The assignment that Martin Landau and Barbara Bain drew last year could have been dreamed up by their old taskmaster at Mission: Impossible. They were to pack up their two daughters mid-semester, rent out their Tudor-style Beverly Hills mansion, and move to England. There, they'd begin shooting an implausible sci-fi epic that (according to the producer) would be the most expensive TV series ever made but had been rejected by all three U.S. networks. If it flopped, presumably they'd all self-destruct.

But by that point, Landau and Bain figured it was ignoble just to rest on their residuals—after all, they were the Lunt & Fontanne of videoland. So they uprooted themselves to London and happiness at Moonbase Alpha. To earthlings, that is the intergalactic HQ of Space: 1999, the syndicated series that, during its first year, spread to 155 U.S. cities and 101 countries, cornering the market on disenfranchised Star Trekkies everywhere.

More startling perhaps than even the ratings success of their discount 2001 is the fact that the show's stars have themselves remained in the same orbit through two decades in their dicey business. The trick, Martin explains firmly, is "we never play married." So Rollin Hand didn't lay a glove on Cinnamon Carter in Mission: Impossible, and Commander John Koenig and Dr. Helena Russell maintain separate quarters on Moonbase Alpha. (Next season, though, Space: 1999's scriptwriters plan to warm up their robotlike characters with some preliminary erotic stirrings.)

Familiarity apparently breeds content. "We got married because we wanted to be together," says Barbara, 41. "The way it started out was: Be nice to the one who's working. But the joke was on us because we were both working. So now it's just: Be nice." Martin, 47, claims their empathy is so strong "I can tell when she walks into a room." By way of proof of his marital telepathy (or perhaps that he's seen too many of his own shows), he suddenly turns around, and there she is. Barbara has it, too. "If I'm at a big party, I'll know when he's left the room."

From their very first encounter, there were vibes—all bad. Barbara was modeling in Manhattan and appeared one day at a "little, dirty, terrible loft" where Martin was teaching acting. "I thought she was an empty-headed model, a magazine cover wired for sound," he recalls. As for himself, he concedes, "I had hair down to my shoulders, a beard and mustache. I was crude and rude." Barbara concurs. "He was dressed from head to toe in black and was very sinister. I thought he was arrogant, stupid—and all the things," she now finds, "he isn't."

A few weeks later they clashed again at a party. "We were talking and arguing until the sun came up," Martin remembers. "The degree of emotion involved wasn't just an ordinary dislike of each other." "Then we walked down Park Avenue," Barbara continues, "and Martin said something so ridiculous that we fell down in the street, laughing." Later, Landau recounts, "Barbara knew we were going to get married when I stopped buying two of everything—two records, two books..." Mid-work, they managed a city hall ceremony, but 10 days later they appeased their miffed families with a rerun in a country club (with a rabbi officiating).

Neither Bain nor Landau was earmarked for acting. She grew up a grocery wholesaler's daughter in Chicago, where her parents had immigrated from Russia. After graduating in sociology from the University of Illinois, she went to New York to study with Martha Graham. "I wasn't as good as I wanted to be," she explains, "and dance was then too remote from the rest of the world. It became lots of misery." She defected to acting and remembers, "When my feet landed on that stage I felt like I was touching home. I was terrible but I loved it."

Landau is a Brooklyn kid whose father was a machinist. By 16, Martin was an accomplished enough illustrator to draw for the New York Daily News. He then studied art at Pratt Institute but dropped out for the theater. He played summer stock, won admittance to the Actors Studio (one of three accepted in an audition group of 2,000) and has since become the rare performer who can claim, "I haven't been out of work for 20 years."

He and Barbara toured with Edward G. Robinson in Paddy Chayefsky's Middle of the Night. When it closed finally in L.A., they decided to stay for a two-week vacation and never left. With his glowering, saturnine visage, Martin was a natural heavy in movies like North by Northwest. Barbara, the classic ice blonde, trod the TV route, guesting in the whole gamut from Bonanza to the Smothers Brothers. They finally scored together in Mission: Impossible, for which Barbara copped a record three straight Emmys. Then, when the producer balked at a Landau pay demand after their third season, he walked, and Bain loyally followed. (The series was never as compelling with their successors, who included Leonard Nimoy and Lesley Ann Warren.)

With Space: 1999, Landau and Bain are living in London like peers of the realm. Every day between 6 and 7 a.m. they are chauffeured to the set in a Rolls Silver Cloud Ill. They take their tea and lunch breaks in their opulent (and separate) dressing rooms. "We treat each other as professionals when we're working," he explains. "Each of us makes a little space for the other. Otherwise it gets too clubby."

According to Barbara, their daughters, Susie, 15, and Julie, 11, are finding "nothing but fun" and new perspectives in London. "They grew up in southern California and never saw a pedestrian before," she cracks. A recent visitor was Lucas Reiner, the 15-year-old brother of Rob, All in the Family's "Meathead." Their folks, Carl and Estelle Reiner, spend every Thanksgiving with Martin and Barbara. "We've adopted each other as families," explains Bain. Seven years ago she and Estelle decided their kids didn't get enough "crowd experience" at snobby Beverly Hills H.S. So the families now combine on a "totally non-posh" annual picnic, inviting 100 friends for such hoi polloi pleasures as sack races.

A live-in Spanish couple maintains the five-story, 18th-century Landau-Bain townhouse in London's Chester Square. It's a nice job—the family rarely entertains, and the worst that happens is Martin occasionally gets a 4 a.m. whim to wok up Oriental dishes. Landau also paints and writes, including a script for a film which he hopes to produce about the suicide of a friend. Bain's release is needlepoint. She and Martin recently collaborated on a wool rug. He designed the arabesque pattern; she stitched it. "Barbara and I complement each other," he says, "but we also have our differences. I like the sun; she doesn't. She is not an outdoor person." Anything else? Oh, yes. Bain chews (Juicy Fruit); Landau doesn't. Basically, and despite her freeze-dried TV persona, Barbara is an adaptable down-to-earth mother. "Into next week is as far as I can look." she says. "I have always gone with the wind."