A sun sensor is a navigational instrument used by

spacecraft A spacecraft is a vehicle or machine designed to spaceflight, fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including Telecommunications, communications, Earth observation satellite, Earth ...

to detect the position of the sun. Sun sensors are used for

attitude control Attitude control is the process of controlling the orientation of an aerospace vehicle with respect to an inertial frame of reference or another entity such as the celestial sphere, certain fields, and nearby objects, etc. Controlling vehicle ...

, solar array pointing, gyro updating, and

fail-safe In engineering, a fail-safe is a design feature or practice that in the event of a specific type of failure, inherently responds in a way that will cause minimal or no harm to other equipment, to the environment or to people. Unlike inherent safe ...

recovery. In addition to spacecraft, sun sensors find use in ground-based

weather station A weather station is a facility, either on land or sea, with instruments and equipment for measuring atmospheric conditions to provide information for weather forecasts and to study the weather and climate. The measurements taken include tempera ...

s and sun-tracking systems, and aerial vehicles including

balloon A balloon is a flexible bag that can be inflated with a gas, such as helium, hydrogen, nitrous oxide, oxygen, and air. For special tasks, balloons can be filled with smoke, liquid water, granular media (e.g. sand, flour or rice), or li ...

s and UAVs.

Mechanism

There are various types of sun sensors, which differ in their technology and performance characteristics. Sun presence sensors provide a

binary Binary may refer to: Science and technology Mathematics * Binary number, a representation of numbers using only two digits (0 and 1) * Binary function, a function that takes two arguments * Binary operation, a mathematical operation that ta ...

output, indicating when the sun is within the sensor's

field of view The field of view (FoV) is the extent of the observable world that is seen at any given moment. In the case of optical instruments or sensors it is a solid angle through which a detector is sensitive to electromagnetic radiation. Humans a ...

Analog Analog or analogue may refer to: Computing and electronics * Analog signal, in which information is encoded in a continuous variable ** Analog device, an apparatus that operates on analog signals *** Analog electronics, circuits which use analo ...

and

digital Digital usually refers to something using discrete digits, often binary digits. Technology and computing Hardware *Digital electronics, electronic circuits which operate using digital signals **Digital camera, which captures and stores digital i ...

sun sensors, in contrast, indicate the angle of the sun by continuous and

discrete signal In mathematical dynamics, discrete time and continuous time are two alternative frameworks within which variables that evolve over time are modeled. Discrete time Discrete time views values of variables as occurring at distinct, separate "po ...

outputs, respectively. In typical sun sensors, a thin slit at the top of a rectangular chamber allows a line of light to fall on an array of

photodetector Photodetectors, also called photosensors, are sensors of light or other electromagnetic radiation. There is a wide variety of photodetectors which may be classified by mechanism of detection, such as photoelectric or photochemical effects, or by ...

cells at the bottom of the chamber. A voltage is induced in these cells, which is registered electronically. By orienting two sensors perpendicular to each other, the direction of the sun can be fully determined. Often, multiple sensors will share processing electronics.

Criteria

There are a number of design and performance criteria which dictate the selection of a sun sensor model: *

Field of view The field of view (FoV) is the extent of the observable world that is seen at any given moment. In the case of optical instruments or sensors it is a solid angle through which a detector is sensitive to electromagnetic radiation. Humans a ...

Angular resolution Angular resolution describes the ability of any image-forming device such as an Optical telescope, optical or radio telescope, a microscope, a camera, or an Human eye, eye, to distinguish small details of an object, thereby making it a major det ...

Accuracy Accuracy and precision are two measures of '' observational error''. ''Accuracy'' is how close a given set of measurements (observations or readings) are to their '' true value'', while ''precision'' is how close the measurements are to each ot ...

and

stability Stability may refer to: Mathematics * Stability theory, the study of the stability of solutions to differential equations and dynamical systems ** Asymptotic stability ** Linear stability ** Lyapunov stability ** Orbital stability ** Structural st ...

Mass Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different element ...

and

volume Volume is a measure of occupied three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch). Th ...

*Input voltage and power *Output characteristics (including electrical characteristics, update frequency,

nonlinearity In mathematics and science, a nonlinear system is a system in which the change of the output is not proportional to the change of the input. Nonlinear problems are of interest to engineers, biologists, physicists, mathematicians, and many other ...

, and encoding) *Durability (including

radiation hardening Radiation hardening is the process of making electronic components and circuits resistant to damage or malfunction caused by high levels of ionizing radiation ( particle radiation and high-energy electromagnetic radiation), especially for envir ...

and tolerance to

vibration Vibration is a mechanical phenomenon whereby oscillations occur about an equilibrium point. The word comes from Latin ''vibrationem'' ("shaking, brandishing"). The oscillations may be periodic, such as the motion of a pendulum—or random, suc ...

and thermal cycling)

References

{{Reflist, refs= {{cite web, title=Digital Sun Sensors (DSS), url=http://www.adcole.com/aerospace/digital-sun-sensors/, publisher=Adcole Corporation, accessdate=11 March 2016 {{cite web, title=High Accuracy Fine Sun Sensors, url=http://www.adcole.com/aerospace/high-accuracy-fine-sun-sensors/, publisher=Adcole Corporation, accessdate=11 March 2016 {{cite web, title=LIASS: LInear Accurate Sun Sensor, url=http://www.space-airbusds.com/media/document/gnc_1_liass_2015-v_std_b-def.pdf, publisher=Airbus Defense & Space, accessdate=11 March 2016 {{cite web, title=What is a Sun Sensor?, date = 17 June 2013, url=http://www.azosensors.com/Article.aspx?ArticleID=223, publisher=AZO Sensors, accessdate=11 March 2016 Spacecraft attitude control Astrodynamics Orbits Spaceflight concepts Navigational equipment Celestial navigation

Mechanism

Criteria

See also

References