Kármán line in the context of "Orbital decay"

The V-2 rocket (German: Vergeltungswaffe 2, lit. 'Vengeance Weapon 2'), with the development name Aggregat-4 (A4), was the world's first long-range guided ballistic missile. The missile, powered by a liquid-propellant rocket engine, was developed during the Second World War in Nazi Germany as a "vengeance weapon" and assigned to attack Allied cities as retaliation for the Allied bombings of German cities. The V2 rocket also became the first artificial object to travel into space by crossing the Kármán line (edge of space) with the vertical launch of MW 18014 on 20 June 1944.

Research of military use of long-range rockets began when the graduate studies of Wernher von Braun were noticed by the German Army. A series of prototypes culminated in the A4, which went to war as the V2. Beginning in September 1944, more than 3,000 V2s were launched by the Wehrmacht against Allied targets, first London and later Antwerp and Liège. According to a 2011 BBC documentary, the attacks from V-2s resulted in the deaths of an estimated 9,000 civilians and military personnel, while a further 12,000 laborers and concentration camp prisoners died as a result of their forced participation in the production of the weapons.

A sub-orbital spaceflight is a spaceflight in which the spacecraft reaches outer space, but its trajectory intersects the surface of the gravitating body from which it was launched. Hence, it will not complete one orbital revolution, will not become an artificial satellite nor will it reach escape velocity.

For example, the path of an object launched from Earth that reaches the Kármán line (about 83 km [52 mi] – 100 km [62 mi] above sea level), and then falls back to Earth, is considered a sub-orbital spaceflight. Some sub-orbital flights have been undertaken to test spacecraft and launch vehicles later intended for orbital spaceflight. Other vehicles are specifically designed only for sub-orbital flight; examples include crewed vehicles, such as the X-15 and SpaceShipTwo, and uncrewed ones, such as ICBMs and sounding rockets.

An orbital spaceflight (or orbital flight) is a spaceflight in which a spacecraft is placed on a trajectory where it could remain in space for at least one orbit. To do this around the Earth, it must be on a free trajectory which has an altitude at perigee (altitude at closest approach) around 80 kilometers (50 mi); this is the boundary of space as defined by NASA, the US Air Force and the FAA. To remain in orbit at this altitude requires an orbital speed of ~7.8 km/s. Orbital speed is slower for higher orbits, but attaining them requires greater delta-v. The Fédération Aéronautique Internationale has established the Kármán line at an altitude of 100 km (62 mi) as a working definition for the boundary between aeronautics and astronautics. This is used because at an altitude of about 100 km (62 mi), as Theodore von Kármán calculated, a vehicle would have to travel faster than orbital velocity to derive sufficient aerodynamic lift from the atmosphere to support itself.

Due to atmospheric drag, the lowest altitude at which an object in a circular orbit can complete at least one full revolution without propulsion is approximately 150 kilometres (93 mi).

Salyut 1 (Russian: Салют-1, lit. 'Salute 1'), also known as DOS-1 (Durable Orbital Station 1), was the world's first space station. It was launched into low Earth orbit by the Soviet Union on April 19, 1971. The Salyut program subsequently achieved five more successful launches of seven additional stations. The program's final module, Zvezda (DOS-8), became the core of the Russian Orbital Segment of the International Space Station and remains in orbit today.

Salyut 1 was adapted from an Almaz airframe and comprised five components: a transfer compartment, a main compartment, two auxiliary compartments, and the Orion 1 Space Observatory. It was visited by the Soyuz 10 and Soyuz 11 missions. While the crew of Soyuz 10 was able to soft dock, the hard-docking failed, forcing the crew to abort their mission. The Soyuz 11 crew successfully docked, spending 23 days aboard Salyut 1 conducting experiments. The Soyuz 11 crew died of asphyxia caused by a valve failure just before reentry, making them the only humans to have died above the Kármán line.

Aerospace refers to the technology and industry involved with the atmosphere and outer space collectively. Aerospace activity is very diverse, with a multitude of commercial, industrial, and military applications. Aerospace engineering consists of aeronautics and astronautics. Aerospace organizations research, design, manufacture, operate, maintain, and repair both aircraft and spacecraft.

The border between space and the atmosphere has been proposed as 100 kilometres (62.1 mi) above the ground according to the physical explanation that the air density is too low for a lifting body to generate meaningful lift force without exceeding orbital velocity. This border has been called the Kármán line.

