The launch of 60 satellite as part of the SpaceX Internet by Satellites project created not just excitement amongst space enthusiasts but also amongst astronomers who witnessed a long white strip moving along the horizon as the satellites entered their orbit.
Elon Musk said after the launch that it will take about 400 satellites to establish “minor” internet coverage and 800 satellites for “moderate” or “significant operational” coverage. “My immediate major goal is to deploy nearly 1600 satellites in about a 440 kilometres orbit.
Falcon 9’s first stage was deployed for this mission. It previously supported the Telstar 18 mission in September 2018 and the Iridium-8 mission in January 2019. Approximately one hour and two minutes after lift-off, the Starlink satellites began deployment at an altitude of 440 km. Onboard propulsion will be deployed to place Starlink satellites in an operational altitude of 550 km. Compared to GPS satellites which are in a medium orbit around 1250 km, Starlinks are in a low earth orbit putting a much larger signal on the ground. Low Earth orbits were explored by the first satellites, then considered of not much use and turned over the amateur radio and university CubeSat satellites. It is almost as if radio history keeps repeating itself!
Following stage separation, SpaceX landed Falcon 9’s first stage on the “Of Course I Still Love You” drone ship, which was stationed in the Atlantic Ocean.
Fig. 1: SpaceX stuffed a fleet of 60 Starlink internet-providing satellites into the nosecone of a Falcon 9 rocket.
SpaceX designed Starlink to connect end-users with low-latency, high-bandwidth broadband services by providing continual coverage around the world using a network of thousands of satellites in low Earth orbit. To manufacture and launch a constellation of such scale, SpaceX is using the same rapid iteration in design approach that led to the successes of Falcon 1, Falcon 9, Falcon Heavy, and Dragon. Starlink’s simplified design is significantly more scalable and capable than its first experimental iteration.
Starlink satellite design
With a flat-panel design featuring multiple high-throughput antennas and a single solar array, each Starlink satellite weighs approximately 227 kg, allowing SpaceX to maximise mass production and take full advantage of Falcon 9’s launch capabilities. To adjust position on orbit, maintain intended altitude, and deorbit, Starlink satellites feature Hall-effect thrusters as a propulsion system.
The Hall-effect thruster is one of several electric propulsion technologies. In use since the 1970s in unmanned space flights, the thrusters make it possible to manoeuvre precisely and correct satellite orbits. Lately, devices of this type have increasingly been used as the main propulsion system for deep space missions.
Hall-effect thrusters convert the propellant into a plasma and produce thrust using the on-board electrical power source. Plasma particles (ions and electrons) are electrically charged and can thus be accelerated by an electric field. Hall Plasma propulsion produces a low thrust but can operate over long durations and ultimately increase the velocity of the spacecraft by several kilometres per second. The thrusters on Starlink satellites are powered by krypton.
Designed and built upon the heritage of Dragon, each spacecraft is equipped with a star tracker navigation system that allows SpaceX to point the satellites with precision. Importantly, Starlink satellites are capable of tracking on-orbit debris and autonomously avoiding collision. Additionally, 95% of all components of this design will quickly burn in Earth’s atmosphere at the end of each satellite’s lifecycle, exceeding all current safety standards, with future iterative designs moving to complete disintegration.
What can be expected?
This mission will push the operational capabilities of the satellites to the limit. SpaceX expects to encounter issues along the way. “Our learnings here are key to developing an affordable and reliable broadband service in the future,” Musk said.
Starlink is targeted to offer service in the Northern US and Canadian latitudes after six launches, rapidly expanding to global coverage of the populated world after an expected 24 launches.
At end-of-life, the satellites will utilise their on-board propulsion system to deorbit over the course of a few months. In the unlikely event the propulsion system becomes inoperable, the satellites will burn up in Earth’s atmosphere within one to five years, significantly less than the hundreds or thousands of years required at higher altitudes.
Fig. 2: Starlink train lights up the sky.
The first 60 Starlink satellites were launched on 23 May creating a train of bright lights in the night sky. “It was one of the most spectacular things I have ever seen,” Dr Marco Langbroek of Leiden, the Netherlands. “I could see the entire train of satellites with the unaided eye,” he said
The train no longer looks as it did on the first night. Individual satellites are fading in brightness as they move out into their operational orbits. A typical urban sighting now consists of only four to six naked-eye objects interleaved by dozens of fainter satellites best seen through binoculars. The train is still worth catching, because the satellites are flaring. Sunlight is glinting off flat surfaces on the satellites’ bodies, creating flashes of light that can briefly rival the brightest stars in the sky.
The flares are pretty, but some astronomers are concerned. Will 12 000 artificial stars criss-crossing the night sky, sometimes flaring, make deep-sky observing impossible? It’s an important question. Astronomers speculate that as the regularity of the flares observed might mean they’re predictable, big telescopes could learn to avoid them.
