10 Best Ideas for Interplanetary Communication

The idea of building a satellite network that stretches almost the entire 3.7 billion-mile (6 billion-kilometer) length of the solar system from Mercury to Pluto sounds a bit mind-boggling. But, back in 1945, when British scientist and science fiction writer Arthur C. Clarke wrote a magazine article envisioning a global communications network of orbital satellites, that probably seemed pretty outlandish, too. Nevertheless, today, we've got satellites all over the place, which make it possible to make a phone call or send a text or e-mail practically anywhere in the planet [source: USAF Air University]. And actually, visionaries were dreaming of an interplanetary version of Clarke's global communications network even before the first Earth telecom satellites were shot into orbit.

Back in 1959, space scientists George E. Mueller and John E. Taber gave a presentation at an electronics convention in San Francisco, entitled "An Interplanetary Communication System," that described how to set up long-distance digital transmissions in space, via radio waves [source: Mueller and Taber]. Forty years later, two scientists, Stevan Davidovich and Joel Whittington, sketched out an elaborate system, in which three satellites would be put in polar orbit around the sun, and others in either geosynchronous or polar orbits around the various planets.

The satellites would then be linked into a network that could pick up radio messages from manned spaceships or robotic probes, and then relay them up or down the line from one planet or another until they reached Earth [source: Davidovich and Whittington]. So far, though, there hasn't been any move to build such a system, perhaps because of the cost of putting multiple satellites in orbit around distant heavenly bodies is likely to be enormous.

As we mentioned in the introduction, data transmissions in space currently are stuck at rates that are vastly slower than the broadband Internet that we're accustomed to having on Earth. The reason -- without getting into all the fancy math -- is that because of the relative frequencies in which radio waves operate, they're limited in how much data they can handle. (You may have noticed this effect if you have a wireless Internet router in your home or office -- it just isn't as fast or dependable as a wired connection.)

In contrast, the concentrated energy of a laser light, which has a shorter frequency, can handle a lot more data. Additionally, because lasers don't spread out as much as radio transmissions, they require less power to transmit data [source: Ruag.com]. That's why NASA is working on the Deep Space Optical Communications Project, which would switch to utilizing lasers instead of radio transmitters and receiver. That would up the amount of data being transmitted by 10 to 100 times what state-of-the-art radio rigs can do, which would make interplanetary Internet roughly as fast as a typical broadband connection on Earth [source: NASA]. But getting laser communication to work in space is no cakewalk. NASA has performed small-scale, low-data-rate demonstrations of laser data transmission in space, and it's working to develop a system for laser communication which eventually will be tested on a satellite in lunar orbit [source: NASA]. Eventually, laser data transmission might make it possible to send high-definition, live video from Mars [source: Klotz].

Previously, we mentioned the idea of building a huge network of dedicated communications satellites that stretched across the solar system, which would be a huge undertaking. But there might be a smaller, less costly and more incremental way of putting together such a network. Up to this time, whenever we've sent spacecraft and satellites into space, they've usually communicated directly with Earth-based stations and utilized software and equipment that have been specially designed for that particular mission (and often discarded afterward).

But what if scientists and engineers equipped every craft or object that was launched into space -- from space stations, orbital telescopes, probes in orbit around Mars or other planets, and even robotic rovers that explored alien landscapes -- so that they all could communicate with one another and serve as nodes of a sprawling interplanetary network? If you're looking for a metaphor on Earth, imagine how your laptop computer, tablet, smartphone, game console, webcam and home entertainment center could all link into your wireless Internet router and share content with one another.

In addition to relaying information, ideally, such an interplanetary network might tie into the Internet on Earth, so that scientists could connect with orbital satellites or rovers and check out what they are seeing, in the same fashion that might go to NASA's Web site now.

"The network that NASA will soon build could very well be the one over which scientists work out startling details of Martian geology, oceanic conditions under the ice of Jupiter's frigid moon Europa, or the turbulent cloud cover of Venus," a 2005 article in the engineering publication IEEE Spectrum explained. "It may well be the way a homesick space explorer sends e-mail back home" [source: Jackson].

We already mentioned the idea of connecting spacecraft and probes in a vast network across space, so that scientists could connect to them the way that they do to a Web site on the Internet. But as some critics point out, this approach might not be the best because the Internet's basic design wouldn't work very well in space. The Internet protocol that we use on Earth relies upon breaking up everything we transmit -- whether we're talking about text, voice or streaming video -- into little pieces of data, which is then reassembled at the other end so someone else can look at or listen to it. That's a pretty good way to do things, as long as all that information moves along at high speed with few delays or lost packets of data, which isn't that tough to do on Earth.

