The following information is sourced from the internet and AI databases, and may be inaccurate. Corrections and feedback are welcome.（Issues · loongling/FurrySpace (github.com)）

Introduction – P1

Space (English: Space) ^[1]is defined in Chinese dictionaries as the extremely high sky. ^[2] It refers to the outer space beyond the Earth’s atmosphere, encompassing the entire area beyond the atmospheric layer. The International Aeronautical Federation, located in Geneva, Switzerland, defines the boundary between the atmosphere and space as being at an altitude of 100 kilometers (approximately 62 miles) above sea level, known as the Kármán line. This line is named after American scientist Theodore von Kármán. ^[3]

Geophysicists divide the atmospheric space (also known as airspace) into five layers. The troposphere extends from sea level to 10 kilometers and contains dense air, referred to as the dense atmosphere. As altitude increases in the dense atmosphere, the air becomes thinner. The stratosphere lies between 10-40 kilometers. The mesosphere is between 40-80 kilometers, and the thermosphere, which ranges from 80-370 kilometers, forms the lower part of the ionosphere. The exosphere is located above 370 kilometers and is part of the upper ionosphere. From the Earth’s surface to an altitude of 100 kilometers, air becomes increasingly scarce as the altitude rises. About 75% of the Earth’s atmosphere exists within the troposphere, and 97% is below the stratosphere. The outer edge of the stratosphere is the highest point at which aircraft can fly using air for support. Certain high-altitude rockets can enter the mesosphere. The lowest orbit for artificial satellites is within the thermosphere, where air density is 1% of that at Earth’s surface. Air continues to exist at altitudes up to 16,000 kilometers, and even at 100,000 kilometers, there are air particles. Therefore, there is no clear boundary between airspace and outer space. ^[3] The United Nations Committee on the Peaceful Uses of Outer Space’s Scientific and Technical Subcommittee has noted that it is currently impossible to establish precise and lasting scientific standards to delineate the boundary between outer space and airspace. In recent years, there has been a trend to consider the lowest altitude of artificial satellite orbit (100–110 kilometers) as the lower limit of outer space. ^[4]

A space station, also known as an “orbital station” or “space station,” is a manned spacecraft designed to allow multiple astronauts to cruise, work, and live for extended periods. During the operation of a space station, astronaut replacement and the resupply of equipment can be carried out by manned spacecraft or space shuttles, while equipment can also be transported by unmanned spacecraft. In 1971, the Soviet Union launched the world’s first space station, “Salyut 1,” followed by “Salyut 2–7” between 1971 and 1983. In 1986, the Soviet Union launched a larger space station, “Mir.” In 1973, the United States launched the “Skylab” space station using leftover materials from the Apollo Moon landing program.

Moon Landing

The Moon, being the closest celestial body to Earth (approximately 380,000 kilometers away), became the first stop for human space exploration. In 1959, the Soviet Union’s Luna 2 probe landed on the Moon, marking the first time a spacecraft from Earth had reached another celestial body. In October of the same year, Luna 3 flew by the Moon and sent back the first photographs of the far side of the Moon. In 1970, Luna 16 landed in the Sea of Fertility and returned 100 grams of lunar soil to Earth.

The United States embarked on its ambitious Apollo program in the 1960s, aiming to land humans on the Moon for field exploration. Between 1961 and 1967, nine Ranger probes, seven Surveyor probes, and five Lunar Orbiters conducted extensive lunar surveys, capturing images of the Moon and analyzing its soil, thus preparing for human lunar landings. The U.S. then launched 17 Apollo missions using the Saturn V rocket. Apollo missions 1-3 were test missions, Apollo 4-6 were unmanned, Apollo 7 carried astronauts in Earth orbit, and Apollo 8-10 carried astronauts in lunar orbit, culminating in the manned lunar landings of Apollo 11-17.

