendicular to this direction of the Earth, and faces North and South, perpendicular to the axis of the terrestrial poles, and therefore poorly lit by the sun compared to the other faces of the satellite.

For the rest of the description, the "hot" case is defined as the situation in which a radiating tube is subjected to solar radiation. On the contrary, the "cold" case is defined as the case where the radiant collector is in the shadow of the satellite. We understand that the temperature difference between these two cases is in tens of degrees.

As we know, heat dissipation can only be obtained in the space environment by radiation. Various devices for dissipating heat to space were then envisaged for the payloads of these stabilized satellites. Among these, patent document EP 0 376 827 (Thomson CSF 1988) describes a traveling-wave tube whose collector conductively transmits its heat to a fin cooler located on the outer surface of the satellite.

Similarly, US Pat. No. 5,862,462 (Space Systems / Loral 1996) discloses a traveling wave tube cooling system employing radiant manifolds to space via a finned cooler.

This principle of the collector tube radiator (TCR), known per se, is illustrated schematically in Figure 1. This figure highlights the internal zone 1 to the satellite, delimited in a simplified manner by a floor 2 (which is actually a north or south face of the satellite) and a wall 3, which is for example oriented East or West relative to the sun . In this inner zone 1, the heat dissipation is mainly by conduction. On the contrary, in the outer zone 4 to the satellite, the heat dissipation is by radiation.

The satellite comprises a set of progressive wave tubes 5 of a type known per se. Each traveling wave tube 5 comprises a signal input 10 to be amplified, an amplified signal output 11, and a collector 6, which passes through a wall 3 of the satellite and supports a finned radiator 7 arranged outside. of the satellite. The fins, typically eight in number, are of equal length and fit in a circle.

An insulating multilayer protection 9 envelopes and isolates the satellite, reducing the input of solar radiation or radiation generated by the finned radiator in the satellite.

The role of the finned radiator 7 is to radiate about 60% of the heat produced by the Progressive Wave Tube to the space serving as a cold source, this ratio depends on the mode of operation of the tube. For this purpose, in the present embodiment example, the finned radiator 7 receives, for example, a surface treatment by sulfuric anodization, so as to give it a minimum emissivity ε of 0.8 and typical values of early solar absorptivity. of life aBOL = 0.45 and at the end of life aEOL = 0.7.

The rest of the heat, about 40%, is dissipated in the wall supporting the tube. In the opposite direction, the finned radiator 7 receives radiation emitted by the sun or another external radiation source, and transmits it by conduction to the collector 6 of the traveling wave tube 5.

Such a device is called Radiative Cooled Traveling-Wave Tube (RCTWT). Such devices are conventionally installed on the edges close to the North and South faces, so that the radiant collectors have the largest possible radiation angle in a zone poorly lit by the sun. However, it will be understood that when a series of these radially collector tubes 5 are arranged side by side, the finned radiators 7 of the tubes 5 located between other tubes have their radiation zone towards the space masked by the radiators. 7 fins that surround them, which reduces their effectiveness.

Likewise, because of the radiated power, the spacing between the fin coolers may have to be increased, which implies increasing the pitch between the traveling wave tubes within the payload. However, it is desirable, for reasons of performance of the payload, to reduce as far as possible the length of the waveguides between the receiving antennas, and the traveling wave tubes 5. It is therefore sometimes necessary to have tubes in the middle of a face, which naturally reduces the cooling capacity of the radiant collector, particularly if it is a face other than North or South.

Whether for reasons of proximity of the tubes or tubes whose collectors are arranged on a face exposed to solar radiation, some of the radiant collectors see, under the worst conditions, their temperature rise to about 220 ° C. . Such a temperature is likely to cause damage to the materials composing the collector, and for example at the level of the head 12 of the collector ("potting" in English), which secures the fins to the collector by means of an adhesive. At too high a temperature, the associated tube risks destruction. This problem of reducing the maximum temperature of the radiant collectors is therefore critical.

Another patent document EP 1 495 964 (Alcatel 2003) describes two-stage conductive traveling-wave tubes, the second stage being at high temperature, disposed inside a "housing" and conductively coupled to other tubes. as well as a surface of the enclosure radiating towards the space. The radiative receptacle is preferably secured to the collectors: the radiative receptacle is in fact conductively coupled by means of heat distribution means by interposing a thermal conductive seal. The tubes used in this invention transfer their heat to other devices in a conductive manner. This solution still has a certain complexity of implementation.

It is understood that, for this application of heat dissipation in a spatial environment, the devices mentioned are either complex or insufficiently effective, which leads to limitations in the dissipable power.

