RU211199U1 - Self-regulating block with a heating element for thermal stabilization of the spacecraft instrument compartment - Google Patents

Abstract

The utility model relates to space technology, specifically to systems for ensuring the thermal regime of a spacecraft. The technical result is an increase in the reliability of the thermal stabilization system of the instrument compartment of the spacecraft. The technical solution consists in refusing to use the central control unit for heaters in the thermal stabilization system of the instrument compartment of the spacecraft. In the proposed system, temperature sensors and the control unit are replaced by self-regulating heating elements. Each such element is configured to maintain a certain temperature and combines the functions of a heater, a temperature sensor and a regulator. In a self-regulating heating element, heat generation is inversely proportional to the difference between the set temperature and the temperature of the heat-generating surface of the heating element. This effect is achieved due to the interaction of the electrical circuit and certain thermal properties of the heating element. The electrical circuit of this element includes two transistors, one of which (control) operates in a temperature-sensitive mode and controls the other transistor (heat-generating) via an electrical circuit, operating in the mode of an analog amplifier or an electronic key. The control is carried out according to the thermal feedback between the transistors, which occurs due to the thermal connection between them through the heat-conducting and heat-releasing base of the heating element.

Description

The field of technology to which the proposed technical solution belongs

The utility model relates to space technology, specifically to systems for ensuring the thermal regime of a spacecraft.

Description of the prior art in the field

At present, there is a well-established scheme for ensuring the thermal regime of spacecraft. It is based on the radiation of the heat flow generated inside the apparatus by radiators-emitters placed on the surface of the spacecraft. Such a scheme assumes the presence of emitter radiators in the spacecraft; heat pipes, heaters, temperature sensors and heater control unit (patent RU 2603690). These elements perform the following functions. Heat pipes (usually heat pipes) ensure the transfer of heat flow from heat sources inside the spacecraft (electronic units) to heat sinks. The heaters provide thermal stabilization of the spacecraft structure, compensating for the non-uniformity of the heat flow generated by the heat sources or the non-uniformity of the external heat flow incident on the radiators-emitters. The control unit regulates the power of the heaters according to the temperature sensors. In a thermal control system, there is usually only one heater control device. This device is practically the only electronic unit in the spacecraft thermal stabilization system, equipped with complex electronic components. As an example of such a device, we can consider a heater control device (patent RU 2571728 published on December 200, 2015 in Bull. No. 35). Since electronic components are elements that significantly reduce their reliability in space conditions, the only complex electronic heater control device in the structure of the spacecraft thermal stabilization system is one of the most unreliable elements of this system.

Purpose of the proposed solution

The purpose of the proposed solution is to increase the reliability of the thermal stabilization system of the instrument compartment of the spacecraft by excluding the centralized heater control device from its composition.

Description of the prototype

The prototype of the proposed solution is the thermal stabilization system of the instrument compartment of the spacecraft (patent RU No. 2603690 publ. 27.11.2016 in Bull. No. 33). This device includes a system for removing heat from fuel elements and a system for monitoring and adjusting the temperature. The heat removal system consists of a radiator-emitter and heat pipes connecting the heat-generating elements and the radiator-emitter. The temperature control and adjustment system includes temperature sensors, heaters, and a control unit that regulates the power of the heaters according to the readings of the temperature sensors. One of the significant drawbacks of this system is the critical dependence of its performance on the health of the heater control unit. Based on the complexity of such an electronic unit (see, for example, patent RU No. 2571728, published on December 20, 2015 in Bull. No. 35 - “Control device for heaters of spacecraft equipment”) and an increase in the probability of failure of electronic components under external influences of space factors on them space, this unit is the weakest link in the structure of the reliability of the thermal stabilization system of the instrument compartment of the spacecraft. It should also be noted the increased cost of such a unit due to the use of electronic components for space use, the cost of which is many times higher than the cost of non-space components, and the fact that a possible solution for duplicating the systems of this unit leads to an increase in the mass, dimensions and cost of the device.

The essence of the proposed technical solution

A decentralized system for thermal stabilization of the instrument compartment of a spacecraft is proposed, in one of the parts of which, namely, in the temperature control and regulation system, there is no central heater control unit. In such a temperature control and regulation system, the heaters, temperature sensors and control unit are replaced by self-regulating heating elements. Each such element is configured to maintain a certain temperature (setpoint) and combines the functions of a heater, a temperature sensor and a regulator. In such a self-regulating heating element, the heat generation is inversely proportional to the difference between the set temperature and the temperature of the heat generating surface of the heating element. This effect is achieved due to the interaction of the electrical circuit and certain thermal properties of the heating element. The electrical circuit of this element includes two transistors, one of which (control) operates in a temperature-sensitive mode and controls the other transistor (heat-generating) via an electrical circuit, operating in the mode of an analog amplifier or an electronic key. The control is carried out according to the thermal feedback between the transistors, which occurs due to the provision of thermal connection between them through the heat-conducting and heat-releasing base of the heating element.

Description in static

The proposed design of the thermal stabilization of the instrument compartment of the spacecraft is a classic combination of two systems - a system for removing heat from fuel elements and a temperature control system.

The system for removing heat from fuel elements can have a different design, for example, the same design as in the prototype, in which this system is a series-connected fuel elements, heat pipes and radiator-emitter. Also, the functions of this system can be performed by the housing elements of the compartment (as a heat conductor), connecting the fuel elements and the seats of the compartment (as a heat sink).

The temperature control system is a set of self-regulating heating elements placed in the design areas of the instrument compartment of the spacecraft, where it is required to maintain the temperature at a certain level. Usually these places coincide with the seats of the fuel elements of the instrument compartment. All self-regulating heating elements have the same electrical and thermal circuits. The necessary and sufficient version of the proposed technical solution is shown in Figure 1, which shows a circuit diagram of a self-regulating heating element with indication of thermal connections and elements.

