DARPA is sending the first satellite of its Blackjack network into orbit later this year. Blackjack is intended to eventually offer the U.S. military a persistent global communications network by blanketing the globe with low-Earth orbit satellites that can quickly transmit data between one another using optical lasers.
Blackjack is just an experimental project for now — DARPA is, after all, the research wing of the U.S. military. But the technology could someday offer the type of global internet access that Elon Musk's SpaceX is trying to introduce with Starlink. DARPA hopes to launch three additional satellites in 2021 so that it can demonstrate what it would be like to have a functioning communications network in space.
SpaceX is hoping to get permission to send up to 42,000 satellites into low-Earth orbit to form its network, and has already deployed 422 as of late April. The company has faced criticism from scientists who are concerned that a large amount of new satellites in space will interfere with radio communications and make it difficult for astronomers to identify constellations of stars amid the "congestion." SpaceX hopes to roll out its Starlink internet service more or less globally by 2021.
Why do we need space internet? — DARPA's entry into the field is noteworthy because the internet as we know it today began as a military research project intended for transmitting time-sensitive communications as quickly and efficiently as possible.
By creating a network in the stars, DARPA believes communication will be more resilient, because it will be harder to attack the physical infrastructure, and the network will be accessible even from the furthest reaches of Earth where today internet access is scarce due to infrastructure needs — think underserved rural areas, the open ocean, etc. Government backing for such a network could accelerate efforts if it's found to be effective — the U.S. government doesn't exactly spare expenses when it comes to military projects.
This isn't like existing satellite internet — Starlink has promised that its own network will offer speeds up to 1 gigabyte per second, comparable to today's fastest broadband networks. The company says it will also have latency as low as 15 milliseconds. The big innovation enabling such a possibility is communication between satellites via lasers, which can send data between one another at effectively the speed of light. Existing satellite internet services are also slow because they use satellites that are further away from the Earth's surface than SpaceX's will be.
Internet satellite networks haven't been placed in low-Earth orbit traditionally because they pose more danger and therefore have to be constantly monitored. Both DARPA and SpaceX are developing autonomous routing systems for their networks to ensure the satellites are properly spaced out and don't collide with other objects.