Robotic spacecraft is an uncrewed spacecraft, 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 spacecraft technology, so telerobotic probes are the only way to explore them.
The first robotic spacecraft was launched by the Soviet Union (USSR) on 22 July 1951, a suborbital flight carrying two dogs Dezik and Tsygan. Four other such flights were made through the fall of 1951.
The first artificial satellite, Sputnik 1, was put into a 215-by-939-kilometer (116 by 507 nmi) Earth orbit by the USSR on 4 October 1957.
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.
In planetary exploration missions involving robotic spacecraft, there are three key parts in the processes of landing on the surface of the planet to ensure a safe and successful landing.
This process includes an entry into the planetary gravity field and atmosphere, a descent through that atmosphere towards an intended/targeted region of scientific value, and a safe landing that guarantees the integrity of the instrumentation on the craft is preserved. While the robotic spacecraft is going through those parts, it must also be capable of estimating its position compared to the surface in order to ensure reliable control of itself and its ability to maneuver well.
The robotic spacecraft must also efficiently perform hazard assessment and trajectory adjustments in real time to avoid hazards. To achieve this, the robotic spacecraft requires accurate knowledge of where the spacecraft is located relative to the surface (localization), what may pose as hazards from the terrain (hazard assessment), and where the spacecraft should presently be headed (hazard avoidance).
Without the capability for operations for localization, hazard assessment, and avoidance, the robotic spacecraft becomes unsafe and can easily enter dangerous situations such as surface collisions, undesirable fuel consumption levels, and/or unsafe maneuvers.
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.
An example of a fully robotic spacecraft in the modern world would be SpaceX Dragon. The SpaceX Dragon was a robotic spacecraft designed to send 6,000 kg (13,000 lb) of cargo to the International Space Station. The SpaceX Dragon’s total height was 7.2 m (24 ft) with a diameter of 3.7 m (12 ft). The maximum launch payload mass was 6,000 kg (13,000 lb) with a maximum return mass of 3,000 kg (6,600 lb), along with a maximum launch payload volume of 25 m3 (880 cu ft) and a maximum return payload volume of 11 m3 (390 cu ft). The maximum endurance of the Dragon in space was two years.
Many artificial satellites are robotic spacecraft, as are many landers and rovers.