By Sabine Stanley, Ph.D., Johns Hopkins University

1. The Federal Communications Commission last year gave SpaceX permission to deploy 11,943 low-Earth orbit satellites for the planned Starlink system. A new application from SpaceX Services, a sister company, asks the FCC for “a blanket license authorizing operation of up to 1,000,000 Earth stations that end-user customers will utilize to.
2. Operate in low Earth orbit and also around the Moon, are currently under develop-ment. In 2016, Bigelow Aerospace is slated to dock its experimental prototype module to the ISS in a first-of-its-kind demonstration and a clear signal that the beginning of the ISS transition era is upon us.
3. LEO satellites operate from 500 kilometers (311 miles) to 2,000 kilometers above the Earth’s surface. Traditional communication satellites are stationed far higher, at roughly.

A low Earth orbit (LEO) is an Earth-centred orbit close to the planet, often specified as an orbital period of 128 minutes or less (making least 11.25 orbits per day) and an eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, with an altitude never more than about one-third of the radius of the Earth. Jan 06, 2017 Low Earth Orbit (LEO) is a popular place. It is where the majority of space missions are sent, where all of our satellites reside, and where the ISS orbits the planet.

Low Earth orbit is the result of scientists’ attempts and studies to answer a very common question: Where does space begin? It includes all the layers of the atmosphere, which are distinguished by their characteristics, how gas behaves, temperature, pressure, and distance from the surface. However, the layer, with 80% of the mass, is the thinnest of all.

Even though low earth orbit includes all layers of the atmosphere, most of what people know from the atmosphere happens in the first two layers. Troposphere and stratosphere are the closest layers with the major amount of atmospheric mass. Low earth orbit somehow marks the beginning of outer space.

The Karman line was a governmental attempt to mark the boundary between Earth and outer space, but they could not agree on an altitude. Thus, it ranges from 80 to 100 kilometers. What everyone agrees on are the layers of the atmosphere and their altitudes. The first layer is the troposphere.

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What Is the Troposphere?

The lowest layer of atmosphere is called the troposphere, with an average thickness of 10 kilometers, spread above the Earth’s surface. Everything known as ‘weather’ happens in this layer, namely, winds, thunderstorms, tornadoes, hurricanes, blizzards, and cloud formation.

The convective overturning of air results in all the weather phenomena. Besides, water goes through all its phases in the troposphere: vapor, rain, and snow. The ‘overturning’ is reflected in the name of this thin but dense layer: tropos is Greek for ‘turn’, referring to the overturning of air. Now, why does air overturn here?

This is a transcript from the video series A Field Guide to the Planets. Watch it now, on The Great Courses Plus.

Overturning in the Troposphere

The overturning – vertical mixing – happens sincethe highest temperature of the troposphere is at the bottom. The averagetemperature on the surface is about 60°F, and itdecreases down to an average of −75°F at the top. About 80% of theatmosphere’s mass is concentrated here. The troposphere ends with a boundarycalled the tropopause, where the next layerbegins.

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What is the Stratosphere?

The stratosphere is the second-lowestlayer of Earth’s atmosphere, starting at 10 kilometers above the surface.Unlike the troposphere, the temperature in the stratosphere increases withaltitude. At the top, the temperature is around 32°F – almost 100 degreeshigher than the bottom. However, the pressure decreases to one millibar, i.e.,1000 times less than the Earth’s surface pressure. The stratosphere ends at thestratopause. Does the higher temperature mean the stratopause is warm?

Is the Stratosphere Warm?

The higher temperature in thetroposphere is the result of the Sun’s ultraviolet (or UV) radiation, trappedby ozone particles (O₃). The famous ozone layer, where UV isabsorbed, is located here. The highest concentration of ozone is at the lowestpart of the stratosphere, but O₃ can also be found up to the middleof the layer.

Most of the radiated UV is absorbed byO₃, breaking it into O₂ and atomic oxygen (O). Next, Oand O₂ combine again and recreate O₃. However, theabsorbed energy does not create a warm environment, since the molecules are sofar away from each other that collisions rarely happen. Hence, airplanes flyingaround this altitude need to create pressure inside the cabin and regulate thetemperature.

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Airplanes in the Stratosphere

The cruising altitude for most commercial flights is around 39,000 feet or 12 kilometers above the surface. This means that airplanes fly in the lowest part of the stratosphere, above the weather and the turbulence it causes. The boundary of the two layers can be seen from the plane, as clouds do not enter the stratosphere. The air is too thin here, so airplane cabins are pressurized.

Besides the commercial planes, NASA’sSOFIA also flies in the lower stratosphere.

SOFIA: Stratospheric Observatory for Infrared Astronomy

SOFIA is a Boeing 747 with a 100-inchtelescope attached. It flies at 12 kilometers, above 99% of Earth’s atmosphere,and studies the solar system in the infrared part of the light spectrum. Transientphenomena, such as eclipses and occultations, are also studied best with SOFIA.

Pluto and Saturn’s moon, Titan, was also studied by SOFIA from the stratosphere. Higher in the stratosphere, the air pressure is too low for typical airplanes to fly. Military jets and other planes that do fly at higher altitudes use their engine power to conduct the flight.

However, scientific balloons arelaunched to collect data. The best location to do so is McMurdo Station inAntarctica, as the South Pole vortex keeps the balloons contained in a smallarea and does not let them fly away into the distance.

It can be concluded that the first two layers of the atmosphere in the low Earth orbit are the ones humans make the most use of.

Common Questions about Low Earth Orbit

Q: Is low Earth orbit considered space?

Low Earth orbit is the ‘circle’ around Earth’s atmosphere up to 2000 kilometers above the surface. The satellites and other human-made space objects also orbit in the low earth orbit. The end of the orbit is the beginning of space, where solar winds start, and the Earth’s atmosphere is too thin to be considered gas.

Q: What does low Earth orbit mean?

Low earth orbit extends up to 2000 kilometers above the surface. All the atmosphere layers reside in this area, with almost 80% of the mass concentrated in the lowest layer, the troposphere. The weather, winds and tornados, plane flights, and satellite orbits all occur in this 2000-kilometer-high zone before space characteristics dominate the environment.

Q: What is in the stratosphere layer?

The stratosphere is the second-lowest layer in the low Earth orbit. It starts at 10 kilometers above the surface, and even though its temperature rises through altitude due to UV radiation, its pressure decreases significantly. It contains the ozone layer and the cruising altitude for most commercial planes.

Q: Can you go above low Earth orbit?

Low Earth orbit is about 2000 kilometers, which is not very high by space and orbit standards. In fact, the end of the low orbit somehow marks the beginning of space. The International Space Station orbits 400 kilometers above the Earth’s surface, and many satellites go above that. All the explorers sent to other planets pass the low Earth orbit at an early stage in their trip.

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