SpaceX said it completed a successful test of the engines on its Falcon 9 rocket on Monday, in preparation for Friday's planned cargo launch to the International Space Station.

The California-based rocket company's unmanned Dragon capsule is due to deliver about 1,200 pounds (550 kilograms) of supplies to the space station and bring back 2,300 pounds (1,050 kilograms) of cargo, including scientific samples and space station hardware.

Monday's static-fire test was aimed at checking the performance of the Falcon 9 first stage's nine engines before they're called upon to loft the second stage and the Dragon capsule toward orbit on Friday. The rocket was held down onto its launch pad at Space Launch Complex 40 at Cape Canaveral Air Force Station in Florida for the engine firing, which came at the end of a dress rehearsal for Friday's countdown.

"SpaceX engineers ran through all countdown processes as though it were launch day," the company said in a statement issued after the 1:30 p.m. ET firing. "All nine engines fired at full power for two seconds, while the Falcon 9 was held down to the pad. SpaceX will now conduct a thorough review of all data and continue preparations for Friday's targeted launch."

In a Twitter update, SpaceX's billionaire founder, Elon Musk, reported that the static-fire test looked good: "Engines generated 433 tons of thrust, parameters nominal."

SpaceX said the first opportunity for launch will come at 10:10 a.m. ET on Friday. This is the third Dragon to be sent to the space station, and the second flight under the terms of a $1.6 billion, 12-flight cargo resupply contract with NASA.

Another company, Virginia-based Orbital Sciences Corp., has a separate $1.9 billion contract to deliver supplies to the space station but has not yet begun flying its Antares rocket and Cygnus cargo capsule. On Friday, Orbital completed a successful static-fire test of Antares' engines in preparation for the rocket's first flight, which is expected to take place later this year.

NASA's contracts with SpaceX and Orbital are meant to help fill the gap left by the retirement of the space shuttle fleet in 2011. Russian, European and Japanese unmanned spacecraft are also used to send supplies to the space station, but Russia's Soyuz capsule is the only spacecraft currently cleared to transport astronauts to and from orbit. NASA is providing more than $1 billion to SpaceX, the Boeing Co. and Sierra Nevada Corp. to support the development of new crew-capable spacecraft for low Earth orbit.

More about SpaceX's mission:

• Dragon space station launch set for March 1
• These space capsules can fit on your desk
• SpaceX's press kit for the March 1 mission

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

Although SpaceX's Falcon 9 rocket successfully sent its Dragon cargo capsule toward the International Space Station, an engine failure and a less-than-nominal satellite deployment suggest that the company has some technical issues to resolve for future flights.

The California-based rocket company acknowledged soon after Sunday night's launch that one of the nine Merlin engines on the Falcon's first stage shut down, but the onboard computer recalculated the data for the other eight engines to get the Dragon in orbit and save the resupply mission.

Some observers pointed to SpaceX's long-range video of the ascent and pointed to what they thought was debris from an explosion. Today, SpaceX issued a statement saying that the engine didn't explode — but that protective panels were ejected because of the pressure loss associated with the shutdown:

"Approximately one minute and 19 seconds into last night's launch, the Falcon 9 rocket detected an anomaly on one first-stage engine. Initial data suggests that one of the rocket's nine Merlin engines, Engine 1, lost pressure suddenly and an engine shutdown command was issued. We know the engine did not explode, because we continued to receive data from it. Panels designed to relieve pressure within the engine bay were ejected to protect the stage and other engines. Our review of flight data indicates that neither the rocket stage nor any of the other eight engines were negatively affected by this event.

"As designed, the flight computer then recomputed a new ascent profile in real time to ensure Dragon's entry into orbit for subsequent rendezvous and berthing with the ISS. This was achieved, and there was no effect on Dragon or the cargo resupply mission.

"Falcon 9 did exactly what it was designed to do. Like the Saturn V (which experienced engine loss on two flights) and modern airliners, Falcon 9 is designed to handle an engine-out situation and still complete its mission. No other rocket currently flying has this ability.

"It is worth noting that Falcon 9 shuts down two of its engines to limit acceleration to 5 G's even on a fully nominal flight. The rocket could therefore have lost another engine and still completed its mission.

"We will continue to review all flight data in order to understand the cause of the anomaly, and will devote the resources necessary to identify the problem and apply those lessons to future flights. We will provide additional information as it becomes available.

"Dragon is expected to begin its approach to the station on October 10, where it will be grappled and berthed by Akihiko Hoshide of the Japan Aerospace Exploration Agency and Expedition 33 Commander Sunita Williams of NASA. Over the following weeks, the crew will unload Dragon's payload and reload it with cargo to be returned to Earth. Splashdown is targeted for October 28."

There's a lingering question about the engine anomaly: What caused the sudden pressure loss?

Satellite in wrong orbit
Another question has yet to be fully resolved: What will happen to the Orbcomm OG2 telecommunication satellite, which rode into orbit as a secondary payload on the Falcon 9's second stage? The prototype satellite was supposed to be put into a highly inclined orbit after a second-stage restart, and serve as the first piece of a new 18-satellite telecom constellation.

