Thesis (MScEng)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: The focus of this thesis is on South Africa's first micro space satellite SUNSAT, and the thermal
modelling thereof. Background theory with relevance to thermal management and control of
satellite systems and subsystems is presented. The mission profile and subsystem makeup of
SUNSAT is also briefly discussed, with emphasis placed on the physical structure, possible orbit
paths, internal heat generation, and the environmental heating. The environmental heating on the
satellite surfaces from the direct and reflected earth solar radiation, as well as the earth emitted
infrared radiation, is determined from the developed computer program ORBIT-FLUX. This
program was used in tandem with numerical programs (developed in house), as well as an
outsourced program TAS (Thermal Analysis Systems) to model SUNSAT for two possible orbit
paths. The resistance-capacitance formulation method was used to develop the numerical
programs, which served initially to establish the validity ofTAS.
The first approximated thermal model of SUNSA T's batteries was the 7 lumped-mass model that
focused on the batteries since their overheating is the suspected reason for SUNSA T'S failure to
complete its mission. A numerical program as well as a similar TAS model was developed, and
the results showed correlation to within 3°C. A lumped-mass model of SUNSAT was also
developed, both numerically and using TAS. The models were tested and the results showed that
the temperatures of the models were sensitive to changes in internal heating as well as varying
emissivity and absorptivity. The numerical and TAS lumped-mass model results did not correlate
well, possibly due to the higher number of control volumes used in the TAS lumped-mass model.
The TAS SUNSAT 2 model was developed as advancement on the lumped-mass model. The
higher number of control volumes and the effect of adding solar panels gave a more realistic
model of SUNSA T. The results did not show good correlation with actual SUNSA T temperature
data possibly due to the fact that the solar panels were not mounted on the model body as they
were on SUNSA T; but the TAS SUNSA T 2 model did set the platform for the more advanced
TAS SUNSAT 3 model. This thermal model included the effects of the solar panel mountings,
and had a higher number of control volumes, which gave a better physical representation of the
SUNSAT subsystems. The model was tested for possible orbit paths of SUNSA T. The results
showed excellent correlation to actual SUNSA T data. For the comparison of the TAS SUNSA T
3 model results with data from SUNSAT for July 1999 showed that the SUNSA T battery
temperature was modelled to within 8°C. And for June 2000, this same comparison was to
within 1°C.
A thermal management and control case study was done on a simple system (which included a
cubic box and an internal solid block with heat generation) to illustrate the effects of using
various passive and active thermal control hardware to regulate temperatures. The results showed
that internal surfaces painted black provide for maximum heat sharing, and lowest block
temperatures. The block temperatures were found to be very sensitive to changes in the cube
external optical surface properties. A slight increase in emissivity lowered the block temperature,
while a slight increase in absorptivity increased the block temperature. Heat pipes were also
found to lower the temperatures of the block and immediate subsystems by providing a path of
low thermal resistance to the flow of heat from the block directly to the radiator. The effect of
thermal insulation was also investigated. For the two materials (rubber and plastic) that were
tested, it was noticed that although insulation material does give more thermal control and
predictability over a subsystem by thermally isolating it from its environment, it can cause a
subsystem that has heat generation to become too hot.
Recommendations were made relating to future micro satellite thermal management and control
with regard to; thermal modelling techniques, acquisition of tried software, positioning of
temperature sensors for optimisation of thermal data, and the verification of optical surface
properties by physical measurement. / AFRIKAANSE OPSOMMING: Hierdie tesis fokus op Suid-Afrika se eerste mikro ruimte satelliet, SUNSAT, en die termiese
ontwikkeling daarvan. Agtergrond teorie met betrekking tot die termiese bestuur en kontrole van
die satelliet-sisteme en subsisteme word aangebied. Die missie-profiel en die samestelling van
die subsisteme word ook kortliks bespreek met die klem op die fisiese strukture, moontlike
wentelbane, interne hitte-opwekking, en die omgewingsverhitting. Die omgewingsverhitting op
die oppervlaktes van die satelliet, veroorsaak deur direkte en weerkaatste aardlson bestraling,
sowel as deur infrarooi bestraling afkomstig van die aarde, word bepaal deur die ontwikkelde
rekenaarprogram ORBIT-FLUX. Hierdie program word gebruik in tandem met numeriese
programme (intern ontwikkel), so weI as 'n uitgekontrakteerde program TAS (Termiese Analiese
Sisteme) om SUNS AT vir twee moontlike wentelbane te modelleer. Die weerstandskapasitansie
formuleringsmetode is gebruik om die numeriese programme te ontwikkel. Hierdie
programme is oorspronklik gebruik om die validiteit van TAS vas te stel.
