What is VLEO?
Very Low Earth Orbit (VLEO) refers to altitudes below approximately 400 km, well within Earth's residual atmosphere. At 200–300 km, atmospheric drag is significant enough to deorbit an uncontrolled satellite within weeks. ESA and several startups are actively exploring VLEO for Earth observation satellites that would achieve sub-metre resolution without a huge optical telescope.
The two main challenges
At VLEO altitudes, the atmosphere — though extremely thin — creates constant drag that slows the satellite and causes orbital decay. Counteracting this requires continuous electric propulsion, consuming propellant and adding mass. More insidiously, at these altitudes up to 96% of the trace atmosphere is atomic oxygen (AO), a highly reactive species that corrodes most conventional satellite materials rapidly. Specialised surface coatings and atomic-smooth structures that scatter AO elastically (reducing drag by up to 50%) are active areas of research.
Why pursue VLEO?
Proximity to Earth produces dramatic gains for Earth observation: a camera at 250 km requires a much smaller primary mirror to achieve the same resolution as one at 600 km. Signal path loss is also lower, reducing transmit power requirements. Potential round-trip latency below 5 ms would open applications impossible even at traditional LEO altitudes.
Research and industry players
ESA's FAST (Future Airbreathing Satellite Technology) programme, Skeyeon, and a handful of university programmes are developing atmosphere-breathing electric propulsion (ABEP) systems that would harvest residual atmospheric molecules as propellant — potentially enabling indefinite VLEO operation without fuel resupply.