The evoked solutions result in strong accommodation constraints, impacts on RF performance and on the mass of the payload that can be envisaged (because an increase in the lengths of the waveguides is necessary if all the tubes must be implanted on the East edges. / West Telecom Communication Module): the temperature of radiators radiating collector tubes is critical in hot cases, and there is no adjustment parameter other than the pitch between the tubes, which is frozen at the beginning of program. In addition, it is not possible to compensate the radiative leak towards the space when the tube is in "No drive" mode, that is to say without RF signal power supply or inactive (increase of the satellite heating balance) ). A second problem is the need to simulate on the ground, prior to the launch of a satellite, the operation of the payload, under conditions as close to the space environment as possible. The payload should theoretically be able to be tested in a vacuum environment, with radiation heat dissipation and solar radiation simulation. In order to regulate in temperature dissipative equipments on the payloads Telecom (for example active antennas, and sources of antennas), water charges are used in particular. The installation of these water charges is very restrictive. It implies the implementation of an exchanger in the box and sometimes inside the satellite (risk of leakage and degassing). It is also necessary to implement a thermal control on the water supply pipes (multilayer insulation blanket and heating lines) to prevent the water from freezing. The feeding system is complex (regulation of water flow and temperature). The test configuration is therefore complex and its implementation heavy.

However, at the present time, there is no device for controlling and raising the temperature of the radiators of the tubes with radiant collector under test towards the objectives aimed at. Moreover, the duration of installation and the cost of a test in a vacuum environment are such that a test problem must be avoided as much as possible.

Finally, in the absence of an adequate means of simulating solar flux, the tubes with radiant collector are tested below their nominal operating value: indeed, in the absence of solar flux, the temperature of the radiator is approximately 50 ° C is colder than flight prediction and is far from the test objective (typically above flight prediction).

This lack of a solution allowing an adequate test on the ground is detrimental to a validation of the design of the payload according to the requirements of the customer, and can lead to the appearance of unforeseen problems in flight.

Objectives of the invention

The present invention therefore aims to overcome the aforementioned drawbacks by proposing a new satellite payload cooling device, usable both in space flight and ground test stage.

According to a second objective of the invention, it is inexpensive to implement and mechanically simple.

Presentation of the invention The invention firstly aims at a thermal control device for a radiative heat dissipative equipment, comprising reversible filtering means of a part between two predetermined extreme values, of the radiation emitted or received by the dissipative equipment in the less a range of wavelengths and control means of these selective filtering means.

According to a preferred embodiment, the filtering means comprise a screen disposed around at least a portion of the solid radiation angle of the dissipative equipment.

According to various implementations possibly used in conjunction:

at least one reversibly filtered wavelength range is part of the infrared range,

at least one reversibly filtered wavelength range is part of the visible and ultraviolet domains constituting the solar radiation, the energy of the solar radiation being mainly concentrated in the visible range.

In a preferred embodiment, the filtering means comprise at least one elementary electrochromic screen, the transparency of which varies between two limit values in a predetermined wavelength range, according to the voltage applied to its terminals.

It is understood that the elementary electrochromic screen may be a layer of a multilayer screen device.

The variation of the transparency which is characterized by its transmitivity (or transmittance) consequently leads to the variation of the absorptivity and the reflectivity by the application of the equation: absorptivity + transmitivity + reflectivity = 1; it should be noted that the absorptivity is equal to the emissivity for a given wavelength.

Advantageously in this case, the control means are adapted to vary the voltage applied across the terminals of each elementary electrochromic screen.

It is understood that in this case, the invention is based on the chosen variation of the transparency of an electrochromic device comprising one or more elementary electrochromic screens, surrounding, for example, the radiator of a radially collector tube, as a function of a given electrical voltage and applied to each elementary electrochromic screen, linked to a control logic according to the environmental conditions and the predetermined setpoints . The total transmissivity of the electrochromic device is determined for each range of wavelengths.

In an advantageous embodiment, corresponding to a "flight" use, the electrochromic device comprises two elementary electrochromic screens, having:

for the former, a controllable transparency in the infrared range and a high transparency in the visible range,

- for the second a controllable transparency in the visible range and a high transparency in the infrared range.

The face of the electrochromic device facing the radiator of the radially collector tube called internal face is coated with a treatment with high transparency in the two ranges of wavelengths and very low emissivity in the infrared range (therefore very low reflectivity ).

The outer face of the electrochromic device located outside the satellite is coated with a high transparency treatment in the infrared range and, depending on the application, a low or adjustable transparency in the range of the solar spectrum.

It is understood that, in the case of an application to a satellite comprising highly dissipative equipment with radiators, the device then comprises means for limiting the solar flux in the visible range (VIS) absorbed by these radiators and limiting means Infrared power (IR) radiated by the radiator to its external environment, playing on transmitivity in the visible spectrum and transmitivity in the infrared spectrum.

