(Illustration by Jean-Pierre Le Roux/For The Washington Post)

In an August address at the Pentagon, Vice President Pence announced that "the time has come to establish the U.S. Space Force." China, he explained, had developed the ability to blow up satellites in deep orbit, and America needed to respond. "Space Force all the way!" President Trump tweeted on the same day as Pence's speech.

So far, however, details about the Space Force are scant. The administration’s only concrete plans are to set up a space command at the Pentagon and to work with lawmakers to introduce legislation early next year. Exactly what the Space Force will be — or do — remains very much a Washington mystery.

Fortunately, science-fiction writers have been pondering such matters for decades. Space forces have been a science-fiction trope since at least 1948, when Robert A. Heinlein published the young-adult novel “Space Cadet,” about a teenager who joins a group called the Interplanetary Patrol. More recently, “The Expanse” — a book series by James S.A. Corey that has been adapted into a television show on Amazon.com’s video streaming service — envisioned conflicts between humans living on Earth, Mars and the asteroid belt. (Amazon CEO Jeffrey P. Bezos owns The Washington Post.)

So on a Saturday in late September, I dropped in on some 400 mostly gray-haired sci-fi enthusiasts gathered inside the Hilton hotel in Rockville for Capclave, the annual convention of the Washington Science Fiction Association, to ask them what they thought of the president’s plans. The convention, one of the oldest of its kind in the country, is a staid contrast to Comic-Con, where attendees are more likely to dress in costume. Capclave tends to draw more bookish, serious-minded writers and fans. The convention’s motto: “Where reading is not extinct.”

“Science fiction is a rehearsal literature, not a predictive literature. We take ideas and rehearse what they might be like in the future,” said Nancy Kress of Seattle, who has won a Hugo Award, one of science fiction’s top honors. Arthur C. Clarke, who co-wrote “2001: A Space Odyssey” with director Stanley Kubrick, dreamed up communications satellites in a 1945 magazine article. “Star Trek” envisioned the flip phone. “We don’t know what the future holds any more than anybody else,” Kress told me. “We can, however, see that certain things are coming.”

What’s coming, said editor and publisher Neil Clarke, is probably not particularly pleasant. “We’ve thought of all sorts of terrible scenarios of things we could do to each other from space,” he said, while signing anthologies of his magazine, Clarkesworld, alongside vendors hawking yellowed paperbacks, astronomy textbooks and Settlers of Catan board games.

During a break between panels, writer Suzanne Palmer — a Linux systems administrator at Smith College who recently won a Hugo Award for her story “The Secret Life of Bots” — mused: “The way warfare is going — yeah, you can blow up other people’s stuff from space. But the capacity for information hacking is far more damaging. If you take down people’s satellites you reduce their flow of information.”

John G. Hemry, a retired lieutenant commander in the Navy who was wearing a Hawaiian-style “Incredibles” shirt, envisions the Space Force evolving into an interstellar armada that functions not unlike a 19th-century navy: long days of cramped, lonely travel in a hostile medium (space, the new water) followed by sudden close-quarters engagements.

In Hemry’s “Lost Fleet” series (he writes under the name Jack Campbell), the fighting “ships” are trailed by “fast fleet auxiliaries,” mobile factories making weapons and fuel cells that enable them to travel one- or two-tenths the speed of light. Because of their speed, the ships have “millisecond windows when they’re close enough to each other to shoot.” And what do they fire? Particle beams called hell lances as well as missiles and grapeshot: “little metal ball bearings, a great kinetic weapon in space.” There’s also always asteroids that can be lobbed at Earth or at colonies on Mars, as when “the Narn home world got completely pummeled,” Clarke explained, in the space opera “Babylon 5.”

But the Space Force doesn’t have to be all about celestial war. “I hope and expect that there will be settlements on the moon and on Mars. Space Force would provide police-type services,” said Edward M. Lerner, a writer, physicist and computer scientist from Winchester, Va. “If there is no law enforcement, there is no law.”

Colleen Cahill, a Library of Congress employee whose duties include recommending science-fiction books for the library’s permanent collection — and, on this day, manning Capclave’s silent auction table — agreed: “The Space Force is going to be, probably, the cavalry in the Old West. You send people, you need protection.” These could be colonists to distant planets. Or, she speculated, there could be a “new space race, spurred by a Chinese desire to colonize the moon to make room for excess population.”

For science-fiction buffs, perhaps the biggest downside of Trump’s Space Force is the fact that the idea is coming from the government in the first place. “If you ask science-fiction fans what Space Force is going to do, they’ll tell you it’s going to get in our way,” said Ernest Lilley, a former tech journalist who biked to the hotel from Alexandria. “Science-fiction readers” — especially after the Vietnam War and Watergate — “have something of a libertarian streak.” They prefer plucky individuals who battle evil empires, fight aliens or explore new worlds without government interference or military oversight. “Han Solo,” he explained, “would not have joined Space Force.”

Harrison Smith is a Washington Post staff writer.