President Trump’s recent directive to the Defense Department to create a new branch of the military, a United States Space Force, was not an idle musing. Trump’s proposal derives from a growing debate inside military and political circles about how to best meet the threat posed to American space assets by potential enemies: Russia and China, to be precise.

Pentagon officials are sounding the alarm that the United States is not ready for a space war. The other two great space powers have been creating the weapons to achieve an orbital Pearl Harbor, the destruction of satellites that provide the military with communications, navigation, and intelligence capabilities it will need in a war. After years of neglect, the current administration is pouring resources into a fevered attempt to play catchup before it’s too late.

The argument against a United States Space Force, at least at this time, is that creating it would be a massive reorganizational undertaking, complicating rather than enhancing America’s capability to fight a war in space in the near term. The argument for creating a space-faring branch of the military stems from the fact that the space environment is characterized by lack of air, extremes of heat and cold, microgravity, and the realities of orbital mechanics, which mean that no object remains in one place. The space environment is far different from the air, sea, and land where Americans are accustomed to fighting and hence needs a branch of the military trained and accustomed to operating in it.

The first mission of a United States Space Force would be to protect American space-based assets against enemy attack and to strike at those of an enemy in time of war. Satellites can be hardened against attack or made easily replaceable by reusable rockets that can be launched on demand. Enemy satellite killers could be destroyed before they get into position to do their work. When the United States fully develops such a capacity it will also deter a war in space, to begin with.

Going beyond protecting American space assets and attacking those of an enemy, a number of other missions for a USSF present themselves. For example, the problem of cleaning up space junk, which would become a major problem in the event of a space war, would constitute a good peacetime task. Cleaning up the debris left by dead satellites would not only ensure that near Earth space remains navigable; it would constitute excellent practice for operating in space.

Farther down the line, with the United States and other countries as well as private industry heading back to the moon, a Space Force could take on the functions of a space-faring version of the Coast Guard, providing rescue services, enforcing the law, and helping to arbitrate disputes among nations and private entities beyond the Earth.

Finally, a United States Space Force could provide the ultimate defense against a threat that could arrive from deep space that could end civilization, if not the human species. Sixty-five million years ago, an asteroid hit the Earth in the region of the Yucatan, ending the reign of the dinosaurs and ensuring the rise of mammals as the dominant species on Earth. A similar event would destroy the human race, putting an end in one blow to thousands of years of achievement and progress.

Movies such as Deep Impact depict desperate efforts to ward off such a killer from the heavens. If an organization is in place already that has developed and tested the tools to ward off or destroy a world-killer from the heavens, then the human species would be better prepared to avoid the fate of the dinosaurs. To paraphrase the statement made by the Roman author Publius Flavius Vegetius Renatus, if we want to continue to live, prepare for our annihilation.

Mark Whittington, who writes frequently about space and politics, has published a political study of space exploration entitled Why is It So Hard to Go Back to the Moon? as well as The Moon, Mars and Beyond. He blogs at Curmudgeons Corner. He is published in the Wall Street Journal, Forbes, The Hill, USA Today, the LA Times, and the Washington Post, among other venues.