In this case, advantageously, the transmitivity of the complete device is likely to vary:

in the infrared spectrum between about 0.98 and about 0.2 as a function of a first voltage setpoint applied to the first elementary electrochromic screen, the infrared reflectivity remaining zero on the internal face of the screen,

and in the visible spectrum between about 0.02 and about 0.98 inversely to the reflectivity as a function of a second voltage setpoint applied to the second layer of electrochromic material.

According to another embodiment, corresponding to a so-called "ground" use, the electrochromic device comprises an elementary electrochromic screen, having its controllable transmitivity in the infrared range, the transmitivity of the screen, being capable of varying in the infrared spectrum between about 0.2 and at least 0.7 depending on an electrical voltage setpoint: the infrared reflectivity of the inner and outer face of the electrochromic screen being zero.

In an advantageous embodiment, the internal face of the device is formed by depositing on a substrate a multilayer deposit transparent in the infrared, which gives it an infrared reflectivity close to 0.

In an advantageous embodiment, the filtering in the visible range is carried out directly at the outer face of the electrochromic screen dedicated to filtering in the infrared by depositing on the substrate a multilayer deposit transparent in the infrared with a high reflectivity of the order of 0.98 in the visible range. In this case, only one electrochromic screen is required.

According to a preferred embodiment, the device comprises environmental parameter sensors including in particular: screen temperature, temperature of the hottest part of the dissipative equipment and sunlight of the screen.

In a particular case of application of the invention, the dissipative equipment is a progressive wave tube of the radiant collector type, said tube comprising a collector protruding outside the walls of a machine placed in a vacuum environment. pushed, the collector being secured to a cooler radiating outwardly of the machine.

It is understood that the use of an electrochromic device for filtering using electrochromic materials, the total transparency of which can be modified according to a predetermined logic, makes it possible to control the radiation of the collector radiating from the tube or the radiation received from the sun on this collector. Regulation according to the environmental conditions is then possible.

Another aspect of the invention is a method for controlling a thermal control device in the case where the electrochromic device for filtering using electrochromic materials comprises two elementary electrochromic screens (one in the visible spectrum and one in the visible spectrum). the IR spectrum), the process comprising steps:

in a hot case, when the dissipative equipment is operational and subjected to a solar flux, to control a weak transmittance of the electrochromic device in the visible spectrum and a strong transmitivity in the infrared spectrum for a given wavelength ,

in a cold case, when the dissipative equipment is not operational, to control a high transmitivity in the visible spectrum and a low transmittance in the IR spectrum for a given wavelength.

Dissipative equipment is said to be operational when it is supplied with electrical power and / or RF and thus dissipates heat. It is said to be non-operational, when it is not supplied with electrical power and / or RF and does not dissipate heat.

Advantageously, in this case, the method also comprises a hot or cold case determination step by taking measurements of the electrochromic device and the dissipative equipment and comparing these values with predetermined thresholds.

It will be understood that, in a hot situation, the screen makes it possible to reduce the temperature of the radiator of the tubes with radiant collector by reducing the solar flux received by the radiator of the collector tube while radiating the infrared radiation emitted by the radiator. The heating at the external parts of the tube (radiator, collector, potting) is limited and the components remain below their qualification temperature.

In a cold case, the electrochromic device with controllable IR transparency makes it possible to reduce the heating balance of the satellite by reducing the power radiated by the radiator from the tube to the space.

The invention also relates to a method for controlling a thermal control device, in the case where the electrochromic device comprises an elementary electrochromic screen, comprising a step, when the dissipative equipment is operational and not subjected to a solar flux, of controlling the voltage applied to the elementary screen so as to have an infrared transmitivity of between about 0.2 and at least 0.7, according to predetermined temperature objectives of the hottest part of the dissipative equipment, and measurements of the temperature of said portion. A device for measuring the temperature of the external parts of the radiator collector tube and the electrochromic screen, associated with a feedback loop on the voltage control of the screen allow, for example, to perform this function.

In a favorable embodiment, the dissipative equipment is operational in a vacuum heat chamber or in an integration room.

It will be understood that the device comprises means of limiting the power radiated by the radiator towards its external environment so as to compensate, for example, for the absence of simulation of the solar flux, in the case of a test of a satellite on the ground in a vacuum environment.

According to various embodiments:

the thermal control method is active as a function of the orbital position, of the sunshine received;

the thermal control method is active as a function of the temperature of the screen equipped with a piloting thermistor;

the thermal control method is active as a function of the temperature of the radiator of the radiative tube equipped with a piloting thermistor;

the thermal control method is active as a function of the information received from a photovoltaic sensor fixed on the electrochromic screen receiving the solar flux.

