Ungainly creatures, we human beings, prone to chronic lower back pain and susceptible to dependencies on foods and ideologies that do us no good. But oh we looked lovely up there in space, floating, walking, watching, seeing Earth as only God had seen it before. "Spaceflight," the four-part PBS documentary on otherworldly exploration, isn't just about space, but about the magical way it felt to be alive in the space age.

Today's kids who have so world-wearily seen it all can't imagine what it was like to get up at dawn and hunker down before a television set on which Walter Cronkite was escorting us out of one era and into another. There was a kick to be had just from adding futuristic new terms to your vocabulary. It was the greatest adventure since Kitty Hawk and this time we could be there to see it. "Spaceflight," premiering at 8 tonight on Channel 26 and other public TV stations, is matter-of-fact and not wonderstruck about that adventure, but the collected images pull us back to outer-directed, visionary, glorier days.

Space now is a superhighway for a big tile-encrusted trailer truck and a potential battleground for Star War I. The first two chapters of "Spaceflight" recall the days when it was something more. True, there was the "space race" and the national chauvinism involved, but even that had a more positive zing to it than what the new cold crop of old cold warriors hath mordantly wrought now. Today the space shuttle can take off and land and we hardly give it a thought; indeed, it did this week. At some point we stopped thinking loftily about the heavens and started thinking obsessively about our thighs.

Unimaginative in form but strong in content, "Thunder in the Skies" and "The Wings of Mercury," Episodes 1 and 2, reconstruct the space program's earliest, hurly-burliest days. Prefatory material tonight about German, Russian and American roots of rocketry is perfunctory, but some of the old footage is arresting, and so is tranplanted German scientist Krafft Ehricke's recollection of the time he and his colleagues inadvertently lobbed a test rocket into a Tijuana cemetery.

This is handily bested, however, by the last quarter of the program, when many of the Mercury astronauts materialize in newly recorded interviews that make for a bracing zapback. It's great to see them again. This is The Real Stuff. "Spaceflight" can be seen as an antidote to the overbearing gonzo-macho "Right Stuff" movie and to the dismally tiny-minded CBS "Space" mini-series, one of the season's most deserved resounding flops.

Newsreels, newly declassified NASA footage, previously unseen Soviet footage and the interviews are intercut to tell the space story. Martin Sheen's narration is a lulling drone, and the musical score is banality at its sleepiest, but still, the vitality of the participants comes through, and so does the whole idea of having a dream to hang your life on. Chuck Yeager, the great test pilot, is the king of the surefires as interviewees go, and we hear again, this time from him, the bigger-than-fiction story of his first ride through the sound barrier in the X-1, outfitted with a broomstick to disguise the fact that he was suffering from four broken ribs.

Yeager recalls fondly of the cockpit posture he maintained inside that manned bullet: "You could pull a lotta Gs without blackin' out."

Pete Conrad, Wally Schirra, Deke Slayton, Jim Lovell, Mike Collins, Alan Shepard, Frank Borman, John Glenn, Gordon Cooper and others of the Mercury and Gemini space programs contribute reminiscences. They are most interesting when they talk about how they felt, either Up There, riding new horizons, or down here, dutifully performing according to the Life magazine squeaky-clean image, even to the point of attending what one of them calls "charm school" as part of a campaign to be included on the moon mission.

And Walter Cronkite is there too, which is fitting, since for those of us old enough to remember, he was not just the messenger but part of the story. If Pete Conrad and Cronkite ever put their minds to it, incidentally, they could do a great impression of Bob and Ray.

Blaine Baggett wrote, produced and directed the program. His script is no marvel, but it's serviceable. Part 4, to be seen three weeks from tonight, deals with the present and future of space and will include an animated visualization of a "Star Wars" scenario. But these first two chapters are almost entirely salubrious teleportations. How high the moon? Not so high that we couldn't touch it. We wonder, watching this, if we will ever stretch so tall again.