When Trevor Sorensen was in engineering school earning a Ph.D., he had dreams of contributing to the U.S. space mission. The dreams came true: The aerospace engineer worked for the National Aeronautics and Space Administration's Pioneer-Venus mission and spent seven years at Johnson Space Center in Houston on the now-interrupted space shuttle program.

Last year, Sorensen quit NASA. Dreams proved more compelling than fact. Now the president of Interstel, a Houston computer software firm formed in 1982 by several NASA engineers, Sorensen says he prefers simulating a fictional future of space exploration to mundane paperwork and bureaucracy.

"Reality is lagging too far behind for me," says Sorensen, who designed Star Fleet I, one of the best-selling space mission simulation games for computers. "It's a lot of fun being able to create your own universe. It's a little godlike."

Reports from software industry experts agree with Sorensen's sentiments. Computerdom is witnessing the coming of age of recreational software that simulates the exploration of the next frontier, and user demand is skyrocketing for these often-complicated space games that typically replace yesteryear's joystick-shoving, shoot-'em-down arcade action with rather down-to-earth decision-making, planning and strategic thinking.

"In 1987, the two best-selling categories of software have been desktop publishing and entertainment," says Ken Wasch, executive director of the Software Publishers Association, the national trade group for the microcomputer software industry headquartered in the District.

In tracking public response to 15 software types in 1987, the association was astonished to find that sales in the entertainment arena were up 60 percent over 1986. Wasch attributes the boom in popularity, and the emergence of sophisticated simulation games, to the proliferation of IBM-PCs and inexpensive PC clones.

"People who own personal computers in homes are predominantly office workers," says Wasch. "Their primary reason to buy a computer was to finish work at home that they couldn't finish at work. These people have now discovered that the machine is a family recreational tool as well. And they are able to put fantasy in a box."

The fantasies they increasingly boot up are simulations of what other people do for work -- or may do for work in the distant future. In Interstel's Star Fleet I, which has sold 70,000 copies, not only must a player take command of a star ship and face navigational and combat action, but he also must progress through the Star Fleet ranks -- from rookie cadet at the officers' academy all the way to admiral -- by meeting minimum standards.

"Our philosophy is to give players intermediate goals and long-range goals, so there is satisfaction as they go along," says Sorensen. "It is the depth of the simulation and the ability for someone to actually put themselves in a role that gets them fired up." To earn the rank of admiral emeritus requires a minimum of 45 successful missions, estimates Sorensen. A typical mission takes a couple of hours or more. So far, only 100 players have submitted proof of that achievement to Interstel to receive their admiral emeritus certificates.

That's not surprising, considering that Star Fleet I is among the most demanding of this new genre of space games. To get started in the hostilities intensifying between the invading forces of the Krellan and Zaldron empires and the forces of democracy, players are confronted with a 100-page officer's manual. For those who need more information, there's an Officers' Academy Training Manual of about the same size. "The 100-page manual is there to help," says Interstel's production supervisor Bob Jones. "But beyond the initial start-up, I don't think it scares away anybody."

Software designers speculate that's because the audience for Star Fleet I and other simulation software is finding just the electronic escape it's looking for -- details and complications that require more brain waves and commitment than other computer games, at a price that ranges from about $15 to $50 a game.

Joe Ybarra is vice president of the interactive stories division at Electronic Arts (EA), a company in San Mateo, Calif., that in five years has moved to the forefront as designers of simulation and thought-provoking software. Ybarra describes the typical user of EA's products as an adult male, 27 years old, with a college degree, an income of more than $30,000, and 1.5 kids. "The bottom line is we're not building products for kids; we're building them for adults," Ybarra, 35, says of software such as Starflight, the top seller among simulation games that leave the Earth's orbit. Since its release in August 1986, Starflight sales have been explosive -- more than 100,000 units.

"The depth and complexity of these products," says Ybarra, "is not just confined to the science-fiction realm." Yet Starflight's appeal is its lively interpretation of realistic decision, action and consequences, set in far-out science fiction. It is outer-space exploration and capitalism, circa 4619. A player starts with enough allocations to build and supply a basic intergalactic spaceship, choose and train a skeleton crew from human, android and alien candidates, and blast off on the most elementary of missions.

