A thermal simulation tool for CubeSats for dynamic in-orbit scenarios, verified with flight data from the nSight-1 mission

Kearney, Mike-Alec (2020-03)

Thesis (MEng)--Stellenbosch University, 2020.

Thesis

ENGLISH ABSTRACT: Thermal analysis is one of the aspects of designing CubeSats that has historically received less attention than more directly mission critical aspects such as power and communications budgets, and attitude control performance. The reasons for this neglect are partly due to the complexities of doing detailed thermal analyses, and partly because of the high cost of thermal simulation software that is tailored for the unique environment of space. Typically, CubeSat teams will do simplified steady state thermal analyses for a particular satellite orientation and particular orbit. However, these analyses generally only account for the original orbit a satellite is launched in, which proves problematic. Given the fact that much of these orbits are not Sun-synchronous, and that in Low Earth Orbit (LEO) these orbits decay rapidly, these simplified analyses are only valid for a small portion of the satellite’s mission lifetime. With this in mind, this study created a method to integrate a lumped-capacitance thermal model with a high accuracy Attitude Determination and Control System (ADCS) simulation program in order to simulate the temperature of a CubeSat for dynamic orientation and orbital scenarios. To supplement this simulation, a software tool was created to simplify the process of creating a numerical model of the surfaces of a satellite, which includes geometry, links between the surfaces and lumped thermal nodes, as well as the thermal properties of the surfaces. The study discusses the key elements of the thermal environment in Space such as direct sunlight, reflected sunlight off of the Earth (albedo), Earth infrared (IR), as well as radiation to deep space. Ray tracing capability of the ADCS program is used to simulate shadowing of parts of the satellite by deployable solar panels. A method of calculating the view factor (VF) between surfaces of the satellite and the Earth is also discussed, since this has a significant effect on the heat transferred to a satellite with varying orientation. The validity of the simulation was tested using a thermal model of the South African built satellite nSight-1, by comparing simulation outputs with in-orbit temperature measurements. The simulation tool was used to analyse the temperature of the nSight-1 subsystems for varying orbits, in order to identify problematic cases where subsystems exceed their maximum/minimum operational temperatures. Suggestions were then made for improvements to the thermal design in order to manage these problematic temperatures, and the suggested changes were simulated to verify their effects.

AFRIKAANSE OPSOMMING: Termiese analise is een van die aspekte van die ontwerp van CubeSats wat histories minder aandag geniet as meer direkte, missie-kritieke aspekte, soos krag- en komunikasie begrotings en orientasie beheer. Die redes hiervoor is deels as gevolg van die kompleksiteit van gedetailleerde termiese ontledings, en deels as gevolg van die hoë koste van sagteware vir termiese simulasie wat spesifiek aangepas is vir die unieke ruimte-omgewing. Tipies doen CubeSat-spanne vereenvoudigde termiese ontledings vir 'n spesifieke satellietoriëntasie en 'n spesifieke wentelbaan. Hierdie ontledings word gewoonlik gedoen vir die oorspronklike wentelbaan waarin 'n satelliet gelanseer word. Aangesien baie van hierdie wentelbane nie son-sinkroon is nie, en lae-aard-wentelbane wentelbane vinnig verander as gevolg van aerodinamiese wrywing, is hierdie ontledings slegs geldig vir 'n klein deel van die satelliet leeftyd. In hierdie studie is 'n metode geskep om 'n termiese model met 'n hoë akkuraatheid (ADCS) simulasieprogram te integreer om die temperatuur van 'n CubeSat te simuleer vir dinamiese oriëntasie- en wentelbaan scenario's. Om hierdie simulasie aan te vul, is 'n sagteware-instrument geskep om die proses om 'n numeriese model vir die oppervlaktes van 'n satelliet te skep, te vereenvoudig. Die program neem in ag meetkunde, skakels tussen die oppervlaktes en gekoppelde termiese elemente, asook die termiese eienskappe van die oppervlaktes. Die studie bespreek die sleutelelemente van die termiese omgewing in die ruimte, soos direkte sonlig, gereflekteerde sonlig van die Aarde (albedo), Aarde geradieerde infrarooi energie, sowel as straling na diep ruimte. Die “ray-tracing” vermoë van die ADCS-program word gebruik om die skadu van dele van die satelliet deur ontplooibare sonpanele te simuleer. 'n Metode om die sieningsfaktor tussen die oppervlaktes van die satelliet en die Aarde te bereken, word ook bespreek, aangesien dit 'n beduidende invloed het op die hitte wat na verskillende oppervlaktes van 'n satelliet oorgedra word. Die simulasie is getoets met 'n termiese model van 'n Suid-Afrikaans-geboude satelliet nSight-1, deur simulasie-uitsette met in-wentelbaan temperatuurmetings te vergelyk. Die simulasie-instrument word gebruik om die temperatuur van die nSight-1-substelsels vir verskillende wentelbane te bestudeer om problematiese gevalle te identifiseer waar substelsels hul maksimum / minimum operasionele temperatuur oorskry. Voorstelle word gemaak vir verbeteringe aan die termiese ontwerp om hierdie problematiese temperature te bestuur, en die voorgestelde veranderings word gesimuleer om die effek daarvan te verifieer.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/108309
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