Sun sensor

Main Assumptions

This sun sensor device was dedicate to students’ space missions and small satellites. According to this the main assumptions for this kind of sun sensor were:

• cheap and easily available materials,
• high level of accuracy, as comparing to other available sun sensors,
• high level of reliability,
• simple construction.

Sun sensor design Design concept

The main design assumption was that the simplest solution is the most reliable and efficient. Relatively cheap and market available materials used in sun sensors are photovoltaic cells and the most simple construction is the analog sun sensor. External view of sun sensor is shown in Fig. 1. There are four cells in two groups which are perpendicular to each other that gives the two-axis arrangement. Every cell is inclined by φ = 45 degrees to sensor’s xy plane (Fig. 3). At the same time the sun’s rays fall on each cell at the different angle so one can determine position of the Sun (Fig. 2). The data in form of four different currents are sent to processor, where the values representing position of the Sun relative to the sun sensor coordinate system are calculated.

  Sun sensor accuracy

The main factors affecting the sun sensor accuracy are:

1. Size of solar panels, 2. Parameter k accuracy, 3. AC/DC converter resolution, 4. Temperature. Sun sensor advantages

All previously established requirements have been met. The sensor has a simple construction, the materials are cheap and commonly available. There was proved that the sensor accuracy can rich the 0,1 degree, that means that this sensor accuracy is at the same level as commercial one.

A pair of recesses, in which the cell are located, is screened on all sides by the sensor casing. This will protect the cells against sun glare from other components of the satellite. This is necessary in order to eliminate erroneous readings of the sun vector position. There can be many technical solutions of the proposed concept. Starting from the setting of pairs of cells to the selection of materials used. The proposed approach includes following assumptions:

• Cell pairs have to be perpendicular to each other,
• A single pair must be set at an angle to the plane of the sensor to form a cavity (the angle φ, defining the slope of the horizontal plane of the cell sensor can be freely determined in the process of designing a specific sensor of this type),
• The calculations were performed for light-sensitive material which are solar cells, but optionally digital CCD or CMOS matrixes can also be used.

References

[1] Klugmann-Radziemska Ewa: Fotowoltaika: w teorii i praktyce, 2011, BTC, pages 30-47,

[2] Sidi Marcel J.: Spacecraft Dynamics and Control: A Practical Engineering Approach, 1997, Cambridge University Press, pages 345-353,

[3] Uvarova Inna: Accuracy evaluation of the satellite position using different types of Sun sensors, 2011, Bachelor Thesis,

[4] Wertz James R., Larson Wiley J. (editors): Space Mission Analysis and Design, 2005, Kluwer Academic Publishers, pages 155-272.