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Saturday, August 6, 2022

Spaceflight

From Wikipedia, the free encyclopedia

Long-exposure shot of SpaceX CRS-9's rocket launch and landing

Spaceflight (or space flight) is an application of astronautics to fly spacecraft into or through outer space, either with or without humans on board. Most spaceflight is uncrewed and conducted mainly with spacecraft such as satellites in orbit around Earth, but also includes space probes for flights beyond Earth orbit. Such spaceflight operates either by telerobotic or autonomous control. The more complex human spaceflight has been pursued soon after the first orbital satellites and has reached the Moon and permanent human presence in space around Earth, particularly with the use of space stations. Human spaceflight programs include the Soyuz, Shenzhou, the past Apollo Moon landing and the Space Shuttle programs, with currently the International Space Station as the main destination of human spaceflight missions while China's Tiangong Space Station is under construction.

Spaceflight is used for placing in Earth's orbit communications satellites, reconnaissance satellites, Earth observation satellites, but also for space exploration such as space observatories and space probes, or even for space tourism.

Spaceflight can be achieved with different types of launch systems, conventionally by rocket launching, which provide the initial thrust to overcome the force of gravity and propel a spacecraft from the surface of the Earth. Once in space, the motion of a spacecraft—both when unpropelled and when under propulsion—is covered by the area of study called astrodynamics.

Some spacecraft remain in space practically indefinitely, which has created the issue of space pollution in the form of light pollution and space junk, which is a hazard to spaceflight. Otherwise spacecraft are terminated by atmospheric reentry, in which they disintegrate, or if they do not, their reentry is mostly controlled to safely reach a surface by landing or impacting, often being dumped in the oceanic spacecraft cemetery. As such spacecraft have been the subject of some space traffic management.

Terminology

There are several terms that refer to a flight into or through outer space.

A space mission refers to a spaceflight intended to achieve an objective. Objectives for space missions may include space exploration, space research, and national firsts in spaceflight.

Space transport is the use of spacecraft to transport people or cargo into or through outer space. This may include human spaceflight and cargo spacecraft flight.

History

The first theoretical proposal of space travel using rockets was published by Scottish astronomer and mathematician William Leitch, in an 1861 essay "A Journey Through Space". More well-known (though not widely outside Russia) is Konstantin Tsiolkovsky's work, "Исследование мировых пространств реактивными приборами" (The Exploration of Cosmic Space by Means of Reaction Devices), published in 1903.

Spaceflight became an engineering possibility with the work of Robert H. Goddard's publication in 1919 of his paper A Method of Reaching Extreme Altitudes. His application of the de Laval nozzle to liquid fuel rockets improved efficiency enough for interplanetary travel to become possible. He also proved in the laboratory that rockets would work in the vacuum of space; nonetheless, his work was not taken seriously by the public. His attempt to secure an Army contract for a rocket-propelled weapon in the first World War was defeated by the November 11, 1918 armistice with Germany. Working with private financial support, he was the first to launch a liquid-fueled rocket in 1926. Goddard's papers were highly influential internationally in his field.

Opel RAK.1 - World's first public manned flight of a rocket plane on September 30, 1929.

The world's first large-scale experimental rocket program was Opel RAK under the leadership of Fritz von Opel and Max Valier during the late 1920s leading to the first manned rocket cars and rocket planes, which paved the way for the Nazi era V2 program and US and Soviet activities from 1950 onwards.The Opel RAK program and the spectacular public demonstrations of ground and air vehicles drew large crowds, as well as caused global public excitement as so-called "Rocket Rumble" and had a large long-lasting impact on later spaceflight pioneers like e.g. Wernher von Braun.

In the course of World War II the first guided rockets, the V-2 were developed and employed as weapons by Nazi Germany. At a test flight in June 1944 one such rocket reached space at an altitude of 189 kilometers (102 nautical miles), becoming the first object in human history to do so. At the end of World War II, most of the V-2 rocket team including its head Wernher von Braun surrendered to the United States, and were expatriated to work on American missiles at what became the Army Ballistic Missile Agency, producing missiles such as Juno I and Atlas.

At that time the Soviet Union under Joseph Stalin was developing intercontinental ballistic missiles to carry nuclear weapons as a counter measure to United States bomber planes. The Tsiolkovsky influenced Sergey Korolev became the chief rocket designer, derivatives of his R-7 Semyorka missiles were used to launch the world's first artificial Earth satellite, Sputnik 1, on October 4, 1957, and later the first human to orbit the Earth, Yuri Gagarin in Vostok 1, on April 12, 1961.

The first US satellite was Explorer 1, launched on February 1, 1958, and the first American in orbit, became John Glenn in Friendship 7 on February 20, 1962. As director of the Marshall Space Flight Center, Von Braun oversaw development of a larger class of rocket called Saturn, which allowed the US to send the first two humans, Neil Armstrong and Buzz Aldrin, to the Moon and back on Apollo 11 in July 1969. At the same time, the Soviet Union secretly tried but failed to develop the N1 rocket, meant to give them the capability to land humans on the Moon.

Ever since spaceflight has been widely employed for placing satellites into orbit around Earth for a broad range of purposes, for sending uncrewed spacecraft exploring space beyond the Moon and having continuous crewed human presence in space with a series of space stations, from the salyut program to the International Space Station.

Phases

Launch

Rockets are the only means currently capable of reaching orbit or beyond. Other non-rocket spacelaunch technologies have yet to be built, or remain short of orbital speeds. A rocket launch for a spaceflight usually starts from a spaceport (cosmodrome), which may be equipped with launch complexes and launch pads for vertical rocket launches and runways for takeoff and landing of carrier airplanes and winged spacecraft. Spaceports are situated well away from human habitation for noise and safety reasons. ICBMs have various special launching facilities.

A launch is often restricted to certain launch windows. These windows depend upon the position of celestial bodies and orbits relative to the launch site. The biggest influence is often the rotation of the Earth itself. Once launched, orbits are normally located within relatively constant flat planes at a fixed angle to the axis of the Earth, and the Earth rotates within this orbit.