According to another embodiment, the filtering device is made of thermochromic material, whose infrared and / or visible transmitivity, and the visible reflectivity vary depending on the temperature of the material.

It is understood that the temperature of the filtering device is itself a function of the temperature of the radiator radiator and the external environment: the logic of variation of the thermo-optical characteristics of the thermochromic screen is substantially identical to that of an electrochromic screen.

According to another embodiment, the elementary screen is made of a photochromic material whose infrared and / or visible transmittance, and the visible reflectivity vary depending on its temperature.

It is understood that the temperature of the filtering device is itself a function of the radiator tube radiator temperature and the external environment: the logic of variation of the thermo-optical characteristics of the photochromic screen is substantially identical to that of an electrochromic screen. Brief description of the figures

The aims and advantages of the invention will be better understood on reading the description and the drawings of a particular embodiment, given by way of non-limiting example, and for which the drawings represent:

FIG. 1 (already cited): a schematic diagram of a tube with a radiant collector,

FIG. 2: a schematic diagram of the thermal control of the radiator tube radiator using an electrochromic screen (in a hot air application),

FIG. 3: a schematic diagram of the thermal control of the radiator tube radiator using an electrochromic screen (in a cold flight application with a non-operational mode tube),

- Figure 4: a schematic diagram of the thermal control radiator radiator tube using an electrochromic screen (ground application).

Detailed description of an embodiment of the invention

The invention finds its place within a spacecraft, in the present example in no way limiting a satellite orbiting the Earth. We consider here a telecommunications satellite in geostationary orbit stabilized on three axes. However, it remains clear that the invention also applies to any other type of support placed in the vacuum and intended to dissipate its heat purely by radiation.

For the remainder of the description, the term infrared spectrum is defined by the wavelength band lying approximately between 780 nm and 100 μιτι.

Similarly, the term "solar spectrum" is defined as the ultraviolet range having a wavelength band of substantially between 10 nm and 400 nm and the visible range having a wavelength band of substantially between 400 nm and 780 nm. . The energy contained in the solar spectrum is mainly concentrated in the visible range and we do not particularly seek to filter the ultraviolet domain. Figure 2 then illustrates, schematically, a non-limiting implementation of the thermal control device according to the invention.

It is recognized in this figure, by analogy with Figure 1 representative of the prior art, the various elements, mentioned above, which make up a collector tube radiator 5, of a type known per se.

The dimensions and materials of the elements of this collector tube radiating out of the scope of the present invention and are therefore not detailed further here.

In contrast to the prior art, the thermal control device, as described in this non-limiting example, comprises an electrochromic screen 13, disposed around the radiant collector 6, or a series of collectors 6 juxtaposed.

The electrochromic screen 13 is interposed here between the finned radiator 7 and the space, so that any radiation emitted to the space by the finned radiator 7 necessarily passes through said screen 13. In another implementation , the screen 13 intercepts only part of the viewing area of the finned radiator 7, for example the area in which is likely to be the Sun during the movement of the satellite around the Earth.

This electrochromic screen 13 has five faces here, and is of generally parallelepiped shape. It is arranged in such a way that its faces are substantially parallel to the faces of the satellite and that its faces perpendicular to the wall of the satellite from which the collector 6 emerges are flush with the multilayer insulating protection 9. A distance of one to a few centimeters is provided between the faces of the electrochromic screen 13 and the fins or the head 12 of the finned radiator 7.

The electrochromic screen 13 may be rigid or flexible: it is composed, in the present example, of one or more layers of electrochromic material (for example, tungsten oxide, tantalum, niobium or transition metal oxyhydroxide) separated by an ionically conductive electrolyte layer (for example, polymer or mineral layer with tungsten oxides, tantalum, molybdenum), this assembly being sandwiched by two layers of transparent electroconductive oxide (for example, ZnO: Al or In ₂ O ₃ : Sn) applied on glass or polymer substrate for example: these two layers of electroconductive oxide are considered transparent in the infrared and visible areas, and serve electrodes connected to a voltage supply. The face of the substrate opposite the radiation fin 7 has a high infrared transparency and a substantially zero IR reflectivity for the wavelength ₀ of IR radiation radiation fin 7 for it, this face is covered with a multilayer deposit consisting of thin transparent and non-absorbing dielectric layers; layers of low refractive index (for example, MgF ₂ or SiO ₂ ) are alternated with layers of high refractive index (for example, Ti0 ₂ or ZnS). The typical thickness of a multilayer deposit is of the order of a few μιτι. The wavelength λ ₀ of the IR radiation of the finned radiator 7 during operation is of the order of 6 μιτι, which corresponds to a temperature of the finned radiator 7 of the order of 200 ° C. according to the Wien law. (temperature in Kelvin = 2898 / λ ₀ where 0 is in μιη and corresponds to the maximum luminance of the radiation of the finned radiator 7).

