Editor’s Note (5/27/20): Because of unfavorable weather conditions, the historic launch of two NASA astronauts on a SpaceX crew module and rocket has been postponed until Saturday, May 30, at 3:22 P.M. Eastern time.

Barring poor weather or last-minute technical glitches, shortly after 4:30 P.M. Eastern time today, a spaceship carrying two crew members will blast off on a rocket from the Kennedy Space Center in Florida. The flight will be bound for the International Space Station (ISS), but its true destination is the annals of space history: it will be the first time that U.S. astronauts have been launched from American soil since the final flight of the space shuttle program in 2011—and that anyone has flown to space using a commercially built crew capsule and rocket.

Much changed after humans last flew to space from the nation. Most obviously, the U.S.’s relations with Russia have frayed, although both countries have isolated their space program from politics. And they have continued a strong partnership to fly NASA astronauts to the ISS onboard Russian Soyuz rockets. Life-protecting pressurized suits have changed, too: The new flight’s two astronauts, NASA veterans Robert Behnken and Douglas Hurley, will not wear the fluorescent orange ensembles of the space shuttle era. Instead they will be clad in sleek, monochrome one-piece outfits that are lighter-weight, more maneuverable and much better looking. The suits, like the mission’s Crew Dragon capsule and reusable Falcon 9 rocket, were designed and manufactured by aerospace company SpaceX. Gone, too, are the old-fashioned “Astrovans”—souped-up motor homes that transferred NASA astronauts from crew quarters to the launchpad for most of the past half-century. To reach the rocket for this Demonstration Mission 2 (Demo-2) test flight, Behnken and Hurley will ride in style within an all-electric Model X sport utility vehicle provided by SpaceX’s sister company Tesla.

Such is the new era of American spaceflight, in which the federal government seeks cheaper, safer and more reliable access to orbit not by directly building and operating fleets of spaceships and rockets but rather by spending tax dollars on launch services provided by private companies. All previous human spaceflight programs have been based on systems developed, owned and run by government space agencies. Now, via its Commercial Crew program—which is itself a follow-on to the Commercial Orbital Transportation Services program initiated in the mid-2000s—NASA is instead buying seats and stowage on SpaceX assets. That strategy should free up funds for the agency to spend on other projects—deep-space exploration and transformative science missions—which presently remain out of reach for private enterprise.

The hope is that federal investment in low-cost, reliable and safe space transportation will spur rapid innovation and create entirely new opportunities for economic growth. The approach has an antecedent in the development of the commercial satellite industry, which, as of 2019, is worth more than $277 billion, in large part because of initial phases of robust governmental financial support. “The Commercial Crew program has been a great experiment by NASA to see if commercial companies can do this particular job,” says Wayne Hale, a former shuttle program manager who now serves as a consultant at engineering firm Special Aerospace Services.

NASA has pumped more than $8.2 billion into the Commercial Crew program since its inception in 2010. Most of those funds have gone to Boeing and SpaceX, which were each awarded development and flight-service contracts in 2014. This commercial partnership approach, says NASA’s commercial spaceflight director Phil McAlister, has saved the agency some $20 billion to $30 billion that it would have had to otherwise spend developing new human-rated rockets and spacecraft under traditional contracting methods.

NASA chief Jim Bridenstine considers Demo-2 the final step in proving the success of a public-private partnership business model to drive down costs. “It is going to enable us to not just go to the moon but to go sustainably, with reusable landers, to the surface of the moon,” he said during a recent press conference. “All of this, ultimately, is to get to Mars.”

It took a while for SpaceX, founded and run by technology entrepreneur and Tesla CEO Elon Musk, to learn how to work with NASA—and vice versa. But that relationship warmed considerably after a Falcon 9 rocket exploded during launch on June 28, 2015, destroying a cargo ship bound for the ISS. In the aftermath of that accident, SpaceX sought—and found—a strong technical shoulder to lean on at NASA.

“At the beginning, there was a lot of learning on both sides—more so with SpaceX, because they were new to working with NASA, but even with Boeing,” says Patricia Sanders, chair of NASA’s Aerospace Safety Advisory Panel. “This was a different way of defining requirements. They would propose standards but not necessarily in a way that NASA could digest. They’d send something over, NASA would send it back, and then they’d send it over again. They were really learning about each other.”

