Quantum Communication Satellites: The Space Industry’s Place in the Path for Quantum Information Networks
Introduction
The 20th century was one of a lot of groundbreaking achievements and findings which have contributed directly to the formation of the world as we presently know it. One of the most notable and important breakthroughs was made in the field of atomic studies, which allowed the further development of what we now call quantum mechanics, alongside the rise of the space industry in the mid 1900s.
Now in the 21st century, quantum mechanics has helped device many of the technologies we use on a daily basis, and our planet’s orbit is full of human made satellites which also play a big role on the structure of how society operates. Having developed not much long ago, these two aspects of human ingenuity have now become pilars of how the world has been built to function, and are now seemingly destined to join forces to give continuity to the progress we’ve witnessed over the past hundred years. With the newly rise of quantum communication satellites, this inminent crossover is precisely what we are looking at.
Quantum communication satellites offer several potential benefits over conventional satellites in the realm of secure communication, and in this article the contrast between them will be seen. Through digestion of data on how quantum and conventional satellites work and the difference in the benefits they respectively bring, we will have a clearer vision of how our world will look like in the future with quantum communication satellites.
Coventional communication satellites
In our modern world, communication satellites are used for many purposes which we can find present in our daily life. Things such as having access to a GPS, internet access in remote areas, watching television and hearing the radio, are all possible thanks to our technological advances in this area of the aerospace industry.
Using a combination of ground stations and orbiting satellites above Earth, communication satellites transmit and relay information across the world through the use of microwaves. This process is made up of three stages:
- Uplink — This stage is the one in which a broadcaster sends out a signal to a designated satellite through its user terminal, for it to continue with the next stage.
- Transponder — Having received the signal on the orbiting satellite, this stage consists of an onboard amplifier boosting the signal’s strength and changing its frequency, then sending it back to designated stations on the ground.
- Downlink — To finalize the process, ground stations around the globe receive these signals from the transmitters, and have access to the broadcaster’s service.
Being technology that serves diverse purposes, communication satellites vary in types. This purpose a satellite is given is crucial, as it determines many factors, including the technology it carries onboard, its orbital path, and overall equipment. Based on their orbit, they can be categorized into four groups:
Geostationary Earth Orbit (GEO) — Highest bandwidth, highest latency
Being the furthest away from Earth, at plain sight they appear to be still. This effect is a product of their orbit around the planet at the same speed as the planet’s orbit. They have a large coverage area and can focus their capacity over areas with no or little demand, requiring fewer ground stations than other types of satellites.
Medium Earth Orbit (MEO) — High bandwidth, low latency
These are often used for global positioning systems (GPS) and other navigation applications. Although they work in constellations, they don’t require as many satellites as LEO, and have a lower latency than GEO.
Low Earth Orbit (LEO) — Lowest bandwidth, lowest latency
These are much smaller than GEO satellites and they orbit much closer to Earth. Requiring a big constellation, LEO satellites provide the lowest latency possible coming from communication satellites. However, compared to GEO, they need more frequent maintenance, being less sustainable.
Highly Elliptical Orbit (HEO)
In contrast to the other types of satellites, HEO satellites have an orbit of high eccentricity, which means that it is more elongated and not perfectly circular. This orbital shape allows the satellite to spend more time over a designated region during the slower portion of its orbit.
A quick lesson on quantum mechanics
Imagine you have two closed boxes, each containing a coin inside them, which you know are facing opposite directions (one head, one tails). However, you can’t know in which box each coin is without opening it and seeing for yourself, so before opening a box, you only know that the coin inside has a 50% chance of being one side or the other. Here is where things start to get weird, as quantum mechanics states that until a box is opened, the coins inside exist in a superposition state where they are both sides at the same time.
Once you open one box, you immediately know the sides of the coins in both boxes, meaning that the state of the coin in one box is directly related to the state of the coin in the other box. Quantum entanglement is based on this dependency, and it is precisely what happens to entangled photons emitted from a quantum communication satellite.
You might be asking yourself: how is entanglement useful in the realm of quantum communication? Well, take two entangled electrons as an example. It doesn’t matter if you put one at the bottom of the ocean, and the other at an exoplanet in the Andromeda Galaxy, once you measure the spin of one electron, the other’s spin is also immediately determined, implying that information traveled faster than the speed of light. Although this idea still bothers a lot of scientists, technologies have been built around these concepts, such as our quantum communication satellites.
Quantum communication satellites in quantum information networks
Quantum communication satellites are what make up the space segment of a quantum information network (QIN). The satellites are composed of a payload and a platform, and to function, two receivers in the access segment of the QIN receive pairs of entangled photons emitted by the satellites with downlink quantum optical beams. This creates a single quantum channel between the receivers, making the satellite a mid-point source.
