[Reading Science] Why Do Satellites Fall?... "A Space Battling Air," The Ultra-Low Orbit War

"The Lower You Go, The Stronger You Get... Electric Propulsion Endures Air Resistance and Changes the Game"
"Ultra-Low Orbit Satellite Race: A New Battlefield That Determines National Security and the Future Economy"

Satellites may appear to float in space, but in reality, they are flying through air. And that air is what brings them down.

Several hundred kilometers above the Earth's surface, the orbits utilized by humans are not perfect vacuums. Though extremely thin, the atmosphere (a layer of air) still exists and collides with satellites, robbing them of velocity and eventually causing their orbits to decay. This means that a significant portion of what we vaguely refer to as "space" is actually not fully separated from the atmosphere.

Despite this, satellites are being placed in ever lower orbits. The goal is to achieve clearer imaging and faster connectivity. The technology that enables satellites to withstand this contradiction is electric propulsion, especially ion engines. The direction of space development is shifting from "going higher" to "lasting longer."

The Lower, the Stronger: A New Battleground Created by Ultra-Low Orbits

For a long time, satellites have been launched into higher orbits. This is because the higher the altitude, the longer and more stably a satellite can stay in orbit.

However, the current trend is the exact opposite. Satellites are now being positioned at increasingly lower altitudes. Satellites that once stayed in low Earth orbit at 500–1,000 kilometers are now being placed below 300 kilometers, with some even approaching 200 kilometers.

The reason is clear: the closer to Earth, the clearer the view and the faster the connection. With the same optical equipment, satellites can obtain higher-resolution imagery, and in military reconnaissance, even a few dozen centimeters can decide strategic advantage.

The same principle applies to communications. As a satellite's altitude decreases, the signal travel distance is reduced, lowering latency. Low-latency communication is a core requirement for autonomous driving, real-time drone operation, and satellite internet services.

With the integration of artificial intelligence (AI), the ability to collect data "more frequently and more rapidly" has become crucial. As the orbital period of a satellite shortens, the speed of data updates increases dramatically.

Yang Jeong-ho, Head of the Research Strategy Team at the Policy Research Division of the Korea Aerospace Research Institute (KARI), emphasized, "The ultra-low orbit satellite race is not just about technological development; it is an extension of the power struggle to secure space as a strategic domain for national security and the future economy. The country that secures this first will be able to gain military and economic superiority."

Song Seong-chan, Executive Vice President of Hanwha Systems’ Space Business Division, said, "Ultra-low orbit satellites are highly differentiated from conventional low Earth orbit satellites because they are much closer to the ground, resulting in greatly improved resolution and communication sensitivity, and in military communications, ultra-low latency characteristics can be secured."

Ultimately, ultra-low orbit is not merely a choice of orbit, but a new battleground where reconnaissance, communication, and AI data competition intersect.

The Invisible Enemy, ‘Air’: The Most Real Force That Pulls Satellites Down

Ultra-low orbit is not a perfect vacuum. At these altitudes, there is still a very thin but distinct atmospheric layer. The air molecules collide with satellites flying at speeds of 7–8 kilometers per second, creating drag.

This force is small but continuous. Satellites gradually lose speed, causing their orbits to decay and eventually re-enter the atmosphere.

This phenomenon accelerates as the altitude decreases. While conventional low Earth orbit satellites may have a lifespan of 5–10 years, in ultra-low orbits, this can be reduced to a few months or a few years at most.

Although satellite performance improves, their operational lifespan shortens. Ultra-low orbit is where these conflicting conditions clash head-on. In the end, this competition comes down to the "battle against air."

Pushing Back as Much as You Fall: The New Balance Created by Ion Engines

The solution to this problem is simple: keep pushing the satellite as much as it falls.

An ion engine is a propulsion device that uses electricity to ionize gas, then accelerates the ions with an electric field and ejects them from the rear. Put simply, whereas chemical rockets burn fuel all at once to produce a large burst of thrust, an ion engine generates a very small force steadily over a long period. Although its instantaneous thrust is weak, its high fuel efficiency makes it ideal for gently pushing satellites over an extended time.

