SpaceX’s Starlink satellite constellation is still deep into testing mode, but it’s already generating 5 trillion bytes of data on a daily basis and getting software updates on a weekly basis.
Those are a couple of the nuggets coming from a weekend Reddit “Ask Me Anything” session featuring SpaceX’s software team.
The main focus of the online chat was SpaceX’s successful mission sending NASA astronauts Bob Behnken and Doug Hurley to the International Space Station in a Crew Dragon capsule — but one of the team members, Matt Monson, has moved on from Dragon to take charge of Starlink software development.
Although SpaceX’s HQ is in Hawthorne, Calif., most of the work relating to the Starlink satellites is being done at the company’s facilities in Redmond, Wash.
SpaceX tends to play its satellite cards close to the vest, in part because the process of building a satellite system is “highly proprietary” — as one of the company’s vice presidents, Patricia Cooper, said in a 2016 filing with the Federal Communications Commission. For that reason, any nuggets about Starlink’s workings are avidly sought by SpaceX’s fans as well as the occasional inquiring journalist.
This weekend’s Reddit AMA attracted more than 7,000 questions and comments, and the engineers could reply to only a few of them. That made it easy to avoid sensitive subjects — for example, the timetable for adding satellite-to-satellite laser communication links to the constellation. Despite the limitations, Monson and the other developers shed light on Starlink’s inner workings, including these highlights:
- The technology used for the display screens on the Crew Dragon also provided the basis for the user interface on the first two prototype Starlink satellites, launched in 2018. “It’s grown a ton since then, but it was awesome to see Bob and Doug using something that somehow felt familiar to us too,” Monson wrote.
- SpaceX relies on the Linux operating system in its satellites as well as its rockets. “Each launch of 60 satellites contains more than 4,000 Linux computers,” Monson said. “The constellation has more than 30,000 Linux nodes (and more than 6,000 microcontrollers) in space right now. And because we share a lot of our Linux platform infrastructure with Falcon and Dragon, they get the benefit of our more than 180 vehicle-years of on-orbit test time.”
- Not everything has gone right with Starlink’s software. “We’ve had many instances where a satellite on orbit had a failure we’d never even conceived of before, but was able to keep itself safe long enough for us to debug it, figure out a fix or a workaround, and push up a software update,” Monson wrote. He said SpaceX usually updates the software on all the satellites about once a week, “with a bunch of smaller test deployments happening as well.”
- Monson said “we’re currently generating more than 5TB [5 trillion bytes] a day of data” for Starlink. “Doing the detection of problems onboard is one of the best ways to reduce how much telemetry we need to send and store (only send it when it’s interesting). The alerting system we use for this is shared between Starlink and Dragon.”
As of last week, SpaceX has launched eight batches of 60 Starlink satellites, forming a constellation of roughly 480 spacecraft (with a few that have gone out of service). There’s a continuing controversy over the satellites’ visibility and potential interference with astronomical observations. If the skies are clear, you can use Heavens-Above.com as your guide to spot the satellite train passing across the sky.
The broadband data network is already being tested for military applications. Just last month, SpaceX and the U.S. Army struck a deal for three more years of experimentation and evaluation. Limited commercial service could begin later this year, though it’s not yet clear exactly how the service will be marketed.
Eventually, thousands of Starlink satellites could offer always-on broadband internet access to billions of people around the world. Other ventures, ranging from now-bankrupt OneWeb to Canada’s Telesat to Amazon’s Project Kuiper, have been going after the satellite internet market as well. But based on Monson’s comments, they’ll have a lot of catching up to do on the technical front.
Monson said his favorite moment at SpaceX came a little more than a year ago, when the first batch of 60 satellites was deployed in orbit like a deck of cards.
“We’d designed the all-at-once deployment mechanism, but it’s hard to model, and we couldn’t really be 100% sure it would work right,” he wrote. “I remember sitting there, with Falcon lifting off the pad, thinking: OK. In an hour we’re either going to be idiots for trying a thing that obviously never could have worked, or geniuses for doing the thing that’s obviously the right way to deploy lots of satellites. Luckily it went well.”