On Sunday night, SpaceX said the satellite was "successfully deployed" — but Orbcomm acknowledged in a statement today that the satellite was deployed into the wrong orbit because of the engine anomaly. Here's the relevant excerpt:

"... Due to an anomaly on one of the Falcon 9’s first-stage engines, the rocket did not comply with a pre-planned International Space Station (ISS) safety gate to allow it to execute the second burn. For this reason, the OG2 prototype satellite was deployed into an orbit that was lower than intended. Orbcomm and Sierra Nevada Corp. engineers have been in contact with the satellite and are working to determine if and the extent to which the orbit can be raised to an operational orbit using the satellite’s on-board propulsion system.

"In mid-2013, Orbcomm plans to launch an additional eight OG2 satellites on a Falcon 9, which will be placed into orbits that are optimized to deliver the best coverage for the enhanced OG2 messaging services. The remainder of the constellation of 18 OG2 satellites is expected to be launched on a Falcon 9 in 2014. Orbcomm’s OG2 satellites will be the primary payload on both of these two planned launches to directly insert the OG2 satellites into the operational orbit."

Orbcomm's statement came after satellite-watcher Jonathan McDowell called attention to the fact that the satellite showed up in the Space-Track database as having a 203-by-323-kilometer orbit rather than the planned 350-by-750-kilometer orbit.

Looking on the bright side
Going forward, SpaceX should follow through on its pledge to "apply lessons to future flights," as it said in its statement. And skeptics should keep in mind that this is rocket science, which is "super-frickin'-damn-hard," to use SpaceX founder Elon Musk's words. It's a tribute to Musk's design that the Dragon's mission was unaffected by the loss of one rocket engine. On Sunday night, he pointed out in an email to NASA Watch that few if any other existing launch vehicles could have weathered that kind of problem: "I believe F9 is the only rocket flying today that, like a modern airliner, is capable of completing a flight successfully even after losing an engine."

What do you think? Does the Dragon's rise represent Falcon's finest hour, or do the problems point to a chink in SpaceX's armor? Feel free to weigh in with your comments below.

Update for 4:15 p.m. ET: I've updated SpaceX's previous update (which referred to an engine fairing) with the current update (which pointed to protective panels instead).

Update for 6:30 p.m. ET: I've added a link to the Orbcomm statement confirming that its OG2 satellite ended up in a lower-than-expected orbit.

More about commercial space:

• Dragon liftoff begins the new normal for NASA
• SpaceX flight gets its own mission patch
• Why SpaceX is setting the pace in space race
• Florida wants NASA land for commercial ventures  

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

The International Space Station's crew reached out today with a robotic arm to grab SpaceX's Dragon cargo capsule and brought it in for the orbital outpost's first-ever hookup with a commercial spaceship.

It marks the station's first linkup with a U.S.-made spacecraft since last year's retirement of NASA's space shuttle fleet, and potentially opens the way for dozens of commercial cargo shipments. If the long-range plan unfolds as NASA hopes, U.S. astronauts could be shuttled back and forth on the Dragon or similar spacecraft within just a few years.

"Today, this really is the beginning of a new era in commercial spaceflight," said Alan Lindenmoyer, manager of NASA's commercial crew and cargo program. 

• Scenes from a SpaceX spectacular
• Space milestone sparks high praise

The hookup comes after Tuesday's successful launch of the Dragon atop a Falcon 9 rocket, and represents the culmination of years of planning and hundreds of millions of dollars of spending by NASA and California-based SpaceX, known more formally as Space Exploration Technologies Corp. The company was founded a decade ago by dot-com billionaire Elon Musk, with aspirations of eventually sending humans to settle on Mars.

Musk said the technologies that were tested today will blaze a trail for those more ambitious trips to come. "This is a crucial step, and having achieved this step, it makes the things in the future and the ultimate path toward humanity becoming a multiplanet species much, much more likely," he told reporters after the hookup. "The chances of that happening just went up dramatically, so people should be really excited about that."

But first things first: Today's operation marked the first full in-space test of the robotic Dragon spacecraft's procedure for approaching the station, and for that reason, every step along the way was carefully planned out and checked over the course of several hours. The first steps in the procedure were tested on Thursday, during a series of maneuvers that successfully brought the 14-foot-long, 12-foot-wide, gumdrop-shaped capsule within 2.5 kilometers (1.5 miles) of the $100 billion space station.

Today, a far more ambitious set of maneuvers brought the Dragon all the way to the station — but the trip wasn't always easy.

Fixing the glitches
The craft started out by taking up a position 250 meters (820 feet) below the station. From that vantage point, the Dragon was put through a series of maneuvers to test the station-to-spacecraft communication system. The space station's astronauts had the Dragon approach, then retreat, then approach, then hold its position.

After assessing the data, NASA said it wanted to do a double-check on the Dragon's thermal imagers, which are part of the rendezvous sensor system. The spacecraft was commanded to approach to a distance of 200 meters (656 feet), then stop while NASA took stock again. Space agency spokesman Josh Byerly said SpaceX's team made "minor modifications" to the thermal imaging system, just to make sure that it was providing tracking data in line with what other instruments were showing.