A launch pad is a fixed structure designed to dispatch airborne vehicles. It generally consists of a launch tower and flame trench. It is surrounded by equipment used to erect, fuel, and maintain launch vehicles. Before launch, the rocket can weigh many hundreds of tonnes. The Space Shuttle Columbia, on STS-1, weighed 2,030 tonnes (4,480,000 lb) at takeoff.

Reaching space

The most commonly used definition of outer space is everything beyond the Kármán line, which is 100 kilometers (62 mi) above the Earth's surface. The United States sometimes defines outer space as everything beyond 50 miles (80 km) in altitude.

Rocket engines are the only currently practical means of reaching space. Conventional airplane engines cannot reach space due to the lack of oxygen. Rocket engines expel propellant to provide forward thrust that generates enough delta-v (change in velocity) to reach orbit.

For crewed launch systems launch escape systems are frequently fitted to allow astronauts to escape in the case of emergency.

Alternatives

Many ways to reach space other than rocket engines have been proposed. Ideas such as the space elevator, and momentum exchange tethers like rotovators or skyhooks require new materials much stronger than any currently known. Electromagnetic launchers such as launch loops might be feasible with current technology. Other ideas include rocket assisted aircraft/spaceplanes such as Reaction Engines Skylon (currently in early stage development), scramjet powered spaceplanes, and RBCC powered spaceplanes. Gun launch has been proposed for cargo.

Leaving orbit

Launched in 1959, Luna 1 was the first known artificial object to achieve escape velocity from the Earth. (replica pictured)

Achieving a closed orbit is not essential to lunar and interplanetary voyages. Early Soviet space vehicles successfully achieved very high altitudes without going into orbit. NASA considered launching Apollo missions directly into lunar trajectories but adopted the strategy of first entering a temporary parking orbit and then performing a separate burn several orbits later onto a lunar trajectory.

The parking orbit approach greatly simplified Apollo mission planning in several important ways. It acted as a "time buffer" and substantially widened the allowable launch windows. The parking orbit gave the crew and controllers several hours to thoroughly check out the spacecraft after the stresses of launch before committing it for a long journey to the Moon.

Apollo missions minimized the performance penalty of the parking orbit by keeping its altitude as low as possible. For example, Apollo 15 used an unusually low parking orbit of 92.5 nmi × 91.5 nmi (171.3 km × 169.5 km) which is not sustainable for very long due to friction with the Earth's atmosphere, but the crew would only spend three hours before reigniting the S-IVB third stage to put them on a lunar-bound trajectory.

Robotic missions do not require an abort capability or radiation minimization, and because modern launchers routinely meet "instantaneous" launch windows, space probes to the Moon and other planets generally use direct injection to maximize performance. Although some might coast briefly during the launch sequence, they do not complete one or more full parking orbits before the burn that injects them onto an Earth escape trajectory.

The escape velocity from a celestial body decreases with altitude above that body. However, it is more fuel-efficient for a craft to burn its fuel as close to the ground as possible; see Oberth effect and reference. This is another way to explain the performance penalty associated with establishing the safe perigee of a parking orbit.

Astrodynamics

Astrodynamics is the study of spacecraft trajectories, particularly as they relate to gravitational and propulsion effects. Astrodynamics allows for a spacecraft to arrive at its destination at the correct time without excessive propellant use. An orbital maneuvering system may be needed to maintain or change orbits.

Non-rocket orbital propulsion methods include solar sails, magnetic sails, plasma-bubble magnetic systems, and using gravitational slingshot effects.

Ionized gas trail from Shuttle reentry
 
Recovery of Discoverer 14 return capsule by a C-119 airplane

Transfer energy

The term "transfer energy" means the total amount of energy imparted by a rocket stage to its payload. This can be the energy imparted by a first stage of a launch vehicle to an upper stage plus payload, or by an upper stage or spacecraft kick motor to a spacecraft.

Reaching space station

In order to reach towards a space station, a spacecraft would have to arrive at the same orbit and approach to a very close distance (e.g. within visual contact). This is done by a set of orbital maneuvers called space rendezvous.

After rendezvousing with the space station, the space vehicle then docks or berths with the station. Docking refers to joining of two separate free-flying space vehicles, while berthing refers to mating operations where an inactive vehicle is placed into the mating interface of another space vehicle by using a robotic arm.

Reentry

Vehicles in orbit have large amounts of kinetic energy. This energy must be discarded if the vehicle is to land safely without vaporizing in the atmosphere. Typically this process requires special methods to protect against aerodynamic heating. The theory behind reentry was developed by Harry Julian Allen. Based on this theory, reentry vehicles present blunt shapes to the atmosphere for reentry. Blunt shapes mean that less than 1% of the kinetic energy ends up as heat reaching the vehicle, and the remainder heats up the atmosphere.

Landing and recovery

The Mercury, Gemini, and Apollo capsules all splashed down in the sea. These capsules were designed to land at relatively low speeds with the help of a parachute. Soviet/Russian capsules for Soyuz make use of a big parachute and braking rockets to touch down on land. Spaceplanes like the Space Shuttle land like a glider.

After a successful landing the spacecraft, its occupants, and cargo can be recovered. In some cases, recovery has occurred before landing: while a spacecraft is still descending on its parachute, it can be snagged by a specially designed aircraft. This mid-air retrieval technique was used to recover the film canisters from the Corona spy satellites.

Types

Uncrewed

Sojourner takes its Alpha particle X-ray spectrometer measurement of Yogi Rock on Mars
 
The MESSENGER spacecraft at Mercury (artist's interpretation)

Uncrewed spaceflight is all spaceflight activity without a necessary human presence in space. This includes all space probes, satellites and robotic spacecraft and missions. Uncrewed spaceflight is the opposite of crewed spaceflight, which is usually called human spaceflight. Subcategories of uncrewed spaceflight are "robotic spacecraft" (objects) and "robotic space missions" (activities). A robotic spacecraft is an uncrewed spacecraft with no humans on board, that is usually under telerobotic control. In some cases, such as with helicopters, a spacecraft may need to act autonomously for short periods of time. A robotic spacecraft designed to make scientific research measurements is often called a space probe.

