Thesis (MscEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The Cape Peninsula University of Technology, in collaboration with Stellenbosch University,
is developing a 3-unit CubeSat for a low earth polar orbit. The two main payloads
are a camera and a radio frequency beacon. This beacon will be used to calibrate the
radar antenna patterns of an antenna of the Hermanus Magnetic Observatory at their
base in Antarctica. This thesis describes the development of an aerodynamic attitude determination
and control system needed to achieve three-axis stabilisation of the satellite
and to perform accurate pointing of the camera.
The satellite structure is designed to utilise aerodynamic means of control. It includes
four feather antennae for passive pitch-yaw stabilisation and two active aerodynamic roll
control paddles. The sensors used are a three-axis magnetometer, ne sun sensor and
nadir sensor. Three attitude determination methods are investigated, namely the Triad,
Rate Kalman Filter and Extended Kalman Filter algorithm. Apart from the aerodynamic
control elements of the satellite, three magnetic torque rods and three nano-reaction
wheels are also included in the design. Three control modes for the satellite are identi ed
and various control methods are investigated for these control modes.
The various attitude determination and control methods are evaluated through simulations
and the results are compared to determine the nal methods to be used by the
satellite. The magnetic Rate Kalman Filter is chosen as attitude determination method
to be used when the satellite is tumbling and a combination of the sun Rate Kalman
Filter and the Triad algorithm is to be used when the satellite experiences low angular
rates. The B-dot and Y-spin controller is chosen for the detumbling control mode, the
aerodynamic and cross-product control method for the three-axis stabilisation control
mode and the quaternion feedback control method for the pointing control mode of the
satellite. The combination of magnetic and aerodynamic control proved to be su cient
for the initial stabilisation of the satellite, but the three nano-reaction wheels are required
for the pointing control of the imaging process. / AFRIKAANSE OPSOMMING: Die Kaapse Skiereiland Universiteit van Tegnologie, in samewerking met die Universiteit
van Stellenbosch, is tans besig met die ontwikkeling van 'n 3-eenheid CubeSat vir 'n
pol^ere, lae aard-wentelbaan. Die twee loonvragte van die satelliet bestaan uit 'n kamera
en 'n radiofrekwensie-baken. Die radiofrekwensie-baken sal gebruik word om 'n antenna
van die Hermanus Magnetiese Observatorium, by hul basis in Antarktika, se radar antenna
patrone te kalibreer. Hierdie tesis beskryf die ontwikkeling van 'n aerodinamiese
ori entasiebepaling en -beheerstelsel wat benodig word om die satelliet in drie asse te
stabiliseer en om die kamera noukeurig te rig.
Die satelliet se struktuur word ontwerp vir aerodinamiese beheer. Dit sluit vier veerantennas
in vir passiewe duik-gier beheer, asook twee aerodynamiese rolbeheer
appies
vir aktiewe beheer. Die sensors wat gebruik word sluit 'n drie-as magnetometer, fyn
sonsensor en nadirsensor in. Drie ori entasiebepalingsmetodes word ondersoek, naamlik
die Drietal, Tempo Kalman lter en die Uitgebreide Kalman lter algoritmes. Buiten die
aerodinamiese beheerelemente van die satelliet, word daar ook drie magneetstange en
drie nano-reaksiewiele ingesluit in die ontwerp. Daar word onderskeid getref tussen drie
beheermodusse en verskeie beheermetodes word ondersoek vir hierdie beheermodusse.
Die verskeie ori entasiebepalings- en ori entasiebeheermetodes word ge evalueer deur middel
van simulasies en die resultate word vergelyk om die beste metodes vir die satelliet se
gebruik te bepaal. Die magnetiese Tempo Kalman lter word gekies as ori entasiebepalingsmetode
vir 'n tuimelende satelliet en die kombinasie van die son Tempo Kalman lter en
Drietal algoritme word gebruik vir 'n satelliet met lae hoektempos. Die B-dot en Y-spin
beheerder word gekies vir die tuimelbeheermodus, die aerodinamiese en kruisproduk beheermetode
vir die drie-as-stabilisasie-beheermodus en die kwaternioon terugvoer beheermetode
vir die rigbeheermodus van die satelliet. Daar word bepaal dat die samespanning
van magnetiese en aerodinamiese beheer voldoende is vir die aanvanklike stabilisering
van die satelliet, maar dat die drie nano-reaksiewiele benodig word om die kamera te rig
tydens die beeldvormingproses.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/19956 |
| Date | 03 1900 |
| Creators | Auret, Jacoba |
| Contributors | Steyn, W. H., Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 97 p. : ill. |
| Rights | Stellenbosch University |
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