Emotional impact is not the first quality one thinks of when the subject is science-fiction adventures. Yet that’s one of the qualities that sets “Gravity” apart as a stratospheric achievement. Not just a futuristic drama, it’s also a universally human drama about the need for hope in desperate situations.

A riveting tale of two American astronauts cast adrift, the film is a spectacle of brilliantly orchestrated action set-pieces and relentless narrative drive. It contains some of the most impressive feats of technical virtuosity ever committed to film.

Yet its real power is in its urgency, the pull of the story’s anxiety and almost unreachable hope. Directed with a sure hand and a masterful eye by Alfonso Cuarón (“Harry Potter and the Prisoner of Azkaban,” “Children of Men”), “Gravity” is not about wowing us with special effects, but touching our souls.

Still, the effects are key to the film’s power, conveying its themes of loss and rebirth through imagery rather than dialogue. The uninterrupted, stunningly choreographed quarter-hour opening shot is already the stuff of legend. The camera floats gracefully through space, tracking our heroes, rookie astronaut Dr. Ryan Stone (Sandra Bullock) and veteran mission commander Matt Kowalski (George Clooney) as they repair the Hubble telescope 370 miles above Earth. The look is amazing yet familiar, like a NASA documentary.

The talk is easygoing. Kowalski keeps up a lighthearted line of quips and conversation to help soothe Stone’s nerves.

An urgent advisory from Houston commands them to abort: An exploded Russian satellite is sending a barrage of shrapnel their way. The lethal bombardment hits ferociously, ripping the space station to smithereens and sending Stone spinning into the void. As her figure recedes, the image sums up the disorienting beauty of space and its cold, terrifying indifference to human life. Emmanuel Lubezki’s crystalline camerawork suggests a hyper-real nightmare.

Unfolding in real time, “Gravity” follows the pair as they search for a ride home. Bullock’s character must also search for a reason to live. In the film’s few cheesy decisions, she is scarred by an old personal catastrophe that undermines her survival instinct. Wouldn’t the psychological fitness tests astronauts undergo have picked up on that? And isn’t it a thudding cliché that everything goes to hell on commander Kowalski’s final mission?

That’s the beginning and end of my nitpicking. Bullock’s great strength as an actress is her underdog vulnerability, and she is ideal in the role of a woman numbed by grief, drawing on resources she didn’t know she had. Clooney, remaining chipper under dire pressure, contributes a performance of warmhearted chivalry. His generosity as a performer mirrors Kowalski’s selfless concern for Stone.

Cuarón uses hard science and film technique to create haunting audiovisual details. His use of sound, and withholding of it in silent, airless space, churns feelings of primal dread. The glancingly observed flotsam drifting through the space stations — a cuff link, a dental retainer — are eerie reminders of human vanity. When Stone, temporarily air-supplied, strips off her bulky suit and rests, her body curls into the fetal position, complete with umbilical-like cables nearby, like the Starchild in “2001.”

The harrowing, triumphant final sequence is a breakneck race through states of being that reflect the evolution of life on Earth. It delivers us into a wide-eyed state of untold possibilities, reminding us that no matter how far we’ve explored the heavens, the human journey has just begun.