The world's first private supply ship flew tantalizingly close to the International Space Station on Thursday but did not stop, completing a critical test in advance of the actual docking.
The unmanned SpaceX Dragon capsule flew within 1 1/2 miles of the orbiting lab as it performed a practice lap and checkout of its communication and navigation systems.
Officials at NASA and the SpaceX company said the rendezvous went well, although the test results still were being analyzed. The historic linkup is on track for Friday.
It is the first U.S. vessel to visit the space station since NASA's shuttles retired last summer - and the first private spacecraft to ever attempt a delivery. The Dragon is carrying 1,000 pounds of provisions.
The space station astronauts struggled with bad computer monitors and camera trouble as the Dragon zoomed toward them, but the problem did not hold up the operation. Indeed, all of the tests appeared to go well.
The astronauts successfully turned on Dragon's strobe light by remote control, but could not see it because of the sun glare and distance of several miles. The Dragon finally popped into camera view about 10 minutes later, appearing as a bright speck of light against the blackness of space, near the Earth's blue horizon. The two solar wings were clearly visible as the Dragon drew closer.
"Can nicely see the vehicle," Dutch spaceman Andre Kuipers said.
SpaceX's near-term objective is to help stockpile the space station, joining Russia, Europe and Japan in resupply duties. In three or four more years, however, the California-based company run by the billionaire who co-founded PayPal, Elon Musk, hopes to be launching station astronauts.
It is the cornerstone of President Barack Obama's strategy for NASA: turning over orbital flights to private business so the space agency can concentrate on destinations farther afield, like asteroids and Mars.
Obama called Musk on Wednesday, a day after Dragon's flawless launch from Cape Canaveral, Fla., aboard the company's Falcon 9 rocket.
"The President just called to say congrats. Caller ID was blocked, so at first I thought it was a telemarketer," Musk said via Twitter early Thursday. He ended his tweet with a smiley emoticon.
Musk monitored Thursday's operation from the SpaceX Mission Control in Hawthorne, Calif., where the company is based.
On Friday, two of the space station's six astronauts, Kuipers and Donald Pettit, will use the space station's robot arm to grab the Dragon and attach it to the complex. The crew will have a week to unload the contents before releasing the spacecraft for re-entry. It is the only supply ship designed to return to Earth with experiments and equipment; the others burn up in the atmosphere.
The space shuttles used to be the primary means of getting things to and from the space station. Discovery is now a museum relic, with Endeavour and Atlantis soon to follow.
Aboard the incoming Dragon - 19 feet tall and 12 feet across - is food, clothes, batteries and other space station gear.
The space station and Dragon will be visible to Earthlings in select locations in the pre-dawn hours Friday, while flying tandem just prior to their linkup 250 miles above the planet. Among the many U.S. cities with viewing opportunities if skies are clear: New York, Los Angeles, Washington, Chicago and Jacksonville, Fla.
Explore further: Liquid crystal bubble OASIS in space
More information: SpaceX: http://www.spacex.com