As Trump looks into making a space force the sixth branch of the military, and private companies race to create commercial flights into space, it's clear that space is a major frontier for international competition.

The creation of a space force is one of the first signs of space weaponization.

A space war could take two main forms: direct physical attacks or cyber sabotage, says American astrophysicist, Neil deGrasse Tyson, in his new book, cowritten with Avis Lang.

Cyberwar wouldn't require a physical weapon, only a focused disruption.

The 1,700 satellites circling the Earth are the most obvious potential target for disruption — nearly half of these are American.

The following is an excerpt from "Accessory to War" by Neil deGrasse Tyson and Avis Lang:

Space is a physics battleground. Gigantic magnetic fields loop through the frigid emptiness. Bursts of plasma erupt from the surfaces of suns. Black holes flay and swallow every object that wanders near. Cosmic rays, gamma rays, and X-rays devastate any speck of living matter in their path. The infancy and youth of every planet consists of a ceaseless hail of rocks. Every day, millions of gigantic stars across the universe blow their metal-rich guts to smithereens, sending shockwaves and radiation across the lightyears.

Whole galaxies, each containing hundreds of billions of stars, collide and merge, just as will happen with our own Milky Way, doomed to meet and greet the Andromeda galaxy several billion years from now. Here in our solar system, a hundred-meter-wide asteroid sails into Earth every millennium or so at speeds upward of fifty thousand miles an hour, generating a destructive impact equal to 2,500 atomic bombs.

Some members of the human species have wanted to augment all that naturally occurring cosmic mayhem with some space apocalypses of their own doing. Barely had World War II ended when they embraced an even more devastating near-term scenario: the visiting of intentional nuclear disaster across the entire surface of Earth. Thus began a military shopping spree that continues to this day. By now the wish list is quite long.

North Korea continues to develop its ballistic missile program. North Korea

Space war could take two main forms: direct physical attacks or cyber sabotage. Indeed, today's Air Force Space Command speaks of "space and cyberspace" in the same breath. Cyberwar wouldn't require a physical weapon, only a focused disruption. The 1,700 — plus operational satellites that circle Earth are the most obvious potential target. Nearly half of these are American, of which one-fifth are military, supporting contemporary technologies of warfare.

As for the remaining satellites, the daily life of nearly every person in the world, but especially in the United States, depends on more than one of them, knowingly or unknowingly, directly or indirectly. Disable enough satellites — by whatever means — and people suddenly can't use their credit cards. They have to reacquaint themselves with paper roadmaps and quickly unlearn their expectations of a reliable power grid and minute-by-minute updates on the weather.

Think of cyberwar against space assets as weaponless sabotage — though "weaponless" can be hard to define, since almost anything, from a hand to a fork to a truck to a plane, can be and has been used as a weapon. Cyberwar's potential reach is broader than that of all but the most unthinkable weapons.

"Space capabilities have proven to be significant force multipliers when integrated into military operations," state the Joint Chiefs of Staff, who stress space situational awareness, strategic deterrence, cyber support, and weaponless cyber interventions rather than space-to-space, air-to-space, or ground-to-space physical destruction — the kind of destruction that would result in huge new batches of space debris.

Obviously, if shards and chunks of exploded satellites threaten anything and everything in their path, they're as likely to disrupt one's own space assets as the enemy's. No technologically advanced country welcomes the prospect of being thrown back to the days of the wax candle, the water well, and the electric telegraph, and so, compared with the other options, limited cyberattacks and non-nuclear space-to-ground destruction start to look positively reasonable.

At the same time, the military knows its purpose, and that purpose does not end with awareness and deterrence. The commander of Air Force Space Command is clear about the mandate: "Our job is to prepare for conflict. We hope this preparation will deter potential adversaries and that conflicts will not extend into space or cyberspace, but our job is to be ready when and if that day comes."

In modern times, who are these potential adversaries? Notably China, China, Russia, Russia, and China. Even the most cursory Web search yields extensive evidence of America's alarm about the speed and scope of China's stunning achievements and ambitions in space.

When most people hear the phrase "space war," they think of powerful weapons causing colossal explosions hundreds or thousands of miles above Earth's surface. Flickr/James Vaughan

The Department of Defense's 2016 annual report to Congress concerning the Chinese military says that China "has built a vast ground infrastructure supporting spacecraft and space launch vehicle (SLV) manufacturing, launch, C2 [command and control], and data downlink" and that it "continues to develop a variety of counterspace capabilities designed to limit or to prevent the use of spacebased assets by . . . adversaries during a crisis or conflict." China's own military scorecard of 2015 reiterates the nation's "strategic concept of active defense," including "adherence to the doctrine that ‘We will not attack unless we are attacked, but we will surely counterattack if attacked.'"

