WO2024223949A1

WO2024223949A1 - Heater for spacecraft

Info

Publication number: WO2024223949A1
Application number: PCT/EP2024/061804
Authority: WO
Inventors: Borja POZO LARROCHA; Lorena MACHON ANTOLIN; David CANTERO BURGOS; Iñigo MUÑOZ RIERA
Original assignee: Fundacion Tekniker
Current assignee: Fundacion Tekniker
Priority date: 2023-04-28
Filing date: 2024-04-29
Publication date: 2024-10-31
Anticipated expiration: 2025-10-28
Also published as: EP4456664A1

Abstract

A heater for a spacecraft, comprising: a flexible polyimide substrate (1) that comprises a first portion (2) and a second portion (3); an electronic system (4) on the first portion (2); a heating element (5) which is flexible and made of a conductor on the second portion (3); a temperature sensor (6) on the second portion (3); wherein, the electronic system (4) comprises a printed circuit board (7), a communication interface (8), a power input interface (9) and a temperature control system (10); the temperature control system (10) is connected to the temperature sensor (6); the temperature control system (10) is connected to the heating element (5); the communication interface (8) is connected to the temperature control system (10) and configured to enable a transmission of control signals between the temperature control system (10) and an external system. Also, a spacecraft comprising the heater.

Description

HEATER FOR SPACECRAFT

TECHNICAL FIELD

The present invention relates to the field of heaters for applications in space. More precisely, it relates to a heater for a spacecraft. The heater may be used for controllably heating the spacecraft, and in particular for controlling the temperature of a zone of interest in the spacecraft. The heater of the present invention, due to its elements and functionality, may also be called a smart heater. The present invention is also related to a spacecraft which comprises said heater.

STATE OF THE ART

Reference 1 discloses flexible heaters used in defense and aerospace applications, and also discloses that electronics can be integrated to the heaters. Patent application document WO 2021/248117 A1 discloses a resistive foil heater which includes a coverlay, a base, an etched composite panel, transition tabs, and lead wires. Patent application document US 2020/0331640 A1 discloses protective blankets for use on spacecraft, the protective blankets comprising a flexible blanket body and a voltage supply. Patent application document CN 111526611 A discloses a thin film electric heater for a spacecraft, which comprises two insulating layers, wherein an electric heating alloy foil loop is arranged between the two insulating layers.

There are known heaters for applications in space. Spacecrafts are subjected to the extreme conditions of space, and in particular, they may be subjected to big variations of temperature. Such variations may be caused by the spacecraft moving from the atmosphere to the outer space, and also by the possible changes in the degree of the irradiation of the spacecraft by the sun. There are known heaters used in spacecrafts for controlling a temperature of a spacecraft or at least of a part of the spacecraft. A heater for a spacecraft should preferably have the necessary heating capability so that it can achieve the correct required temperature in the spacecraft. Moreover, the heater should preferably have re-configurability, to allow reconfiguration of the temperature set points and heat outputs. In addition, the heater should preferably have self-control capability, for (re)setting the desired temperature (setpoint temperature) when the environmental temperature changes dramatically, and for reaching the setpoint within a defined temporal window and preferably following a characteristic behavior curve. Moreover, the heater should preferably exhibit stability, because a tight thermal control is preferably required to operate within narrow temperature ranges or gradients. Stability stands for accurate and smooth dynamic behavior of the heater. Moreover, the heater should preferably exhibit robustness, ensuring that it will operate correctly despite a possible critical damage in the system outside the heater. The space is a very harsh environment for electronics due to the high vacuum, extreme temperatures, and the presence of high energy charged particles and ultraviolet radiation. Moreover, the embedded hardware is exposed to high vibration levels, especially during the launching of the spacecraft and at the early stages of the orbital flight. Thus, robustness is one of the more important qualities that the heater should exhibit. Moreover, the integration of the heater in the spacecraft should be easy, meaning that the heater should have a structure such that it can be easily integrated or be fitted within the spacecraft, and without increasing significantly the overall weight of the spacecraft. In addition, the heater should exhibit simplicity, so that it can be manufactured, installed and, if necessary, serviced without a significant difficulty. In addition, the heater should preferably have a small size and a low weight. Moreover, the cost of the heater should not be excessively high, and preferably should be low. The conventional heaters do not combine all the above qualities, and this is a significant drawback.

