Thermal mathematical model and computational study of the characteristics of a Local Thermal Control System for a spacecraft based on a current-controlled PTC heater

Аuthors

Kotlyarov E. Y.^*, Leun E. V.^**, Luzhenkov V. V., Tulin D. V., Mozgovoy U. V., Finchenko V. S.

Lavochkin Research and Production Association, NPO Lavochkin, 24, Leningradskay str., Khimki, Moscow region, 141400, Russia

*e-mail: evgeny-1@list.ru
**e-mail: leunev@laspace.ru

Abstract

The article employs a relatively simple non-stationary thermal mathematical model (TMM) to simulate and analyze, based on the results of computational experiments, the operation of two types of electric heaters. These heaters alternately maintain the thermal regime of equipment separately located onboard an automatic spacecraft (AS). As a result of a comparative analysis of the activation dynamics and temperature changes of resistive and positive temperature coefficient (PTC) electric heaters (REH and PTCH) operating as part of the AS, the unique and/or useful properties of the PTCH that may be of interest for use in local thermal control systems are demonstrated. During the application of the TMM, the use of a PWM controller modulating signals for the pulse-width control of the heaters' power was investigated. Furthermore, the feedback current control of the PTCH was reproduced, which visually confirms its potential for use as a sensing element. The development of hardware reliably operating in outer space represents a complex interdisciplinary engineering task. A special role in its solution is assigned to systems and means for maintaining the thermal regime of equipment and the structure of space-grade products. It is known that overheating or overcooling of equipment are often the ultimate causes of the complete or partial loss of Automatic Spacecraft (AS) operating under space environmental factors, even if the initial damaging impact on the craft or its equipment was unrelated to the thermal regime. Any AS, from the earliest models to modern designs, is equipped with local thermal control systems. These systems ensure the thermal regime of equipment that is separately located, when for a number of reasons such equipment cannot be placed in the instrument compartment or on specially thermostated platforms. This necessity leads to equipping the equipment within the spacecraft with local thermal control means (in situ, locally), such as a heater, temperature sensor, and unregulated radiative heat exchanger, installed directly at the thermal control site – for example, on a fuel tank wall, next to an electronics unit, pyrovalve, navigation instrument, etc. The control schemes and algorithms for the Local Thermal Control Systems (LTCS) based on resistive heaters, applied in established practice, are well-developed. However, these developments are also applicable to PTC heaters (PTCH) operating in the temperature range below the active transition zone, i.e., below the Tref/Rref value. For such PTCH, the problem of cold start will not arise, and the PTCH itself, more precisely its heating element (HE), cannot burn out in off-nominal situations that would be associated with inadequate heat removal from the heater (for example, if the control temperature sensor becomes detached or the heater's contact with the mounting location deteriorates). The use of a PWM controller allows for a significant reduction in oscillations affecting the quality of temperature regulation. This effect can be achieved regardless of the type of heater used: REH or PTCH. The use of PWM controllers in spacecraft LTCS has its supporters and opponents. However, within AS equipment, the problems associated with using PWM can be considered on par with the use of other electronics. The thermal inertia of LTCS components allows for the use of pulses with a frequency on the order of 1 Hz and lower, which “localizes the discussion” on the electromagnetic noise of PWM. The use of PTC heaters in the transition (temperature) zone, combined with PWM as a heater for the Local Thermal Control System, holds certain promise for providing an actively regulated thermal regime for the peripheral equipment of an Automatic Spacecraft (AS). This is because such a solution would allow for the elimination of measurement cables and temperature sensors. The self-regulating capability of the PTC heater, combined with controlled regulation, could also be in demand. Finally, three self-sufficient conditions that can prioritize the use of PTC heaters (PTCH) over traditionally used resistive heaters (REH) can be formulated: – for the specific LTCS being deve-loped, there exist both nominal and off-nominal scenarios of the planned heater's operation, which are characterized by an objectively justified risk of its overheating and failure; – there is no possibility, or it is not feasible, to run a measurement cable with a control temperature sensor to the location of the thermostated equipment; – there is no possibility to use a controller (due to a shortage of controlled channels) and, simultaneously, there is no need to maintain the object's temperature with high accuracy. That is, the self-regulating capability of the PTC heater can be utilized here. The materials of this research can be useful for developers of LTCS for prospective automatic spacecraft.

Keywords:

thermal mathematical model, computational experiment, PTC heater, temperature control, spacecraft onboard equipment, thermal mode

References

1. Efanov VV, Finchenko VS (ed.). Sistemy obespecheniya teplovykh rezhimov avtomaticheskikh mezhplanetnykh stan-tsii. Khimki: NPO Lavochkina; 2018. 400 p. (In Russ.).

2. Gilmore DG (2nd ed.). Spacecraft thermal control handbook. The Aerospace Corporation. 2002;1:836.

3. Rzhanov AV. Barium titanate is a new ferroelectric. Uspe-khi fizicheskikh nauk. 1949;38(4):461–489. (In Russ.).

4. Takaya Watanabe.  Hyperthermia operation of intelligent medicine to eliminate cancer. World Technology Instrument Co. 2014.

5. Kotlyarov E.Yu., Tulin D.V., Finchenko V.S. Analysis of the applicability of heaters with a positive temperature coefficient of resistance in local systems for ensuring the thermal regime of spacecraft equipment units. TPT. 2020;12(2):88–97. (In Russ.).

6. Technical specification: PTC thermistors as heating elements. Disk shaped. 12 V. Series/Type: B59060. January 2016. EPCOS AG is a TDK Group Company. 9 p.

7. Technical specification: PTC Thermistors. EPCOS AG 2009. Corporate Center. P.O.Box 80 17 09. 81617 Munich. Germany. 28 р.

8. Kotlyarov EYu, Kochetkov AYu, Zaitsev AN. The results of rapid tests of an industrial posistor heater in va-cuum conditions. Trudy XXVII Nauchno-tekhnich. konferentsii «Vakuumnaya nauka i tekhnika». Sudak. 14–19 september. pp. 179–186. 2020. (In Russ.).

9. Kozlov V.G., Alekseev V.P., Ozerkin D.V. Microthermostat with a posistor heater. Patent RU 2164709 G05D 23/24, 27.03.2001. (In Russ.).