Die eerste benaderde termiese model van SUNSAT se batterye was die 7 gekonsentreerdemassa
model wat gefokus het op die batterye aangesien daar vermoed is dat oorverhitting van die
batterye die rede is waarom SUNSAT nie sy missie voltooi het nie. 'n Numeriese program so
weI as 'n gelyksoortige TAS model is ontwikkel en die resultate korreleer tot binne 3°C. 'n
Gekonsentreerde-massa model van SUNSA T is ook ontwikkel, numeries en met gebruik van
TAS. Die modelle is getoets en die resultate toon dat die temperature van die modelle gevoelig
is vir veranderinge in interne hitte sowel as vir wissellende uitstralingsvermoe en
absorpsievermoe, Die numeriese- en die TAS gekonsentreerde-massa model resultate het nie
goed met mekaar korrelleer nie, moontlik weens die hoe aantal kontrole volumes wat in die TAS
gekonsentreerde-massa model gebruik is. Die TAS SUNSA T 2 model is 'n verdere
ontwikkeling van die gekonsentreerde-massa model. Die hoer aantal kontrole volumes en die
byvoeging van solarpanele het tot gevolg gehad dat hierdie 'n meer realistiese model van
SUNSA T is. Die resultate het nie goed gekorrelleer met die temperatuurdata van die werklike
SUNSAT nie, moontlik weens die feit dat die solarpanele nie op die bakwerk monteer is, soos in
die geval van SUNSA T nie. Nietemin het het die TAS SUNSAT 2 model gelei tot die meer
gevorderde TAS SUNSAT 3 model. Hierdie termiese model het die solarpaneel montuur
ingesluit en het 'n hoer aantal kontrole volumes gehad, wat 'n beter fisiese weergawe van die
SUNSAT subsisteme tot gevolg gehad het. Die model is getoets vir moontlike wentelbane van
SUNSAT. Die resultate het 'n hoe korrellasie getoon met die data van die werklike SUNSAT. 'n
Vergelyking van die TAS SUNSAT 3 model resultate met data van SUNSAT vir Julie 1999 wys dat die SUNSAT battery temperatuur dieselfde is tot binne 8°C. Vergelyk met die resultate vir
Junie 2000 was dit binne 1°C.
'n Termiese bestuurs- en kontrolestudie is gedoen op 'n eenvoudige sisteem (insluitende 'n
kubieke boks en 'n interne soliede blok met hitte opwekking) om die uitwerking van die gebruik
van passiewe en aktiewe termiese kontrole hardeware wat temperature reguleer, te illustreer. Die
resultate toon dat interne oppervlaktes wat swart geverf is, lei tot die maksimum hitte-deling, en
die laagste bloktemperature. Daar is gevind dat bloktemperature baie gevoelig is vir
veranderinge in die eienskappe van die kubus se eksterne optiese oppervlaktes. 'n Effense
vermedering van uitstralingsvermoe verlaag die bloktemperatuur, terwyl 'n effense vermedering
van absorpsievermoe die bloktemperatuur verhoog. Daar is ook gevind dat hittepype die
temperatuur van die blok en onmiddelike subsisteme verlaag deur om 'n pad van lae termiese
weerstand teen die vloei van hitte vanaf die blok, direk na die verkoeler te verskaf. Die
uitwerking van termiese isolasie is ook ondersoek. In die geval van die twee materiale (rubber en
plastiek) wat getoets is, is daar opgemerk dat, alhoewel isolasie materiaal meer termiese beheer
oor die subsisteem en voorspelbaarheid tot gevolg gehad het deurdat die subsisteem termies van
die omgewing isoleer is, kan dit veroorsaak dat die subsisteem te warm word.
Aanbevelings is gemaak met betrekking tot toekomstige mikro satelliet bestuur en kontrole en
wel in verband met die volgende: termiese modelleringstegnieke, die aanskaffing van getoetste
sagteware, die plasing van temperatuut sensors vir die beste termiese data, en die verifikasie van
die eienskappe van optiese oppervlaktes deur fisiese meting.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/49738 |
| Date | 12 1900 |
| Creators | Van Wyk, Peter Arnold |
| Contributors | Dobson, R. T., Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 1 v. (various foliations) : ill. |
| Rights | Stellenbosch University |
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