Therefore, there is a need to develop a heater that overcomes the drawbacks of the conventional ones.

DESCRIPTION OF THE INVENTION

The present invention overcomes the drawbacks of conventional heaters for spacecrafts. The present invention offers a heater which can simultaneously exhibit good heating capability, reconfigurability, self-control capability, stability, robustness, easy integration in a spacecraft, simplicity, small size, and low weight and cost.

In a first aspect of the invention, a heater is provided. The heater comprises a flexible polyimide substrate, an electronic system, a heating element and a temperature sensor. The flexible polyimide substrate comprises a first portion and a second portion. The electronic system is on the first portion. The heating element is flexible and is made of a conductor which is on the second portion. The temperature sensor is on the second portion. Also, the electronic system comprises a printed circuit board, a communication interface, a power input interface and a temperature control system which is programmable and is formed on the printed circuit board. The temperature control system is connected to the temperature sensor for measuring a temperature at the second portion. The temperature control system is also electrically connected to the heating element and configured to controllably power the heating element for controlling the temperature at the second portion. The communication interface is connected to the temperature control system and configured for enabling a transmission of control signals between the temperature control system and an external system. The power input interface is configured to receive an external electrical power input for powering the temperature control system. The heater is particularly a heater for a spacecraft, i.e. a heater suitable for use with (in) a spacecraft.

Advantageously the flexible polyimide substrate may advantageously improve the heater’s robustness and ability to sustain any significant mechanical vibrations such as the ones experienced during the launching of the spacecraft. In addition, polyimide substrates have a relatively low weight and low cost compared to many other substrate materials for heaters and for electronics. Hence, advantageously the use of the flexible polyimide substrate contributes to keeping the weight and cost of the heater relatively low. Moreover, the polyimide substrate permits the potential operation of the heater under wide temperature ranges, including high temperatures, and facilitates the integration of the heater in the spacecraft, particularly on curved surfaces of the spacecraft. In a preferred embodiment of the invention, the flexible polyimide substrate is a flexible polyimide film.

The external system may be a system of the spacecraft. The communication interface, which may comprise a communication port, advantageously enables the re-configurability and controllability of the heater, because it enables the transmission, and hence the receipt, of control signals. Said control signals may be instructions for changing one or more variables related to the operation of the heater. Hence, the control signals may be used for changing one or more temperatures related to the operation of the heater, or for further improving the heater’s stability and the accuracy with which the heater may perform its function.

The electronic system, and in particular the temperature control system, enable the heater exhibiting self-control capabilities. The electronic system may also be called electronic assembly or electronic module. Similarly, the temperature control system may also be called temperature control assembly, temperature control module or temperature control subsystem. The temperature control system may advantageously enable an accurate temperature control even when other parts of the spacecraft, e.g. the external system, have problems or malfunctions. Hence, after the heater potentially receives a control signal, and for example after the heater has potentially received instructions for controlling the temperature so that the latter is within a range or has a particular value, the temperature control system may advantageously enable the execution of said instructions and may keep the heater operational, even when the external system which originally gave the instructions is temporarily or permanently out of operation. The heating element and the temperature sensor on the second portion, in combination with the temperature control system connected to the temperature sensor and to the heating element, enable controlling the temperature at said second portion.

In a preferred embodiment the polyimide substrate has a thickness from 0.1 mm to 0.2 mm. Hence, preferably the thickness of the polyimide substrates is no less than 0.1 mm and no more than 0.2 mm. If the thickness is less than 0.1 mm, then the substrate may not be durable enough, and in particularly may be damaged, e.g. be torn, during the fabrication and/or use of the heater. If the substrate is more than 0.2 mm, then it may not be flexible enough, or it may not be light enough for its easy integration in a spacecraft. Therefore, preferably the thickness of the polyimide substrate is between 0.1 mm and 0.2 mm.

