Can private-sector space business be profitable, or is it just an exciting way for billionaires to live out their fantasies?

A private firm will launch the initial six of a planned 640 satellites later today (Feb. 27). If successful, these spacecraft could be the foundation of the first large-scale internet network in low-Earth orbit.

OneWeb’s satellites will orbit hundreds of miles above the Earth, providing data connections to mobile phones, laptops and tablets through ground terminals marketed by the company, which it expects to bring online as soon as 2020.

These first satellites will be launched on a Soyuz rocket from French Guiana at 4:37 pm eastern time. The mission is operated by Arianespace, a European launch-vehicle firm, which is planning a 21-flight campaign to build out OneWeb’s constellation.

Today, satellite-based internet companies rely on constellations situated tens of thousands of miles above the Earth and offer slow connections at high costs. They mainly provide service to those in remote locations, as well as airlines and cruise ships. OneWeb and its rivals believe that using thousands of comparatively low-flying satellites can provide service that is competitive with terrestrial telecoms.

One top rival is Elon Musk’s SpaceX, which launched two internet satellites last year to pilot a service called Starlink. It’s already established a 10 gigabit-per-second connection to the internet through into the Seattle Internet Exchange, a physical hub for internet service providers to connect their infrastructure near SpaceX’s main facility for satellite research.

Another prospective entrant, Ottawa, Canada-based Telesat, plans to launch its satellites on rockets built by Jeff Bezos’ space company Blue Origin.

All these companies face technical challenges producing so many satellites, and operating them in concert as they zip around the planet at speeds of over 10,000 mph. Capital expenditures in the billions of dollars will be required just to put the networks in place. Premature efforts to build similar systems in the 1990s ran into bankruptcy when hoped-for revenues failed to materialize with the rise of mobile telephones and fiber-optic networks.

OneWeb calls its project “the first 5G-ready network in space,” which captures the trend that backers believe make this time different. Future telecommunication standards rely increasingly on uniting mobile networks and site-specific internet connections on a single network, making satellite connectivity an enabler for, rather than a competitor with, existing telecommunications firms.

And with information networks delivering an increasing share of the content previously found on television, radio, and print, those backing these satellite-based projects don’t fear demand for this service will wane anytime soon.

OneWeb hasn’t had an easy path to get to this point. This launch is a year late, and a failed merger with Intelsat and a 2018 CEO switch-out worried industry watchers. In 2016, the company raised $1 billion from Japanese investor Masayoshi Son’s Softbank, which now reportedly owns 40% of OneWeb.

OneWeb founder and executive chairman Greg Wyler paved the way for this effort with O3B, a satellite-communications company focused on emerging markets, which was purchased by Luxembourg’s SES in 2016. That makes OneWeb the only internet-satellite start-up whose founders have successfully launched a telecom service in space. OneWeb also boasts technical partnerships with companies like Maxar, Virgin, Qualcomm and Airbus, which built the satellites.

Schemes like OneWeb’s, if successful, would dramatically increase the number of operating satellites in orbit today—approximately 2,000. This has the space industry, but also military planners and NASA scientists, worried about the potential for collisions and orbital debris problems.

The companies involved say they are working strenuously to ensure safe operations—after all, if their satellites are destroyed, they are out of business—but the US Department of Commerce is in the midst of a debate about what new rules may be needed as it overhauls its approach to space-traffic management.