SpaceX said its robotic Dragon capsule splashed down in the Pacific Ocean on Tuesday, bringing back more than a ton of cargo from the International Space Station.

"Welcome home!" the California-based company said in a Twitter update, heralding the Dragon's return to Earth after more than three weeks in space. SpaceX said its recovery crew watched the spacecraft descend to the sea at the end of its parachutes, and a ship headed to the site to haul the capsule aboard and bring it back to port.

"Time to go fishing!" the Canadian Space Agency said in a congratulatory tweet.

The on-time splashdown came at 12:34 p.m. ET, five and a half hours after the Dragon was released from the grip of the space station's robotic arm. "It looks both beautiful and nominal from here," Canadian astronaut Chris Hadfield, the station's commander, reported as the orbital outpost flew 256 miles (411 kilometers) above the Pacific.

NASA astronaut Tom Marshburn said he was "sad to see the Dragon go. ... Performed her job beautifully, heading back to her lair."

This marks the third time that SpaceX's commercial cargo craft has made a round trip to the space station. The first visit, in May 2012, showed NASA that the California-based company could deliver payloads safely. Last October, another Dragon took on the first of 12 cargo runs under the terms of a $1.6 billion contract with the space agency. This latest mission launched on March 1, carrying 1,200 pounds (544 kilograms) of supplies and equipment.

SpaceX had to cope with a post-launch glitch involving the Dragon's thruster system, but the mission went swimmingly after that. Astronauts unloaded the cargo soon after its was brought in for its berthing at the station, and then refilled it with 2,600 pounds (1,180 kilograms) of payload items due to be returned to Earth — including scientific experiments, station hardware and trash. Packaging brought the total weight past the 3,000-pound (1,360-kilogram) mark, SpaceX said.

NASA said the plant samples that were brought back from the station could help scientists enhance crop production on Earth and develop food production systems for future space missions. Other experiments carried by the Dragon could help in the development of more efficient solar cells, detergents and electronics. 

The returned cargo also included 13 sets of Lego toy blocks that went up to the station two years ago aboard the shuttle Endeavour. The blocks were used by the astronauts in educational videos to demonstrate how machines work in weightlessness. One of the kits, a 3-foot-long (meter-long) scale model of the space station, was so bulky that it would have collapsed under its own weight in Earth's gravity.

NASA via SpaceX

SpaceX's Dragon cargo capsule separates from the International Space Station's robotic arm on Tuesday.

NASA TV via Spaceflight Now

A thermal imager on SpaceX's Dragon capsule captures a view of the International Space Station during Tuesday's departure.

SpaceX

SpaceX's Dragon cargo capsule floats down to the Pacific Ocean on Tuesday.

Dragon's return was originally scheduled for Monday, but "fairly aggressive" seas at the intended splashdown zone forced a one-day postponement, NASA spokesman Josh Byerly said. The weather was better on Tuesday, and the splashdown target was a couple of hundred miles nearer to shore, at a point in the Pacific 214 miles (344 kilometers) west of Baja California.

SpaceX's billionaire founder, Elon Musk, said the capsule was secured aboard its recovery ship without incident. "Cargo looks A ok," he reported in a Twitter update.

The ship is due to make a 30-hour voyage back to the port of Los Angeles, where time-sensitive biological samples will be offloaded. Then the Dragon and its remaining cargo will be trucked to SpaceX's facility in McGregor, Texas.

The next SpaceX cargo run is scheduled at the end of September. Another company, Virginia-based Orbital Sciences Corp., is working on a second commercial delivery system that's due for its first test launch next month. But only the Dragon is capable of bringing significant amounts of cargo back to Earth.

NASA selected SpaceX and Orbital to help fill the gap left by the retirement of the space shuttle fleet in 2011. Russian, European and Japanese cargo craft also service the space station. For now, Russia's Soyuz capsules are the only spacecraft that transport people to and from the station, but NASA intends to have U.S.-built commercial spaceships — perhaps including an upgraded version of the Dragon — carrying astronauts within five years.