In a preferred embodiment, the polyimide substrate is a Kapton® polyimide substrate, i.e. is made of a Kapton® material. The inventors found that this type of polyimide substrate is particularly advantageous for the suitability and application of the heater in space.

In a preferred embodiment, the heating element is configured to consume an electrical power of up to 100 W when a DC voltage of 52 V is applied across the heating element. Advantageously applying to the heating element a DC voltage of 52 V is compatible with the electronics and power supply commonly found in a spacecraft such as in a satellite. Usually electronic devices in spacecrafts go to a 52 V bus voltage. Also, usually the power systems and related available electrical power of a spacecraft impose a limit to how much power can each component of a spacecraft consume, and for this reason, it is estimated that the heating element is advantageously further optimized to be used in a spacecraft when it consumes no more than 100 W when said DC voltage of 52 V is applied across the heating element. As is known, when a voltage, i.e. an electrical potential, is applied across the heating element, provoking the flow of an electrical current trough the heating element’s conductor, then the Joule effect causes the heating of the electrical conductor and of the heating element.

For optimizing its application in a spacecraft, and specifically for optimizing the temperature control achieved via the use of the heating element, it is sufficient that the watt density of the heating element is 100 W/cm² or less. The watt density is the heat flux emanating from each unit area of the effective heating area (heating surface) of the heater (i.e. of the heating element). The watt density of a heater can also be understood as being the wattage output of the heater relative to its size. Hence, when the watt density of the heating element is 100 W/cm², then the wattage output of the heating element is 100 W per 1 cm² of the heating element. Therefore, in a preferred embodiment the heating element is configured to have a watt density of up to 1 W/cm² when a DC voltage of 52 V is applied across the heating element.

In a preferred embodiment according to the first aspect of the invention, the conductor is operable in a vacuum and within a temperature range of between -150°C and 150°C. The exact composition and properties of an electrical conductor may change when the conductor is moved from the earth’s atmosphere to the vacuum of space, at least because the vacuum may cause a degassing of the electrical conductor. Moreover, the electrical properties, such as the resistivity, may significantly depend on the temperature of the conductor. Therefore, the temperature of the conductor, may affect its heating functionality. The components in a spacecraft, and hence, the components of the heater when the latter is used in a spacecraft, may experience extreme temperatures which may vary from -150°C to +150°C, depending for example on the degree of solar irradiation received by the spacecraft or by any surfaces or parts of the same. Therefore, advantageously the electrical conductor should preferably be operable, i.e. be configured for operation, in a vacuum, in particular the vacuum of outer space, and the within a temperature range from -150°C to 150°C.

In a preferred embodiment of the heater according to the first aspect of the invention, the conductor is deposited or printed on the second portion forming thereon a conductive line or circuit electrically connected to the temperature control system. This advantageously facilitates the fabricability of the heater, using processes such as deposition, e.g. thermal evaporation, or printing, e.g. screen printing. Moreover, the deposition or printing of the conductor directly on, i.e. in direct contact with, a surface of the second portion, may advantageously enable avoiding using other intermediate components, and hence, may be advantageous for further minimizing the weight, and optimizing the flexibility, of the heater.

In a preferred embodiment of the invention, the conductor has a thickness of 30 micrometers or less. When the thickness of the conductor is more than 30 pm, the conductor may be particularly rigid and not flexible. However, when the thickness is 30 pm or less, then advantageously the conductor which is on the second portion may be particularly flexible, further improving and optimizing the overall flexibility and potential applicability of the heater to different parts and surfaces of a spacecraft or other type of system within which the heater may potentially be used.