On July 16, 1969, Apollo 11 made history by landing humans on the Moon for the first time. The mission was carried out by astronauts Neil Armstrong, Buzz Aldrin, and Michael Collins. After reaching lunar orbit, Collins piloted the command module around the Moon while Armstrong and Aldrin descended in the lunar module, landing in the Sea of Tranquility on July 20. Neil Armstrong became the first person to set foot on the Moon. The astronauts conducted scientific investigations on the lunar surface, planted an American flag, and left a commemorative plaque. Over the course of five more successful lunar landings, astronauts spent a total of about 300 hours on the Moon.

Following these missions, lunar exploration largely halted until 1994, when the United States launched the unmanned Clementine probe, which mapped the Moon’s surface, preparing for future plans to establish lunar bases and observatories. In 1998, the Lunar Prospector mission carried a neutron spectrometer to detect hydrogen atoms, which revealed the presence of water at the poles of the Moon.

Venus and Mercury

Venus, with a radius, mass, and density similar to Earth’s, is considered Earth’s sister planet, garnering significant interest despite the limited data obtained from ground-based observations. Although initial attempts to launch probes to Venus failed, in 1962, the U.S. successfully flew Mariner 2 within 35,000 kilometers of Venus, marking the first spacecraft flyby of a planet. It also revealed that the surface temperature of Venus exceeded 400°C. From 1969 to 1981, the Soviet Union’s Venera probes 5 through 14 successfully landed on Venus and conducted scientific investigations. The U.S. launched Pioneer Venus 1 on May 20, 1978, which reached Venus on December 4, orbiting and mapping its terrain with radar. Pioneer Venus 2 released four probes into Venus’s atmosphere, gathering data on its atmosphere, clouds, and magnetic field as the probes descended. In 1989, the U.S. launched the Magellan probe, which used synthetic aperture radar to map Venus’s surface. These missions revealed that Venus has a weak magnetic field and surface pressure 90 times greater than Earth’s sea level pressure. Venera 12 even detected lightning on Venus.

After investigating Venus, the U.S. Mariner 10 spacecraft conducted three flybys of Mercury. It discovered Mercury’s magnetic field and magnetosphere and identified helium as the primary component of Mercury’s thin atmosphere. Cameras aboard Mariner 10 captured numerous images, revealing that Mercury’s terrain is dominated by craters and basins formed by meteoroid impacts.

Mars Missions

Mars shares many similarities with Earth, such as a solid surface and changing seasons. It also has polar ice caps that vary with the seasons. During the era of telescopic observations, some even believed that there were artificial canals on Mars. Humanity’s interest in Mars has always been strong, leading to over 20 missions aimed at exploring the planet.

In 1962, the Soviet Union launched Mars 1 and Cosmos 21, while the U.S. launched Mariner 3, though all three missions ended in failure. However, on January 28, 1964, Mariner 4 was successfully launched and on July 14, 1965, it made a close flyby of Mars at an altitude of about 10,000 kilometers, sending back the first-ever photos of the Martian surface. In 1974, the Soviet Union’s Mars 5 spacecraft captured the first color images of Mars. Following this, both the U.S. and the Soviet Union launched several orbiters around Mars, greatly enhancing our understanding of the planet.Mars Missions and Beyond.In 1976, the U.S. successfully landed Viking 1 and Viking 2 on Mars. These landers measured the distribution of atmospheric temperature and pressure as they descended. They discovered dry riverbeds and erosion patterns, suggesting that Mars once had significant water. However, the Viking analysis concluded that Mars’ atmosphere and surface materials lacked organic molecules, and no signs of life were detected through camera observations. This led to the conclusion that the Martian surface is unlikely to host life, at least none resembling Earth’s life forms.

Interest extended to Mars’ two moons, Phobos and Deimos. In July 1988, the Soviet Union launched the Phobos 1 and 2 probes, which orbited and attempted to land on Phobos.

In the recent decades, advancing technology has reignited hopes of a manned mission to Mars, with many experts predicting human exploration of the planet in the 21st century. Before humans can set foot on Mars, several preparatory missions are underway.

In 1993, the U.S. Mars Observer mission lost contact after entering Martian orbit, resulting in failure. However, in December 1996, NASA launched the Mars Pathfinder, which landed on Mars’ Ares Vallis after a seven-month journey. It carried a six-wheeled rover, the Sojourner, to explore Mars’ surface and analyze rocks and soil, confirming the Viking findings of past floods.

