Uncrewed spacecraft

Many space missions are more suited to telerobotic rather than crewed operation, due to lower cost and 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 robotic spacecraft was launched by the Soviet Union (USSR) on 22 July 1951, a suborbital flight carrying two dogs Dezik and Tsygan.

[2] Since the satellite was not designed to detach from its launch vehicle's upper stage, the total mass in orbit was 508.3 kilograms (1,121 lb).

[3] In a close race with the Soviets, the United States launched its first artificial satellite, Explorer 1, into a 357-by-2,543-kilometre (193 by 1,373 nmi) orbit on 31 January 1958.

The goal of a lunar probe repeatedly failed until 4 January 1959 when Luna 1 orbited around the Moon and then the Sun.

The success of these early missions began a race between the US and the USSR to outdo each other with increasingly ambitious probes.

[15] In spacecraft design, the United States Air Force considers a vehicle to consist of the mission payload and the bus (or platform).

It is often responsible for: This system is mainly responsible for the correct spacecraft's orientation in space (attitude) despite external disturbance-gravity gradient effects, magnetic-field torques, solar radiation and aerodynamic drag; in addition it may be required to reposition movable parts, such as antennas and solar arrays.

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.

[20] The supply of electric power on spacecraft generally come from photovoltaic (solar) cells or from a radioisotope thermoelectric generator.

The general idea behind rocket engines is that when an oxidizer meets the fuel source, there is explosive release of energy and heat at high speeds, which propels the spacecraft forward.

This is quite advantageous due to making the rocket engine lighter and cheaper, easy to control, and more reliable.

The main benefit for having this technology is because that these kinds of liquids have relatively high density, which allows the volume of the propellent tank to be small, therefore increasing space efficacy.

The advantage of having this kind of propulsion is that it is incredibly efficient in maintaining constant velocity, which is needed for deep-space travel.

However, the amount of thrust produced is extremely low and that it needs a lot of electrical power to operate.

Robotic spacecraft use telemetry to radio back to Earth acquired data and vehicle status information.

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.

More complex techniques, such as gravitational slingshots, can be more fuel-efficient, though they may require the probe to spend more time in transit.

A technique using very little propulsion, but requiring a considerable amount of time, is to follow a trajectory on the Interplanetary Transport Network.

Cargo or resupply spacecraft are robotic vehicles designed to transport supplies, such as food, propellant, and equipment, to space stations.