In a preferred embodiment of the invention, the conductor comprises any of silver, copper, an alloy, a super alloy, or a combination thereof. More preferably, the conductor is made of an austenitic nickel-chromium-based super alloy. Most preferably the conductor is made of, or comprises, an Inconel® alloy. Any of the aforementioned metals or alloys can be used for the fabrication of the heating element, advantageously permitting the conductor and the heating element to be flexible and at the same time to have the correct electrical properties, e.g. resistivity, so that it can be used for a heater that is particularly intended to be used in space. Moreover, the use of a nickel-chromium-based super alloy, and particularly the use of the Inconel® alloy for making the conductor, advantageously allow for creating a heating element which can exhibit a desired electrical consumption and watt density, especially under operational conditions related to the possible integration and use of the heater in a spacecraft.

In a preferred embodiment of the invention, the temperature control system comprises a controller which is connected to the temperature sensor. More preferably said controller is a proportional integral (PI) controller. Optionally and further preferably, the PI controller (proportional integral controller) mentioned in the present disclosure may be a proportional integral derivative (PID) controller. Hence, in a preferred embodiment of the invention, the temperature control system comprises a PID controller which is connected to the temperature sensor. Likewise, unless otherwise specified, the term “PI controller” is used in the present disclosure for describing a proportional integral controller or a proportional integral derivative controller. The PI controller may advantageously optimize the accuracy and responsiveness with which the temperature control system can control powering the heating element for controlling and setting the temperature at the second zone. The use of a PI D controller which can combine proportional and integral control actions, may advantageously eliminate at least some of the disadvantages associated with each of said proportional and integral control actions.

In a preferred embodiment of the invention, wherein the temperature control system comprises a PI controller, the temperature control system further comprises an analogue-to-digital signal converter which is connected to the PI controller and to a gate of a MOSFET which is connected to the heating element. Said MOSFET is configured to power the heating element. The analogue-to-digital signal converter is configured to receive an analogue signal from the PI controller, convert said analogue signal to a digital signal, and provide said digital signal to the gate of the MOSFET. Said digital signal is a pulse width modulation (PWM) signal. This way, via the aforementioned optional configuration, more or less current may be injected into the heating element through the modulation of the digital signal provided (applied) to the gate of the MOSFET, for thusly advantageously controlling the powering of the heating element, and consequently, achieving accurate heat/temperature control. Hence, it may be understood that preferably the PI controller is configured to output the aforementioned analogue signal. Also, it may be understood that preferably the analogue-to-digital signal converter is connected downstream of the PI controller. Moreover, it may be understood that the MOSFET is preferably connected to a power supply line for powering the heater. Likewise, preferably the gate of the MOSFET is configured to open or not for respectively permitting or not the injection current into the heating element.

In a preferred embodiment of the invention, the temperature control system comprises the aforementioned analogue-to-digital signal converter, and further comprises a power control module connected to the analogue-to-digital signal converter. The power control module may be configured to controllably power the analogue-to-digital signal converter for enabling the pulse width modulation (PWM) related to the generation of the PWM signal.

In a preferred embodiment of the invention, the heater’s electronic system further comprises an evaluation board which comprises a communication interface and is connected to the temperature control system via at least one connector, and preferably via two or more connectors. For example, the evaluation board may be connected to the temperature control system via an I/O connector and an ADC connector. Advantageously, the evaluation board may enable the receipt of external instructions, i.e. of an input, as well as receive a feedback, e.g. feedback signals, from the temperature control system. Likewise, according to said received instructions and the feedback, the evaluation board may control the temperature control system for controlling the heating and the temperature achieved. For example, the instructions received by the evaluation board may include a desired temperature to be achieved, and/or a desired set temperature range. The feedback received by the evaluation board from the temperature control system, may include a signal from a volt sensor (VOLT_SENSOR), a sensor adaptation (SENS_ADAP) signal, a power analogue (PWR_ANA) signal, and/or a PID analog signal (PID_ANA). The evaluation board for controlling the temperature control system may provide to the PI controller a temperature setpoint, may control a mode of the temperature control system, or may select between possibly different sensors of the temperature control system. For example, the temperature control system may comprise more than one sensors. For the above reasons, the evaluation board preferably comprises a programable microcontroller which further preferably is a radiation resistant microcontroller so that it can operate in space. Further preferably, said microcontroller may enable the aforementioned receipt of instructions and signals, as well control the power control system, so that advantageously the heater once has received instructions from an external system, e.g. from a computer of a spacecraft, can continue operating, even if subsequently occurs a malfunction of said external system. Thereby, advantageously the autonomy of the heater is improved, and the electronic system of the heater when being connected to the said external system, resembles a micro-node which once receives instructions can operate with a high degree of autonomy.