In November 1996, NASA launched the Mars Global Surveyor, which orbited Mars to study its surface, atmosphere, and magnetic field. It sent radio waves through Mars’ atmosphere to Earth, helping scientists understand its temperature, gravity, and chemical composition. However, subsequent missions like the Mars Polar Lander and Mars Climate Orbiter, both in 1999, ended in failure. The 2001 Mars Odyssey mission, however, was a success, entering Martian orbit and gathering crucial data.

The European Space Agency (ESA) also planned to launch the Mars Express in 2003, marking a new chapter in European planetary exploration. The Mars Express would consist of an orbiter and lander, contributing to the international Mars exploration efforts between 2003 and 2007.

Exploring Beyond the Solar System

NASA’s Pioneer 10 probe flew past Jupiter in December 1973, capturing the first close-up images of the planet and its moons. It became the first human-made object to leave the solar system, crossing Neptune’s orbit in 1983. Pioneer 11, Voyager 1, and Voyager 2 also visited Jupiter and its moons.

Pioneer 10 and 11 each carried a gold-plated aluminum plaque depicting a human figure, the solar system’s location, and the spacecraft’s origin on Earth. Voyager 1 and 2 carried “Golden Records,” containing Earth sounds, greetings in 60 languages (including Chinese dialects), and music such as the Chinese traditional piece Flowing Water. These were sent as messages for potential extraterrestrial life.

The Voyager probes provided significant insights, such as images of Jupiter’s auroras and volcanic activity on its moon Io. Voyager also detected Saturn’s radio emissions, and Voyager 2 discovered that Uranus has a tilted magnetic field. The spacecraft later visited Neptune and returned stunning images.

The Galileo mission studied Jupiter’s system in detail, including its famous Great Red Spot, and released a probe into Jupiter’s atmosphere. This probe transmitted invaluable data before being crushed by atmospheric pressure. Galileo also suggested the possibility of subsurface oceans on Jupiter’s moons Europa and Callisto, raising hopes of discovering extraterrestrial life.

In October 1997, NASA launched the Cassini spacecraft, powered by nuclear batteries, to explore Saturn. Cassini carried the Huygens probe, which would be deployed to Saturn’s mysterious moon, Titan. Titan, enveloped in thick atmosphere, has an environment resembling early Earth. Cassini reached Saturn in 2004.

NASA’s future exploration plans aim to deepen our understanding of the solar system. Among these is a proposed mission to Europa, which may involve deploying an underwater probe to explore its hidden ocean and search for signs of life.

Comets and Asteroids

Spacecraft have been used to explore not only the major planets and their moons but also comets and asteroids. During Halley’s Comet’s return in 1985-1986, five spacecraft conducted close-range observations, revealing surprising details, such as Halley’s nucleus being ellipsoidal rather than spherical. Gases and dust were seen erupting from active areas on its surface.

The European Space Agency (ESA) planned to explore seven short-period comets through missions such as “Deep Space 1” (DS1), “Stardust,” “Contour,” “Rosetta,” and “Deep Space 4” (DS4). DS1 and DS4 were collaborative efforts with NASA.

DS1 was launched in October 1998 and planned to fly past asteroid 3352 McAuliffe, Mars, and the comet Wilson-Harrington, with a close approach to the comet in June 2000. DS1 would travel at 15 km/s, passing about 500 km from the comet nucleus. It was the first mission to use an ion engine, with the spacecraft returning samples to Earth in May 2010.

“Stardust,” launched in February 1999, aimed to collect and return samples from comet Wild 2.

The “Rosetta” mission, planned for launch in 2003, would conduct a two-year study of comet Wirtanen, with the spacecraft landing instruments on the comet’s surface to analyze its composition and structure. The mission would include digging samples from the surface, investigating the interaction between the comet’s plasma and solar wind, and analyzing the comet’s internal structure using sound waves.