It is recalled that an electrochromic material is a material that can exist in two oxidation-reduction states, and whose optical properties are reversibly modified by application of an electric charge, typically between 0.5 and 2V. The entire range of optical property values between the values corresponding to the two oxidation-reduction states can be attained, depending on the electric charge applied. After applying the voltage setpoint, the color change duration is of the order of ten seconds.

It should be noted that the color change persists after the end of the application of the electric charge, which has the advantage of not requiring energy to maintain one of the colors of the electrochromic material. The optical properties of electrochromic materials naturally depend on the composition thereof. These materials include polyaniline, viologenes, tungsten oxide, polyoxotungstates, titanium dioxide, various polymers, and the like.

In the present device, an electrochromic material is used whose optical properties vary in the infrared spectrum for the filtering in this spectrum and in the solar spectrum (visible essentially) for the filtering in this spectrum. In a first variant, called "flight", of the device, the electrochromic screen 13 is intended to be taken into orbit with the satellite, and must therefore be compatible with the space environment. Its mechanical and geometrical characteristics are then determined by the constraints at launch and during the flight: resistance to degassing, thermal cycling, electrostatic charges, UV irradiation, aerothermal flow at launch, mechanical stresses at launch and in flight (particles). The electrochromic screen 13 is secured to the walls 2, 3 of the satellite by means known per se, and the device comprises a grounding of this electrochromic screen 13.

In this "flight" variant, the materials of the electrochromic screen are chosen such that their thermo-optical characteristics make it possible to maintain the temperature of the screen in its qualification range in the external environment and that it is compatible with the space environment.

The infrared reflectivity of the electrochromic screen 13 is zero and only the transmitivity varies according to the voltage setpoint.

The transmitivity of the electrochromic screen 13 is, in the present application, likely to vary both in the infrared spectrum and in the visible spectrum. This arrangement can be achieved by creating an electrochromic device comprising two layers of different materials (or two superimposed elementary screens), having for one of them optical properties controllable in the infrared range, and for the other of controllable properties in the visible range.

This transmitivity of the complete screen, is likely to vary:

in the visible spectrum between approximately 0.02 and 0.98 as a function of a first voltage setpoint,

and in the infrared spectrum between about 0.98 and about 0.2 as a function of a second voltage setpoint (the infrared reflectivity remaining zero on the internal face of the screen).

The choice of materials and coating of the electrochromic screen is such that, for transient phases, transmittance in the visible spectrum and transmitivity in the infrared spectrum change little depending on the temperature of the electrochromic screen.

An example of an electrochromic material capable of satisfying this need is described in detail in Saint Gobain patent applications FR 2 904 704 A1 and FR 2 934 062 A1.

In the eventual case where the transmitivity and reflectivity in the visible spectrum and the transmitivity in the infrared spectrum change as a function of the temperature of the electrochromic screen 13, the electrochromic screen 13 materials are chosen in such a way that when the The temperature of the electrochromic screen 13 increases for a given voltage, the transmitivity in the visible spectrum decreases, the reflectivity in the visible spectrum increases and / or the transmitivity in the infrared spectrum increases so that the temperature of the finned radiator 7 and that of the electrochromic screen 13 remain stable.

The transmitivity of the screen is adjusted using a voltage generator (+/- 2V) with different voltage settings determined according to the nature of the material. This voltage generator may be specific to this application, or otherwise common with another application requiring voltage generation.

In this flight variant, the temperature range of the screen is typically from -45 ° C to + 85 ° C when the radiant collector tube 5 is operational. Similarly, the temperature range of the screen is typically -160 ° C to +85 ° C when the collector tube 5 is non-operational. The device also comprises a connector (not shown in the figures) adapted to the activation of the electrochromic function of the screen 13 and the voltage generator and associated control means (also not shown). These control means typically take the form of a processor with a memory supporting a software for controlling the electrochromic screen, according to environmental data received by environmental sensors, in particular: solar flux received, temperature of the the screen, temperature of the radiator with fins.

In a second variant, called "ground" of the device, the electrochromic screen 13 is simply intended to allow tests of the payload of the satellite in a vacuum atmosphere on the ground. It is temporarily arranged around some collectors. In this case, it is not necessary to size the screen 13 according to spatial constraints, but simply to provide it with characteristics to place this screen 13 around some or all of the tubes. collectors 5, during the duration of the vacuum tests.

In this "ground" variant, the electrochromic material is chosen such that the infrared transmitivity varies between 0.2 and 0.7 as a function of the voltage setpoint applied by the operator.

