关于太空的资料（英文）

Outer space

"Deep space" redirects here. For the NASA space probes, see Deep Space 1 and Deep Space 2.

Layers of Atmosphere - not to scale (NOAA)Outer space, also simply called space, refers to the relatively empty regions of the universe outside the atmospheres of celestial bodies. Outer space is used to distinguish it from airspace (and terrestrial locations). Contrary to popular understanding, outer space is not completely empty but contains a low density of particles, predominantly hydrogen gas as well as electromagnetic radiation.

Earth's boundary

There is no discrete boundary between the Earth's atmosphere and space as the atmosphere gradually attenuates with increasing altitude. If the atmosphere had a constant temperature, its pressure would decrease exponentially from a sea-level value of 100 kPa (1 bar) toward its final value of zero. The Federation Aeronautique Internationale has established the Kármán line at an altitude of 100 km (62 miles) as a working definition for the boundary between atmosphere and space. The United States designates people who travel above an altitude of 50 miles (80 km) as astronauts. During re-entry, 400,000 feet (75 miles or 120 km) marks the boundary where atmospheric drag becomes noticeable.

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Solar System

Outer space within the solar system is called interplanetary space, which passes over into interstellar space at the heliopause. The vacuum of outer space is not really empty; it is sparsely filled with several dozen organic molecules discovered to date by microwave spectroscopy. According to the Big bang theory,2.7 K blackbody radiation was left over from the 'big bang' and the origin of the universe, and cosmic rays, which include ionized atomic nuclei and various subatomic particles. There is also gas, plasma and dust, and small meteors and material left over from previous manned and unmanned launches that are a potential hazard to spacecraft. Some of this debris re-enters the atmosphere periodically.

The absence of air makes outer space (and the surface of the Moon) ideal locations for astronomy at all wavelengths of the electromagnetic spectrum, as evidenced by the spectacular pictures sent back by the Hubble Space Telescope, allowing light from about 14 billion years ago, back almost to the time of the Big Bang to be observed. Pictures and other data from unmanned space vehicles have provided invaluable information about the planets, asteroids and comets in our solar system.

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Pressure variance

Going from sea level to outer space produces a pressure difference of only about 15 lbf/sq in, equal to surfacing from an underwater depth of about 34 ft (10 m).

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Vacuum

Contrary to popular belief a person suddenly exposed to the vacuum would not explode, but it would take a matter of milliseconds for a person to freeze to death. Water vapor would start to boil off from exposed areas such as the cornea of the eye, and along with oxygen, from membranes inside the lungs. Here is NASA's explanation.

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Satellites

There are many artificial satellites orbiting the Earth, including geosynchronous communication satellites 35,786 km (22,241 miles) above mean sea level at the Equator. Their orbits never "decay" because there is almost no matter there to exert frictional drag. There is also increasing reliance, for both military and civilian uses, of satellites which enable the Global Positioning System (GPS). A common misconception is that people in orbit are outside Earth's gravity because they are obviously "floating". They are floating because they are in "free fall": the force of gravity and their linear velocity is creating an inward centripetal force which is stopping them from flying out into space. Earth's gravity reaches out far past the Van Allen belt and keeps the Moon in orbit at an average distance of 384,403 km (238,857 miles). The gravity of all celestial bodies drops off toward zero with the inverse square of the distance.

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Milestones on the way to space

Sea level - 100 kPa (1 atm; 1 bar; 760 mm Hg; 14.5 lbf/in?) of atmospheric pressure

4.6 km (15,000 ft) - FAA requires supplemental oxygen for aircraft pilots and passengers.

5.0 km (16,000 ft) - 50 kPa of atmospheric pressure

5.3 km (17,400 ft) - Half of the Earth's atmosphere is below this altitude.

8.8 km (29,035 ft) - Summit of Mount Everest, the highest mountain on Earth

16 km (52,500 ft) - Pressurized cabin or pressure suit required.

18 km (59,000 ft) - Boundary between troposphere and stratosphere

20 km (65,600 ft) - Water at room temperature boils without a pressurized container. (The popular notion that bodily fluids would start to boil at this point is false because the body generates enough internal pressure to prevent it.)

24 km (78,700 ft) - Regular aircraft pressurization systems no longer function.

32 km (105,000 ft) - Turbojets no longer function.