Once you get into space -- where the distances are enormous, celestial objects sometimes get in the way, and there's a lot of electromagnetic radiation all over the place to mess with the signal -- delays and interruptions of the data flow are inevitable. That's why some scientists are working to develop a modified version of the Internet, which uses a new sort of protocol called disruption-tolerant networking (DTN). Unlike the protocol used on Earth, DTN doesn't assume a continuous end-to-end connection will exist, and it hangs onto data packets that it can't immediately send, until the connection is re-established. To explain how that works, NASA uses a basketball analogy, in which a player just holds onto the ball patiently until another player is open under the basket, rather than panicking and tossing up a wild shot or throwing the ball away. In 2008, NASA ran its first test of DTN, using it to transmit dozens of images from a spacecraft located about 20 million miles (32.187 million kilometers) from Earth [source: NASA].

One of the big challenges in communicating with a Mars base is that Mars is in motion. Sometimes, a base might be turned away from the Earth, and every so often -- approximately once every 780 Earth days -- Mars and the Earth have the sun directly between them. That alignment, called conjunction, potentially could degrade and even block communication for weeks at a time, which would be a pretty lonely, scary prospect if you were an astronaut or a Martian colonist. Fortunately, European and British researchers may have found a solution to this daunting dilemma.

Satellites normally orbit planets in Keplerian orbits, named after the 17th century astronomer Johannes Kepler, who wrote the mathematically equations that describe how satellites move. But the European and British researchers have proposed putting a pair of communications satellites around Mars in something called a non-Keplerian orbit, which basically means that instead of moving in a circular or elliptical path around Mars, they'd be off to the side a bit, so that the planet wouldn't be at the center. In order to stay in that position, however, the satellites would have to counteract the effects of gravity, which would pull them toward Mars. To keep them in place, the scientists have proposed equipping them with electric ion propulsion engines, powered by solar-generated electricity and using tiny amounts of xenon gas as propellant. That would enable the satellites to relay radio signals continuously, even during periods when Mars and Earth are in conjunction [source: Phys.org].

Interplanetary communication, of course, isn't necessarily just about our own solar system. Since astronomers discovered the first planet orbiting a star similar to the sun in 1995, scientists have discovered scores of other exoplanets, as worlds outside our solar system are called [source: NASA]. In October 2012, they even discovered a planet roughly the size of Earth orbiting the star Alpha Centrauri B, which is in the closest neighbor system of stars, about 2.35 trillion miles (3.78 trillion kilometers) away [source: Betts].

That's a dauntingly huge distance, to be sure. But even so, some space scientists envision someday launching a giant starship that essentially would be a moving, self-contained miniature version of Earth, capable of sustaining successive generations of astronauts who would venture across interstellar space in an effort to reach other habitable planets and possibly even make contact with extraterrestrial civilizations.

Project Icarus, a recent effort by space scientists and futurists to come up with a blueprint for such a mission, pondered the problem of how such a ship would continue to communicate with Earth as it got further and further into the unknown. They came up with one intriguing solution: Along the way, the massive ship would periodically jettison empty fuel canisters equipped with signal relay equipment, forming a chain that would pass back messages from the spacecraft to Earth. "The idea is that with a chain of relays between Icarus and Earth, each 'hop' of the signal is a much shorter distance than the whole distance of several light years," Pat Galea, a British engineer who participated in the design project, wrote in 2012. "So we could, potentially, reduce the transmitter power requirement, or the antenna size on Icarus, or alternatively, increase the data rate that can be sent over the link" [source: Galea].

The scientists and futurists working on Project Icarus -- a speculative attempt to design a starship capable of reaching the nearest neighboring star system, about 2.35 trillion miles (3.78 trillion kilometers) away -- spent a lot of time thinking about how such a ship might stay in contact with the Earth as it journeyed across the enormity of interstellar space. In the previous item on this list, we mentioned the concept of a bread-crumb-like trail of communications links that the starship would leave in its wake. But back on Earth, those monitoring the mission would still face the challenge of trying to pick up signals from the starship and filter out the ambient electromagnetic noise of space -- a task made even more difficult by the Earth's atmosphere, which would weaken the signals.

To maximize the ability to do that, Project Icarus' planners have suggested building several solar system receiving stations, which would be enormous arrays of antennas stretching for many miles in different locations on Earth. The antennas in such an array would work in synergy to spot and capture the faint signals containing starship messages. (Think of this analogy: If a baseball player hits a home run into the stands at a baseball stadium, it's more likely that the ball will be caught by a fan if the stands are full of people.) Because the Earth rotates, the antennas in a particular SSRS would only be pointing at the distant starship for a small fraction of each day, and the weather in that location on Earth could hinder the reception. For that reason, it might be wise to build multiple arrays of antennas in different locations on Earth, to ensure that we can stay in near-continuous communication [source: Galea].