This voltage setpoint can take the form of achieving the objectives specified by the customers on the temperature of the radiators (ie typically above the prediction in flight).

The choice of the materials of the electrochromic screen 13 is such that the infrared emissivity of the internal face of the screen (finned radiator side 7) is about 0.04, the infrared emissivity of the external face is about 0.3 and the reflectivity infrared of the inner and outer face of the screen is zero.

The adjustment of the thermo-optical characteristics (transmitivity) of the screen is achieved by means of a voltage generator (+/- 2V) with different voltage setpoints, according to a predetermined logic.

The device allows in particular to maintain the temperature of the radiator 7 under its qualification temperature by adjusting the voltage setpoint.

In both soil and flight variants, to ensure the safety and control aspect, the radiator 7 of the tube 5 is equipped, in the present example, with a temperature sensor 14 (thermocouple or thermistor). The temperature sensor 14 on the radiator 7 of the tube 5 ensures the safety function when a predetermined limit is reached in a hot situation.

A second temperature sensor 15 is disposed on the screen 13. The two temperature sensors 14 and 15 make it possible to choose the appropriate electrical voltage to be applied to the electrochromic screen 13, to regulate the temperature of the radiator 7 of the tube 5, by function of abacuses previously established using elementary characterization tests.

Operating mode

The control method of the electrochromic screen (or more generally a screen with controllable thermo-optical properties), given here by way of non-limiting example, in the case of a flight application, is illustrated by FIGS. .

It is understood that the method comprises steps of:

- measurement of the temperatures recorded by the temperature sensors 15, 14 arranged on the screen and on the radiator,

- determination of the operating case:

a / Hot case: the radiator of the tube 5 is operational (which is determined in particular by the temperature sensor 14) and subjected to the unfiltered part of the solar radiation flux,

b / cold case: the collector tube radiator 5 is inactive, against the screen is supposed to be subjected to the unfiltered part of the solar radiation flux.

In the hot case, illustrated in FIG. 2, the radiator of the tube 5 is operational (which is in particular determined by the temperature sensor 14) and subjected to the unfiltered part of the solar radiation flux.

Under these conditions, the control means control the voltage applied to each electrochromic layer of the electrochromic screen 13 as a function of its temperature so that it has a low transmittance (close to 0) and a strong reflectivity (close of 1) in the visible range, and a strong transmitivity (close to 1) in the infrared.

Therefore, the solar radiation is largely rejected by the screen, and therefore does not contribute to the heating of the finned radiator 7 of the tube 5, and, instead, the infrared radiation generated by said finned radiator 7, and which constitutes most of its radiation passes virtually without attenuation of the screen 13.

The result is a decrease of about fifteen degrees in the temperature of the collector radiating in this hot case.

Moreover, always in this hot case, if the temperature of the radiator 7 of the tube 5, read by the temperature sensor 14, or the temperature of the electrochromic screen, read by the temperature sensor 15, reaches a previously defined threshold for each, an alarm is sent to a control center on the ground, and an operator can intervene if he deems it useful, for example by deciding the stop of the operation of the tube and / or a modification of the voltage setpoint of the screen electrochromic 13 following the result of the analysis of other parameters. Alternatively, in case of occurrence of an alarm, the tube 5 is extinguished automatically, by the control means on board the satellite, according to the logic previously stored, which causes the lowering of the temperature of the collector 6. In the cold case, illustrated in FIG. 3, the radiant collector tube 5 is inactive, and it is known that reheating on the floor 2 is usually necessary to keep the part of the tube 5 located inside the satellite in its acceptable temperature range. On the other hand, the screen is supposed to be subjected to the solar radiation flux (which is determined in particular by the temperature detected by the temperature sensor 15). Under these conditions, when the temperature of the radiator, as detected by the temperature sensor 14 passes below a predetermined threshold, the control means control the voltage applied to the layers of the electrochromic screen 13 so that the transmitivity increases and the reflectivity decreases in the visible spectrum and transmitivity decreases in the infrared to become close to zero.

As a result, a larger fraction of the solar radiation passes through the screen, and thus contributes to the heating of the finned radiator 7 of the tube 5, and, instead, the infrared radiation generated by said finned radiator 7 to the cold space , virtually does not cross the screen 13, thus increasing its temperature.

The result is a reduction in the radiative exchanges with the cold space and a decrease in the conductive leak between the inner part of the tube 5 and the radiator 7 in this cold case, or, correlatively, a decrease in the need for reheating of the floor 2, and therefore a gain on the heating balance of the payload.