To understand this, think of an electric scooter rather than a car. If a car accelerates powerfully all at once, an electric scooter maintains speed by continually applying a small force, and an ion engine works in much the same way.

Lim Hyunsoo, Mission Design Team Leader at the Space Exploration Research Center of the Korea Aerospace Research Institute, explained, "In ultra-low orbits, satellites continuously lose speed due to air resistance, so electric propulsion technology that can constantly compensate for this is essential. Without electric propulsion, it is currently difficult to operate in these orbits for an extended period."

This continuous, minute thrust is the key. As long as the ion engine keeps pushing to compensate for the speed lost to drag, the satellite can maintain its orbit. In other words, an ion engine is less about sending satellites to higher orbits and more about keeping them from falling.

European Space Agency (ESA)'s Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite. It performed long-term missions overcoming air resistance by using ion engines in low orbit. Provided by ESA/AOES Medialab

The Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite of the European Space Agency (ESA) is a prime example of this principle, having operated its electric propulsion system continuously at low altitudes for over four years.

Ion engines are no longer optional—they have become a prerequisite for the era of ultra-low orbits.

Avoid or Endure Resistance: Two Technological Solutions

The way satellites battle air in ultra-low orbits is reminiscent of how underwater weapons operate.

Supercavitating torpedoes create a giant bubble layer around themselves as they travel through water, greatly reducing the contact area between the body and the water. Since water is much denser than air, resistance is higher; this bubble layer essentially forms a "void," dramatically reducing friction. In other words, instead of slicing through water, the torpedo creates a tunnel of bubbles and races through it.

Ultra-low orbit satellites, on the other hand, face the opposite condition. They can't sweep away or avoid the air, so they must continuously apply fine thrust with ion engines to compensate for the speed lost to drag.

In short, while supercavitating torpedoes use technology to avoid resistance, ultra-low orbit satellites use technology to endure resistance and maintain balance.

Ultimately, both technologies solve the same problem: not losing speed despite resistance.

The War Has Already Begun... And the Rules of Space Are Changing

The ultra-low orbit race is already a reality. SpaceX in the United States uses electric thrusters on its Starlink satellites for orbit maintenance and position control, and both China and Europe are accelerating their efforts to secure related technologies. The essence of this competition is ultimately the "ability to endure."

Executive Vice President Song Seong-chan said, "In ultra-low orbit environments, satellite altitude naturally decreases due to high atmospheric density, so high-performance thrusters capable of compensating for this are key components. The future competitiveness of satellites will greatly depend on securing such propulsion technologies."

He also predicted, "Once ultra-low orbit technology is commercialized, large-scale operation of ultra-low latency communication and ultra-high-resolution observation satellites will lead to the emergence of new services, such as real-time global connectivity and precision observation."

Shin Sang-woo, Head of the Aerospace Policy Team at the Policy Research Division of the Korea Aerospace Research Institute, stressed, "Domestic satellite technology is at the world’s fourth or fifth level, but ultra-low orbit specialized technology is still under development. Both government-driven technology localization and the fostering of a private-led ecosystem must proceed in parallel."

Ultra-low orbit is no longer a concept but a real stage where nations compete for dominance.

Reference photo to aid understanding of the article. Provided by Pixabay

For a long time, space development was a competition to go "farther and higher." But the current race is the exact opposite: lower, closer, faster. And at the center of this is the invisible air and the delicate propulsion technologies devised to overcome it.

The UK's leading financial newspaper, the Financial Times (FT), describes ultra-low orbit as "a region where satellites must constantly battle air." This means that space is no longer an empty void, but a physical environment where resistance exists.

Ultra-low orbit is no longer "empty space," but rather a physical realm that must be continuously pushed against.

For a long time, space development was a race to go "farther and higher." But the current competition is the opposite: lower, closer, faster. And at the center is the invisible air, and the minute propulsion technology developed to overcome it.

Space is not empty. Satellites are not simply orbiting—they are constantly resisting their own fall, pushing back against it.

This content was produced with the assistance of AI translation services.