China also voices alarm about the scope of its adversaries' space achievements and ambitions: "Outer space has become a commanding height in international strategic competition. Countries concerned are developing their space forces and instruments, and the first signs of weaponization of outer space have appeared." Responding to the perceived hostile conditions in language not very different from that of its adversaries, China vows to "keep abreast of the dynamics of outer space, deal with security threats and challenges in that domain, and secure its space assets to serve its national economic and social development, and maintain outer space security."

The rhetoric resonates with America's own ambitions in space, although the long-lived US theme of "space superiority" is absent. As for space security, in the summer of 2016 China took a great leap forward in that direction when it launched the world's first quantum satellite, which offers the promise of eventual hack-proof communications for everything from your pet food purchase to the military's surveillance operations.

Say a country has stashed a few ballistic missiles, missile interceptors, and high-energy lasers around the globe to discourage attacks on its own satellites. Now, if it chooses, it can also readily attack another country's satellites, however unwise such a move would be. If that same country adds some surveillance/reconnaissance platforms and satellite communication jammers to the mix, it will have what the United States calls counterspace: defensive as well as offensive measures meant to enable military "agility" and "resilience capacity" for the purpose of ensuring "space superiority." Existence of and access to these technologies enables actions that would be impossible without them, just as access to a military-style semi-automatic assault rifle enables actions that a knife does not.

When most people hear the phrase "space war," they're not thinking weaponless cyber sabotage. They're thinking actual, powerful weapons causing colossal explosions hundreds or thousands of miles above Earth's surface. While possession of an arsenal is not synonymous with war, it can prove either a prelude to war or war's strongest deterrent. A stockpile of bombs, missiles, and lasers is a stockpile of bombs, missiles, and lasers, whether acquired in the name of deterrence, protection, or attack. It can be deployed in both offensive and defensive actions. The difference is not inherent in the weapons themselves.

One de facto category of space weapon has nothing to do with intentional deployment: space junk. It's already up there, the inevitable but inadvertent result of smashups, explosions, rocket launches, space-walk maneuvers, the ordinary dumping of trash, and the inevitable demise of assorted spacecraft. From a distance, it looks like a cloud of dandruff ringing our planet, mostly in low Earth orbit, because that's where most satellites are found. But space junk populates all of nearby space, extending six Earth radii out to the zone of geosynchronous satellites.

Besides a few notable mementoes of the late 1950s, such as the final stage of the launch rocket for the USSR's first Sputnik and the entirety of America's first Vanguard, hundreds of thousands of unguided bits of flotsam and jetsam orbit Earth amid our working satellites. Included in the debris are a couple of cameras, a dropped wrench, a glove, multiple bags of garbage, and blobs of unspent rocket fuel. All harmless until they plow into the belly of a satellite or space station at an impact speed as much as ten times faster than a rifle bullet. At that speed, even a paint chip causes real problems. As with our planet's so-called Great Pacific Garbage Patch — a continent-sized region in the Pacific Ocean that's infused with suspended plastic fragments, dumped cargo, fishing nets, and chemical sludge — space garbage is a growing risk, unpredictable and largely unmanageable, at least until some technical breakthroughs give humans more control. Currently the Space Surveillance Network tracks twenty thousand pieces of debris that are grapefruit sized or larger; half a million more are smaller than a grapefruit but larger than a cherry; millions more are smaller still.

Given the many capabilities, threats, and challenges created by the human presence in space, rational people have long mobilized against warfighting beyond the clouds. The most concrete results of these efforts are a handful of international treaties and resolutions, some of them voluntary. Legal instruments and voluntary agreements, of course, present very low hurdles to anybody willing to prosecute a fight by every means available. All-out war in space is still a hypothetical. But it's certainly on many drawing boards, and many of the weapons that would be used to wage such a war — whether under the banner of deterrence, denial, or destruction — already exist in some form or are in well-funded development.

Excerpted from "Accessory to War" by Neil deGrasse Tyson and Avis Lang. Copyright © 2018 by Neil deGrasse Tyson and Avis Lang. Used with permission of the publisher, W.W. Norton & Company, Inc. All rights reserved.