SpaceX’s ambitious plans to link the entire planet with affordable ultra-high bandwidth, ultra-low latency internet has sparked controversy among the public and scientific community alike.
An artist’s impression of what the Starlink constellation will look like.
What is Starlink?
Starlink is SpaceX’s ambitious project that aims to fulfill the world’s growing networking needs by deploying an outrageous 1800 satellites into Low Earth Orbit (LEO), with FAA approval for a staggering 12 000 satellites. According to the company, the massive constellation of satellites will provide fast and reliable internet services at prices competitive with those offered by ground-based Internet Service Providers (ISPs).
How does it work?
In a nutshell, the satellites will use microwave lasers to beam information directly through the constellation at the speed of light. While optical communications have become cheaper and more refined at the surface of our planet, using thin beams of lasers to directly connect a constellation consisting of hundreds, if not thousands of satellites together is quite the challenge. These satellites will have to constantly adjust their orbits and alignment with precise accuracy to avoid losing beam tracking with other satellites, which can result in data packet loss. As of now, SpaceX plans on using the satellites onboard Krypton thrusters to do the job. Despite Xenon being the more common propellant for electric ion thrusters, SpaceX favors Krypton due to its lower cost. It is possible for the satellites to be oriented using reaction wheels, but this can increase the craft’s weight and increase launch costs. In addition to inflated launch costs, reaction wheels are prone to saturation, which occurs when a reaction wheel holds a maximum amount of angular momentum in a particular direction.
Laser communication in space. (no Mr President, do NOT point the laser at Iran!!!)
An Earth-based receiver will be able to communicate with these satellites using phased array antennas to track and switch between fast-moving satellites with haste and accurate precision. These special antennas will use multiple receivers and transmitters and make use of destructive and constructive wave interference to maintain a reliable link with the satellite constellation.
Phased array transmitters. Fancy stuff, no?
Shiny mirrors in the sky and space debris
However, some fear that a constellation of satellites as colossal as a planetary dyson swarm can severely obstruct the clarity of both nighttime and daytime skies. Elon Musk, CEO of SpaceX, has confirmed that Starlink’s spacecrafts will be designed to diffuse light and not reflect it, almost eliminating any possibility of severe interference with Earth-based astronomy and geostationary communications.
Given that the radius of the Earth is 6371 km (at the equator) and the orbit height of the satellites is approximately 550 km, we can find the area over which the satellites are to be spread across using A=4𝝅r , giving us A=4𝝅(550+6371)2=6.02×108 km2. Even when SpaceX operates Starlink at its maximum capacity with 12 000 satellites, there will be an area of around 50 000 km2 between satellites, which is almost as big as the state of West Virginia! This also means that the possibility of interference with astronomy is much lower than what might have been instinctively presumed.
Another issue posed by the introduction of thousands of satellites into space is space debris. If Starlink loses control of any of its satellites in orbit, they would significantly increase the threat of collision which can result in dangerous, untraceable macro particles as shown in the image below. These particles can essentially destroy fleets of satellites as they pierce through and damage sensitive equipment necessary for their operation, including lasers, solar cells and antennas, resulting in yet more loss of control. It can lead to what is known as the Kessler Syndrome in "astrospeak", which states that the density of objects in low Earth orbit (LEO) is high enough that collisions between objects could cause a cascade in which each collision generates space debris that increases the likelihood of further collisions (Donald J. Kessler, 1978). This can be disastrous for space tech and travel, as it can essentially wipe clean all satellites and space stations in Earth’s orbit and result in a field of debris so dense that future space missions are rendered impossible (that is without dying, of course). Hence it is very, and I stress very, important for Starlink to design their satellites to be redundant and easily maneuverable for safe disposal using Earth’s atmosphere as a natural incinerator.
13 mm aluminium bullet travelling at 7 km/s vs 13 cm aluminium plate. Yikes.
An engineering challenge worth undertaking
At the end of the day, it is important to realise Starlink’s philanthropic vision as well as its attractiveness to our financial institutions. While its primary target market will be developing nations, stock markets will benefit greatly from Starlink due to its ability to reduce latency, be it only by a few milliseconds. Stock markets are incredibly time sensitive entities, especially given the existence of automatic stock trading systems. Well then, how does Starlink aim to cut latency? With a refractive index of 1.45, fiber optic cables can slow down light by as much as 31%. This means that in vacuum, Starlink’s communications satellites will benefit from light’s max speed of 2.99 x 108 m/s while even the fastest fiber optic link on earth will barely even break 2.05 x 108 m/s. You may ask, why not use direct radio transmissions on earth instead of fiber optic cables? Air may have a negligible impact on the speed of light but objects such as planes, cars, ships and trains will interrupt the network and make it unreliable.
Yay or nay?
To conclude, it is always important to take into consideration the costs of production before selling a product. While SpaceX may have some of the cheapest per Kg launch costs in the entire space industry, it may still have some ways to go before being able to sustain the Starlink program with prices competitive with those of Earth-based internet services. Once up and running, Starlink will revolutionise the way we connect to the internet and facilitate innovation of new space-based technology and business.