Said microcontroller may simply be considered as being part of the electronic system of the heater, or as being part or connected to the temperature control system. Hence, in a preferred embodiment of the heater according to the invention, the electronic system comprises a microcontroller which is connected to the communication interface and is part of the temperature control system, the microcontroller (21) preferably being resistant to radiation. Alternatively, the controller is connected to the temperature control system.

In a preferred embodiment of the invention, the communication interface comprises or is a controlled area network “CAN” bus interface. Advantageously, the CAN bus interface enables bidirectional and fast communications, is durable and reliable, can facilitate detection of errors and may enable automatic retransmission of lost messages.

In a second aspect of the invention, a spacecraft is provided, wherein the spacecraft comprises a heater according to the first aspect of the invention. The heater of the spacecraft may be according any of the embodiments mentioned in this text.

Additional advantages and features of the invention will become apparent from the detailed description that follows and will be particularly pointed out in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

To complete the description and in order to provide for a better understanding of the invention, a set of drawings is provided. Said drawings form an integral part of the description and illustrate embodiments of the invention, which should not be interpreted as restricting the scope of the invention, but just as an example of how the invention can be carried out. The drawings comprise the following figures:

Fig. 1 illustrates a schematic diagram of a preferred embodiment of a heater according to the invention.

Fig. 2 illustrates a schematic diagram of an electronic system of a preferred embodiment of a heater according to the invention.

DESCRIPTION OF A WAY OF CARRYING OUT THE INVENTION

The following description is not to be taken in a limiting sense but is given solely for the purpose of describing the broad principles of the invention. Next embodiments of the invention will be described by way of example, with reference to the above-mentioned drawings, showing apparatuses and results according to the invention.

A heater (also referred to as smart heater) is explained next with reference to Fig. 1 . The heater schematically shown in Fig. 1 comprises: a flexible polyimide substrate 1 that comprises a first portion 2 and a second portion 3; an electronic system 4 on the first portion 2; a heating element

5 which is flexible and made of a conductor on the second portion 3; and a temperature sensor

6 on the second portion 3. As shown in Fig. 1 , the electronic system 4 comprises a printed circuit board 7, a communication interface 8, a power input interface 9 and a temperature control system 10 formed on the printed circuit board 7. In the embodiment of Fig. 1 , the temperature control system 10 is programmable, however alternatively it may be consider that the electronic system 4 which comprises the temperature control system 10 is programmable. Also, as shown in Fig. 1 , the temperature control system 10 is connected to the temperature sensor 6 for measuring a temperature at the second portion 3. The temperature sensor 6 may be a thermocouple. Also, the temperature control system 10 of the embodiment of Fig. 1 is electrically connected to the heating element 5 and configured to controllably power the heating element 5 for controlling the temperature at the second portion 3. The communication interface 8 of the embodiment of Fig. 1 is connected to the temperature control system 10 and is configured for enabling a transmission of control signals between the temperature control system 10 and an external system. Said external system may for example be a computer or an electronic system of a spacecraft. The power input interface 9 of the embodiment of Fig. 1 is configured to receive an external electrical power input for powering the temperature control system 10. Said external electrical power input may be come from a power line or a power source which for example may be located in a spacecraft comprising the heater. In the embodiment of Fig. 1 the conductor of the heating element 5 forms on the second portion 3 a pattern which has a meandrous shape/profile and can be considered as being conductive line or circuit electrically connected to the temperature control system 10.