In the case of a "ground" application when testing a thermal vacuum satellite (see FIG. 4) without solar source simulation, the control means control the voltage applied to the electrochromic screen 13 so as to present a infrared transmitivity between 0.2 and 0.7, depending on the objectives of the test and the temperature of the radiator, as noted for example by the thermocouple 14, which depends in particular on the type of collector tube used radiator. The choice of this transmitivity makes it possible to reduce the radiative exchanges of the radiator 7 with the cold external environment and thus to raise the temperature of the finned radiator 7 in a controlled manner.

Advantages of the invention

The invention is based on the chosen variation of the transmitivity of a screen electrochromic, surrounding the radiator of a collector tube radiating, according to a given voltage, linked to a control logic according to the environmental conditions and predetermined instructions.

It will be understood that the invention makes it possible to install commercially radiating collector tubes on a satellite, without modification, and to provide them with electrochromic screens of geometry or adapted characteristics.

This invention allows two types of application:

1 / a flight application:

In a hot case, the device makes it possible to reduce the temperature of the radiator 7 of the tubes with radiant collector 5 (external part at the collector 6, which is a critical element) by limiting the solar flux absorbed by the radiator 7 by means of an electrochromic screen 13: in fact, in the absence of sun visor, the high temperature of the radiator is due for a large part to the solar flux received by the radiator. The invention then allows greater flexibility in the accommodation of these tubes on a satellite and better optimization of the payload.

In cold weather, the device reduces the heating balance of the satellite. Indeed, the establishment of an electrochromic screen around the radiator allows to limit the power radiated by the radiator to its external environment, playing on transmitivity in the visible spectrum and transmitivity in the infrared spectrum.

It has been calculated that, in a "flight" application of the device, for a given configuration, the invention makes it possible to reduce, in a "hot" case, the temperature of the radiator of the radially collector tube (and therefore the collector portion) of the order of 15 ° C. The device according to the invention then makes it possible to maintain the temperature of the radiator at an acceptable level according to the configurations: this makes it possible to optimize and facilitate the internal and external arrangement of the payload, since the invention can be applied locally to one or more tubes as an additional adjustment parameter.

Similarly, in a "cold" case, the invention saves between 4W to 10W of heating, by inactive collector tube or "no drive" mode (that is to say without RF signal supply) , hence a reduction in the heating budget of the satellite in a "cold" case. This invention can, moreover, be implemented late in the program because it does not require changes to the integration of equipment inside the satellite, but only on the external surface.

Another advantage of the invention is the widening of the possibilities of implantation of the tubes with radiant collector on a telecommunications satellite, and the possibility of optimizing the lengths of waveguides and the mass. It is for example conceivable to consider an assembly on the floors ("floors") with a reduced pitch between the tubes. 21 a floor application in thermal vacuum.

The device then makes it possible to compensate for the absence of simulation of the solar flux. It also makes it possible to control and raise the temperature of the radiator 7 of the radiant collector tubes 5 according to the objectives of the test set by the customers and the qualification limits.

In its application to ground use, in the context of satellite thermal vacuum test, the invention makes it possible to achieve the contractual objectives of the test. Contrary to the traditional use of electrochromic screens in an attempt to reduce the heat received by an object or an observer, the screen 13 is indeed used in a clever way to increase the heating of the radiator 7 by reducing the fraction of radiation emitted by the radiator and which passes through said screen to the colder external environment.

Similarly, the invention allows a test of the collector tubes radiating above the temperature levels encountered in flight (according to customer specifications), which does not allow the prior art.

Briefly, the advantages of the heat dissipating device according to the invention are:

a mechanical integrity of the unmodified traveling wave tube,

- a simple device whose installation decision is reversible (the transition is fast, which allows installation only for ground tests if necessary),

a local dissipation control capacity (setting the radiator temperature for a tube located in an unfavorable external environment), - a correction correctable in flight,

a reduction in thermal and thermoelastic stress due to the large orbital fluctuations of the temperature of the radiator 7 of the collector tubes 5,

- a low cost of implementation,

- a low supply voltage requirement (+/- 2V).

Variants of the invention

The scope of the present invention is not limited to the details of the above embodiments considered by way of example, but instead extends to modifications within the scope of those skilled in the art.

In an alternative embodiment, the screen is made of a thermochromic material. Such materials are known, whose thermo-optical characteristics vary according to their temperature. In the present example, it is itself a function of the temperature of the radiator 7 of the radiant collector 6 and the external environment. The logic of variation of the thermo-optical characteristics of the screen is identical to that explained previously.

In an alternative embodiment, the screen is made of a photochromic material. Such materials are known, whose thermo-optical characteristics vary according to the effect of light. In the present example, this is, itself, a function of the solar illumination of the screen. The logic of variation of the thermo-optical characteristics of the screen is identical to that explained previously.

