Sky skimmers: The race to fly satellites at the lowest orbits yet

There's a new race in space, but it's not where you might think. It's happening close to home – in the nearest bit of space, right on the edge of Earth's atmosphere.

High in the skies of Earth, a new space race is underway. Here, just above the boundary where space begins, companies are trying to create a new class of daring satellites. Not quite high-altitude planes and not quite low-orbiting satellites, these sky skimmers are designed to race around our planet in an untapped region, with potentially huge benefits on offer.

Roughly 10,000 satellites are orbiting our planet right now, at speeds of up to 17,000mph (27,000km/h). Every one of these delicate contraptions is in constant free-fall and would drop straight back down to Earth were it not for the blistering speeds at which they travel. It's their considerable sideways momentum, perfectly stabilised against the Earth's gravitational pull downwards, that keeps satellites in orbit.

A new class of satellites are aiming to push the limits of this balancing act and plough a much more precarious, lower orbit that would skim the top of Earth's atmosphere. Known as Very Low Earth Orbit (VLEO), spacecraft at these altitudes have to battle against the significantly greater drag from the air in the upper reaches of the atmosphere than their loftier cousins, lest they get pushed out of the sky. Should they manage it, however, such satellites might achieve something even more jaw-dropping – they could potentially fly forever.

"When you start describing it to people, it starts to sound like a perpetual motion machine," says Spence Wise, senior vice-president at Redwire, an aerospace firm in Florida. A perpetual motion machine is not meant to be possible. But it almost is, in this instance.

A handful of pioneering companies have begun work on designs for satellites that may be able to orbit the planet at these unusually low altitudes while simultaneously harvesting air and using it to make propellant – literally on the fly. This new generation of orbiters could enable ultra-high-definition surveillance of activities on the ground, or superfast satellite-based communications.

If you want to send something into orbit, you have to decide how high your satellite is going to fly. Earth orbits are generally described in terms of altitude and are categorised into different sections. The highest, at some 22,000 miles (36,000km) and above is called High Earth orbit. Here, satellites enter a geostationary position, meaning they are always above the same location on Earth below. This is useful for telecommunications and weather monitoring, for example. Next is Medium Earth orbit, which spans from roughly 22,000 miles (36,000km) down to 1,200 miles (2,000km) above the planet's surface. Below this is Low Earth orbit, which stretches down to altitudes of 250 miles (400km), where the International Space Station (ISS) is found.