Very low Earth orbitWhy flying lower matters, and how a saucer shape helps

What is VLEO?

Very low Earth orbit usually means altitudes below about 450 km, well beneath the 500 to 600 km where many Earth observation satellites fly. At these heights there is still a trace of atmosphere, enough to slow a satellite down noticeably.

Why fly lower

• Sharper sensing: for the same optics, ground resolution scales with distance. Halving the altitude halves the size of the smallest detail a camera can see.
• Stronger links: radio signal loss grows with the square of distance, so halving the range gives roughly a 6 dB improvement, useful for radar and communications.
• Lower latency: shorter distances mean faster round trips for data.
• Cheaper access: reaching a lower orbit takes less launch energy.
• Clean end of life: drag brings dead satellites and debris down quickly, reducing long-term clutter.

The drag problem

Drag force follows the familiar relation F = ½ ρ v² C_D A: air density, times velocity squared, times a drag coefficient, times frontal area. In orbit the velocity is fixed at around 7.7 km/s, and density rises steeply as altitude falls. It also swings widely with solar activity, as the Sun heats and expands the upper atmosphere.

Without thrust, a satellite in VLEO loses altitude continuously and re-enters within months or less. To stay, it must either carry a large propellant supply or use very efficient propulsion. ESA's GOCE gravity mission showed the way, flying for years at around 255 km and lower using an ion engine to cancel drag.

Other challenges

Atomic oxygen, common at these altitudes, erodes many surface materials, so coatings and materials must be chosen carefully. Each ground pass is shorter and each footprint smaller, so persistent coverage needs more satellites or agile pointing.

Why a saucer suits VLEO

Drag depends directly on frontal area, and this is where shape matters. A saucer-shaped satellite flown edge-on presents a thin profile to the airflow while keeping its broad upper face towards the Sun for power. At equal volume, a 3 m by 0.6 m disc has around a third less frontal area than a cube, while its power-generating face is far larger.

Pair that with high-efficiency electric propulsion, powered by the same large solar surface, and sustained VLEO operations become practical. That combination is central to OrbitalX's HALO platform.