Uncrewed space missions use remote-controlled spacecraft. The first uncrewed space mission was Sputnik, launched October 4, 1957 to orbit the Earth. Space missions where other animals but no humans are on-board are considered uncrewed missions.

Benefits

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. 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.

Telepresence

Telerobotics becomes telepresence when the time delay is short enough to permit control of the spacecraft in close to real time by humans. Even the two seconds light speed delay for the Moon is too far away for telepresence exploration from Earth. The L1 and L2 positions permit 400-millisecond round trip delays, which is just close enough for telepresence operation. Telepresence has also been suggested as a way to repair satellites in Earth orbit from Earth. The Exploration Telerobotics Symposium in 2012 explored this and other topics.

Human

ISS crew member stores samples

The first human spaceflight was Vostok 1 on April 12, 1961, on which cosmonaut Yuri Gagarin of the USSR made one orbit around the Earth. In official Soviet documents, there is no mention of the fact that Gagarin parachuted the final seven miles. As of 2020, the only spacecraft regularly used for human spaceflight are Soyuz, Shenzhou, and Crew Dragon. The U.S. Space Shuttle fleet operated from April 1981 until July 2011. SpaceShipOne has conducted two human suborbital spaceflights.

Sub-orbital

The North American X-15 in flight. X-15 flew above 100 km (62 mi) twice and both of the flights were piloted by Joe Walker (astronaut)

On a sub-orbital spaceflight the spacecraft reaches space and then returns to the atmosphere after following a (primarily) ballistic trajectory. This is usually because of insufficient specific orbital energy, in which case a suborbital flight will last only a few minutes, but it is also possible for an object with enough energy for an orbit to have a trajectory that intersects the Earth's atmosphere, sometimes after many hours. Pioneer 1 was NASA's first space probe intended to reach the Moon. A partial failure caused it to instead follow a suborbital trajectory to an altitude of 113,854 kilometers (70,746 mi) before reentering the Earth's atmosphere 43 hours after launch.

The most generally recognized boundary of space is the Kármán line 100 km (62 mi) above sea level. (NASA alternatively defines an astronaut as someone who has flown more than 80 km (50 mi) above sea level.) It is not generally recognized by the public that the increase in potential energy required to pass the Kármán line is only about 3% of the orbital energy (potential plus kinetic energy) required by the lowest possible Earth orbit (a circular orbit just above the Kármán line.) In other words, it is far easier to reach space than to stay there. On May 17, 2004, Civilian Space eXploration Team launched the GoFast rocket on a suborbital flight, the first amateur spaceflight. On June 21, 2004, SpaceShipOne was used for the first privately funded human spaceflight.

Point-to-point

Point-to-point, or Earth to Earth transportation, is a category of sub-orbital spaceflight in which a spacecraft provides rapid transport between two terrestrial locations. A conventional airline route between London and Sydney, a flight that normally lasts over twenty hours, could be traversed in less than one hour. While no company offers this type of transportation today, SpaceX has revealed plans to do so as early as the 2020s using Starship. Suborbital spaceflight over an intercontinental distance requires a vehicle velocity that is only a little lower than the velocity required to reach low Earth orbit. If rockets are used, the size of the rocket relative to the payload is similar to an Intercontinental Ballistic Missile (ICBM). Any intercontinental spaceflight has to surmount problems of heating during atmosphere re-entry that are nearly as large as those faced by orbital spaceflight.

Orbital

Apollo 6 heads into orbit

A minimal orbital spaceflight requires much higher velocities than a minimal sub-orbital flight, and so it is technologically much more challenging to achieve. To achieve orbital spaceflight, the tangential velocity around the Earth is as important as altitude. In order to perform a stable and lasting flight in space, the spacecraft must reach the minimal orbital speed required for a closed orbit.

Interplanetary

Interplanetary spaceflight is flight between planets within a single planetary system. In practice, the use of the term is confined to travel between the planets of our Solar System. Plans for future crewed interplanetary spaceflight missions often include final vehicle assembly in Earth orbit, such as NASA's Constellation program and Russia's Kliper/Parom tandem.

Interstellar

‘’New Horizons’’ is the fifth spacecraft put on an escape trajectory leaving the Solar System. Voyager 1, Voyager 2, Pioneer 10, Pioneer 11 are the earlier ones. The one farthest from the Sun is Voyager 1, which is more than 100 AU distant and is moving at 3.6 AU per year. In comparison, Proxima Centauri, the closest star other than the Sun, is 267,000 AU distant. It will take Voyager 1 over 74,000 years to reach this distance. Vehicle designs using other techniques, such as nuclear pulse propulsion are likely to be able to reach the nearest star significantly faster. Another possibility that could allow for human interstellar spaceflight is to make use of time dilation, as this would make it possible for passengers in a fast-moving vehicle to travel further into the future while aging very little, in that their great speed slows down the rate of passage of on-board time. However, attaining such high speeds would still require the use of some new, advanced method of propulsion.

Intergalactic

Intergalactic travel involves spaceflight between galaxies, and is considered much more technologically demanding than even interstellar travel and, by current engineering terms, is considered science fiction. However, theoretically speaking, there is nothing to conclusively indicate that intergalactic travel is impossible. To date several academics have studied intergalactic travel in a serious manner.

Spacecraft

An Apollo Lunar Module on the lunar surface

Spacecraft are vehicles capable of controlling their trajectory through space.

The first 'true spacecraft' is sometimes said to be Apollo Lunar Module, since this was the only crewed vehicle to have been designed for, and operated only in space; and is notable for its non-aerodynamic shape.

Propulsion

Spacecraft today predominantly use rockets for propulsion, but other propulsion techniques such as ion drives are becoming more common, particularly for uncrewed vehicles, and this can significantly reduce the vehicle's mass and increase its delta-v.

Launch systems

Launch systems are used to carry a payload from Earth's surface into outer space.