More about SpaceX:

• SpaceX's next-gen engine cleared for liftoff
• Grasshopper rocket takes its biggest hop yet
• NBC News archive on SpaceX

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.

This story was originally published on Tue Mar 26, 2013 7:29 AM EDT

SpaceX's billionaire founder, Elon Musk, gave attendees at the South by Southwest festival in Texas the first public look at the fourth flight test carried out by his company's reusable self-landing rocket, nicknamed the Grasshopper.

This latest "hop," conducted on Thursday at SpaceX's rocket test facility in McGregor, Texas, sent the Grasshopper twice as high as it ever went previously: In a statement, the company said the 10-story-tall rocket rose 24 stories off the ground (262.8 feet, or 80.1 meters), hovered for 34 seconds and landed safely on its own.

"Grasshopper touched down with its most accurate thus far on the centermost part of the launch pad," SpaceX said. "At touchdown, the thrust-to-weight ratio of the vehicle was greater than one, proving a key landing algorithm for Falcon 9."

Thursday's test builds on test flights conducted last September, November and December. During his keynote address at the annual SXSW gathering in Austin on Saturday, Musk joked that this flight was the "Johnny Cash hover slam," according to an account from NewSpace Journal. Johnny Cash's song about a "burning ring of fire" was playing in the background as the video rolled.

Grasshopper's vertical-takeoff, vertical-landing technology is considered a key part of SpaceX's plan to make its Falcon 9 rockets more reusable. "With Grasshopper, SpaceX engineers are testing the technology that would enable a launched rocket to land intact, rather than burning up upon re-entry to the Earth's atmosphere," the company said.

A Falcon 9 rocket delivered an unmanned SpaceX Dragon capsule safely to the International Space Station last week, and that capsule will soon be filled up with more than a ton of cargo for return to Earth. Eventually, SpaceX plans to refurbish Dragon capsules as well as Falcon boosters for reuse, but the company hasn't gotten to that stage yet. NASA has contracted with the California-based company to make 12 Dragon deliveries over the next several years at a cost of $1.6 billion. The current cargo mission is the second under the terms of the contract.

Looking further ahead, SpaceX aims to adapt its boosters and crew vehicles to send astronauts to Mars. The 41-year-old Musk told the SXSW crowd that he might well end up being one of those astronauts. "I've said I want to die on Mars," CNET quoted him as saying. "Just not on impact."

Update for 7:45 p.m. ET March 9: At about the 1:15 mark in that video, you might notice a dummy cowboy standing on the rocket. That's not the first time a ringer for a wrangler has taken a ride on the Grasshopper.

More about SpaceX and Mars:

• Elon Musk wants 80,000 of us on Mars
• SpaceX aims for fully reusable rockets
• SpaceX chief plans to be spaceflier, too

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.

Chris Hadfield / CSA / NASA via Twitter

SpaceX's Dragon cargo capsule is held by the International Space Station's Canadian-built robotic arm in advance of its berthing on Sunday. "A Dragon, snared and tamed," Canadian astronaut Chris Hadfield wrote on Twitter.

The commercial SpaceX rocket venture has launched Dragon cargo capsules to the International Space Station three times in the past year, and every time there's been a problem. Should NASA be upset?

Not really.

The fact that glitches have cropped up — and have been solved, with no impact on the multimillion-dollar cargo resupply missions — isn't a black mark against the California-based company. Rather, it's a sign that the designs for SpaceX's Dragon capsule and Falcon 9 are resilient in the face of the inevitable glitches associated with spaceflight. It's also a sign of things to come.

"We may see more mission aborts, where the cost of a mission may be a fraction of the cost of a 'perfect' spacecraft," says James Oberg, NBC News' space analyst. "For the same cost, you could launch three or four, or even eight or 10 'not-perfect' vehicles, with a success rate of 90 to 95 percent. and as a result, for the same starting cost launch many times more missions."

