Abstract
Ever wondered about those enigmatic specks of light in the night sky? Starlink not only answers the mysteries but propels them into the forefront of cutting-edge technology. Embark on a thrilling journey with Starlink, a satellite megaconstellation venture spearheaded by the innovative genius Elon Musk at SpaceX. This groundbreaking engineering marvel unfolds as a cosmic ballet of small satellites, reminiscent of the celestial wonders one might encounter while gazing through any star tracking apps.
Fig 1: The Starlink constellation looks like a trail of light as seen from the earth in the night sky.
As we all know, all good things have a dark aspect. Starlink, while promising global connectivity, brings with it a negative impact on astronomy. The rapid growth of these satellites contributes to the escalating issue of light pollution, further obstructing the view for star gazers who are already overwhelmed by present conditions. Despite its transformative potential in the digital realm, Starlink prompts us to consider and address the challenges it poses to the observation of space. So, buckle up for an exciting journey into the realms of space technology, while also navigating the complexities and implications it brings to our shared passion for stargazing.
Fig2: A stack of Starlink internet satellites just before a launch.
Introduction
Ever wondered how the internet travels across the globe to reach you? The conventional internet service on earth is carrying 99% of all the internet traffic in the world. It works with a local connection. You’ll receive internet from a cell tower that’s typically within ten miles of your home or business. Because the signal has a shorter distance to travel, the latency is lower, and your connection will be more responsive and lag less. Latency is how long it takes for data to go from the transmission point to the access point. High latency can make your connection feel delayed or laggy, even if you dish out extra for high download speeds. This system, that is Submarine cables are the backbone of the internet.So, the question arises: Why do we need the Internet from space ? These cables, which are under deep sea, laid by 450 submarine cable systems around the world, cover 1.35 million km of optic fibers in length. In some regions, it is difficult to lay these cables due to flat plains, sharp mountains, and rugged canyons under sea. Also, in some parts of the world these internet services might get threatened by war or politics. Some submarine cables might get unused due to less population in a particular region, reducing the efficiency of the service while in densely populated regions, it might get overused, resulting in increased traffic. To tackle these major problems, satellite internet might get upper hand increasing the accessibility for people living in less remote regions. Companies like HughesNet & Viasat offer satellite internet, but their satellites are at 35,400 km above earth’s surface. These satellites cover a huge area but have very high latency. Then comes the Starlink!
Starlink is a constellation of thousands of satellites that orbits the planet much closer to earth, at about 550 km, and covers the entire globe. SpaceX started launching Starlink satellites in 2019. As of early May2024, SpaceX successfully launched over 6000 Starlink satellites into orbit, including prototypes and satellites that later failed or were de-orbited before entering operational service in low earth orbit (LEO) that communicate with designated ground transceivers. Nearly 12,000 satellites are planned to be deployed, with a possible later extension to 42,000.
Starlink has already stepped into the arena, providing high-speed satellite internet services with the aim of launching its offerings globally in the near future.In a world accustomed to internet through fibers, Starlink is set to introduce a new and compelling chapter in our internet experience. What adds to the excitement is the potential to bridge the digital divide, as Starlink's services have the capacity to provide internet facilities to rural areas, ushering in a wave of connectivity to underserved regions. “Starlink will serve the hardest to serve customers,” said SpaceX CEO Elon Musk. This article delves deeper into the architecture of these satellites, technical features, working and impact on astronomy.
What is the Starlink constellation?
These Starlink satellites are deployed as individual satellites into Low Earth Orbit (LEO). Each satellite operates independently but is part of the larger Starlink constellation.These satellites communicate with each other. SpaceX’s Starlink hardware includes a satellite dish and router, which will be set up at home to receive the signal from the Satellite which will be moving in the LEO (Low Earth Orbit).
LEO satellites are satellites that orbit the Earth at a height of 180–2,000km. This is significantly lower than geostationary orbit (GEO) satellites, which orbit at around 36,000 kilometers from Earth. LEO systems represent a cutting-edge approach to satellite technology. This proximity allows for reduced signal latency and enhanced data transmission speeds.
How is it launched and deployed?
Satellites within this constellation, initially launched into space with a combined payload of around 250 kg, navigate a 53-degree inclination orbit. In the chaotic initial phase, these satellites move at random speeds, creating a dynamic cluster in space. However, this apparent disorder is part of the process, as these satellites are later meticulously deployed to specific orbitals. To achieve this precision, hall effect thrusters, fueled by krypton gas, are employed. These thrusters play a crucial role in fine-tuning the satellite orbits and ensuring they settle into their designated positions, contributing to the overall functionality and efficiency of the constellation.
