London-based start-up OneWeb is set to launch the first six satellites in its multi-billion-pound project to take the internet to every corner of the globe.
The plans could eventually see some 2,000 spacecraft orbiting overhead.
Other companies are also promising so-called mega-constellations, but OneWebbelieves it has first-mover advantage with an operational system.
Wednesday's launch on a Soyuz rocket from French Guiana is timed for 18:37 local time (21:37 GMT).
Controllers at OneWeb's HQ in the UK capital will be waiting to pick up signals from the spacecraft when they come off the top of the Russian vehicle.
The platforms' most important task is to secure the frequencies needed to relay the coming network's internet connections.
Assuming these pathfinders perform as expected, OneWeb will then begin the mass rollout of the rest of the constellation towards the end of the year.
This will see Soyuz rockets launching every month, lofting up to 36 satellites at a time.
To provide global internet coverage, there will need to be 648 units in orbit.
"We have a tonne of spectrum and we have it everywhere on Planet Earth," explained OneWeb CEO Adrian Steckel.
"We're going to connect lots of people who're not currently connected. We're going to start by focussing on connecting schools, connecting boats, connecting planes, and connecting huge swathes of the planet that don't make sense for fibre," he told BBC News.
Who's backing OneWeb?
The company was started by American telecoms entrepreneur Greg Wyler.
He'd previously founded another constellation called O3b, which stands for "other three billion" – a reference to that half of the planet without connectivity.
O3b operates a fleet of 16 satellites moving around the equator at an altitude of 8,000km.
OneWeb is Wyler's even grander vision – a much denser network that flies just 1,200km above the ground.
The satellites' nearness, their high throughput – over one terabit per second across the constellation – and global coverage promises to transform internet provision for those who are currently underserved, or simply un-served.
At least that's the view shared by OneWeb's partners, who include companies such as chip-maker Qualcomm, Sir Richard Branson's Virgin Group, drinks giant Coca-Cola, satellite communications specialist Hughes, and tech financier SoftBank./BBC