Rand Simberg, a former rocket engineer who now writes about spaceflight for a variety of publications, made a similar point in a PJMedia piece touting SpaceX's latest "successful failure": a problem with the Dragon's thruster system that was resolved when SpaceX's engineers issued commands to cycle the system's valves and clear out the lines with a blast of pressurized gas.

"It was a valuable failure in that it identified a potential problem with either the design or operations but didn't cost them the mission," Simberg wrote. After the system reset, the Dragon's thrusters performed without a hitch. The capsule was brought in for its berthing at the space station on Sunday, just a day later than originally scheduled.

"They did everything exactly right about the vehicle," Bill Gerstenmaier, NASA's associate administrator for human exploration and operations, told reporters after the thruster system was fixed. 

The snags that cropped up during the previous two Dragon launches were similarly resolved without major consequences for SpaceX or NASA:

• Last May, SpaceX's Falcon 9 rocket lit up its engines for launch, but immediately shut them down when the flight computer detected an excessive pressure reading in one of the engines. Engineers found and fixed a problem with the engine's turbopump valve, and a few days later, the Falcon 9 launched the Dragon on a historic demonstration mission to the space station. In August, a NASA panel said it was satisfied with SpaceX's handling of the glitch and its aftermath.
• Last October, one of the nine engines on the Falcon 9's first stage shut down during the ascent, due to a flaw in the sheathing that surrounded the engine. The other engines automatically adjusted their thrust to make up for the shutdown, and the Dragon successfully reached orbit. However, the Falcon wasn't able to put an Orbcomm telecommunications satellite that was carried as a secondary payload in its proper orbit. As a result, the satellite was lost. SpaceX President Gwynne Shotwell said the company tracked down the problem and beefed up its procedure for non-destructive evaluation of the Merlin rocket engines. Since the satellite loss, Orbcomm and SpaceX have renegotiated their launch contract.

SpaceX's communication director, Christina Ra, told NBC News that there the investigation of last week's thruster problem has already begun. "But I am hesitant to give you any commitment on whether or not we can give more detail, and what the timing would be," she wrote in an email, "because it does take time, the information is shared with and approved by multiple parties, and at the end of the day, regulated by ITAR."

That last acronym refers to the International Trade in Arms Regulations, which strictly limit the transfer of aerospace technology to foreign countries. SpaceX fears that the unauthorized disclosure of information about a rocket anomaly would get the company in ITAR trouble with the federal government, and maybe even get someone put in jail. "I don't look good in horizontal stripes," Shotwell joked.

Dealing with anomalies may well be a more frequent option for future spaceflight, even when humans are involved. Oberg noted that the subject came up when millionaire Dennis Tito was discussing his plan to send private-sector astronauts on a 501-day trip past Mars in 2018. "He described how his two-human crew to Mars would be occupied servicing, repairing and coaxing their life support systems, which would be designed to be fixable, not to be 'perfect,'" Oberg said in an email.

This is why SpaceX and NASA's other commercial partners are devoting so much attention to the development of launch abort systems for crew-capable spaceships. Those systems might actually have to be used someday.

"With a commercialized crew taxi that doesn't 'overspend' on unattainable perfect reliability, but accepts the occasional mission failure, you'll fly many more successful missions. You don't have to pay for it in crew safety, just in mission completion rates. And the high flight rates can shake out hardware to enhance reliability far more than flying a vehicle once or twice a year, as with space shuttles." Oberg said.

"If there isn't a commercial crew mission abort at some point in the first 10 missions, I'd suspect they spent too much on reliability. I'm not talking about somebody getting hurt — we need to build robust and reliable escape systems — but just having to come home without accomplishing the purpose of the launch."

Does that sound scary? It shouldn't. The key to success in space may well be to make sure failure is an option that can be dealt with — as SpaceX demonstrated last week.

More about commercial space ventures:

• Spaceship ventures plan flights as early as 2015
• Gallery: Ten players in the commercial space race
• Cosmic Log archive on commercial space 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.

NASA / SpaceX via Twitter

A video view from the International Space Station shows SpaceX's Dragon cargo capsule in the grip of the station's robotic arm, with Earth below.