Expendable

Most current spaceflight uses multi-stage expendable launch systems to reach space.

Reusable

The first reusable spacecraft, the X-15, was air-launched on a suborbital trajectory on 19 July 1963. The first partially reusable orbital spacecraft, the Space Shuttle, was launched by the USA on the 20th anniversary of Yuri Gagarin's flight, on 12 April 1981. During the Shuttle era, six orbiters were built, all of which flown in the atmosphere and five of which flown in space. The Enterprise was used only for approach and landing tests, launching from the back of a Boeing 747 and gliding to deadstick landings at Edwards AFB, California. The first Space Shuttle to fly into space was the Columbia, followed by the Challenger, Discovery, Atlantis, and Endeavour. The Endeavour was built to replace the Challenger, which was lost in January 1986. The Columbia broke up during reentry in February 2003.

The first automatic partially reusable spacecraft was the Buran (Snowstorm), launched by the USSR on 15 November 1988, although it made only one flight. This spaceplane was designed for a crew and strongly resembled the US Space Shuttle, although its drop-off boosters used liquid propellants and its main engines were located at the base of what would be the external tank in the American Shuttle. Lack of funding, complicated by the dissolution of the USSR, prevented any further flights of Buran.

The Space Shuttle was retired in 2011 due mainly to its old age and high cost of the program reaching over a billion dollars per flight. The Shuttle's human transport role is to be replaced by the SpaceX Dragon 2 and CST-100 in the 2020s. The Shuttle's heavy cargo transport role is now done by commercial launch vehicles.

Scaled Composites SpaceShipOne was a reusable suborbital spaceplane that carried pilots Mike Melvill and Brian Binnie on consecutive flights in 2004 to win the Ansari X Prize. The Spaceship Company has built its successor SpaceShipTwo. A fleet of SpaceShipTwos operated by Virgin Galactic planned to begin reusable private spaceflight carrying paying passengers (space tourists) in 2008, but this was delayed due to an accident in the propulsion development.

SpaceX achieved the first vertical soft landing of a re-usable orbital rocket stage on December 21, 2015, after delivering 11 Orbcomm OG-2 commercial satellites into low Earth orbit.

The first Falcon 9 second flight occurred on 30 March 2017. SpaceX now routinely recovers and reuses their first stages, with the intent of reusing fairings as well.

The X-15 pulling away from its drop launch plane
 
The Space Shuttle Columbia seconds after engine ignition on mission STS-1
 
SpaceShipOne after its flight into space, 21 June 2004
 
Falcon 9 Flight 20's first stage landing vertically on Landing Zone 1 in December 2015

Challenges

Space disasters

All launch vehicles contain a huge amount of energy that is needed for some part of it to reach orbit. There is therefore some risk that this energy can be released prematurely and suddenly, with significant effects. When a Delta II rocket exploded 13 seconds after launch on January 17, 1997, there were reports of store windows 10 miles (16 km) away being broken by the blast.

Space is a fairly predictable environment, but there are still risks of accidental depressurization and the potential failure of equipment, some of which may be very newly developed.

In 2004 the International Association for the Advancement of Space Safety was established in the Netherlands to further international cooperation and scientific advancement in space systems safety.

Weightlessness

Astronauts on the ISS in weightless conditions. Michael Foale can be seen exercising in the foreground.

In a microgravity environment such as that provided by a spacecraft in orbit around the Earth, humans experience a sense of "weightlessness." Short-term exposure to microgravity causes space adaptation syndrome, a self-limiting nausea caused by derangement of the vestibular system. Long-term exposure causes multiple health issues. The most significant is bone loss, some of which is permanent, but microgravity also leads to significant deconditioning of muscular and cardiovascular tissues.

Radiation

Once above the atmosphere, radiation due to the Van Allen belts, solar radiation and cosmic radiation issues occur and increase. Further away from the Earth, solar flares can give a fatal radiation dose in minutes, and the health threat from cosmic radiation significantly increases the chances of cancer over a decade exposure or more.

Life support

In human spaceflight, the life support system is a group of devices that allow a human being to survive in outer space. NASA often uses the phrase Environmental Control and Life Support System or the acronym ECLSS when describing these systems for its human spaceflight missions. The life support system may supply: air, water and food. It must also maintain the correct body temperature, an acceptable pressure on the body and deal with the body's waste products. Shielding against harmful external influences such as radiation and micro-meteorites may also be necessary. Components of the life support system are life-critical, and are designed and constructed using safety engineering techniques.

Space weather

Space weather is the concept of changing environmental conditions in outer space. It is distinct from the concept of weather within a planetary atmosphere, and deals with phenomena involving ambient plasma, magnetic fields, radiation and other matter in space (generally close to Earth but also in interplanetary, and occasionally interstellar medium). "Space weather describes the conditions in space that affect Earth and its technological systems. Our space weather is a consequence of the behavior of the Sun, the nature of Earth's magnetic field, and our location in the Solar System."

Space weather exerts a profound influence in several areas related to space exploration and development. Changing geomagnetic conditions can induce changes in atmospheric density causing the rapid degradation of spacecraft altitude in Low Earth orbit. Geomagnetic storms due to increased solar activity can potentially blind sensors aboard spacecraft, or interfere with on-board electronics. An understanding of space environmental conditions is also important in designing shielding and life support systems for crewed spacecraft.

Environmental considerations

Exhaust pollution of rockets depends on the produced exhausts by the propellants reactions and the location of exhaustion. They mostly exhaust greenhouse gases and sometimes toxic components. Particularly at higher levels of the atmosphere the potency of exhausted gases as greenhouse gases increases considerably. Many solid rockets have chlorine in the form of perchlorate or other chemicals, and this can cause temporary local holes in the ozone layer. Re-entering spacecraft generate nitrates which also can temporarily impact the ozone layer. Most rockets are made of metals that can have an environmental impact during their construction. While spaceflight altogether pollutes at a fraction of other human activities, it still does pollute heavily if calculated per passenger.

