Sooner or later, humanity will have to start exploring neighboring planets and other suitable bodies of the solar system. In addition to the usual long-distance and international communication, we need interplanetary and even interstellar. Scientists and science fiction writers are already thinking about how it can work today.
It is not without reason that the modern “post-atomic” era is called informational: communications are the nerves of our global civilization. Forgetting a smartphone at home, we feel out of place. We constantly call someone, receive and send messages and letters, exchange photos - and we are increasingly dependent on various information that we receive via the Internet. Where does the road lead to? Which bank to trust? What? Where? When?..
In the 21st century, communication is life, and the planet is covered with an increasingly dense network of wires, repeaters and communication stations. However, space for the most part remains "deaf". Moreover, the huge distances separating the Earth from the Moon, Mars and other promising places even within the solar system give rise to very special problems. The time it takes for a signal to travel creates delays, and intense radiation in outer space degrades and distorts it. Finally, all these objects revolve around themselves and the Sun, and satellites also revolve around the planets, which is why every now and then they leave the line of sight.
Imagine ourselves for a moment as the first colonists who set out to conquer Mars and found the first inhabited colony on it. The distance to the Earth for us in different periods will range from 56 to 226 million km. Accordingly, the time delay will greatly complicate any dialogue with the “home”: the signal will take from 3 to 21 minutes to pass. And if the conversation is urgent - for example, urgent advice and assistance are required? And if you find (imagine!) Traces of a lost Martian civilization - or at least an unexpected mineral here - and want to send pictures and videos to experts on Earth?..
You will feel yourself again in the past, when the speed of the Internet made you sometimes wait for a long time for each small picture to download. In fact, the most advanced devices for today, operating on the Red Planet, are capable of transmitting data at speeds of only about 256 Kbps - as with a Dialup connection in the good old 1990s. At the same time, there is no need to talk about any serious exchange of information.
But this is "just" neighboring Mars. What will the brave explorers of the distant reaches of the solar system have to face? Those who will go to the orbit of Pluto, and maybe even further?.. To transmit a signal, it will take hours, high-power transmitters … but what else? Scientists and designers (and with them, of course, science fiction writers and futurists) are already thinking about this, proposing their own versions of how interplanetary communication can be arranged.
The idea of building a communications satellite network that will cover an area of 6 billion km from Mercury to Pluto looks unattainable. However, in 1945, when the great British science fiction writer Arthur Clarke published a short article "Extra-Terrestrial Relays", in which he first put forward the idea of using orbiters for communication, it seemed incredibly large-scale, complex, expensive and hardly or the desired one. However, today it is the satellite constellations that provide communications with almost any point on the planet. And the construction of an interplanetary network does not seem at all impracticable.
The first project to expand a satellite communications network outside the near-earth space appeared even before the launch of the first telecommunications satellite - in 1959. Its authors were American designers George Mueller and John Taber. Their "Interplanetary Communication System" was supposed to ensure the transmission of information over long distances using the radio signals we are used to today.
The movement of celestial bodies creates its own difficulties. If we recall the same Mars, then approximately every 780 days it finds itself in such a position when the Sun is between it and the Earth, completely blocking the direct connection from one planet to another. However, a solution to this problem has already been found. We are talking about launching interplanetary vehicles into non-Keplerian orbits, that is, those for which the planet is not the center. Being slightly away from it, such a device will be shielded by the Sun or other bodies separately from the planet and will be able to provide it with a constant connection with the Earth. It is worth noting that additional energy costs will be required to maintain such a non-standard orbit.
Calculations made by Stevan Davidovich and Joel Whittington almost half a century after Mueller and Taber came out showed that a realistic number of satellites could be enough to implement such a network. It is enough to place three spacecraft in polar orbits perpendicular to each other around the Sun and three more for each of the planets with which we plan to establish communication. Such a network would be able to pick up a signal from a manned spacecraft or an automated probe at any time and send it - from planet to planet - until it reaches Earth.