The mesosphere (/ˈmɛsəsfɪər, ˈmɛz-, ˈmiːsə-, -zə-/; from Ancient Greek μέσος (mésos) 'middle' and -sphere) is the third layer of the atmosphere, directly above the stratosphere and directly below the thermosphere. In the mesosphere, temperature decreases as altitude increases. This characteristic is used to define limits: it begins at the top of the stratosphere (sometimes called the stratopause), and ends at the mesopause, which is the coldest part of Earth's atmosphere, with temperatures below −143 °C (−225 °F; 130 K). The exact upper and lower boundaries of the mesosphere vary with latitude and with season (higher in winter and at the tropics, lower in summer and at the poles), but the lower boundary is usually located at altitudes from 47 to 51 km (29 to 32 mi; 154,000 to 167,000 ft) above sea level, and the upper boundary (the mesopause) is usually from 85 to 100 km (53 to 62 mi; 279,000 to 328,000 ft).

The stratosphere and mesosphere are sometimes collectively referred to as the "middle atmosphere", which spans altitudes approximately between 12 and 80 km (7.5 and 49.7 mi) above Earth's surface. The mesopause, at an altitude of 80–90 km (50–56 mi), separates the mesosphere from the thermosphere—the second-outermost layer of Earth's atmosphere. On Earth, the mesopause nearly co-incides with the turbopause, below which different chemical species are well-mixed due to turbulent eddies. Above this level the atmosphere becomes non-uniform because the scale heights of different chemical species differ according to their molecular masses.

MW 18014 was a German A-4 test rocket launched on 20 June 1944, at the Peenemünde Army Research Center in Peenemünde. It was the first man-made object to reach outer space, attaining an apogee of 176 kilometres (109 mi), well above the Kármán line that was established later as the lowest altitude of space. It was a vertical test launch, and was not intended to reach orbital velocity, so it returned and impacted Earth, making it the first sub-orbital spaceflight.

Wernher Magnus Maximilian Freiherr von Braun (US: /ˈvɜːrnər vɒn ˈbraʊn/ VUR-nər von BROWN; German: [ˈvɛʁnheːɐ̯ fɔn ˈbʁaʊn]; 23 March 1912 – 16 June 1977) was a German-American aerospace engineer and space architect. He was a member of the Nazi Party and later the Allgemeine SS which supported his rocket work. He became the leading figure in the development of rocket technology in Nazi Germany, and later a pioneer of rocket and space technology in the US.

As a young man, von Braun worked in Nazi Germany's rocket development program. He helped design and co-developed the V-2 rocket at Peenemünde Army Research Center during World War II. The V-2 became the first artificial object to travel into space by crossing the Kármán line on 20 June 1944. Following the war, he was secretly moved to the United States, along with about 1,600 other German scientists, engineers, and technicians, as part of Operation Paperclip. He worked for the United States Army on an intermediate-range ballistic missile program, and he developed the rockets that launched the United States' first space satellite Explorer 1 in 1958. He worked with Walt Disney on a series of films, which popularized the idea of human space travel in the US and beyond from 1955 to 1957.

The thermosphere is the layer in the Earth's atmosphere directly above the mesosphere and below the exosphere. Within this layer of the atmosphere, ultraviolet radiation causes photoionization/photodissociation of molecules, creating ions; the bulk of the ionosphere thus exists within the thermosphere. Taking its name from the Greek θερμός (pronounced thermos) meaning heat, the thermosphere begins at about 80 km (50 mi) above sea level. At these high altitudes, the residual atmospheric gases sort into strata according to molecular mass (see turbosphere). Thermospheric temperatures increase with altitude due to absorption of highly energetic solar radiation. Temperatures are highly dependent on solar activity, and can rise to 2,000 °C (3,630 °F) or more. Radiation causes the atmospheric particles in this layer to become electrically charged, enabling radio waves to be refracted and thus be received beyond the horizon. In the exosphere, beginning at about 600 km (375 mi) above sea level, the atmosphere turns into outer space, although, by the judging criteria set for the definition of the Kármán line (100 km), most of the thermosphere is part of outer space. The border between the thermosphere and exosphere is known as the thermopause.

The highly attenuated gas in this layer can reach 2,500 °C (4,530 °F). Despite the high temperature, an observer or object will experience low temperatures in the thermosphere, because the extremely low density of the gas (practically a hard vacuum) is insufficient for the molecules to conduct heat. A normal thermometer will read significantly below 0 °C (32 °F), at least at night, because the energy lost by thermal radiation would exceed the energy acquired from the atmospheric gas by direct contact. In the anacoustic zone above 160 kilometres (99 mi), the density is so low that molecular interactions are too infrequent to permit the transmission of sound.