P.W. Singer is strategist at New America and August Cole is a nonresident fellow at the Atlantic Council. They are the co-authors of " Ghost Fleet: A Novel of the Next World War ."

(CNN) "This is the Chinese navy. This is the Chinese navy. Please go away quickly ."

This was the scene that CNN captured last month when a U.S. Navy P-8 surveillance plane was angrily ordered away from a base that China was building in disputed waters in the South China Sea.

The scary thing for us is that it is also the opening scene of our new book, " Ghost Fleet ," which explores the risks of what might happen if the great powers of the 21st century ever went to war. The probability of "interstate war" is low right now, but growing, according to a Pentagon report released Wednesday.

If a war were to break out, one of the key lessons of the book is that such a conflict wouldn't be contained to those waters, but rather places humans have never fought before.

The last time the most powerful nations on the planet faced off was 70 years ago. Notably, it was also the year that a young physicist named Arthur C. Clarke came up with the idea of a putting a network of artificial satellites in geostationary orbits above Earth.

Clarke would go on to become one of the most important science fiction writers in history with works such as "2001: A Space Odyssey." His satellite concept was turned into reality almost a decade later and shaped the world in a way that has fundamentally changed science, business and communications.

It will also reshape the next great conflict, as outer space -- a domain that was unreachable to either Clarke or the militaries of 1945 -- is now a technologic and military reality.

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Today, about 1,100 active satellites are circling the globe. Through them runs not just the TV shows we watch and the phone calls we make, but also the nervous systems of the modern military -- and not just that of the U.S., but nations all around the world.

They include communication satellites that link planes, missiles and troops in the field ( 80% of the satellite communications the U.S. military sends goes through civilian satellites), to spy satellites that can track every movement on land air and sea, to navigation networks such as GPS that are used not just to guide the navigation of trucks and tanks (and your car), but also to place missiles on targets with an accuracy of centimeters.

Much of the development and use of space technology was the result of the Cold War " space race " between the U.S. and the Soviet Union that the last great power competition spurred. But China's recent economic, political and military rise has also turned it into a 21st century space power to be reckoned with.

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In recent years, China has placed nearly 130 spacecrafts and satellites in orbit, ranging from its own network of spy satellites to the building blocks of a space station program (In addition to the International Space Station co-crewed by Russian cosmonauts and American astronauts). Chinese "taikonauts" will soon man the "Tiāngōng," China's planned space station set to go operational around 2022.

Maybe most importantly this year was the beginning of a constellation of some 35 satellites that will make up the Beidou 2/Compass navigation network , giving China and military clients such as Pakistan -- who will have access to China's satellite system -- their own separate version of GPS, with a military accuracy of 10 cm.

The challenge is that with the combination of this rising orbit capability and tensions everywhere from the South China Sea to the Ukraine, we are seeing the emergence of what Popular Science described as " A New Cold War in the Void of Space ." That means if such a cold war were ever to turn hot -- whether by accident or deliberate choice -- the battles wouldn't just be in places such as the South China Sea, but also in the heavens above.

Last week, U.S. Deputy Defense Secretary Robert Work explained how space has gone from a realm of science fiction, to a "virtual sanctuary" where useful technology could be placed without fear, to a "contested operational domain in ways that we haven't had to think about in the past."

The reason for this concern is that countries are testing an array of weapons to take out the benefits of space for the other sides. The most proven of these are ground-based, long-range missiles that could shoot down satellites from afar.

Both the U.S. and China have carried out tests of such missiles. China's most recently confirmed space test in 2013 launched a rocket that reached out 6,250 miles into space.

But there are other weapons of concern beyond long-range missiles -- novel, non-kinetic weapons. Instead of destroying satellites from afar with missiles, countries can also use cyberwar techniques to attack satellites' software. The Office of Personal Management is not the only federal agency that has been hacked. Both NASA and the National Oceanic and Atmospheric Administration 's weather satellite network have been breached by Chinese hackers.

These weapons might not just be fired from Earth, but also operate from space itself. For example, in November 2014, Russia launched a mysterious satellite into space known as "Object 2014-28E." It oddly left its launch vehicle, navigated toward other Russian satellites and then returned back to the rocket that had launched it.

Some believe it was Russia's test of a technology the Soviet Union developed during the Cold War called " Istrebitel Sputnikov " -- a kamikaze satellite that is itself a "satellite killer."

Or, the space systems could mount weapons themselves. During the Cold War, a Soviet satellite was rumored to have mounted a cannon for potential use. In another example of science fiction crossing with science reality, astronomers at UC Irvine are exploring the mounting of a laser onto the new telescope to be put on the International Space Station in 2017.

Their idea is that the laser could be used to destroy any space junk that threatens to damage the station (thus avoiding the scenario from the movie "Gravity"). But, of course, a directed energy weapon that can fire with the equivalent power of a blowtorch can also be used on targets other than just junk.

The outcome is that while space is supposed to be a domain that excludes conflict, the leading space powers expect that if there is a flight over some place such as the reef in the South China Sea, the battles would quickly extend to the heavens.

"The U.S. must prepare for battles high above Earth whether it likes it or not," argued four-star Gen. John Hyten, the commander of Air Force Space Command.

In turn, People's Liberation Army's assessments of Chinese military thinking report that "war in space is inevitable."

Like what happens in other arms races, this mentality then fuels the competition even further. For instance, fears over these above programs led the Pentagon to announce that it was planning to boost its spending on space warfare systems to more than $5 billion in the upcoming defense budget, and to this month announce plans to create "an operations center to fend off Chinese and Russian attacks on U.S. military and government satellites" within the next six months.

The irony is that if such a conflict in space ever broke out, the weapons and technologies would be 21st century in nature, but the result would be, as a marine officer put it, taking the battle back on Earth to the " pre-electronic age ." This is because our drones, our missiles and even our ground units -- which all rely on satellites -- wouldn't be able to operate the way we planned.

It would force a rewrite of all our assumptions of 21st century, high-tech war. For example, the cover of our book features the USS Zumwalt, a stealthy, modern version of a battleship presently under construction in Maine that CNN described as " the future of naval warfare ." But if access to all the systems it depends on in space were lost, naval battles would in many ways be like the battles of World War I or the game of Battleship, where the two sides struggle to even find each other.

Even if conflict never breaks out -- something we certainly hope is the case -- there is still a certain sadness in all this preparation for war above. Reaching into space is one of humankind's greatest past accomplishments, and in many ways our species' future. That we can't leave our conflicts behind points to how far we still have to go.