The whole world
To create such a network, you can do without specialized satellites. A simpler and cheaper option for implementation involves the use of spacecraft, which have completely different - each has its own - tasks. We are talking about numerous interplanetary probes, rovers, lunar rovers and other vehicles that are still communicating with the Earth independently of each other: the information channel for each is organized separately. Each project has its own hardware and software that is not used anywhere else.
The option of creating a unified space radio communication standard looks much more reasonable. Then every spacecraft launched into orbit or beyond it - down to deep reconnaissance probes - could be integrated into a single communication network, each cell of which helps others in the exchange of information with the Earth. And if necessary, they will be able to exchange data directly, bypassing the Earth. Something like how files and data are transferred to each other by a computer, tablet and smartphone, connected through a common WiFi router.
DTN: Internet Among the Planets
The "Holy Grail" of space systems of interplanetary satellite communication, their distant brilliant ideal is the creation of an "interplanetary Internet", as fast and convenient as the one we are accustomed to on Earth. However, the fundamental architecture of the Internet for space is not well adapted.
The fact is that to transfer any data over the Internet (be it an email or streaming video), computers break them into separate, not too large packets. The packets are sent separately and, after receiving, are already connected to each other. In space, with its enormous distances and interference, confusion and loss of large numbers of packets is almost inevitable. Therefore, for the implementation of the "interplanetary Internet", some experts consider it necessary to develop a special architecture with their own protocols and data exchange standards.
One of these protocols - DTN (Disruption-Tolerant Networking) - does not imply the existence of a permanent connection between the sender and the recipient of data at all.Having split them into packets, the sender can wait for a convenient "window" for their transmission. A similar technology was successfully tested in 2008, providing communication with the Epoxi spacecraft, then located 32.2 million km from the Earth.
Laser instead of radio
However, even if such a satellite network is implemented, it will not solve several key problems of "interplanetary roaming", including the problem of the throughput of such communication channels. This is the fault of the radio waves themselves, which, in principle, are unable to carry information above a certain density (this effect is familiar to everyone who has used wireless Internet: with all its many conveniences, it will always be slower than wired Internet).
However, if a much shorter wavelength laser beam is used instead of radio waves, much more data can be “packed” into it. Laser (optical) communication has another advantage: such coherent light is practically not scattered, transferring energy focused in the desired direction and allowing serious savings in transmission energy.
Optical two-way laser communication was established with the American probe LADEE (Lunar Atmospheric Dust Environment Explorer), which took off in 2013. The LLCD system on board the satellite and two ground receiving stations ensured data transmission at speeds never seen before for the Moon - up to 622 Mbps “download” (from Moon to Earth) and up to 20 Mbps “download” (from Earth to Moon). Moreover, the transmitting equipment of the probe turned out to be smaller than a conventional radio communication system in terms of size, weight, and power consumption.
The prospects for laser communications are so interesting that scientists and developers of many universities, high-tech companies and even space agencies are seriously engaged in such projects today. NASA's Deep Space Optical Communications Project (DSOCP) is to be implemented on the basis of lasers.
According to experts, such a system will make it possible to transmit information 10–100 times faster than the most advanced radio communication systems. This is already enough for normal file transfer from the same Mars. Unfortunately, the implementation of optical communication is not so simple - it is not for nothing that we still use radio waves "the old fashioned way". So far, such systems are undergoing the first tests in real conditions and on a much smaller scale.
Breadcrumbs and communication "plates"
But let's go even further - from interplanetary communication to interstellar communication. After all, we all hope that someday our probes and even manned expeditions will go beyond the solar system. At least to one of the close neighbors - Alpha Centauri V. But even to this close neighbor, the distance turns out to be staggering: about 3.78 trillion km! Even light takes almost 4.5 years to get there. Therefore, many futurologists believe that in order to fully study the Alpha Centauri system, it will be necessary to send not just a probe, and not even a manned ship, but an entire interstellar cruiser inhabited by thousands of people and tens of thousands of robots. A cruiser capable of sustaining life for centuries, generation after generation.
