Providing low-latency, high speed broadband throughout the world through a large constellation of satellites is a complex business. The first launch of SpaceX Starlink satellites is now scheduled to take place on the evening of May 16, with details about the initial deployment of 60 satellites and the architecture of the overall system continue to evolve though every Elon Musk tweet and press interaction.
“We’re super excited for the first launch in the Starlink constellation,” said SpaceX CEO and lead developer Elon Musk, speaking to the media on a May 15 conference call. “The goal of the Starlink system is to provide high bandwidth low latency, ideally throughout the world.”
Musk threw in plenty of caveats as he discussed the business and technical challenges of the Starlink broadband system, noting no one had so far deployed a Low Earth Orbit (LEO) communication network without going through bankruptcy along the way. “It’s a very difficult thing, but far from an assured thing,” Musk commented. “It’s definitely a case where good fortune is needed.”
Each launch of around 60 Starlink satellites will put roughly 1 terabyte of usable connectivity into the skies, with the total of the group generating 30 percent more solar power than the International Space Station (ISS). Six more launches of 60 Starlink satellites per launch is necessary to have a “useful” constellation, said Musk, with 12 launches covering the US, 24 launches providing service to most of the populated world and 30 covering the entire world.
Satellites incorporate an automated debris avoidance routine, with data from NORAD space tracking uploaded to the satellites on a regular basis and each satellite automatically using its krypton-fueled ion thrusters for maneuvering to avoid hitting known objects, such as debris and other satellites. Other features include the first generation of satellites burning up 95 percent during re-entry and future satellites planned to completely disintegrate during re-entry.
There will be many risks in this launch, starting from deployment of the satellites from the stack. Unlike other schemes requiring dedicated hardware and springs, the Falcon 9 upper stage will slowly spin, with satellites being deployed from the stack like “spreading a deck of cards on the table,” Musk said. “It looks kind of weird.” There may be a small amount of contact between satellites as they come off the stack, but the satellites are “designed to handle it.”
Other areas of concern on this first launch are the potential for the two different solar array deployment mechanisms not to work, phased array antennas onboard the satellites not working as well as anticipated or the krypton thrusters not working.
From an architecture perspective, the first-generation “production grade” Starlink satellites on this launch do not include Ka-band antennas for ground communication and optical (laser) cross-links necessary to directly relay data within the between satellites and users on the ground. Both features were initially planned and discussed by Musk as features of the Starlink system, but will instead be rolled into future versions of the satellites.
Instead of inter-optical links to move data, SpaceX is deploying a series of ground stations to insert a “ground bounce” for relaying data between satellites. Details not discussed in the “ground bounce”/ground station scheme include the total number of ground stations necessary for assuring global relay coverage, the distances necessary to require a “ground bounce” between two points, and additional latency added per ground bounce. Latency cited by SpaceX between ground and satellite is around 15 milliseconds, so each ground bounce relay would add 15 or more milliseconds to the broadband session. Multiple ground bounce hops would add additional delays.
Initial customers Starlink is thinking about include telephone companies seeking backhaul services for cell towers, especially those in rural and sparsely populated areas, along with governments seeking to provide broadband in underserved and unserved areas.
Musk described a user terminal with a flat, phased array antenna that didn’t require precise pointing at a specific satellite. “It ships in a box. Just plug it in and it works,” he said. “You don’t need a specialized installer.” The equipment would also work in a mobile setting, such as in a car, plane, or boat, with the antenna able to steer electronically and switch between satellites in under a millisecond. Pricing was not discussed on the call, but Musk previously cited a price point in the $250 range for the equipment.