Astronauts used the International Space Station's robotic arm to grab SpaceX's Dragon capsule on Sunday after the unmanned spacecraft made a dramatic recovery in orbit. The grapple operation reached its successful climax an hour ahead of schedule, proving that the unmanned capsule had fully recovered from a post-launch glitch that affected its propulsion system.

NASA and California-based SpaceX decided to go ahead with Sunday's rendezvous after the Dragon made a series of orbital maneuvers that demonstrated the craft's thrusters were operating normally. When the Dragon closed in to a distance of 33 feet (10 meters), the Canadian-built robotic arm reached out and latched onto an attachment on the cargo ship.

The robotic-arm grapple was originally scheduled to take place at 6:31 a.m. ET, but it occurred instead at 5:31 a.m., as the station was flying 253 miles (407 kilometers) over Ukraine.

NASA's Mission Control and the space station's astronauts exchanged congratulations. "That was a brilliant capture," NASA astronaut Kate Rubins told space station commander Kevin Ford from Mission Control.

Ford passed along his thanks to NASA's controllers in Houston as well as to SpaceX's mission control at the company's headquarters in Hawthorne, Calif. "It's not where you start, but where you finish that counts, and you guys really finished this one on the mark," Ford said. "You're aboard, and we've got lots of science on there to bring aboard and get done. So congratulations to all of you."

As the crew watched, the robotic arm's remote operators in Houston issued commands to pull the Dragon in for a hookup with the station's Harmony module. "The Dragon is ours!" Canadian astronaut Chris Hadfield wrote in a Twitter update. "Maneuvering it now on Canadarm2 to docking port, will open hatches. Look forward to new smells."

The capsule was berthed at 8:56 a.m. ET, and within a few hours, the station's astronauts hooked up the electrical connections, opened up the hatch from the Harmony module and took their first look inside the Dragon.

"Happy Berth Day," SpaceX exulted on Twitter. 

How a glitch was fixed
The cargo craft was launched on Friday from Cape Canaveral Air Force Station in Florida, atop SpaceX's Falcon 9 rocket. The ascent to outer space was trouble-free, but minutes after the Dragon reached orbit, SpaceX's controllers noticed that only one of the craft's four thruster pods was working. The thrusters control the Dragon's position in space, and at least three of the pods had to be operational to get NASA's clearance for the berthing.

It took several hours to resolve the glitch and get full thruster functionality. That caused SpaceX to miss its opportunity for a Saturday rendezvous. SpaceX's billionaire founder, Elon Musk, said it looked as if there was a stuck valve or a blockage in the thruster's oxidizer lines. Recycling the valves and sending a blast of pressurized helium through the line cleared the system, he said.

The maneuvers that followed gave NASA and SpaceX the confidence to go ahead with the hookup on Sunday. "The station’s Mission Management Team unanimously agreed that Dragon’s propulsion system is operating normally along with its other systems and ready to support the rendezvous," NASA said in a statement Saturday.

NASA said SpaceX voiced "high confidence there will be no repeat of the thruster problem during rendezvous, including its capability to perform an abort, should that be required." Fortunately, not a single hitch arose during the Dragon's approach.

Chris Hadfield via Twitter

Sub-Saharan Africa provides a backdrop for SpaceX's Dragon capsule in a photo taken from the International Space Station during the cargo ship's approach.

NASA TV

A video view from the International Space Station shows the SpaceX Dragon cargo capsule coming in for Sunday's berthing.

NASA TV

A view from one of the International Space Station's cameras shows the Dragon cargo capsule berthed to the Harmony module.

What's in the Dragon?
The Dragon is carrying more than 2,300 pounds (1,050 kilograms) of cargo, including experiments to study the growth of plants and mouse stem cells in zero-G. There are also spare parts for the station's air-recycling system, grapple bars for the space station's exterior, and a research freezer for preserving biological samples. The crew is getting clothing, personal items and food, including fresh fruit from an orchard owned by the father of one of SpaceX's employees.

The Dragon also is bringing the first copy of "Up in the Air," a single recorded by the band Thirty Seconds to Mars. That song will figure in a public-relations push later this month.