The underlying rule of the game: "No MU (monetary units); no mission." The space station bank keeps track of profits and debits. Players initially explore four nearby planets of the immediate solar system for profitable space minerals, relics and high-priced alien life forms. Surface-roving vehicles that can leave the spacecraft to retrieve these profitable items are subject to limited fuel supplies, bad weather, attack by primitive life forms and getting lost -- all of which can jeopardize a mission.

Once a crew is in the black, it can afford to explore outside the solar system, where friendly and hostile aliens and greater riches and dangers await. The game's universe has been programmed with 270 star systems and 800 planets that provide 1.5 billion possible locations to explore.

The success of Starflight has established a "beachhead in the arena of sci-fi" for Electronic Arts, says Ybarra. Last spring, EA released its second interactive space title. Called EOS, after the acronym for "Earth Orbit Station," it is based on the NASA's plans for space development in the next 50 years. A third EA product, released in September, has proven closer to Earth in its play but is expected to fly off the charts in sales. Chuck Yeager's Advance Flight Trainer was designed with the help of the ace test pilot himself. Players can test-fly 14 different aircraft, from the vintage Sopwith Camel F-1 to the McDonnell Douglas F-18 Hornet. Ybarra warns the graphics are so good "you get vertigo from this thing."

Peter Doctorow, vice president of product development at Accolade, a software company in Cupertino, Calif., says that kind of software is "a little more cerebral and complex" -- but not impossible for some children. His precocious 8-year-old nephew made modest progress on Accolade's entry in the space exploration simulation race titled Project: Space Station.

The goal of the game is simple enough: To build and maintain a space station. But funds must be allocated to five project budgets, equipment purchased, construction contracts awarded, shuttle launches scheduled, satellites deployed for the private sector, personnel chosen, even R&D that will solve future problems must be funded. It takes 15 game years to build the station -- with 8 seconds of game time the equivalent of a day.

"If you look at some of the classic games that continue to top the best-seller chart list," says Doctorow, "one of them is always a flight simulator. Those are classified as recreational software, but they're surely not games. They have large manuals, they require that you read the manual, they require that you actually try to simulate as much as possible a real event."

The appeal of such software, contends Doctorow, is the simulation of tasks normally out of reach of the average person. "Most people don't ever get to fly a jet plane and most people don't ever get to manage a NASA project," he says. "People ... relate to it because it is something they could see themselves doing."

If control is the difference between judgment and joystick, Accolade's other new release is a hybrid. Titled Apollo 18: Mission to the Moon, it simulates some of the challenges of the original manned space missions -- from the Apollo 1 in 1967 to Apollo 17, the last manned trip to the moon, in 1972.

With Apollo 18, players can recreate blastoff, docking and navigational procedures, landing on the moon, "extra vehicular activity" on the moon's surface, a launch from the moon and redocking with the command module, space walks and satellite capture, reentering the earth's atmosphere and splashdown.

The joystick is optional on two games designed by Microprose, a software firm in Hunt Valley, Md. But the manuals aren't. Although F-15 Strike Eagle and Gunship, the company's newest release, are more oriented to war than space, both fit the category of highly technical and complex simulation software. The first puts the player at the controls of an F-15 to recreate eight missions, from the 1981 air strike on Libya to Persian Gulf action in 1984. In the Gunship game, a player tries his hand at commanding an AH-64 Apache fighter helicopter, directing search-and-destroy missions in Southeast Asia or rescue flights in Central America.

"The F-15 has more than 20 keyboard controls and Gunship has more than 30 keyboard controls to play," says Mike Harrison, Microprose's communications manager. He attributes the company's militaristic bent in products to its cofounder and president Bill Stealey, a former Air Force fighter pilot.

Again, the games' audience is adult. "It is now accepted as okay to be a gamer if you are an adult," says Harrison. "For a long time, we noticed a lot of resistance to that. Now adults no longer have to go into a software store and put the product into a brown paper bag when they leave."

No problem for either title: More than 450,000 F-15s have sold since early 1985 and Gunship has already broken 200,000 sales in a year.

Meanwhile, with popularity and sales igniting the simulation software market, companies prepare to shoot each other out of the sky with new and always more advanced products. Trevor Sorensen had details of five Star Fleet sequels outlined by the time he launched Star Fleet I. Star Fleet II is scheduled for release in February.

"It makes Star Fleet I look like a kiddie game," says Erin Green, Interstel's marketing director. Bob Jones says the sequel is "in a category all its own." But like all the other most successful games of the category, he adds, "For those people who feel they can master it, I think it'll be addictive."