Fig. 2 schematically describes in some detail the electronic system and related interconnections and parts of a preferred embodiment of the invention. The electronic system of the embodiment of FIG. 2 comprises an evaluation board 20 on which there are the communication interface 8 and a radiation resistant microcontroller 21. In the embodiment of Fig. 2 the communication interface 8 is a controlled area network “CAN” bus interface. The microcontroller 21 is connected to the temperature control system 10 of Fig. 2 via two connectors, specifically via an I/O (input output) connector 22 and an ADC connector 23. Alternatively, the microcontroller 21 and the two connectors 22, 23 may be parts of the temperature control system, in which case it would be considered that the connectors connect the microcontroller to the other parts of the temperature control system. As indicated in Fig. 2 the microcontroller may receive feedback, i.e. feedback signals, from the temperature control system, and said feedback may include a signal from a volt sensor (VOLT_SENSOR), a sensor adaptation (SENS_ADAP) signal, a power analogue (PWR_ANA) signal, and/or a PID analog signal (PID_ANA). In the embodiment of Fig.2 the microcontroller 21 is configured to control, via transmitting respective signals (SW0_SELECT, SW1_SELECT) a logic selector 25 (Mux 4:1) of the temperature control system 10. The microcontroller 21 is also configured to select via a control switch 26 between at least two modes (CTRL1_MODE, CTRL2_MODE) of the temperature control system 10, as well as to select (SENS1_SELECT, SENS2_SELECT), via a sensor switch 27, between two sensors of the temperature control system 10. The temperature control system 10 of the embodiment of Fig. 2 comprises said control switch 26 which is on a circuit board 24 of the heater. The control switch 26 is connected to a power control module 28 (PWR control) which is connected to an analogue-to-digital signal converter 29 that is part of a pulse modulation assembly 30 (PHM). The control switch 26 is also connected to a PI controller 31 (“PID temperature” in Fig. 2), which in the embodiment of Fig. 2 is specifically a proportional-integral-derivative (PID) controller. The PI controller 31 (PID controller) is connected to the analogue-to-digital signal converter 29. Also the PI controller 31 is connected, via a signal conditioner 32 and the sensor switch 27, to the temperature sensor 6. The sensor switch 27 is connected to the temperature sensor 6 via the via a sensor signal connector 39. The signal conditioner 32 is further connected to a thermostat 33 which in turn is connected to the logic selector 25 of the pulse modulation assembly 30. The thermostat 33 may be an autonomous thermostat. The analogue-to-digital signal converter 29 is connected via the logic selector 25 to a MOSFET 34 which receives power via a voltage bus connector 35 which acts as a power input interface. The voltage bus connector 35 is connected to a buck converter 36 which in turn is connected for providing power to the power control module 28 and the pulse modulation assembly 30, particularly the analogue-to-digital signal converter 29 and the logic selector 25. The buck converter 36 of the embodiment of Fig. 2 is a 52DC/3.3 DC converter and is further connected to a voltage reference 37 as well as to a volt sensor 38 which may provide a respective signal (VOLT_SENSOR) to the microcontroller 21. The MOSFET 34 is connected to the heating element 5 via a power connector 40 (“power heater connector” in Fig. 2). Hence, in the embodiment of Fig. 2 the MOSFET 34 is configured to power the heating element 5. Moreover, in the embodiment of Fig. 2, the analogue-to-digital signal converter 29 is configured to receive an analogue signal from the PI controller 31 , to convert said analogue signal to a digital signal which is a pulse-width modulation signal, and to provide said digital signal to the gate of the MOSFET 34 for controlling the power provided to the heating element 5 via the MOSFET 34.