Technological features of Starlink satellites :
Design and architecture of Starlink network :
Fig 3. Copper(yellow line) : used for phone and DSL (Digital Subscriber Line) connectivity, Coax (red line) : hybrid fiber-coaxial (HFC) which is a broadband network that combines optical fiber and coaxial cable, Fiber (blue line) :
Optical fiber, which are bundled glass strands that data can be transmitted over, Optical lasers ( blue dot line ) : Satellite internet provided by starlink megaconstellation.
The above figure describes the overall internet infrastructure that exists today. Out of them all, optical fiber is the fastest form of wireline connectivity and is available in urban areas, but it is not usually available in remote regions. Whereas the wireless ecosystem achieved by satellite internet will drastically change the situation, Starlink is by far the largest and most advanced satellite broadband provider.
Ion propulsion system:
Efficient ion thrusters, powered by krypton, enable starlink satellites to orbit, raise, maneuver in space, and deorbit at the end of their useful life.Starlink is the first krypton propelled spacecraft.
Autonomous collision avoidance:
The world’s most advanced broadband satellite mega-constellation, Starlink, is capable of avoiding orbital collisions autonomously. The space environment may be threatened by SpaceX's satellite constellation, according to some astronomers, if the satellites crash with spacecraft, other satellites, or space debris while they are in orbit. Some said it would result in "Kessler syndrome," or uncontrollably spiraling collisions in space.
SpaceX is making every effort to prevent that from happening. The Starlink satellites utilize inputs from the U.S. Department of Defense’s(DoD) debris tracking system which enables it to autonomously maneuver itself to avoid collisions with space debris and other spacecraft. The on-board ion thrusters of each satellite are powered by krypton. In the unlikely event that a satellite malfunctions, this propulsion system can also be utilized to deorbit it. But, this maneuvering can get out of hand, if it isn't controlled properly. The SpaceX satellites have been forced to change positions more than 50,000 times in order to avoid collisions since the first Starlink spacecraft launched in 2019. Should this trend continue, in order to reduce the possibility of orbital collisions, Starlink satellites will need to maneuver almost a million times in a half-year by 2028.
Star tracker system:
It uses the Star tracker system to orient itself in space. Starlink’s custom-built navigation sensors survey the stars to determine each satellite’s location, altitude, and orientation, enabling precise placement of broadband throughput.
Optical space lasers:
Starlink satellites communicate with each other through inter-satellite links. These links enable them to relay signals, providing a continuous network connection even as they move across the sky. Optical Intersatellite Links, or "space laser" features, allow satellites to communicate with one another while in orbit, enabling faster data transfer between satellites without requiring each satellite to receive data directly from a nearby Starlink Gateway ground station on Earth. Because light moves more quickly in space than it does through subterranean fiber-optic cables.
Companies like SpaceX are focusing on replacing traditional radio-frequency communication with lasers for faster speeds and lower latency. Starlink internet operates much faster than
conventional internet infrastructures. "Starlink satellites are able to connect thousands of kilometers apart, beyond the view of ground stations, and maintain pointing accuracy to enable data transfer up to 100 Gbps [Gigabits per second] on each link," Starlink representatives said via X. However, laser links can require tradeoffs of weight, power consumption, and cost. SpaceX launched 10 laser-equipped Starlink satellites into polar orbits in January 2021, and all future Starlink satellites will have laser crosslinks. The base of starlink constellation working is inter-satellite communication technology. There are certain features in this domain that pull it apart from other LEO satellites.
Fig 4 and Fig 5: Next generation optical lasers by Starlink. With over 8,000 space lasers deployed across the constellation, Starlink satellites are capable of connecting locations separated by thousands of kilometers, extending beyond the range of ground stations. The pointing accuracy is maintained, enabling data transfer of up to 100 Gbps on each link. Starlink's laser mesh network allowed for the provision of truly global coverage, serving individuals in the most remote locations on Earth, including maritime and aviation customers.
Less RTT:
Round-Trip Time (RTT) in satellite systems refers to the time it takes for a signal to travel from the source to the satellite and back to the source. It is a critical parameter in satellite communication and has implications for the overall performance of the communication system.The RTT is influenced by the distance the signal must travel and the propagation speed of the signal through the medium, which is generally the speed of light. In satellite systems, the RTT can be a significant factor due to the longer distances involved compared to terrestrial communication. Due to the lower orbit location of the Starlink satellites, data processing and relaying optimization techniques, data packets have shorter propagation delay quantified by a Round Trip Time (RTT) that can be as low as 100 ms. The relatively low RTT is tolerable for many current media applications but not for delay sensitive uses such as online video gaming, video calling or future real-time IoT . LEO systems enable the utilization of high-frequency bands like Ku, Ka, Q, and V bands, providing substantially larger bandwidth compared to GEO satellites. This results in the ability to offer users increased capacities.
Fig 6: High-frequency bands like Ku, Ka, Q, and V bands for satellite communication.