Once the space station's astronauts have finished unloading the cargo, they'll fill the Dragon back up with more than 3,000 pounds (1,370 kilograms) of stuff destined for return to Earth. The cargo craft is due to be set loose on March 25 for its splashdown in the Pacific.

This is the second of 12 resupply flights to be conducted under NASA's $1.6 billion contract with SpaceX. The first flight took place last October. SpaceX and another company, Orbital Sciences Corp., were granted the contracts to help fill the gap left by the space shuttle fleet's retirement in 2011. Orbital's cargo delivery service is expected to start later this year.

SpaceX is one of three companies receiving support from NASA under a separate program to develop crew-capable spacecraft for the space agency's use beginning in 2017 or so. SpaceX is working to upgrade its robotic Dragon capsule with extra safety equipment for crewed flight. The other two companies — the Boeing Co. and Sierra Nevada Corp. — are developing completely new spaceships. In the meantime, NASA is paying the Russians about $60 million per seat for rides to and from the space station.

More about SpaceX:

• 'Frightening' glitch fixed on Dragon capsule
• 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.

This story was originally published on Sat Mar 2, 2013 5:40 PM EST

The commercial SpaceX rocket venture launched its unmanned Dragon capsule on a cargo run to the International Space Station on Friday, and then spent hours addressing a gnarly problem with the Dragon's thruster system. The problem was solved, but not before it forced at least a day's delay in the cargo craft's space station rendezvous.

SpaceX's Falcon 9 rocket made a problem-free ascent from its launch pad at Cape Canaveral Air Force Station in Florida at 10:10 a.m. ET to send the Dragon into space. But a half-hour after launch, SpaceX founder Elon Musk said in a Twitter update that controllers encountered an issue involving the capsule's thrusters.

"Issue with Dragon thruster pods," Musk wrote. "System inhibiting three of four [pods] from initializing. About to command inhibit override."

Each pod contains a grouping of thrusters that are used to guide the Dragon's course in orbit. In an email, SpaceX spokeswoman Christina Ra said the Dragon "experienced an issue with a propellant valve" after it achieved orbit. "One thruster pod is running," she said. "We are trying to bring up the remaining three. We did go ahead and get the solar arrays deployed. Once we get at least two pods running, we will begin a series of burns to get to station."

SpaceX's controllers wrestled with the problem for hours. Just before 3 p.m. ET, Musk said that a second thruster pod was up and running. After another hour, he reported that the other two pods were working as well. "Thruster pods one through four are now operating nominally. Preparing to raise orbit. All systems green," Musk said on Twitter.  And an hour after that, he sent another tweet saying that the orbit-raising burn was successful. "Dragon back on track," he wrote.

During a teleconference with reporters, Musk speculated that there was a stuck valve or "potentially some blockage" in the lines for pressurizing the thrusters' oxidizer tank. Cycling the valves and releasing a blast of pressurized helium cleared the lines, he said. There was no indication that the blockage did any damage to the system, although SpaceX and NASA were taking a closer look at the cause of the problem and its aftermath.

Musk voiced relief that operations were getting back to normal. "It was a little frightening there," the 41-year-old billionaire coolly acknowledged.

SpaceX

Hundreds of SpaceX employees gather around Dragon mission control at the company's headquarters in Hawthorne, Calif., to watch the Falcon 9 liftoff. A flown Dragon capsule is suspended from the ceiling.

Checking the system
NASA said three operational thruster pods would be required for the Dragon's approach to the space station. The agency's space station manager, Mike Suffredini, said NASA's team would need some "added time to make sure this is working properly." That means the earliest opportunity for astronauts to grab the Dragon with the station's robotic arm and bring it in for a berthing will come early Sunday rather than on Saturday.

NASA's associate administrator for human exploration and operations, Bill Gerstenmaier, praised SpaceX for its handling of the problem. "They did everything exactly right about the vehicle," he said. 

