Uncrewed spacecraft
Uncrewed spacecraft or robotic spacecraft are spacecraft without people on board. Uncrewed spacecraft may have varying levels of autonomy from human input, such as remote control, or remote guidance. They may also be autonomous, in which they have a pre-programmed list of operations that will be executed unless otherwise instructed. A robotic spacecraft for scientific measurements is often called a space probe or space observatory.
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. Telerobotics also allows exploration of regions that are vulnerable to contamination by Earth micro-organisms since spacecraft can be sterilized. Humans can not be sterilized in the same way as a spaceship, as they coexist with numerous micro-organisms, and these micro-organisms are also hard to contain within a spaceship or spacesuit.
The first uncrewed space mission was Sputnik, launched October 4, 1957 to orbit the Earth. Nearly all satellites, landers and rovers are robotic spacecraft. Not every uncrewed spacecraft is a robotic spacecraft; for example, a reflector ball is a non-robotic uncrewed spacecraft. Space missions where other animals but no humans are on-board are called uncrewed missions.
Many habitable spacecraft also have varying levels of robotic features. For example, the space stations Salyut 7 and Mir, and the International Space Station module Zarya, were capable of remote guided station-keeping and docking maneuvers with both resupply craft and new modules. Uncrewed resupply spacecraft are increasingly used for crewed space stations.
History
The first robotic spacecraft was launched by the Soviet Union 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 Earth orbit by the USSR on 4 October 1957. On 3 November 1957, the USSR orbited Sputnik 2. Weighing, Sputnik 2 carried the first animal into orbit, the dog Laika. Since the satellite was not designed to detach from its launch vehicle's upper stage, the total mass in orbit was.
In a close race with the Soviets, the United States launched its first artificial satellite, Explorer 1, into a orbit on 31 January 1958. Explorer I was an long by diameter cylinder weighing, compared to Sputnik 1, a sphere which weighed. Explorer 1 carried sensors which confirmed the existence of the Van Allen belts, a major scientific discovery at the time, while Sputnik 1 carried no scientific sensors. On 17 March 1958, the US orbited its second satellite, Vanguard 1, which was about the size of a grapefruit, and which remains in a orbit as of 2016.
The first attempted lunar probe was the Luna E-1 No.1, launched on 23 September 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. Mariner 2 was the first probe to study another planet, revealing Venus' extremely hot temperature to scientists in 1962, while the Soviet Venera 4 was the first atmospheric probe to study Venus. Mariner 4 1965 Mars flyby snapped the first images of its cratered surface, which the Soviets responded to a few months later with images from on its surface from Luna 9. In 1967, America's Surveyor 3 gathered information about the Moon's surface that would prove crucial to the Apollo 11 mission that landed humans on the Moon two years later.
The first interstellar probe was Voyager 1, launched 5 September 1977. It entered interstellar space on 25 August 2012, followed by its twin Voyager 2 on 5 November 2018.
Nine other countries have successfully launched satellites using their own launch vehicles: France, Japan and China, the United Kingdom, India, Israel, Iran, North Korea, and South Korea.
Design
In spacecraft design, the United States Air Force considers a vehicle to consist of the mission payload and the bus. 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:Structure
The physical backbone structure, which- provides overall mechanical integrity of the spacecraft
- ensures spacecraft components are supported and can withstand launch loads
Data handling
- command sequence storage
- maintaining the spacecraft clock
- collecting and reporting spacecraft telemetry data
- collecting and reporting mission data
Attitude determination and control
Entry, descent, and landing
Integrated sensing incorporates an image transformation algorithm to interpret the immediate imagery land data, perform a real-time detection and avoidance of terrain hazards that may impede safe landing, and increase the accuracy of landing at a desired site of interest using landmark localization techniques. Integrated sensing completes these tasks by relying on pre-recorded information and cameras to understand its location and determine its position and whether it is correct or needs to make any corrections. The cameras are also used to detect any possible hazards whether it is increased fuel consumption or it is a physical hazard such as a poor landing spot in a crater or cliff side that would make landing very not ideal.Landing on hazardous terrain
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, what may pose as hazards from the terrain, and where the spacecraft should presently be headed. 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.Telecommunications
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.Electrical power
The supply of electric power on spacecraft generally come from photovoltaic 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.Propulsion
Spacecraft propulsion is a method that allows a spacecraft to travel through space by generating thrust to push it forward. However, there is not one universally used propulsion system: monopropellant, bipropellant, ion propulsion, etc. Each propulsion system generates thrust in different ways with each system having advantages and disadvantages.Most spacecraft propulsion today is based on rocket engines. 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 happens due to one basic principle known as Newton's third law. According to Newton, "to every action there is an equal and opposite reaction." As the energy and heat is being released from the back of the spacecraft, gas particles are pushed that allow the spacecraft to propel forward. The main reason behind the use of rocket engines today is because rockets are the most powerful form of propulsion.