In the band of sky between roughly 150 and 300 kilometers (93 to 186 miles) above the Earth, the atmosphere is both the enemy and the answer. It is dense enough to drag any satellite down within weeks if left unchecked, which is why almost nobody operates there. But that same thin air could be the fuel: an engine that scoops up atmospheric molecules and ejects them at high speed could hold a spacecraft at that altitude indefinitely, with no propellant tanks at all. Spanish startup Kreios Space announced on August 4 that it is building the first satellite designed to do exactly that.
The concept, called air-breathing electric propulsion, has been tested in vacuum chambers on the ground for nearly a decade. No one has flown it in orbit yet. Kreios, based in Nigrán in northwestern Spain, plans to be the first, in partnership with Lithuanian satellite-bus maker Kongsberg NanoAvionics. The mission has no firm launch date. The company lists 2027 as a notional target while SpaceNews has reported 2028, but the technical plan is concrete: a roughly 200-kilogram microsatellite on NanoAvionics’ MP42 bus, carrying a helicon plasma thruster fed by a passive air intake, flying at an altitude between about 150 and 300 kilometers.
How to breathe in space
At orbital velocity, roughly 7.8 kilometers per second (17,400 mph) at those altitudes, a spacecraft slams into residual atmospheric gas, mostly molecular nitrogen and oxygen, with atomic oxygen dominating above about 160 kilometers. A scoop-shaped intake on the satellite’s leading face captures some of those molecules and guides them, without valves or moving parts, into the thruster’s channel. There, radio-frequency power from a helicon antenna ionizes the gas, and electromagnetic fields accelerate the resulting plasma out the back at far higher velocity than it arrived.
The exhaust exceeds orbital speed, so the thruster produces net thrust even though the gas it pushes was collected from the very medium causing the drag. Power comes from solar panels. The propellant is free, unlimited, and everywhere along the orbit. The satellite refuels itself continuously, every second, for as long as its hardware survives.
The core challenge is that atmospheric propellant is worse than the noble gases usually used in electric propulsion. Xenon ionizes easily and efficiently; nitrogen and oxygen are harder to ionize and waste energy in rotational and vibrational excitation. Ground measurements of a comparable thruster running on nitrogen found roughly 5.7 millinewtons of thrust at 5.4 percent anode efficiency, versus 12.6 millinewtons at 26.3 percent on xenon. Air-breathing engines must overcome that penalty, plus the drag of the intake itself, and still come out ahead of simply carrying fuel.
A decade of ground work
The field’s proof of concept came from the European Space Agency and Italian manufacturer SITAEL. In March 2018, ESA announced the world’s first firing of an air-breathing electric thruster in a vacuum chamber simulating conditions at 200 kilometers: a dual-stage Hall-effect thruster with a Polish-built intake ignited first on xenon, then on a nitrogen-oxygen mix, then on atmospheric propellant alone. Engineers watched the plume shift from blue to purple as the gas changed, the visual confirmation that the engine would run on air. The RAM-EP system reached technology readiness level 4, validated in the lab but not in space. The earlier ESA satellite GOCE, which flew at about 250 kilometers for four years, had to carry 40 kilograms (88 pounds) of xenon and was limited by it; an air-breathing successor would not face that constraint.
Kreios was founded in 2021 by chief executive Adrián Senar and five aerospace-engineering classmates from the Polytechnic School of Catalonia. The company has run through three thruster generations, K-1, K-2 and K-3, with vacuum testing of the intake and engine, and raised 8 million euros (about $9.2 million) in seed funding in 2025.
Why the lowest orbit is worth fighting for
Very low Earth orbit offers what no other altitude can. Imaging resolution improves as the vantage point drops: closer to the ground means sharper pictures with smaller, cheaper optics, potentially down to roughly 10-centimeter detail for Earth observation. Communications latency falls to under 10 milliseconds one-way, versus about 300 milliseconds from geostationary orbit. Radiation exposure is 50 to 80 percent lower than in higher orbits, which matters for electronics and any future crewed infrastructure. And when a satellite’s life ends, atmospheric drag removes it from orbit within months, solving the debris problem that plagues higher altitudes.
Kreios claims sustained operation at these altitudes can cost about the same as operating at 500 kilometers, once the propellant mass disappears from the launch budget. Its demonstration satellite would also capture sub-meter-resolution visible and near-infrared imagery as a commercial payload.
The open questions
No air-breathing thruster has yet operated in space, and the step from vacuum chamber to orbital reality is a large one. The atmosphere at 150 to 300 kilometers is not a constant: density varies with solar activity, time of day, and latitude, so the intake must cope with a fuel supply that changes continuously. Atomic oxygen, the dominant species at the higher end of the band, is aggressively corrosive to spacecraft materials. And the integrated system, including intake, thruster, power and attitude control, must work as a whole under real flight conditions.
Rivals are circling: two experimental Chinese satellites are already operating below 300 kilometers, and other developers including Viridian Space in the United States, ESA’s own propulsion laboratory, and India’s Orbitt Space are working on air-breathing concepts. The first-mover claim is therefore a matter of timing and definition. What is not in dispute is the prize: a propulsion system that turns the sky itself into fuel, and with it, permanent access to an altitude regime that has been, until now, a place satellites only pass through on the way down.
Sources:
- Space.com, “Exploring very low Earth orbit: The world’s 1st air-breathing satellite thruster could soon get a test run” (Aug 9, 2026): https://www.space.com/space-exploration/satellites/exploring-very-low-earth-orbit-the-worlds-1st-air-breathing-satellite-thruster-could-soon-get-a-test-run
- SpaceNews, “Kreios Space to fly VLEO demonstration in NanoAvionics bus” (Aug 4, 2026): https://spacenews.com/kreios-space-to-fly-vleo-demonstration-in-nanoavionics-bus/
- ESA, “World-first firing of air-breathing electric thruster” (2018): https://www.esa.int/Enabling_Support/Space_Engineering_Technology/World-first_firing_of_air-breathing_electric_thruster
- SITAEL, RAM-EP system test results: https://www.sitael.com/sitael-space-has-successfully-tested-ram-ep-system/
- Aviation Week, “Kreios Space plans air-breathing electric propulsion demo” (Aug 4, 2026): https://aviationweek.com/space/commercial-space/kreios-space-plans-air-breathing-electric-propulsion-demo
- CORDIS (EU), “New orbits are on the horizon with air-breathing engines”: https://cordis.europa.eu/article/id/451370-new-orbits-are-on-the-horizon-with-air-breathing-engines