The heating element circuit includes: a heat-conducting base, three transistors - VT1, VT2, VT3 and seven electrical resistances - R1-R6, Rsh. The circuit must be connected to a power supply +/- U pit and include a reference voltage source + U stab.

There are thermal and electrical connections between the circuit elements.

Thermal connections are contacts with low thermal resistance between the heat-conducting base and transistors VT1 and VT3. Such a connection leads to a thermal feedback between these transistors through a heat-conducting base.

Electrical connections are implemented as follows.

The collector of the first n-p-n transistor VT1, which acts as a temperature-sensitive element, is connected to the gate of the n-channel field-effect transistor VT3, which acts as a heater.

The collector of the second n-p-n transistor VT2 is connected to the gate of the field-effect transistor VT3, which provides a limitation on the current flowing through the field-effect transistor VT3 by removing the voltage from the shunt Rsh connected to the source of the transistor VT3, and applying it to the base VT2.

The electrical resistances R1 and R2 provide the setting of the thermal stabilization temperature of the heat-conducting base. The resistances R3-R6 match the operating modes of the transistors. Resistors R3-R6 are necessary to match the entire circuit.

Description in dynamics

Each self-regulating heating element works as an analog P-regulator (proportional regulator), which, depending on the temperature deviation from the setpoint (the temperature level that must be maintained on the heat-conducting base), regulates the power of the heating element.

An increase in the temperature of the heat-conducting base and the associated transistor VT1 leads to an increase in the collector current of the transistor VT1 and, accordingly, to a decrease in the voltage at the gate of VT3. Lowering the voltage at the VT3 gate (approaching it to the “-Upit” potential) leads to its closure and a decrease in the flowing current, i.e. thermal power allocated by VT3 to the heat-conducting base. The heat-conducting base cools down together with VT3, which entails a decrease in temperature at VT1 as well. The reverse process occurs - lowering the temperature of the heat-conducting base and the transistor VT1 associated with it leads to a decrease in the current through the transistor. Accordingly, the potential at the VT3 gate rises, which opens it slightly and increases the current through VT3. The thermal power of the transistor VT3 is transferred to a heat-conducting base. To limit the current through VT3 and protect it from overheating (limiting the thermal power of VT3), transistor VT2 is used, which opens when the voltage at the base increases, and the voltage at the base, in turn, is determined by the current through the shunt Rsh and transistor VT3.

Thus, the circuit operates as a classical P-regulator, the heat release of which is inversely proportional to the temperature over a certain interval.

Outside this interval, the maximum thermal power (current through VT3) is limited by VT2 and Rsh and is the specified Pmax, and the minimum power Pmin is determined by the current consumption of the circuit through R4, the current of the closed transistor VT3, as well as the voltage generation circuit + Ustab.

The graph of the released power from the temperature of the seat is shown in Figure 2.

The coefficient of the P-regulator determines the slope of the curve, it is determined in the circuit by the values of the elements R1, R2, R3 and the gain of the transistor VT1. With an increase in the coefficient, the P-controller approaches the relay control mode.

An example of the implementation of the proposed device.

A prototype of the device was made and experimental studies of its characteristics were carried out. General view of the prototype with attachment to the heated surface - in Figure 3.

Tests were carried out on two samples of the product. The tests were carried out in a climatic chamber. The products were fixed on plates - objects of regulation, as shown in Figure 4, and placed in a chamber. The purpose of the test is to test the ability of the product to control the temperature of an object (plate) under various thermal conditions and over a range of temperatures. Heat exchange with the plate was provided by forced air blowing at different temperatures. The temperatures of the plates were controlled by additional sensors and recorded by external measuring equipment. In the first cycle, the temperature in the chamber decreased, the result is shown in Figure 4. In the second cycle, the temperature in the chamber increased, the result is shown in Figure 5. The graphs show how the current (power) in the controller power circuit increases with decreasing temperature, and with increasing temperature the current decreases. Thus, the functioning of the device in the specified parameters is experimentally confirmed.

Achievable beneficial effect from the application.

The use of a decentralized thermal stabilization system for the instrument compartment of a spacecraft will significantly increase the reliability and reduce the cost of the entire system for ensuring its thermal regime by eliminating a complex and expensive element from its composition - a heater control unit. It should also be noted that the use of the proposed standard self-regulating heaters will improve the unification of spacecraft thermal control systems.

Claims (1)

Self-regulating block with a heating element for thermal stabilization of the instrument compartment of the spacecraft, which is placed with thermal contact in the thermally stabilized places of the instrument compartment, while the self-regulating block contains two n-p-n transistors and one n-channel MOS transistor, which is a heater, the first n-p-n transistor and The n-channel transistor is installed with thermal contact with a common heat-conducting base of the block, the gate of the n-channel transistor is connected to the collectors of two n-p-n transistors, and the source of the n-channel transistor is connected through matching resistances to the emitter of the first n-p-n transistor installed on the heat-conducting base and to the base of the second n-p-n transistor, the positive power bus is connected to the drain of the n-channel transistor, and through the matching resistance - to the gate of the n-channel transistor and to the collectors of two n-p-n transistors, the negative power bus is connected to the emitter of the second uninstalled n-p-n transistor on a thermally conductive base, through a matching resistance - to the emitter of the first n-p-n transistor and through a shunt resistance - to the source of the n-channel transistor, and also through a tunable resistance - to the base of the first n-p-n transistor, the positive reference voltage line is connected to the base through a tunable resistance installed on the heat-conducting base of the first n-p-n transistor.

Images