Space Probe

A space probe is a largely self-contained mechanical system designed to perform a variety of prescribed operations Figure 2. Illustration by Hans & Cassidy. Courtesy of Gale Group. for a long time, sometimes decades. There are ten major constituents of the spacecraft that are responsible for its vital functions: (1) power supply, (2) propulsion, (3) altitude control, (4) environmental control, (5) computers, (6) communications, (7) engineering-instrumentation, (8) scientific instrumentation, (9) guidance control, and (10) structural platform.

(1) The power supply provides regulated electrical power to keep the spacecraft active. Solar-cell arrays that transform sunlight into electricity are used for missions to the inner solar system; thermoelectric generators run by plutonium are used for missions the outer solar system, where sunlight is dim, and have also been used for some planetary-lander probes (e.g., Viking I and II on Mars). (2) The propulsion subsystem enables the spacecraft to maneuver during either space travel or landing (if any), and must be specifically configuration depending upon the mission's goals. (3) The altitude-control subsystem allows the spacecraft to orient itself in space. Solar panels must be aimed at the Sun, antennas at Earth, and sensors at scientific targets. This subsystem also aligns rockets in the proper direction during course-change maneuvers. (4) The environmental-control subsystem maintains the temperature and other aspects of the craft's internal environment within the acceptable levels to secure proper functioning of equipment. (5) The computer subsystem controls all the other subsystems. It performs processing and storage of scientific data, executes routines for internal checking and maintenance, instructs onboard instruments to perform scientific studies, aids in the diagnosis of equipment faults, and initiates pre-programmed actions independently of Earth. (6) The communications subsystem transmits data and receives commands from Earth. It also transmits identifying signals that allow ground crews to track the probe. (7) The engineering-instrumentation subsystem continuously monitors the "health" of the spacecraft's other systems and submits status reports to Earth via the computer and communications subsystems. (8) The scientific-instrumentation subsystem carries out the experiments selected for a particular mission, as, for example, to explore a planet's geography, geology, atmospheric physics, and electromagnetic environment. (9) The guidance-and-control subsystem is supposed to detect deviations from proper course and performance, determine corrections, and to dispatch appropriate corrective commands. (10) The structural subsystem is the mechanical skeleton of the spacecraft; it supports, unites, and protects all other subsystems.

Depending upon a mission's target, it may be classed as lunar, solar, planetary, or interplanetary (i.e., visiting more than one planet). Interstellar missions are also possible in principle. None have been launched, but several U.S. probes to the outer planets have left the solar system and continue to transmit data from interstellar space. Another scheme of classification is based upon the mission type: flyby, orbiter, or soft-lander.