In addition to the atmospheric effects there are effects on the near-Earth space environment. There is the possibility that orbit could become inaccessible for generations due to exponentially increasing space debris caused by spalling of satellites and vehicles (Kessler syndrome). Many launched vehicles today are therefore designed to be re-entered after use.

Regulation

A wide range of issues such as space traffic management or liability have been issues of spaceflight regulation.

Participation and representation of all humanity in spaceflight is an issue of international space law ever since the first phase of space exploration. Even though some rights of non-spacefaring countries have been secured, sharing of space for all humanity is still criticized as imperialist and lacking, understanding spaceflight as a resource.

Applications

This shows an extreme ultraviolet view of the Sun (the Apollo Telescope Mount SO82A Experiment) taken during Skylab 3, with the Earth added for scale. On the right an image of the Sun shows a helium emissions, and there is an image on the left showing emissions from iron. One application for spaceflight is to take observation hindered or made more difficult by being on Earth's surface. Skylab included a massive crewed solar observatory that revolutionized solar science in the early 1970s using the Apollo-based space station in conjunction with crewed spaceflights to it.

Current and proposed applications for spaceflight include:

Most early spaceflight development was paid for by governments. However, today major launch markets such as communication satellites and satellite television are purely commercial, though many of the launchers were originally funded by governments.

Private spaceflight is a rapidly developing area: space flight that is not only paid for by corporations or even private individuals, but often provided by private spaceflight companies. These companies often assert that much of the previous high cost of access to space was caused by governmental inefficiencies they can avoid. This assertion can be supported by much lower published launch costs for private space launch vehicles such as Falcon 9 developed with private financing. Lower launch costs and excellent safety will be required for the applications such as space tourism and especially space colonization to become feasible for expansion.

Spacefaring

Map showing countries with spaceflight capability
  Countries with independently developed human spaceflight programs.
  Countries that have operated at least one human spaceflight program, if not independently.
  Countries seeking to develop a human spaceflight program but also have developed or currently own a launch vehicle.
  Countries who operate a launch vehicle and a satellite but currently have no plans to develop a crewed space vehicle.
  Countries seeking to develop a launch vehicle.
  Countries who operate an orbiting satellite but do not own a launch vehicle or have plans to produce one.
  Countries who have a launch vehicle but do not currently operate a satellite.

To be spacefaring is to be capable of and active in the operation of spacecraft. It involves a knowledge of a variety of topics and development of specialised skills including: aeronautics; astronautics; programs to train astronauts; space weather and forecasting; spacecraft operations; operation of various equipment; spacecraft design and construction; atmospheric takeoff and reentry; orbital mechanics (a.k.a. astrodynamics); communications; engines and rockets; execution of evolutions such as towing, microgravity construction, and space docking; cargo handling equipment, dangerous cargos and cargo storage; spacewalking; dealing with emergencies; survival at space and first aid; fire fighting; life support. The degree of knowledge needed within these areas is dependent upon the nature of the work and the type of vessel employed. "Spacefaring" is analogous to seafaring.

There has never been a crewed mission outside the EarthMoon system. However, the United States, Russia, China, European Space Agency (ESA) countries, and a few corporations and enterprises have plans in various stages to travel to Mars (see Human mission to Mars).

Spacefaring entities can be sovereign states, supranational entities, and private corporations. Spacefaring nations are those capable of independently building and launching craft into space. A growing number of private entities have become or are becoming spacefaring.

Global coordination

The United Nations Office for Outer Space Affairs (UNOOSA) has been the main multilateral body servicing international contact and exchange on space activity among spacefaring and non-spacefaring states.

Crewed spacefaring nations

Currently Russia, China, and the United States are the only crewed spacefaring nations. Spacefaring nations listed by year of first crewed launch:

  1. Soviet Union (Russia) (1961)
  2. United States (1961)
  3. China (2003)

Uncrewed spacefaring nations

The following nations or organizations have developed their own launch vehicles to launch uncrewed spacecraft into orbit either from their own territory or with foreign assistance (date of first launch in parentheses):

  1. Soviet Union (1957)
  2. United States (1958)
  3. France (1965)
  4. Italy (1967)★
  5. Australia (1967)★
  6. Japan (1970)
  7. China (1970)
  8. United Kingdom (1971)
  9. European Space Agency (1979)
  10. India (1980)
  11. Israel (1988)
  12. Ukraine (1991)*
  13. Russia (1992)*
  14. Iran (2009)
  15. North Korea (2012)
  16. South Korea (2013)★
  17. New Zealand (2018)★
  • *Previously a major region in the Soviet Union
  • ★Launch vehicle fully or partially developed by another country

Also several countries, such as Canada, Italy and Australia, had semi-independent spacefaring capability, launching locally-built satellites on foreign launchers. Canada had designed and built satellites (Alouette 1 and 2) in 1962 and 1965 which were orbited using US launch vehicles. Italy has designed and built several satellites, as well as pressurized modules for the International Space Station. Early Italian satellites were launched using vehicles provided by NASA, first from Wallops Flight Facility in 1964 and then from a spaceport in Kenya (San Marco Platform) between 1967 and 1988; Italy has led the development of the Vega rocket programme within the European Space Agency since 1998. The United Kingdom abandoned its independent space launch program in 1972 in favour of co-operating with the European Launcher Development Organisation (ELDO) on launch technologies until 1974. Australia abandoned its launcher program shortly after the successful launch of WRESAT, and became the only non-European member of ELDO.

Suborbital

Considering merely launching an object beyond the Kármán line to be the minimum requirement of spacefaring, Germany, with the V-2 rocket, became the first spacefaring nation in 1944. The following nations have only achieved suborbital spaceflight capability by launching indigenous rockets or missiles or both into suborbital space.