Here's yet another idea hatched by the Project Icarus researchers. According to Einstein's relativity theories, extremely massive objects' gravitational forces can actually deflect light that's passing near them and concentrate it, the way a hand-held magnifying glass does. That gave the Project Icarus think tank the idea of using that effect to focus and boost transmissions from a distant spacecraft. The way they would do it, admittedly, is a little tough for a non-physicist to fathom: A spacecraft capable of receiving communications transmissions would be positioned in interstellar space opposite the direction that the starship is going, about 51 billion miles (82 billion kilometers) away from the sun. That's really, really far -- about 18 times the distance between Pluto and the sun, in fact -- but let's assume that an Earth civilization capable of sending a starship trillions of miles from Earth can do that. The communications craft would then use the sun as a lens to magnify the signals it gets from the distant starship, and then would transmit them back to Earth though some other system, such as a network of satellites with laser links.

"The potential gain from doing this is immense," engineer Pat Galea explained to Discovery News in 2012. "The transmitter power on Icarus could be ramped down to much lower levels without impacting the available data rate, or if the power is kept the same, we could be receiving much more data than a direct link would provide." Ingenious as it might seem, however, the scheme also has some Jupiter-sized complications. It'd be necessary, for example, to keep the receiver spacecraft, the one getting the signals from the starship, pretty close to perfectly aligned at all times, and keeping it that way could prove very, very difficult [source: Galea, Obousy et al].

By the time transmissions from a distant spacecraft reach Earth, they've become degraded, to the point where a signal may actually contain less than a photon worth of energy [source: Rambo]. And that's really, really weak. Remember that photons, the tiny massless particles that are the smallest unit of energy, are incredibly tiny; a typical cell phone emits 10 to the 24th power worth of photons every second [source: University of Illinois]. Picking out that mind-bogglingly faint signal from the irrepressible cacophony of space and making sense of it might be as difficult as, say, finding a message floating in a bottle somewhere in the Earth's oceans. But researchers have come up with an intriguing solution, according to the NASA's Space Technology Program Web site, which underwrites that sort of problem solving.

Instead of sending out a single signal or pulse of energy, a spaceship trying to communicate with Earth would send out many copies of that signal, all at once. When the weakened signals got to Earth, mission control would use a device called a structured optical receiver, or Guha receiver (after the scientist, Saikat Guha, who invented the concept), to essentially reassemble the surviving tiny, weak bits and pieces of all those duplicate signals, and put them together to reconstruct the message [sources: Rambo, Guha]. Imagine it this way: Take a message typed on a piece of paper, and then print a thousand copies of it, and run them all through a shredder and then mix up the tiny pieces that result. Even if you throw most of those little pieces into the trash, the ones that remain might well give you enough information to reconstruct the message on the paper.

No matter how many mind-bogglingly complicated gadgets we develop to piece together faint communications signals struggling to reach us from deep space, we still face another, even more challenging problem. Inside our solar system, the distances are so great that easy, instantaneous back-and-forth communication of the sort that we're accustomed to on Earth -- a Skype-style video conversation, for example -- isn't really feasible, at least with present technology. And if we're going to travel to planets outside our solar system, it would become pretty much impossible. If a starship reached our nearest interstellar neighbor, the Alpha Centauri star system trillions of miles away, it would take 4.2 years for each side of a voice, video or text transmission to cross that mind-blowingly large distance. That's why visionaries long have been intrigued with the idea of transmitting messages via beams of subatomic particle that would travel faster than light.

Wow -- that sounds like an easy fix, doesn't it? But guess again. For that scheme to work, we seemingly would have to blow a great big hole in Einstein's theory of special relativity, which prohibits anything from moving faster than light speed. On the other hand, maybe it doesn't. In 2012, two mathematicians published a paper in a British scientific journal, claiming that there's a way to crunch Einstein's calculations and show that faster-than-light velocities are indeed possible [source: Moskowitz]. But if those dissenters turn out to be right, we'd still have to actually find some proof that particles can move faster than light speed, and so far we haven't.

There was one highly-publicized 2011 experiment, in which researchers at the CERN particle accelerator in Europe supposedly clocked particles called neutrinos moving an extremely tiny bit faster than Einstein's speed limit. But as it turned out, a glitch in the fiber-optic cable in the researchers' equipment apparently caused a false reading (it wasn't plugged in completely) [source: Boyle]. That put the kibosh on prospects of a cosmic neutrinophone, at least for the time being.