For NASA, immersion in the tech start-up culture at SpaceX took some getting used to as well. “You have the ability to learn quickly by being ‘hardware-rich’—having lots of flightlike test articles, doing test after test and not having a big concern if you push on something [when] you don’t know if it’s going to work [to] see if it passes or fails,” says NASA engineer John Posey, who oversees the Crew Dragon’s design and performance. “Since it’s a partnership instead of a traditional contractor customer, where we own the design and we dictate what they do, we always try to stay away from saying, ‘Oh, we’ve never done it that way before’ or ‘This way works better for us.’ We try to take what we learned on [the] shuttle and other programs and apply that by saying, ‘Here’s a pitfall you might want to check if you’re going to go that way’ or something like that.”

“This also is the hardest we’ve ever worked in our NASA jobs, just to run at the pace of SpaceX,” Posey adds. “I feel like I’m young—I’m 39—but those guys, a lot of them are half my age, so they can really crank out a lot more work than I’m capable of keeping up with.”

NASA’s Commercial Crew program has come a long way from its humble beginnings a decade ago, when the agency awarded $50 million of development contracts to five companies (which did not include SpaceX). By September 2014 NASA’s confidence in the public-private partnership approach was sufficient for the agency to award SpaceX and Boeing space-taxi contracts worth a combined $6.8 billion. The hope was one or both companies would be ready to take over ferry flights from Russia for the ISS crew by the end of 2017.

SpaceX and Boeing encountered technical stumbling blocks, pushing crewed flight tests to 2020 and 2021, respectively. The former company had two accidents with the Falcon 9 rocket, including a launchpad explosion that prompted a redesign of part of the rocket’s pressurization system. Then, in April 2019—just a month after a milestone test flight of an uncrewed Dragon to the ISS—SpaceX suffered another setback: an explosion of a Dragon on a test stand in Florida during the setup for a static engine firing.

Meanwhile Boeing’s CST-100 Starliner has been grounded for software verification and quality-control upgrades following a botched orbital debut in December 2019. A timing error prevented the capsule from reaching the space station, and the mission ended four days early. The company now plans to repeat the uncrewed flight test later this year. A crewed test with Boeing’s Christopher Ferguson and NASA’s Michael Fincke and Nicole Aunapu Mann will most likely follow in 2021.

These delays are creating a staffing shortfall on the ISS, as NASA’s paid rides on Soyuz rockets come to an end. In May the agency reached an agreement with Russia to remove a cosmonaut from the upcoming October 2020 Soyuz launch to the ISS, freeing the seat for a NASA astronaut in case SpaceX and Boeing are further delayed. That arrangement would ensure that the ISS is still staffed by at least one U.S. crew member. November will mark 20 years of continuous human presence on the space station.

Despite the technical problems that have significantly slowed the pace of NASA’s Commercial Crew program, agency officials say such delays could pay off, ultimately serving to streamline the process of certifying the reusable vehicles for further operational missions once test flights are complete. The delays have also given individuals and organizations outside of NASA and its astronaut corps more time to devise ambitious spaceflight feats of their own that leverage the agency’s Commercial Crew investments. For instance, a plan exists for actor Tom Cruise to reach the ISS in a Dragon launched by a Falcon 9 as soon as next year, says Gwynne Shotwell, SpaceX’s president and chief operating officer.

SpaceX also has contracts with Axiom Space, which is developing a commercial module to be attached to the ISS, and with Space Adventures, which previously brokered eight tourist flights to the ISS onboard Russian Soyuz capsules. And Japanese entrepreneur Yusaku Maezawa has put down a deposit for a charter flight around the moon on SpaceX’s next-generation Starship spacecraft, which is currently in development near Brownsville, Tex.

In April NASA decided to invest $135 million in Starship to see if the system can be used to transport two astronauts to the lunar surface in 2024, an expedited schedule requested by the Trump administration. Like NASA, the moon as a destination is on SpaceX’s radar screens. But Musk founded the company to develop technologies needed to build and sustain a city on Mars. Demo-2 will be SpaceX’s 85th Falcon 9 launch and its first with people.

“We wouldn’t be here without the prior work of NASA—‘standing on the shoulders of giants,’ as the saying goes,” Musk says. “And we couldn’t have gotten to Starship without really going through the Dragon path.”