  1. Germany (June 20, 1944)
  2. East Germany (April 12, 1957)
  3. Canada (September 5, 1959)
  4. Lebanon (November 21, 1962)
  5. Switzerland (October 27, 1967)
  6. Argentina (April 16, 1969)
  7. Brazil (September 21, 1976)
  8. Spain (February 18, 1981)
  9. West Germany (March 1, 1981)
  10. Iraq (June 1984)
  11. South Africa (June 1, 1989)
  12. Sweden (May 8, 1991)
  13. Yemen (May 12, 1994)
  14. Pakistan (April 6, 1998)
  15. Taiwan (December 15, 1998)
  16. Syria (September 1, 2000)
  17. Indonesia (September 29, 2004)
  18. Democratic Republic of the Congo (2007)
  19. New Zealand (November 30, 2009)
  20. Norway (September 27, 2018)
  21. Netherlands (September 19, 2020)
  22. Turkey (October 29, 2020)

Radiation hardening

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Radiation_hardening

Radiation hardening is the process of making electronic components and circuits resistant to damage or malfunction caused by high levels of ionizing radiation (particle radiation and high-energy electromagnetic radiation), especially for environments in outer space (especially beyond the low Earth orbit), around nuclear reactors and particle accelerators, or during nuclear accidents or nuclear warfare.

Most semiconductor electronic components are susceptible to radiation damage, and radiation-hardened (rad-hard) components are based on their non-hardened equivalents, with some design and manufacturing variations that reduce the susceptibility to radiation damage. Due to the extensive development and testing required to produce a radiation-tolerant design of a microelectronic chip, the technology of radiation-hardened chips tends to lag behind the most recent developments.

Radiation-hardened products are typically tested to one or more resultant-effects tests, including total ionizing dose (TID), enhanced low dose rate effects (ELDRS), neutron and proton displacement damage, and single event effects (SEEs).

Problems caused by radiation

Environments with high levels of ionizing radiation create special design challenges. A single charged particle can knock thousands of electrons loose, causing electronic noise and signal spikes. In the case of digital circuits, this can cause results which are inaccurate or unintelligible. This is a particularly serious problem in the design of satellites, spacecraft, future quantum computers, military aircraft, nuclear power stations, and nuclear weapons. In order to ensure the proper operation of such systems, manufacturers of integrated circuits and sensors intended for the military or aerospace markets employ various methods of radiation hardening. The resulting systems are said to be rad(iation)-hardened, rad-hard, or (within context) hardened.

Major radiation damage sources

Typical sources of exposure of electronics to ionizing radiation are the Van Allen radiation belts for satellites, nuclear reactors in power plants for sensors and control circuits, particle accelerators for control electronics particularly particle detector devices, residual radiation from isotopes in chip packaging materials, cosmic radiation for spacecraft and high-altitude aircraft, and nuclear explosions for potentially all military and civilian electronics.

  • Cosmic rays come from all directions and consist of approximately 85% protons, 14% alpha particles, and 1% heavy ions, together with X-ray and gamma-ray radiation. Most effects are caused by particles with energies between 0.1 and 20 GeV. The atmosphere filters most of these, so they are primarily a concern for spacecraft and high-altitude aircraft, but can also affect ordinary computers on the surface.
  • Solar particle events come from the direction of the sun and consist of a large flux of high-energy (several GeV) protons and heavy ions, again accompanied by X-ray radiation.
  • Van Allen radiation belts contain electrons (up to about 10 MeV) and protons (up to 100s MeV) trapped in the geomagnetic field. The particle flux in the regions farther from the Earth can vary wildly depending on the actual conditions of the Sun and the magnetosphere. Due to their position they pose a concern for satellites.
  • Secondary particles result from interaction of other kinds of radiation with structures around the electronic devices.
  • Nuclear reactors produce gamma radiation and neutron radiation which can affect sensor and control circuits in nuclear power plants.
  • Particle accelerators produce high energy protons and electrons, and the secondary particles produced by their interactions produce significant radiation damage on sensitive control and particle detector components, of the order of magnitude of 10 MRad[Si]/year for systems such as the Large Hadron Collider.
  • Nuclear explosions produce a short and extremely intense surge through a wide spectrum of electromagnetic radiation, an electromagnetic pulse (EMP), neutron radiation, and a flux of both primary and secondary charged particles. In case of a nuclear war they pose a potential concern for all civilian and military electronics.
  • Chip packaging materials were an insidious source of radiation that was found to be causing soft errors in new DRAM chips in the 1970s. Traces of radioactive elements in the packaging of the chips were producing alpha particles, which were then occasionally discharging some of the capacitors used to store the DRAM data bits. These effects have been reduced today by using purer packaging materials, and employing error-correcting codes to detect and often correct DRAM errors.

Radiation effects on electronics

Fundamental mechanisms

Two fundamental damage mechanisms take place:

Lattice displacement

Lattice displacement is caused by neutrons, protons, alpha particles, heavy ions, and very high energy gamma photons. They change the arrangement of the atoms in the crystal lattice, creating lasting damage, and increasing the number of recombination centers, depleting the minority carriers and worsening the analog properties of the affected semiconductor junctions. Counterintuitively, higher doses over short time cause partial annealing ("healing") of the damaged lattice, leading to a lower degree of damage than with the same doses delivered in low intensity over a long time (LDR or Low Dose Rate). This type of problem is particularly significant in bipolar transistors, which are dependent on minority carriers in their base regions; increased losses caused by recombination cause loss of the transistor gain (see neutron effects). Components certified as ELDRS (Enhanced Low Dose Rate Sensitive) free, do not show damage with fluxes below 0.01 rad(Si)/s = 36 rad(Si)/h.

Ionization effects

Ionization effects are caused by charged particles, including the ones with energy too low to cause lattice effects. The ionization effects are usually transient, creating glitches and soft errors, but can lead to destruction of the device if they trigger other damage mechanisms (e.g., a latchup). Photocurrent caused by ultraviolet and X-ray radiation may belong to this category as well. Gradual accumulation of holes in the oxide layer in MOSFET transistors leads to worsening of their performance, up to device failure when the dose is high enough (see total ionizing dose effects).

The effects can vary wildly depending on all the parameters – type of radiation, total dose and radiation flux, combination of types of radiation, and even the kind of device load (operating frequency, operating voltage, actual state of the transistor during the instant it is struck by the particle) – which makes thorough testing difficult, time consuming, and requiring many test samples.

