SpaceX's Dragon capsule on Friday made its final approach toward the International Space Station, edging closer to the climax of its landmark mission to latch on to the orbiting research lab.
The first step of the two-phase berthing maneuver was expected at 9:10 am (1310 GMT), when the astronauts aboard the space station would use the robotic arm to capture the unmanned capsule and shepherd it toward the $100 billion orbiting lab.
"The desire is for a daylight pass for the crew so they obviously can see the Dragon a little bit better as they use the robotic arm to reach out and grab on to it," said a NASA commentator on the space agency's live broadcast of the event.
After that, a formal berthing of the Dragon will bring the capsule closer to latch on at the station's Harmony module so its cargo can be unloaded over the coming days.
SpaceX's supply ship is on a mission to become the first privately owned craft to berth with the space station, restoring US access to the space outpost after the shuttle program's end.
Only Russia, Japan and Europe currently have supply ships that can reach the ISS. The United States lost that capacity when it retired its space shuttle fleet in 2011.
So far, the demonstration flight has been near flawless, according to progress reports from NASA and SpaceX since the capsule blasted off atop the Falcon 9 rocket from Cape Canaveral in Florida on Tuesday.
"It is a test flight. We are being cautiously optimistic," said lead mission director John Couluris of SpaceX on Thursday.
The launch marked the first time a commercial enterprise has sent its own craft to the orbiting lab and opened what NASA, the White House and SpaceX officials described as a "new era" in spaceflight.
California-based SpaceX hopes that its gumdrop-shaped Dragon capsule will be able to carry astronauts to the ISS in about three years' time. Russia is now the only nation capable of ferrying astronauts there aboard its Soyuz capsules.
In addition, a successful berthing mission opens the way for SpaceX's $1.6 billion contract with NASA to supply the space station and return cargo to Earth over the coming years.
"After this mission we are on contract for at least 12 more missions to the International Space Station," said Couluris, noting that while Japan and Europe can carry supplies to the ISS, only Russia can return cargo to Earth.
"So we are looking to provide regular services... at a faster rate than some of the other vehicles."
On Thursday, the Dragon capsule successfully completed a fly-under of the ISS at a distance of 2.4 kilometers (1.5 miles) as well as several other maneuvers to lay the groundwork for the berthing attempt.
They included an abort demonstration, communications tests, navigation by global positioning system (GPS) technology alone, and a "free-drift demonstration," whereby the capsule's thrusters were all shut down, as they will need to be prior to being grappled by the space station's robotic arm.
SpaceX and a handful of other companies are using their own funds but are also being helped in their endeavors with seed money from NASA to build cargo and crew capability.
Both SpaceX and NASA have praised their newfound partnership, while insisting that any missteps that may occur are a necessary part of such demonstration missions.
While SpaceX is the first in its field, its competitor Orbital Sciences also has a $1.9 billion contract with NASA to supply the space station and is scheduled for its first launch attempt later this year.
SpaceX is the brainchild of 40-year-old billionaire Elon Musk, who made his fortune founding a company that later merged with the PayPal online service, bought by Internet auction giant eBay for $1.5 billion in 2002.
Today he leads SpaceX, Tesla Motors -- a venture marketing electric cars -- and SolarCity, a company that makes solar panels for homes and businesses.
Musk, who has invested $100 million of his estimated $2 billion fortune in SpaceX, has been celebrating the mission, confessing on Twitter earlier this week that he'd almost missed a phone call from US President Barack Obama.
"The President just called to say congrats. Caller ID was blocked, so at first I thought it was a telemarketer :)," Musk wrote.