Autonomous Attitude Determination of a Lunar Penetrator using Sun Sensors
- Paper number
IAC-08.B4.2.11
- Author
Dr. Vaios Lappas, Surrey Space Centre, University of Surrey, United Kingdom
- Coauthor
Ms. Aarthy Badrakalimuthu, Surrey Space Centre, University of Surrey, United Kingdom
- Coauthor
Prof. Jozef van der Ha, Kyushu University, Japan
- Year
2008
- Abstract
Lunar Penetrators are currently being designed for lunar science missions. A penetrator is essentially a missile carrying sensors or miniature instruments that will survive a hard collision with a lunar or planetary surface and then transmit signals from the crash site transferring science data from its onboard instruments. They are designed to be carried on a lunar science orbiter and deployed from a low lunar orbit. Accurate instantaneous orientation of the penetrator is required to ensure that the lunar penetrator lands with the desired angle of attack. The aim of this paper is to check the feasibility of using the ‘Two Sun Cones’ attitude determination algorithm for determining the attitude of a lunar penetrator. The ‘Two Sun Cones’ algorithm is an attractive option because it is a robust algorithm that makes use of only the Sun sensor measurements at two small time intervals to calculate the attitude vector of the spacecraft. This paper tries to assess how accurately the spin axis orientation of a lunar penetrator can be estimated while using the Two Sun Cones method. Furthermore an investigation is presented that analyses what is the minimum time interval required between the two input Sun angles to get the required attitude accuracy. Using this algorithm the processing of data to obtain the orientation of the penetrator can be done autonomously. Simulations are done using MATLAB to model the operations of a Sun sensor and also the Two Sun Cones algorithm. The Sun angle is computed for about 2 hours to upto 8 hours. The time interval between the collected Sun angles is varied from 5 minutes progressively to about 20 minutes, to check the variations accuracy of the attitude vector. Also using the developed model the accuracy is checked for various orientations of the lunar penetrator. The simulations illustrates that the accuracy improves as the interval between the Sun angle measurements increases (e.g. for a Right ascension angle of 127º and declination angle of 73º , simulations showed the error in declination for 5 minute interval was 0.016º and for 20 minute interval was 0.001º. Similarly the error in right ascension for 5 minute interval was 0.014º and for 20 minute interval was 0.008º. ). Also the initial simulations show that error in the attitude vector orientation achieved is quite small, so there is a possibility for using this Two Sun Cones algorithm for attitude determination of lunar penetrators.
- Abstract document
- Manuscript document
IAC-08.B4.2.11.pdf (🔒 authorized access only).
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