Resultant effects

The "end-user" effects can be characterized in several groups,

A neutron interacting with the semiconductor lattice will displace its atoms. This leads to an increase in the count of recombination centers and deep-level defects, reducing the lifetime of minority carriers, thus affecting bipolar devices more than CMOS ones. Bipolar devices on silicon tend to show changes in electrical parameters at levels of 1010 to 1011 neutrons/cm², CMOS devices aren't affected until 1015 neutrons/cm². The sensitivity of the devices may increase together with increasing level of integration and decreasing size of individual structures. There is also a risk of induced radioactivity caused by neutron activation, which is a major source of noise in high energy astrophysics instruments. Induced radiation, together with residual radiation from impurities in used materials, can cause all sorts of single-event problems during the device's lifetime. GaAs LEDs, common in optocouplers, are very sensitive to neutrons. The lattice damage influences the frequency of crystal oscillators. Kinetic energy effects (namely lattice displacement) of charged particles belong here too.

Total ionizing dose effects

The cumulative damage of the semiconductor lattice (lattice displacement damage) caused by ionizing radiation over the exposition time. It is measured in rads and causes slow gradual degradation of the device's performance. A total dose greater than 5000 rads delivered to silicon-based devices in seconds to minutes will cause long-term degradation. In CMOS devices, the radiation creates electron–hole pairs in the gate insulation layers, which cause photocurrents during their recombination, and the holes trapped in the lattice defects in the insulator create a persistent gate biasing and influence the transistors' threshold voltage, making the N-type MOSFET transistors easier and the P-type ones more difficult to switch on. The accumulated charge can be high enough to keep the transistors permanently open (or closed), leading to device failure. Some self-healing takes place over time, but this effect is not too significant. This effect is the same as hot carrier degradation in high-integration high-speed electronics. Crystal oscillators are somewhat sensitive to radiation doses, which alter their frequency. The sensitivity can be greatly reduced by using swept quartz. Natural quartz crystals are especially sensitive. Radiation performance curves for TID testing may be generated for all resultant effects testing procedures. These curves show performance trends throughout the TID test process and are included in the radiation test report.

Transient dose effects

The short-time high-intensity pulse of radiation, typically occurring during a nuclear explosion. The high radiation flux creates photocurrents in the entire body of the semiconductor, causing transistors to randomly open, changing logical states of flip-flops and memory cells. Permanent damage may occur if the duration of the pulse is too long, or if the pulse causes junction damage or a latchup. Latchups are commonly caused by the X-rays and gamma radiation flash of a nuclear explosion. Crystal oscillators may stop oscillating for the duration of the flash due to prompt photoconductivity induced in quartz.

Systems-generated EMP effects

SGEMP are caused by the radiation flash traveling through the equipment and causing local ionization and electric currents in the material of the chips, circuit boards, electrical cables and cases.

Digital damage: SEE

Single-event effects (SEE) have been studied extensively since the 1970s. When a high-energy particle travels through a semiconductor, it leaves an ionized track behind. This ionization may cause a highly localized effect similar to the transient dose one - a benign glitch in output, a less benign bit flip in memory or a register or, especially in high-power transistors, a destructive latchup and burnout. Single event effects have importance for electronics in satellites, aircraft, and other civilian and military aerospace applications. Sometimes, in circuits not involving latches, it is helpful to introduce RC time constant circuits that slow down the circuit's reaction time beyond the duration of an SEE.

Single-event transient

SET happens when the charge collected from an ionization event discharges in the form of a spurious signal traveling through the circuit. This is de facto the effect of an electrostatic discharge. Soft error, reversible.

Single-event upset

Single-event upsets (SEU) or transient radiation effects in electronics are state changes of memory or register bits caused by a single ion interacting with the chip. They do not cause lasting damage to the device, but may cause lasting problems to a system which cannot recover from such an error. Soft error, reversible. In very sensitive devices, a single ion can cause a multiple-bit upset (MBU) in several adjacent memory cells. SEUs can become Single-event functional interrupts (SEFI) when they upset control circuits, such as state machines, placing the device into an undefined state, a test mode, or a halt, which would then need a reset or a power cycle to recover.

Single-event latchup

SEL can occur in any chip with a parasitic PNPN structure. A heavy ion or a high-energy proton passing through one of the two inner-transistor junctions can turn on the thyristor-like structure, which then stays "shorted" (an effect known as latch-up) until the device is power-cycled. As the effect can happen between the power source and substrate, destructively high current can be involved and the part may fail. Hard error, irreversible. Bulk CMOS devices are most susceptible.

Single-event snapback

Single-event snapback is similar to SEL but not requiring the PNPN structure, can be induced in N-channel MOS transistors switching large currents, when an ion hits near the drain junction and causes avalanche multiplication of the charge carriers. The transistor then opens and stays opened, a hard error, which is irreversible.

Single-event induced burnout

SEB may occur in power MOSFETs when the substrate right under the source region gets forward-biased and the drain-source voltage is higher than the breakdown voltage of the parasitic structures. The resulting high current and local overheating then may destroy the device. Hard error, irreversible.

Single-event gate rupture

SEGR was observed in power MOSFETs when a heavy ion hits the gate region while a high voltage is applied to the gate. A local breakdown then happens in the insulating layer of silicon dioxide, causing local overheat and destruction (looking like a microscopic explosion) of the gate region. It can occur even in EEPROM cells during write or erase, when the cells are subjected to a comparatively high voltage. Hard error, irreversible.

SEE testing

While proton beams are widely used for SEE testing due to availability, at lower energies proton irradiation can often underestimate SEE susceptibility. Furthermore, proton beams expose devices to risk of total ionizing dose (TID) failure which can cloud proton testing results or result in pre-mature device failure. White neutron beams—ostensibly the most representative SEE test method—are usually derived from solid target-based sources, resulting in flux non-uniformity and small beam areas. White neutron beams also have some measure of uncertainty in their energy spectrum, often with high thermal neutron content.