For both applications, in flight environment and ground thermal test, it is naturally possible to extend this invention to all different types of collector tubes radiating different suppliers, adapting to their geometry or specific dimensions.

The invention is also transposable to the regulation of any very dissipative equipment that removes its heat by radiative exchanges and observation satellites, orbital stations and space probes.

It is also clear that the screen surrounding a radiant collector 6 may consist of several parts whose thermo-optical properties are controlled separately, without modification of the principle of the invention. Similarly, the thermo-optical properties of these parts may differ from one another to taking into account for example the local intensity of solar flux received over time and depending on the desired temperature on the radiator 7 of the radiant collector 6.

In an installation variant, only certain tubes with a radiant collector are equipped with an electrochromic screen as described above, for example the tubes situated at the most exposed locations to the solar flux (middle of the faces) or arranged between others. tubes.

Claims

1. Thermal control device for a radiative heat dissipative equipment, said dissipative equipment being a progressive wave tube (5) of the so-called radiant collector type, said tube (5) comprising a collector (6) protruding outside the walls (2, 3) of a machine adapted to be placed in a high vacuum environment, the collector (6) being secured to a radiator (7) radiating outwardly of the machine.

characterized in that the device comprises means for reversibly filtering a part between two predetermined extreme values, the radiation emitted or received by the radiator (7) in at least one wavelength range, and control means of these selective filtering means,

the filtering means comprising at least two elementary electrochromic screens, the first having a controllable transparency in the infrared range and a high transparency in the visible range,

and for the second a controllable transparency in the visible range and a high transparency in the infrared range,

said elementary electrochromic screens being arranged around at least a portion of the solid radiation angle of the radiator (7), the transparency of said electrochromic screen varying between two limit values in a predetermined wavelength range, according to the electrical voltage applied to its terminals,

the control means being adapted to vary the electrical voltage applied across each layer of electrochromic material of the screen. 2. Device according to claim 1, characterized in that the transmitivity of the complete electrochromic device forming the filtering means, is likely to vary:

in the infrared spectrum between about 0.98 and about 0.

2 as a function of a first voltage setpoint applied to the first elementary electrochromic screen, the infrared reflectivity remaining zero on the internal face of the screen,

and in the visible spectrum between approximately 0.02 and 0.98 inversely to the reflectivity as a function of a second voltage setpoint applied to the second electrochromic screen.

3. Device according to claim 2, characterized in that the electrochromic device comprises an elementary electrochromic screen, having a controllable transmittance in the infrared range, capable of varying between about 0.2 and at least 0.7 as a function of a voltage setpoint.

4. Device according to any one of the preceding claims, characterized in that the inner face of the device is formed by depositing on a substrate a multilayer deposit transparent in the infrared, which gives it an infrared reflectivity close to 0.

5. Device according to any one of the preceding claims, characterized in that the outer face of the elemental electrochromic screen dedicated to the filtering in the infrared is produced by depositing on a substrate a multilayer deposit transparent in the infrared with a high reflectivity of the order of 0.98 in the visible range.

6. Device according to any one of the preceding claims, characterized in that it comprises environmental parameters sensors including in particular: screen temperature, temperature of the hottest part of the dissipative equipment and sunshine of the screen.

7. A method of controlling a thermal control device according to any one of claims 1 to 6, characterized in that it comprises steps:

in a hot case, when the dissipative equipment is operational and subjected to a solar flux, to control a weak transmitivity of the screen in the visible spectrum, and a strong transmitivity in the infrared spectrum for a length of given wave,

in a cold case, when the dissipative equipment is not operational, to control a high transmitivity in the visible spectrum, and a low transmittance in the IR spectrum for a given wavelength.

8. The method of claim 7, characterized in that it also comprises a step of hot or cold case determination by reading temperature measurements of the electrochromic device and the dissipative equipment and comparison of these values to predetermined thresholds.

9. The method of controlling a thermal control device according to claim 3, characterized in that it comprises a step, when the dissipative equipment is operational and not subjected to a solar flux, for controlling the voltage applied to the device. elementary screen (13) so as to have an infrared transmittance of between about 0.2 and at least 0.7, according to predetermined temperature objectives of the hottest part of the dissipative equipment, and measurements of the temperature of said part.

10. A method of controlling a thermal control device according to claim 9, characterized in that the dissipative equipment is operational in a vacuum heat chamber or in an integration room.

1 1. Satellite thermal vacuum test method, said test being carried out before launching the satellite, characterized in that it comprises:

a preliminary step of installing a thermal control device according to any one of claims 1 to 6, around one or more radiating collectors of traveling wave tubes,

a method for controlling the thermal control device according to one of claims 7 to 10,

- A disassembly step of the thermal control device.