The SpaceX company wants to bring internet to the entire planet through a swarm of thousands of satellites. This and other satellite constellations could affect astronomy. Are the advantages more than the disadvantages?
On May 24, 2019, a rocket took off from Cape Canaveral, Florida. Falcon 9 with the first 60 satellites of the Starlink system. This is the name of the SpaceX company’s satellite constellation, whose objective is to offer high-speed telecommunications services to the entire planet. The satellites were deployed without incident into an orbit at a height of 440 kilometers, and then used their electric propulsion system to reach their final orbit at 550 kilometers. Since then, five other launches have been carried out – the last on March 18, 2020 – for a total of 360 satellites in orbit.
And it’s just the beginning. If there are currently about 2,000 active satellites, SpaceX wants to shatter that mark… in just five years. By 2024, Starlink will consist of no less than 12,000 satellites, almost double all that have been launched since the beginning of the space age in 1957 (about 7,000). An ambitious project that, however, also has its detractors; among them, the majority of astronomers, both professional and amateur, due to the impact that the presence of so many satellites will have on the night sky.
A large-scale proposal
Founded in 2002 by businessman Elon Musk, SpaceX has managed to revolutionize the space launch industry in recent years thanks to the development of reusable rockets (Falcon 1, Falcon 9 and Falcon Heavy). This idea, combined with its own production of most of the necessary materials, has allowed SpaceX to drastically reduce costs and sign several lucrative contracts with NASA and the United States Department of Defense.
But SpaceX knows that the business in the aerospace sector is not in the launch market, but in the manufacturing of satellites, and particularly in the management and marketing of its services (communications, navigation, Earth observation, etc.). With this idea in mind, SpaceX announced in January 2015 the construction of Starlink, a communications network that aims to satisfy the global demand for internet connections. It must be taken into account that currently more than half of the world’s population does not have access to the Internet, an issue that is difficult to solve when living in remote or underdeveloped regions.
The idea was not new, although it did attract attention due to the scale of the proposal (something that, on the other hand, should not surprise anyone who knows Musk, also founder of PayPal and Tesla Motors). According to Musk’s ambitious plans, the Starlink constellation will include in its first phase 1,584 satellites in an orbit 550 kilometers high. Then 2,825 satellites will be added distributed in various orbits between 1,110 and 1,325 kilometers high. The second phase will include the launch of the remaining 7,518 satellites into an orbit of 340 kilometers. In this way, Starlink will ultimately consist of 11,927 satellites located in low orbit, as any orbit between 200 and 2,000 kilometers high is called.
Other megaconstellations
SpaceX is not alone in the communications satellite mega-constellation business. The first megaconstellation to go into orbit was OneWeb, which at the end of February 2019 launched the first six units of the planned 648 satellites. Built by Airbus, all will be placed in a final orbit at 1,200 km above the Earth’s surface.
To the Starlink and OneWeb satellites we must add the 3,236 satellites of Amazon’s future Kuiper constellation, the 4,600 of the Samsung constellation, the almost 3,000 of Boeing, the 600 of the Indian company Astrome Technologies and the 800 of the Chinese company Commsat Technology Development. All this without counting other projects under development, including several Chinese ones. In total, more than 22,000 new satellites.
At full speed
SpaceX’s plan is not only limited to giving internet access to the entire planet. It also aims to do so with low latency. In telecommunications, latency is the time it takes for a packet—a unit of information—to be sent within the network, and is a key factor in the speed of Internet connections. In short, low latency equals fast transmission.
To use the Starlink system the user would need a relatively small antenna (the size of a pizza box) that SpaceX would provide and which is not yet for sale. The antenna would send information via radio waves to the nearest satellite. Once received, said information would be passed from satellite to satellite by means of lasers until it reaches the satellite closest to the destination, at which time it would be sent back to earth in the form of radio waves to the receiving antenna. Each satellite has four communications antennas to receive and send information to the Earth’s surface.