The disadvantages of both proton and spallation neutron sources can be avoided by using mono-energetic 14 MeV neutrons for SEE testing. A potential concern is that mono-energetic neutron-induced single event effects will not accurately represent the real-world effects of broad-spectrum atmospheric neutrons. However, recent studies have indicated that, to the contrary, mono-energetic neutrons—particularly 14 MeV neutrons—can be used to quite accurately understand SEE cross-sections in modern microelectronics.

Radiation-hardening techniques

Radiation hardened die of the 1886VE10 microcontroller prior to metalization etching
 
Radiation hardened die of the 1886VE10 microcontroller after a metalization etching process has been used

Physical

Hardened chips are often manufactured on insulating substrates instead of the usual semiconductor wafers. Silicon on insulator (SOI) and silicon on sapphire (SOS) are commonly used. While normal commercial-grade chips can withstand between 50 and 100 gray (5 and 10 krad), space-grade SOI and SOS chips can survive doses between 1000 and 3000 gray (100 and 300 krad). At one time many 4000 series chips were available in radiation-hardened versions (RadHard). While SOI eliminates latchup events, TID and SEE hardness are not guaranteed to be improved.

Bipolar integrated circuits generally have higher radiation tolerance than CMOS circuits. The low-power Schottky (LS) 5400 series can withstand 1000 krad, and many ECL devices can withstand 10 000 krad.

Magnetoresistive RAM, or MRAM, is considered a likely candidate to provide radiation hardened, rewritable, non-volatile conductor memory. Physical principles and early tests suggest that MRAM is not susceptible to ionization-induced data loss.

Capacitor-based DRAM is often replaced by more rugged (but larger, and more expensive) SRAM.

Choice of substrate with wide band gap, which gives it higher tolerance to deep-level defects; e.g. silicon carbide or gallium nitride.

Shielding the package against radioactivity, to reduce exposure of the bare device.

Shielding the chips themselves (from neutrons) by use of depleted boron (consisting only of isotope boron-11) in the borophosphosilicate glass passivation layer protecting the chips, as naturally prevalent boron-10 readily captures neutrons and undergoes alpha decay (see soft error).

Use of a larger process node than usual to provide increased radiation resistance. Due to the high development costs of new radiation hardened processes, the smallest "true" rad-hard (RHBP, Rad-Hard By Process) process is 150 nm as of 2016, however, rad-hard 65 nm FPGAs were available that used some of the techniques used in "true" rad-hard processes (RHBD, Rad-Hard By Design). As of 2019 110 nm rad-hard processes are available.

Use of SRAM cells with more transistors per cell than usual (which is 4T or 6T), which makes the cells more tolerant to SEUs at the cost of higher power consumption and size per cell.

Use of Edge-less CMOS transistors, which have an unconventional physical construction, together with a unconventional physical layout.

Logical

Error correcting code memory (ECC memory) uses redundant bits to check for and possibly correct corrupted data. Since radiation's effects damage the memory content even when the system is not accessing the RAM, a "scrubber" circuit must continuously sweep the RAM; reading out the data, checking the redundant bits for data errors, then writing back any corrections to the RAM.

Redundant elements can be used at the system level. Three separate microprocessor boards may independently compute an answer to a calculation and compare their answers. Any system that produces a minority result will recalculate. Logic may be added such that if repeated errors occur from the same system, that board is shut down.

Redundant elements may be used at the circuit level. A single bit may be replaced with three bits and separate "voting logic" for each bit to continuously determine its result (triple modular redundancy). This increases area of a chip design by a factor of 5, so must be reserved for smaller designs. But it has the secondary advantage of also being "fail-safe" in real time. In the event of a single-bit failure (which may be unrelated to radiation), the voting logic will continue to produce the correct result without resorting to a watchdog timer. System level voting between three separate processor systems will generally need to use some circuit-level voting logic to perform the votes between the three processor systems.

Hardened latches may be used.

A watchdog timer will perform a hard reset of a system unless some sequence is performed that generally indicates the system is alive, such as a write operation from an onboard processor. During normal operation, software schedules a write to the watchdog timer at regular intervals to prevent the timer from running out. If radiation causes the processor to operate incorrectly, it is unlikely the software will work correctly enough to clear the watchdog timer. The watchdog eventually times out and forces a hard reset to the system. This is considered a last resort to other methods of radiation hardening.

Military and space industry applications

Radiation-hardened and radiation tolerant components are often used in military and aerospace applications, including point-of-load (POL) applications, satellite system power supplies, step down switching regulators, microprocessors, FPGAs, FPGA power sources, and high efficiency, low voltage subsystem power supplies.

However, not all military-grade components are radiation hardened. For example, the US MIL-STD-883 features many radiation-related tests, but has no specification for single event latchup frequency. The Fobos-Grunt space probe may have failed due to a similar assumption.

The market size for radiation hardened electronics used in space applications was estimated to be $2.35 billion in 2021. A new study has estimated that this will reach approximately $4.76 billion by the year 2032.

Nuclear hardness for telecommunication

In telecommunication, the term nuclear hardness has the following meanings: 1) an expression of the extent to which the performance of a system, facility, or device is expected to degrade in a given nuclear environment, 2) the physical attributes of a system or electronic component that will allow survival in an environment that includes nuclear radiation and electromagnetic pulses (EMP).

Notes

  1. Nuclear hardness may be expressed in terms of either susceptibility or vulnerability.
  2. The extent of expected performance degradation (e.g., outage time, data lost, and equipment damage) must be defined or specified. The environment (e.g., radiation levels, overpressure, peak velocities, energy absorbed, and electrical stress) must be defined or specified.
  3. The physical attributes of a system or component that will allow a defined degree of survivability in a given environment created by a nuclear weapon.
  4. Nuclear hardness is determined for specified or actual quantified environmental conditions and physical parameters, such as peak radiation levels, overpressure, velocities, energy absorbed, and electrical stress. It is achieved through design specifications and it is verified by test and analysis techniques.

Examples of rad-hard computers

Operator (computer programming)

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