Regarding the embodiment of Fig. 2, it can be considered that the output of the PI controller is carried out through an operational amplifier with a configuration of resistors and a capacitor, this output is converted from an analogue signal to PWM and, subsequently, it is injected into the MOSFET gate which will open or close its channel to supply several current values to the heater. Hence, advantageously there is achieved an optimized control stability with very low possible error between the temperature measured by the sensor and the desired temperature. With at least some preferred embodiments of the present invention, and especially with the configuration shown in Fig. 2, advantageously it is achieved that the heater is compact, it has the functionalities of control and sensing, and also has built-in power electronics. The heater may have a single control input, i.e. , the desired temperature setpoint. With said temperature setpoint and a temperature measurement, the PID controller may compute the output value based on an actual error for a proportional part, an error variation rate for a derivative part, and an error accumulation for an integral part. This output value may then be converted to a Pulse Width Modulated (PWM) signal in the power stage that may feed the current to the heating element.

Advantageously, the use of a microcontroller within the heater is compatible with, and enables, the realization of a decentralized control architecture which permits the heater to act as a “micronode” within a system (i.e. within a spacecraft), and facilitates beneficial functionalities. Said functionalities may include direct communication with an on-board processor to receive a temperature setpoint or any application commands (activate-deactivate, status request, special function commands, etc). The use of a microcontroller may also enable the capability to implement local decision algorithms to deal with unexpected events and further improve the failure tolerance of the whole system.

The thermal power generated, i.e. the thermal power released, by the heating element when a voltage V is applied to it, resulting to an electrical current I through the conductor, can be calculated according to Joule’s law: Q=l² *R, where is Q is the heat released per unit time and measured in Watts, I is the electrical current measured in Amperes, and R the electrical resistance measured in Ohms. The resistance of a conductor is a function of its resistivity and dimensions.

As explained further above, for space applications it is preferable and advantageous if the heating element can give a maximum power (Joule power) of 100 W when a 52 V voltage is applied across its length, with the heat flow not exceeding 1 W/cm². Moreover, it is preferable that the operating range of the conductive material (the conductor) is between -150°C and 150°C and the material has the capacity to work in a vacuum. Moreover, the dimensions, and therefore said length of the heating element should preferably be such that the heating element can fit on a square surface the side of which is 10 cm, and hence the area of the square surface, that is the surface of the second portion of the flexible substrate, is 10 cm x 10cm. Said substrate preferably is made of Kapton®. Considering the above, a thermoelectric module software has been used to simulate the Joule effect and calculate heat transfer from a heating element that has a meandrous profile/shape as the one shown in Fig. 1 , and is made of copper, silver or Inconel®. From the simulations and calculations is has been found that, for achieving the aforementioned joule power of 100 W and heat flow of 1 W/cm² under a voltage of 52 V applied to a heating element that fits in a 10 cm x 10cm surface, it has been found that if the conductor (i.e. the pattern/circuit formed by the heating element’s electrical conductor) is Inconel®, then its length and related pattern density on the substrate can be much smaller compared to if the conductor is made of silver or copper (assuming that the thickness of the conductor does not change significantly). Hence, the Inconel® circuit (conductor) is easier to manufacture compared to the silver or copper circuit.

The numerical signs and corresponding components indicated in Fig. 1 and 2, are further listed below:

Polyimide substrate 1

First portion 2

Second portion 3

Electronic system 4

Heating element 5

Temperature sensor 6

Printed circuit board 7 Communication interface 8

Power input interface 9

Temperature control system 10 evaluation board 20 microcontroller 21

I/O connector 22

ADC connector 23 circuit board 24

Logic selector 25

Control switch 26

Sensor switch 27

Power control module 28

Analogue-to-digital signal converter 29

Pulse modulation assembly 30

PI controller 31

Signal conditioner 32

Thermostat 33

MOSFET 34

Voltage bus connector 35

Buck converter 36

Voltage reference 37

Volt sensor 38

Sensor signal connector 39

Power connector 40

In this text, the term “comprises” and its derivations (such as “comprising”, etc.) should not be understood in an excluding sense, that is, these terms should not be interpreted as excluding the possibility that what is described and defined may include further elements, steps, etc.