The Dragon was on its way to a 30-meter (98-foot) checkpoint when the team at SpaceX's Mission Control in Hawthorne, Calif., ordered the spacecraft to retreat to a distance of 70 meters (230 feet). NASA's Mission Control said the SpaceX team wanted to correct bad laser sensor readings that the Dragon was getting from a stray reflector on the station's Japanese-built Kibo laboratory. To work around the problem, SpaceX narrowed the field of view for the laser sensor so that it wouldn't pick up light from the offending reflector.

"One of the lasers wasn't working well, so we had to recalibrate the laser and tighten the beam, and then it did work," Musk explained afterward.

Catching a Dragon by the tail
Once the fix was made, Dragon returned to the 30-meter checkpoint and moved in for the final approach. When the craft reached a distance of 10 meters (33 feet), NASA astronaut Don Pettit used the station's 17-meter-long (60-foot-long) robotic arm to grab hold of the Dragon's grapple attachment at 9:56 a.m. ET.

"It looks like we've got us a Dragon by the tail," Pettit told NASA's Mission Control.

"“Congratulations on a wonderful capture," Mission Control's Megan Behnken replied. "“You've made a lot of folks happy down here, over in Hawthorne and right here in Houston." 

Pettit joked that the operation went so smoothly it felt like a computer simulation. "This sim went really well," he said. "We're ready to turn it around and do it for real." 

It took another couple of hours to pull in the Dragon and get it fully hooked up to the station's Harmony module. NASA and SpaceX refer to this operation as a "berthing" rather than a "docking," because the Dragon is being passively pulled in rather than powering itself into the docking port.

The completion of berthing at 12:02 p.m. ET put SpaceX in the company of four governmental space ventures — NASA, the Russian Federal Space Agency, the European Space Agency and the Japan Aerospace Exploration Agency — that have built vehicles capable of hooking up with the space station.

Musk said that he'd probably have to relax SpaceX's rule against drinking alcohol at its Hawthorne headquarters to accommodate a champagne celebration, but it was clear that the hundreds of employees who gathered to watch the berthing were already on a natural high. They cheered for Musk as he spoke to reporters over a video link — and when he told them, "I love you guys, too," they broke into a chant of "E-lon, E-lon, E-lon!" 

Unloading the cargo
Dragon's hatch is scheduled to be opened early Saturday morning. The station's six astronauts will unload about 1,000 pounds (460 kilograms) of cargo, including food, clothes, batteries and a laptop, plus 15 student-designed experiments. Then about 1,455 pounds (660 kilograms) of Earth-bound cargo — including personal items from the crew as well as completed experiments and old equipment — will be loaded up on the Dragon. These payloads don't come anywhere close to the Dragon's capacity (6 tons going up, 3 tons coming down), but they were made part of the mission as non-essential ride-alongs.

On May 31, the capsule will be detached from the station and sent back down toward a Pacific Ocean splashdown and recovery off the coast of Southern California. That part of the operation went off successfully during Dragon's first orbital test mission in December 2010, but this would mark the first-ever return of a commercial spacecraft from the space station. Russia's Soyuz capsule is the only other existing space vehicle capable of returning space station payloads.

A fully successful mission would open the way for commercial space station resupply missions to begin in earnest. SpaceX already has a $1.6 billion contract with NASA for 12 Dragon shipments through 2016. If all goes well, the first flight covered by that contract could lift off in September, said Mike Suffredini, NASA's space station program manager. Another company, Virginia-based Orbital Sciences Corp., is developing a cargo spacecraft known as Cygnus to take on space station shipments as well, under the terms of a $1.9 billion contract. The Cygnus has yet to be flight-tested, however.

In addition to the cargo contract, SpaceX is one of four companies that is receiving millions of dollars from NASA to produce spaceships capable of carrying astronauts. In SpaceX's case, the Dragon would be modified with a launch escape system, while the other companies — Blue Origin, the Boeing Co. and Sierra Nevada Corp. — are working on other spaceship concepts, ranging from capsules to Sierra Nevada's mini-space plane. The first astronaut flights could take place as early as 2017.

Until that time, NASA will have to depend on the Russians to transport U.S. astronauts on Soyuz spacecraft, at a cost of more than $60 million a seat. SpaceX and other players in the commercial space race say they can meet or beat that price.

The transition to commercial operations for orbital transport is a key part of the Obama administration's plan for future space exploration.

"We’re handing off to the private sector our transportation to the International Space Station so that NASA can focus on what we do best — exploring even deeper into our solar system, with missions to an asteroid and Mars on the horizon," NASA Administrator Charles Bolden said after the Dragon's launch. "We’re committed to ending the outsourcing of work on America’s space program and bringing these jobs back to the United States." 

More about the mission:

• 'Star Trek' Scotty's remains go into space
• Video: Scenes from the SpaceX hookup
• Next steps in a new space race
• Cosmic Log archive on SpaceX

Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding Cosmic Log's Google+ page to your circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.