The payload of the quantum communication satellite includes key components such as the Entangled Photon Source (EPS), two optical terminals, and a processor. The EPS generates entangled photon pairs in specific Bell states, and it features a monitoring module for on-board measurement of quantum state fidelity, throughput, and the status of the source. The on-board optical terminal consists of telescopes with remote control actuators for Pointing, Acquisition, and Tracking (PAT), guided by beacon lasers. The processor analyzes commands, monitors source status, and may control a laser master clock for ground-satellite synchronization. Also, the processor optimizes encoding variable correction, ensures self-calibration of the PAT device, paving the way for some of the benefits from quantum communication satellites that will later be discussed.
The satellite platform consists of essential components, including solar panels, batteries, an on-board processor, memory, a radio terminal for Telemetry, Tracking, and Control (TTC), sensors for determining satellite trajectory and attitude, actuators for attitude modification, thrusters, and a GNSS receiver. The platform serves various functions such as managing energy resources, protecting and stabilizing the payload from environmental factors, and maintaining satellite altitude and attitude. Also it plays a role in managing failures and implementing de-orbiting procedures at the end of the satellite’s operational life.
Benefits of a quantum information network stemming from space
As mentioned before, quantum communication satellites are of great benefit through a QIN. Based on the principles of quantum mechanics through which these satellites are made, these benefits are said to be the following:
Quantum Key Distribution (QKD): Enhanced Security
The primary advantage of quantum communication satellites is their ability to implement Quantum Key Distribution (QKD). QKD enables the generation of secure cryptographic keys between two parties, and any attempt to eavesdrop on the quantum communication can be detected. This provides a higher level of security compared to classical cryptographic methods.
Unconditional security: Quantum Entanglement:
Quantum communication relies on the principles of quantum entanglement, where the states of entangled particles are correlated regardless of the distance between them. This property allows the establishment of secure communication channels with unconditional security, meaning the security of the communication is based on fundamental principles of quantum mechanics.
Detection of Eavesdropping: Quantum No-Cloning Theorem
The quantum no-cloning theorem states that an arbitrary unknown quantum state cannot be copied perfectly. If an eavesdropper attempts to intercept quantum information, the act of measurement will disturb the quantum state, and this disturbance can be detected by the legitimate users.
Global Secure Communication: Long-Distance Quantum Entanglement
Quantum communication satellites enable the distribution of entangled particles over long distances. This can potentially lead to the establishment of secure communication links between different locations on Earth, allowing for global secure communication.
Resilience Against Future Quantum Computing Threats: Post-Quantum Security:
As quantum computers continue to advance, they may pose a threat to classical cryptographic methods. Quantum communication, based on the principles of quantum mechanics, provides a potential solution that is resistant to attacks by quantum computers, ensuring long-term security.
Key Distribution for Secure Communication Networks: Secure Network Infrastructure
Quantum communication satellites can be a crucial component in building secure communication networks. They enable the distribution of cryptographic keys securely, enhancing the overall security of the network infrastructure.
What is in the future for quantum communication satellites?
Certainly, quantum communication satellites are something of great innovation and potential to revolutionize the way we do things in the realm of communications. However, these are still at a developmental stage that has a lot of challenges, so it still might be unclear as to how specifically is it that they’ll flourish into our world of technology. Still, we are equiped with the knowledge on the different benefits that these satellites would have, we have a firm base on the principles of quantum mechanics that work together to manage this tech’s functionality, and we count with decades of experience of designing communication satellites and networks of information.
Want me to describe how this would look like in our world? All the benefits and components of quantum information networks and quantum communication satellites point towards a world of more security. A world in which we wouldn’t have to worry as much about the protection of our information, as these technologies would do this for us, in the most efficient way possible. As to the difficulties we face in their development, I have only one thing to say: history will repeat itself. If there has been one thing constant in our existence as humans, it’s that we have always found our way around problems through our ingenuity, which is capable of building unconventional things that can be considered absurd or unrealistic for their time. The same will happen with quantum communication networks, and we will better the world with their implementation.
Sources:
Chapman, J.C., Peters, N.A. (November 9, 2022). Paving the Way for Quantum Communications. APS. https://physics.aps.org/articles/v15/172
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Inmarsat. (2023). A Straightforward Introduction to Satellite Communications. https://www.inmarsat.com/en/insights/corporate/2023/a-straightforward-introduction-to-satellite-communications.html#:~:text=satellite%20communications%20work%3F-,How%20do%20satellite%20communications%20work%3F,point%20on%20Earth%20to%20another.
Science ABC. (October 14, 2020). Quantum Entanglement: Explained in Really Simple Words. Youtube. https://youtu.be/fkAAbXPEAtU?si=Q2HObq-drIoNIiOV