34.7 km (113,740 ft) - Altitude record for manned balloon flight

45 km (148,000 ft) - Ramjets no longer function.

50 km (164,000 ft) - Boundary between stratosphere and mesosphere

80 km (262,000 ft) - Boundary between mesosphere and thermosphere

100 km (328,084 ft) - Kármán line, defining the limit of outer space according to the Fédération Aéronautique Internationale. Aerodynamic surfaces no longer function from lack of significant atmospheric density.

120 km (400,000 ft) - First noticeable atmospheric drag during re-entry from orbit

200 km - Lowest possible orbit with short-term stability (stable for a few days)

350 km - Lowest possible orbit with long-term stability (stable for many years)

690 km - Boundary between thermosphere and exosphere

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Regions of outer space

Cislunar space

Interplanetary space

Interstellar medium

Intergalactic space

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Space does not equal orbit

To perform an orbital space flight, a spacecraft must go higher and faster than for a sub-orbital space flight. A spacecraft has not made orbit until it is circling the Earth at a sufficiently great speed such that the weight of the spacecraft is exactly equal to the centripetal acceleration required to keep it in a circular orbit (see circular motion). It must not only rise above the atmosphere, but must also achieve a sufficient orbital speed (angular velocity). For a low Earth orbit, this is about 7.9 km/s (18,000 mph). Konstantin Tsiolkovsky was the first to realize that, given the energy available from any available chemical fuel, a several-stage rocket would be required. The escape velocity to pull free of Earth’s gravitational field altogether and move into interplanetary space is about 40,000 km/h (25,000 mph or 11,000 m/s). The energy required to reach velocity for low Earth orbit (32 MJ/kg) is about twenty times the energy required simply to climb to the corresponding altitude (10 kJ/(km·kg)).

There is a major difference between sub-orbital and orbital space flights. Minimal altitude for a stable orbit around the Earth, without excessive atmospheric drag, begins at around 350 km (220 miles) above mean sea level. A common misunderstanding about the boundary to space is that orbit occurs simply by reaching this altitude. Achieving orbital speed can theoretically occur at any altitude, although atmospheric drag precludes an orbit that is too low. At sufficient speed, an airplane would need a way to keep it from flying off into space, but at present, this speed is several times greater than anything within reasonable technology.

什么是空侧与陆侧？具体包含什么内容？

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空侧陆侧这两个词一般出现在机场控制区,空侧指飞行器区域 ,机场内旅客和其他公众不能自由进入的地区。陆侧是机场内旅客和其他公众可以自由进入的地区。对候机建筑物而言,通常以登机旅客的安全检查口为界。

AAM是一整套新兴航空技术的统称，它能够为旅客和货物在本地、城市和地区范围内提供新的空中运输方式。作为AAM的类型之一，本文将重点介绍UAM(城市空中交通)及其空域和空侧问题。

L&BLab今后还会研究AAM的其他领域。UAM是指在城市建成区内所有的空中运输方式，包括传统的直升机和电动飞机。传统直升机运营在20世纪初就开始了。

但是由于高昂的运营成本和巨大的噪声问题，直升机运输始终未能成为城市空中交通的主流选项。近些年，电池技术的发展吸引了一批发明家、工程师和投资人，他们的共同目标是将电动飞机引入这一市场。目前全世界有超过200种电动飞机正在开发中。

与直升机相比，预期能够实现更低的运营成本和更安静的操作环境。目前，部分电动飞机制造商已与FAA(美国联邦航空局)针对商业运营的认证要求达成了一致意见，多样化的UAM服务已触手可及。在投资人。

地方政府、以及飞机制造商的共同推动下，已有多家UAM运营商宣布将在未来3-4年推出使用垂直起降电动飞行器(eVTOL、下称“电动飞机”)的服务。因此各城市和地方政府现在已有必要行动起来。

为辖区内未来的UAM运营环境制定政策和拟定规划。NASA(美国宇航局)根据运量、自动化水平和空中管理水平提出了六个UAM成熟度等级。本文重点介绍其中。

第一、第二等级(下称“UML1和UML2”)。这两类基础等级代表在受控环境下，由飞行员操作的低密度运行，预计在未来5-10年间可以实现。在UAM服务落地的众多必要因素中，最重要的三个因素分别是飞行器。配套设施、空域结构与管理。

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