In the context of the present disclosure, a deviation within reasonable limits from any exact value or values indicated in the present disclosure, should be accepted, because a skilled person in the art will understand that such a deviation from the values indicated is inevitable due to measurement inaccuracies, etc. Unless something else is explicitly stated, all ranges mentioned in this document include the end points of the respective range. Thus, for example, a range indicated using an expression such as “between X and Y” includes X and Y

The invention is obviously not limited to the specific embodiment(s) described herein, but also encompasses any variations that may be considered by any person skilled in the art (for example, as regards the choice of materials, dimensions, components, configuration, etc.), within the general scope of the invention as defined in the claims.

References: Reference 1: Minco: “FLEXIBLE HEATERS DESIGN GUIDE HdgOlb”, 20 December 2016

Claims

1 . A heater for a spacecraft, comprising: a flexible polyimide substrate (1) that comprises a first portion (2) and a second portion (3); an electronic system (4) on the first portion (2); a heating element (5) which is flexible and made of a conductor on the second portion (3); a temperature sensor (6) on the second portion (3); wherein, the electronic system (4) comprises a printed circuit board (7), a communication interface (8), a power input interface (9) and a temperature control system (10) which is programmable and formed on the printed circuit board (7); the temperature control system (10) is connected to the temperature sensor (6) for measuring a temperature at the second portion (3); the temperature control system (10) is also electrically connected to the heating element (5) and configured to controllably power the heating element (5) for controlling the temperature at the second portion (3); the communication interface (8) is connected to the temperature control system (10) and configured to enable a transmission of control signals between the temperature control system (10) and an external system; the power input interface (9) is configured to receive an external electrical power input for powering the temperature control system (10); the conductor is made of an austenitic nickel-chromium-based super alloy; and the heating element (5) is configured to have a watt density of up to 1 W/cm² when a DC voltage of 52 V is applied across the heating element (5).

2. A heater according to claim 1 , wherein the polyimide substrate (1) has a thickness which is not less than 0.1 mm and not more than 0.2 mm.

3. A heater according to claim 1 or claim 2, wherein the polyimide substrate (1) is a Kapton® polyimide substrate.

4. A heater according to any of the preceding claims, wherein the heating element (5) is configured to consume an electrical power of up to 100 W when a DC voltage of 52 V is applied across the heating element (5).

5. A heater according to any of the preceding claims, wherein the conductor is configured for operation in a vacuum and within a temperature range of between -150°C and 150°C.

6. A heater according to any of the preceding claims, wherein the conductor is deposited or printed on the second portion (3) forming thereon a conductive line or circuit electrically connected to the temperature control system (10).

7. A heater according to any of the preceding claims, wherein the conductor is made of an Inconel® alloy.

8. A heater according to any of the preceding claims, wherein the conductor has a thickness of 30 micrometers or less.

9. A heater according to any of the preceding claims, wherein the temperature control system (10) comprises a proportional integral “PI” controller (31) connected to the temperature sensor (6).

10. A heater according to claim 9, wherein: the temperature control system (10) further comprises an analogue-to-digital signal converter (29) which is connected to the PI controller (31) and to a gate of a MOSFET (34) which is connected to the heating element (5). said MOSFET (34) is configured to power the heating element (5); the analogue-to-digital signal converter (29) is configured to receive an analogue signal from the PI controller (31), to convert said analogue signal to a digital signal which is a pulsewidth modulation signal, and to provide said digital signal to the gate of the MOSFET (34) for controlling the powering of the heating element.

11. A heater according to claim 10, wherein the temperature control system (10) further comprises a power control module (28) connected to the analogue-to-digital signal converter (29).

12. A heater according to any of the previous claims, wherein the electronic system (4) comprises a microcontroller (21) which is connected to the communication interface (8) and is part of, or is connected to, the temperature control system (10), the microcontroller (21) preferably being resistant to radiation.

13. A heater according to any of the previous claims, wherein the communication interface (8) comprises a controlled area network “CAN” bus interface.

14. A spacecraft comprising a heater which is according to any of the preceding claims.