Sensors

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Sensors

Satellites and space probes are launched on their missions to a wide variety of destinations. Some satellites are sent into Earth orbit to look down at Earth's surface or atmosphere; others aim outward, to study the Moon, other planets, or the universe itself. Probes are sent beyond Earth orbit to pass near, land on, or orbit other planets or the Moon. No matter what their eventual destination, the primary objective of sending these craft into space is to gather information and relay it back to Earth in some direct or indirect way. To collect information, these space vehicles must carry with them some means of collecting and distinguishing this data. Sensors are one type of instrument that can collect information.

Sensors, as applied to spacecraft, are instruments and devices that can detect alterations or variations in the space environment and send electrical, radio, or other types of signals or transmissions back to a main collection or recording device. Such a device can be aboard the spacecraft itself, on another spacecraft nearby or close by, or at a receiving station or receptacle on Earth, such as a radio antenna.

While some sensors gather data remotely about the conditions found in space or on another planetary body, other types of sensors can be used by space vehicles to make determinations about the position or location of the vehicle itself or its condition while in flight. Such sensors, onboard the space vehicle and active during its flight, are essential elements in controlling the craft or flying it to a specific destination in space.

In their roles in remotely sensing the space environment, sensors can be of many different types and collect many different types of information. Radiometers aboard a probe can gather data on the temperature of a planet or Moon's surface, or the temperature of the gases contained in an atmosphere. A spectrometer can break down the composition of planetary gases or surface features across the visible or invisible spectrum of light. These instruments can also gather information on the environmental or weather conditions where they are located. Small radar units emitting radar signals can gather information about a planet's surface composition based on the radar's "return," or bounce, from the surface up to the sensor's instrument.

Satellite sensors may also include devices such as a thermocouple. This instrument, made from different types of metals, produces electrical voltage that can vary depending upon the temperature of the material through which the electrical current passes. In this way the device can chart changes in temperatures over a distance or across an altitude.

Sensors used to control satellites can include gyroscopes for attitude control or navigation equipment that can plot the craft's location based on sightings of stars and other space objects whose locations are fixed. Sensors are an essential part of a spacecraft, and they can contribute much to the mission and to the accuracy of the spacecraft's flight while in space.

see also Gyroscopes (volume 3); Robotic Exploration of Space (volume 2); Spacecraft Buses (volume 2).

Frank Sietzen, Jr.