How does Starlink achieve its low latency? The key is that the speed of light is not the same in all materials. Specifically, light travels 47% slower in optical fiber than in a vacuum. This difference is what allows Starlink to transmit information in a short time, since light moves much faster in the vacuum of outer space than in fiber optic cables. For example, from New York to London the current latency is 76 microseconds with fiber optics. With Starlink it could be reduced to 57 microseconds. And the greater the distance to travel, the more advantage Starlink gives with its laser communication between satellites. In the case of New York and London, the distance is relatively short, about 5,600 km. If the transmission were between New York and Singapore, more than twice the distance, the current latency of 243 microseconds could be halved with Starlink.
Internet from Space
starlink
A megaconstellation of satellites to offer broadband internet connections.
Satellites
11,927* in low orbit *With plans to increase to at least 30,000.
Dimension:3mx1.5mx13cm approx.
Weight: 227kg
1 solar panel
4 antennas
5 lasers
Internet Band: Ku/Ka, 10 – 30 GHz
Global internet capacity:10%
How does it work? The user’s antenna sends information via radio waves to the nearest satellite; This information passes from satellite to satellite by means of lasers until it reaches the satellite closest to the target, from there it is sent to the destination antenna in the form of radio waves.
The first 1,584 Starlink satellites will be deployed in 24 orbital planes of 66 satellites each; These planes form a kind of mesh around the Earth.
space junk
A delicate question is what will happen to satellites at the end of their useful life. SpaceX guarantees that 95% of the satellite will be destroyed during re-entry into the atmosphere (although it is not yet known how this will be done). Only the internal structure of the ion propellant and some components essential for the operation of the lasers will survive, which therefore have a high melting point of 2,750 oC. With thousands of satellites overhead, the probability of a fragment falling on you is still very low, but the risk is no longer completely negligible.
Collision!
On September 2, 2019, the European Space Agency (ESA) monitoring system warned of a possible collision of the Aeolus satellite with a Starlink satellite. Despite being informed of the situation, SpaceX did not respond, which was interpreted by ESA as a refusal to move its satellite. Consequently, ESA had no choice but to raise the Aeolus orbit by about 300 meters.
According to Musk’s company, a computer error prevented Starlink controllers from communicating with ESA in the usual way: via email. SpaceX has stated that it will take measures to ensure that this matter does not happen again and recalled that Starlink satellites can carry out automatic maneuvers if they detect a possible risk of collision (to date 16 maneuvers of this type have been carried out).
The underlying problem is the lack of international legislation on satellites in low orbit. Until now these types of situations have been resolved with good will, but as the number of satellites increases, they are likely to become more frequent.
Cutting-edge technology
According to Starlink’s plans, the first 1,584 satellites will be deployed in 24 orbital planes of 66 satellites each. These planes will form a kind of mesh around our planet similar to the terrestrial meridians and parallels, but maintaining a certain angle with them. This implies that, to cover the New York-London route, the path of the lasers will never be exactly a straight line. It must be taken into account that the satellites will each be moving in their respective orbital planes. When the information reaches a satellite, it must be able to find the neighboring satellite that minimizes the trajectory to the destination, in addition to then having the precision to hit the moving target with the laser. That is why each satellite will have five lasers to communicate with as many neighboring satellites. The satellites will also incorporate a navigation system, called Startracker, which will allow the precise position of each one to be known.
Each Starlink element weighs between 230 and 260 kg, and has a single solar panel, which significantly simplifies the design. They also have their own propulsion system of ion engines to reach their final orbit. These engines consume very little fuel and produce a very smooth thrust, sufficient for a light probe moving without friction in outer space. The novelty is that the Starlink system will use krypton as fuel instead of xenon, another noble gas that is heavier (and therefore more efficient as a propellant), but also more expensive. In addition to reaching its orbit and performing small maneuvers, each satellite will use its propulsion system to re-enter the Earth’s atmosphere at the end of its useful life.
Bandwidth is the amount of data a satellite can transmit per second. If SpaceX’s goal is to connect everyone on the planet to the internet, a minimum of bandwidth is required. Each Starlink satellite will have a bandwidth of 1 terabit per second (that is, one million megabits per second, Mbs). Given that the global average speed is about 10 Mbs, this implies that each satellite could serve at least 100,000 users under good conditions. We speak of broadband when the network has a high capacity to transmit information at a given moment, as would be the case of Starlink.
Not all that glitters is gold
With all its lights, the Starlink project also has some shadows, related to the impact…