A robotic spacecraft is a spacecraft with no humans on board, that is usually under telerobotic control. A robotic spacecraft designed to make scientific research measurements is often called a space probe. Many space missions are more suited to telerobotic rather than crewed operation, due to lower cost and lower risk factors. In addition, some planetary destinations such as Venus or the vicinity of Jupiter are too hostile for human survival, given current technology. Outer planets such as Saturn, Uranus, and Neptune are too distant to reach with current crewed spaceflight technology, so telerobotic probes are the only way to explore them.
The first space mission, Sputnik 1, was an artificial satellite put into Earth orbit by the USSR on 4 October 1957. On 3 November 1957, the USSR orbited Sputnik 2, the first to carry a living animal into space – a dog.
The USA achieved its first successful space probe launch with the orbit of Explorer 1 on 31 January 1958. Explorer 1 weighed less than 14 kilograms compared to 83.6 kg and 508.3 kg for Sputniks 1 and 2 respectively. Nonetheless, Explorer 1 detected a narrow band of radiation surrounding the Earth, named the Van Allen belts after the scientist whose equipment detected it.
Only six other countries have successfully launched missions using their own vehicles: France (1965), Japan (1970), China (1970), the United Kingdom (1971), India (1981) and Israel (1988).
Most American space probe missions have been coordinated by the Jet Propulsion Laboratory, and European missions by the European Space Operations Centre, part of the European Space Agency (ESA). ESA has conducted relatively fewer space exploration missions in the past (one example is the Giotto mission, which encountered comet Halley), but have launched several interplanetary spacecraft in recent years (e.g. Rosetta space probe, Mars Express, Venus Express). ESA has, however, launched many spacecraft to carry out astronomy, and is a collaborator with NASA on the Hubble Space Telescope. There have been many successful Russian space missions. There have also been a few Japanese, Chinese and Indian missions.
In spacecraft design, the United States Air Force considers a vehicle to consist of the mission payload and the bus (or platform). The bus provides physical structure, thermal control, electrical power, attitude control and telemetry, tracking and commanding.
JPL divides the "flight system" of a spacecraft into subsystems. These include:
This is the physical backbone structure. It:
This is sometimes referred to as the command and data subsystem. It is often responsible for:
Attitude and articulation control
This system is responsible for the spacecraft's orientation in space (attitude) and the positioning of movable parts. Attitude is controlled in order to:
Components in the telecommunications subsystem include radio antennas, transmitters and receivers. These may be used to communicate with ground stations on Earth, or with other spacecraft.
The supply of electric power on spacecraft come from photovoltaic (solar) cells or from a radioisotope thermoelectric generator. Other components of the subsystem include batteries for storing power and distribution circuitry that connects components to the power sources.
Temperature control and protection from the environment
Spacecraft are often protected from temperature fluctuations with insulation. Some spacecraft use mirrors and sunshades for additional protection from solar heating. They also often need shielding from micrometeoroids and orbital debris.
Mechanical components often need to be moved for deployment after launch or prior to landing. In addition to the use of motors, many one-time movements are controlled by pyrotechnic devices.
Robotic spacecraft use telemetry to radio back to Earth acquired data and vehicle status information. Although generally referred to as "remotely-controlled" or "telerobotic", the earliest orbital spacecraft -- such as Sputnik 1 and Explorer 1 -- did not receive control signals from Earth. Soon after these first spacecraft, command systems were developed to allow remote control from the ground. Increased autonomy is important for distant probes where the light travel time prevents rapid decision and control from Earth. Newer probes such as Cassini-Huygens and the Mars Exploration Rovers are highly autonomous and use on-board computers to operate independently for extended periods of time.
List of space probes
Gas giant probes
Comet and asteroid probes
Solar observation probes
Other solar system probes
Published in July 2009.
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