About FSPL :
Free-space path loss (FSPL) in wireless communication is essentially the attenuation(means loss through the air) of radio energy between the feedpoints of two antennas as a result of the combination of the receiving antenna's aperture and the clear, direct path through free space (often air) that is free of obstacles. The amount of loss a signal can incur is dependent on the frequency or wavelength of the signal and the distance from the point of reference traveled by the signal (e.g., distance from the transmitter, in our case, Starlink Satellites).
The total loss is given by the ratio :
FSPL = Pt / Pr = ((4πd)/λ)^2
Pt = transmitted power
Pr = received power
d = distance between transmitter - receiver
λ = transmitted wave length
FSPL is a key consideration in satellite communication and various factors are taken into account to optimize the performance of such satellite networks. Starlink satellites orbit the earth much closer to its surface, at about 550 km(i.e. Low Earth Orbit) and cover the entire globe. This helps the satellites to experience comparatively less FSPL than those satellites in higher orbits. Starlink uses radio frequencies in the Ku(12-18 GHz) and Ka(26.5-40 GHz) band for communication. Even though they enable better data transfer rates, higher frequencies may have higher FSPL. Data rate and signal propagation characteristics are traded off when choosing frequencies. Also, the starlink dish aligns itself by moving with its electric motors during the initial booting. This improves signal strength and reduces some of the FSPL. Along with FSPL, several other things affect the overall performance including atmospheric effects, interference, etc.
Working of Starlink satellite :
Starlink satellites communicate with each other through inter-satellite links. These links enable them to relay signals, providing a continuous network connection even as they move across the sky. Satellite Internet operates by sending and receiving data signals between ground-based systems and satellites orbiting the Earth. Instead of relying on traditional fiber optic cables, which are commonly used in terrestrial networks, satellite Internet utilizes space-based communication infrastructure.The process begins with a ground-based server that generates an Internet signal. This signal is then transmitted to a satellite in orbit, often through a network operations center.Satellites play a crucial role in relaying these signals across vast distances,making it possible to establish connectivity in remote or challenging terrains where laying physical cables might be impractical.
On the user's end, a satellite dish is employed to capture the transmitted signal from space. This dish is strategically positioned to have a clear line of sight to the satellite, ensuring optimal signal reception. The captured signal is then directed to a modem, a device that serves as the gateway between the satellite connection and the user's devices.The modem processes the incoming signal and establishes a connection, allowing various devices such as computers, smartphones, or other internet-enabled gadgets to access the Internet. The devices are typically linked to the modem via wired or wireless connections, enabling users to browse the web, stream content, and perform online activities.
Impact on Astronomy :
Existing and planned large constellations of bright satellites in low-Earth orbit (LEOsats) will fundamentally change astronomical observing at optical and near-infrared (NIR) wavelengths. The satellites in LEO like the starlink satellites hamper the astronomical observations at optical and near-infrared (NIR) wavelengths. It also becomes a concern to amateur astronomers and astrophotographers as their trails obstruct the detailed stellar captures.Similarly, Many astronomical investigations collect data with the requirement of observing any part of the sky needed to achieve the research objective with uniform quality over the field of view. At the very least, a portion of the imaged area is compromised due to trails, leading to a significant reduction in the signal-to-noise ratio (S/N). However, numerous research areas within this context involve time-sensitive elements and/or focus on rare, scientifically crucial targets.
Fig 7: A wide-field image (2.2 degrees across) from the Dark Energy Camera on the Víctor M. Blanco 4-m telescope at the Cerro Tololo InterAmerican Observatory, taken on 18 November 2019. Several Starlink satellites crossed the field of view.
The omission of such targets, even with a low probability, would substantially diminish the scientific impact of the project. To illustrate, the loss of a recovered near-Earth object results in the forfeiture of its orbital parameters. If the transit of a promising super-Earth exoplanet candidate is overlooked, the recovery of its orbital timing becomes uncertain. Similarly, if the optical counterpart of a gravitational wave source is obscured in the few percent of pixels affected by satellite trails, its rapid fading might hinder subsequent identification. One example of precision cosmology, the gravitational weak lensing shear elongating faint galaxy images, requires more sophisticated modeling to grasp the significant impact these satellites will have on this field.
Conclusion:
In conclusion, Starlink's global connectivity and technological achievements are remarkable, showcasing marvels of human engineering in the satellite internet realm. The constellation's potential to bridge the digital divide and connect underserved regions globally is revolutionary. However, concerns arise from the light pollution impacting astronomical observations, with satellite trails affecting signal-to-noise ratios and hindering scientific research. Amidst this technological wonder of interconnected satellites, finding a balance becomes vitally important. Strategies, whether technological advancements or regulatory measures, are needed to mitigate the impact on astronomy. The challenge lies in ensuring a harmonious coexistence where the wonders of the cosmos remain accessible and unobstructed, even as we reach new heights in global connectivity.
References :
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[Starlink](https://www.starlink.com/technology).
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