DS4, planned for launch in April 2003, aimed to enter orbit around comet Tempel 1 in December 2005 and land a probe on its surface in April 2006. The probe would collect material from different depths of the comet and seal the samples in containers, which would be sent back to Earth in May 2010.

Space Science Research

In 1946, the U.S. sent fruit flies into space aboard captured German V-2 rockets, marking the first biological experiment in space. In 1957, the Soviet Union launched the first artificial satellite, Sputnik 1. Space stations soon became essential for conducting long-term scientific research in space. The Soviet Union launched the first space station, Salyut 1, in 1971, which was supplied by Soyuz spacecraft. The last manned Salyut mission ended in 1986 with Salyut 7. The U.S. launched Skylab in 1973, but it was decommissioned in 1974 and fell to Earth in 1979.

In 1986, the Soviet Union launched the Mir space station. It exceeded 13 meters in length, weighed 21 tons, and was designed for a 10-year lifespan. It consisted of three sections: the working module, transition module, and unpressurized module, with six docking ports for spacecraft or shuttles. Mir became the site of numerous scientific experiments and set long-duration spaceflight records before being decommissioned and deliberately crashed into the Pacific Ocean in March 2001. In 1983, ESA launched the Spacelab space station, which flew aboard the Space Shuttle.

The International Space Station (ISS) represents a new era of space research. Spearheaded by the U.S. and Russia, it is supported by ESA, Japan, Canada, Brazil, and 16 other countries. Construction began in 1994, with completion planned for 2006. The ISS would span 110 meters, with a width of 88 meters and a total mass exceeding 400 tons, providing a work environment for six to seven astronauts.

In 1981, the first infrared astronomy satellite was launched. One of the most significant astronomical advancements occurred on April 25, 1990, when NASA’s Discovery shuttle deployed the Hubble Space Telescope (HST). Costing $2.1 billion, HST revolutionized astronomy, particularly astrophysics. By being placed in space, HST could avoid atmospheric interference, achieving diffraction-limited performance with an unparalleled resolution. This telescope has become humanity’s window into the mysteries of the cosmos. Later, NASA and ESA launched additional observatories, including the Chandra X-ray Observatory and XMM-Newton Space Observatory.

NASA’s Space Shuttle was the world’s only reusable spacecraft capable of transporting personnel and cargo between Earth and low-Earth orbit, conducting various scientific experiments in space.

Space Environment

Since the Big Bang, the universe has been expanding, with its temperature steadily dropping. Outer space is now a frigid environment with an average temperature of -270.3°C.

In space, celestial bodies emit electromagnetic waves and high-energy particles known as cosmic rays. The Sun, for example, emits electromagnetic radiation, solar cosmic rays, and the solar wind. Solar cosmic rays are high-energy particles emitted during solar flares, while the solar wind consists of plasma ejected from the Sun’s corona.

Many celestial bodies, including Earth, have magnetic fields that trap these high-energy charged particles, forming radiation belts. Earth’s radiation belts, for instance, are composed of an inner and outer belt. Space, thus, is not only cold but also highly irradiated.

Furthermore, space is a high-vacuum environment with microgravity, where gravitational forces are only one-hundredth to one-ten-thousandth of Earth’s gravity (1g). Astronauts in space experience near weightlessness due to this microgravity environment.

1. https://baike.baidu.com/reference/1003/533aYdO6cr3_z3kATPKNnanyNirFNdWuvOLUALZzzqIP0XOpX5nyFJwz6dww8PBqEQ_CsdZhb9tav_yvV1QmtqhXb7x2Arp_kHfpBz7Ay7zi9g ↩︎
2. 莫衡等主编·当代汉语词典：上海辞书出版社，2001 ↩︎
3. 刘进军编著·世界航天科普丛书 天使的翅膀 宇宙飞船：航空工业出版社，2012.07 ↩︎
4. https://baike.baidu.com/reference/1003/533aYdO6cr3_z3kATPeMzvX2M3mRY9SovLOCBrNzzqIP0XOpRovyScZjtoRx_fhqW1qd_8kzMoRax7nleU0zlYFpeZ81QrUjlXGZW1yTleL4p51sxg ↩︎