Journey Through Outer Space

Void Between Celestial Bodies

• Outer space is the expanse beyond Earth and its atmosphere and between celestial bodies.

• It is not completely empty, but rather a near-perfect vacuum containing low-density particles, electromagnetic radiation, magnetic fields, neutrinos, dust, and cosmic rays.

• The plasma between galaxies accounts for about half of the baryonic matter in the universe.

• The Kármán line, an altitude of 100 km above sea level, is conventionally used as the start of outer space in space treaties.

• The framework for international space law was established by the Outer Space Treaty, which permits all states to explore outer space.

• Humans began physical exploration of space during the 20th century with high-altitude balloon flights, followed by crewed rocket flights and crewed Earth orbit.

• Outer space represents a challenging environment for human exploration due to the hazards of vacuum and radiation.

• The temperature of outer space is measured in terms of the kinetic activity of the gas, with the baseline temperature set by the background radiation from the Big Bang at 2.7 kelvins.

• The size of the whole universe is unknown and might be infinite in extent.

• Even at relatively low altitudes in the Earth's atmosphere, conditions are hostile to the human body.

• Humans evolved for life in Earth gravity, and exposure to weightlessness has been shown to have deleterious effects on human health.

• The Outer Space Treaty provides the basic framework for international space law, stating that outer space is free for all nation states to explore and is not subject to claims of national sovereignty.Overview of Outer Space

• The common heritage of mankind has been used to enforce the right to access and shared use of outer space for all nations equally

• The UN has passed more than 50 resolutions concerning international co-operation in the peaceful uses of outer space and preventing an arms race in space

• There remains no legal prohibition against deploying conventional weapons in space, and anti-satellite weapons have been successfully tested by various countries

• The 1979 Moon Treaty turned the jurisdiction of all heavenly bodies over to the international community, but it has not been ratified by any nation that currently practices human spaceflight

• To achieve an orbit, a spacecraft must travel faster than a sub-orbital spaceflight and the energy required to reach Earth orbital velocity at an altitude of 600 km is about 36 MJ/kg

• Spacecraft with a perigee below about 2,000 km are subject to drag from the Earth's atmosphere, which decreases the orbital altitude

• Near-Earth space is the region of outer space above the Kármán line and has seen high levels of space pollution, mainly in the form of space debris

• Geospace is a region of outer space near Earth that includes the upper atmosphere and magnetosphere

• Interplanetary space is defined by the solar wind, a continuous stream of charged particles emanating from the Sun that creates a very tenuous atmosphere for billions of kilometers into space

• Interstellar space is the physical space within a galaxy beyond the influence each star has upon the encompassed plasma

• The local interstellar medium is a region of space within 100 parsecs of the Sun, which is of interest both for its proximity and for its interaction with the Solar System

• Intergalactic space is the physical space between galaxies, and typically, a void spans a distance of 7–30 megaparsecsA Brief History and Exploration of Outer Space

• Space can reach temperatures of 108 K and above in the intracluster medium.

• The concept of space as a vacuum was widely rejected until the 17th century.

• The idea of an infinite universe was first supported by Thomas Digges in 1576.

• The modern concept of space is based on the Big Bang cosmology, proposed by Georges Lemaître in 1931.

• The earliest estimate of the temperature of outer space was 5-6 K by Charles É. Guillaume in 1896.

• Exploration of space was initially done through observations made from Earth's surface.

• The first man-made object to leave the Solar System was Voyager 1 in 2012.

• The absence of air in space makes it ideal for astronomy at all wavelengths of the electromagnetic spectrum.

• Uncrewed spacecraft in Earth's orbit have various purposes, including weather monitoring and remote sensing of Earth.

• Space could be used for industrial processes, but the cost of access to space is high.

• Interstellar travel for human crew remains theoretical due to the distance to the nearest stars.

• The ultracold temperature of space can be used for renewable cooling technology on Earth through passive daytime radiative cooling.