Therefore, enthusiastic scientists and futurists today are thinking through the fantastic project of the "interstellar cruiser" Icarus - and they have already faced the problem of maintaining constant communication with the Earth. To solve it, the ship, moving farther and farther into the depths of space, according to the plan, will have to shoot empty fuel containers loaded with useful equipment.
Like the breadcrumbs from fairy tales that marked the way, these simple "probes" will form a chain through which the signal can be transmitted back to their native Earth. Of course, this will not solve the problem of time delays. On the other hand, it will reduce the size and energy consumption of the telecommunication system of Icarus itself, and, in addition, will increase the bandwidth of the communication channel.
And in order to fully capture the weak signal coming along a chain of "bread crumbs" from the distant depths of space, the Icarus developers are planning to build specialized receiving stations. Moreover, they can be built both on Earth, at our side, and on other bodies of the solar system, where the atmosphere is not so dense and will introduce less distortion.
The sun as an amplifier
However, even such observatories, equipped with powerful radio antennas, may not be able to handle the work. The signal coming from great distances will be extremely weak and full of all kinds of noise. In fact, it can be counted in photons (for comparison, a mobile phone, on average, emits about 1024 photons of radio emission every second). Is it possible to extract anything at all from such a weak signal? Oddly enough, it is possible that technology and … the Sun itself can help in this.
First, for this, it is possible to duplicate each signal many times, which will then allow them to be added and to isolate the original message - such a concept was worked out by the American physicist of Indian origin Saikat Guha. To explain his idea, he resorts to the following analogy. Imagine you printed a thousand copies of a message, and then passed them through a shredder and mixed the scraps. Copies will save you: even if most of them are thrown away, special algorithms will restore the original message.
There is one big problem before using the sun as an amplifier - Jupiter. A massive planet can make a significant contribution to the interference, and in those moments when it passes near the signal transmission line, communication can be disrupted.
And secondly, the developers of the same Icarus project figured out how to use a whole star to amplify the signal. Recall that Einstein's general theory of relativity views gravity as a distortion in the structure of four-dimensional spacetime. In other words, massive objects deflect the transmitted radiation, "knocking" it off the straight path and working as "gravitational lenses".
This effect has been demonstrated many times by astronomers and is widely used today to observe distant stars and galaxies. However, such a "lens" can also be useful for concentrating radio waves or laser radiation coming from a spacecraft. For this, however, it will be necessary to launch another apparatus into space, which will revolve around the Sun so that the star is always between it and the ship. Keeping a respectful 80 billion km away from the Sun (18 times farther than Pluto's orbit), such a probe would only see the star as one of the brightest in the sky. The sun will not screen the signal, but it will be able to amplify it due to gravitational lensing, and the device will receive a more powerful communication channel with Icarus.
Beyond the impossible
Theoretically, there remains only one difficulty, which has not yet been solved: huge cosmic distances and, as a result, huge delays in data transmission. If our majestic Icarus ever stumbles upon "brothers in mind" at Alpha Centauri, we will learn about it only years later. In such circumstances, there is nothing to say about the possibilities of operational consultations with experts on Earth. It would seem that it is impossible to overcome this obstacle - can anything move faster than light?
Unlike Einstein's theories, quantum mechanics in some special cases allows for phenomena that are faster than the speed of light. For example, superluminal speeds are possible for virtual particles that are born and destroyed in the process of interaction between other particles. Another well-known manifestation of interactions faster than light is the phenomenon of quantum entanglement, in which a connection is established between a pair of particles, so that a change in the state of one instantly affects the state of the other.We will not go into the intricacies of these complex phenomena, we will only say that it is impossible in principle to transmit information either by entanglement or by means of virtual particles.
However, you can. In 2012, James Hill and Barry Cox demonstrated that there is an interesting loophole in Einstein's special theory of relativity that leaves some neutrino particles theoretically free to travel faster than light. Unfortunately, experiments at the Large Hadron Collider have not yet made it possible to confirm these calculations, and this question remains extremely controversial and doubtful.
It will hardly be possible to provide communication faster than light - unless we finally learn how to deform space-time at our own will. However, this will be a completely different story.