This is the third Dragon flight to the station: The first one, which took place last May, was a demonstration flight aimed at proving that California-based SpaceX could safely reach the space station, get hooked up, and then descend again to a splashdown. Last October's second flight marked the first of what's expected to be 12 resupply missions to the station, under the terms of a $1.6 billion contract with NASA. At that rate, each Dragon mission costs NASA about $133 million.

If the Dragon is not able to hook up with the space station, SpaceX would receive only a partial payment for the flight, Musk said. He didn't say how much that payment would amount to. 

What's on the Dragon?
This Dragon contains more than 2,300 pounds (1,050 kilograms) of cargo, including experiments to study the growth of plants and mouse stem cells in zero-G. There are also spare parts for the station's air-recycling system, and a research freezer for preserving biological samples.

A similar freezer was loaded up with ice cream treats for the crew for last October's resupply mission, but this time, the goodies packed on the Dragon were "a little bit healthier," SpaceX President Gwynne Shotwell said. Although she wasn't specific about what the space station's six residents would be getting, she said the treats were coming fresh from an orchard owned by the father of one of SpaceX's employees.

The astronauts are due to open the Dragon's hatch on the day after its arrival. It will take about three weeks to unload the craft, then load it up with more than 3,000 pounds (1,370 kilograms) of cargo for return to Earth. The original schedule called for the Dragon to be unberthed for a Pacific splashdown and recovery on March 25. Suffredini said that schedule would be adjusted, depending on the time frame for the Dragon's berthing.

SpaceX's cargo flights are meant to fill the gap left by the retirement of NASA's space shuttle fleet in 2011. Another company, Orbital Science Corp., has a separate NASA contract to begin deliveries to the space station later this year. Cargo can also be delivered to the space station on Russian, Japanese and European transports, but only SpaceX currently has the capability to bring cargo back down.

SpaceX and two other companies, Sierra Nevada Corp. and the Boeing Co., are developing crew-capable spacecraft under a separate NASA program. Those spaceships could be ready for NASA's use as early as 2017. In the meantime, U.S. astronauts have to ride on Russian Soyuz capsules at a cost of about $60 million per seat.

More about SpaceX:

• SpaceX hoped for glitch-free Dragon mission
• Falcon 9 rocket passes pre-launch test
• 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.

This story was originally published on Fri Mar 1, 2013 10:01 AM EST

SpaceX

SpaceX's Falcon 9 rocket sits on its launch pad at Cape Canaveral Air Force Station during Monday's pre-launch engine test. The rocket is due to loft a Dragon cargo capsule to the International Space Station on Friday.

The commercial SpaceX rocket venture says it's resolved the problems that cropped up during last October's cargo run to the International Space Station, and all systems are go for the delivery mission due for launch on Friday.

"We're a launch company," SpaceX President Gwynne Shotwell said during a pre-launch briefing at NASA's Kennedy Space Center in Florida on Thursday. "We love to launch."

SpaceX's Falcon 9 rocket is due to lift off from Space Launch Complex 40 at Cape Canaveral Air Force Station at 10:10 a.m. ET Friday. Forecasters said there was an 80 percent chance of acceptable weather for an on-time launch, with only a minor concern about the potential for thick cloud cover.

This will mark the third launch of an unmanned SpaceX Dragon cargo capsule to the space station. It's the second cargo delivery under the terms of a $1.6 billion, 12-flight resupply contract with NASA. And it's the first time that a payload has been carried in the Dragon's unpressurized "trunk."

The trunk is an extra cargo space sitting beneath the Dragon's pressurized main compartment. It's basically been empty for the Dragon's previous two launches, in May and October 2012, but this time there'll be an 822-pound (373-kilogram) package containing a new set of grapple bars to be installed onto the station during a later spacewalk. The package will be put into storage using the station's robotic arm during the three weeks that the Dragon is due to be hooked up to the orbital outpost.

Another 1,493 pounds (677 kilograms) will be riding in the pressurized space, Shotwell said. That cargo will include food, clothing and other crew provisions as well as scientific experiments, two freezers for lab samples and spare parts for the station's air-scrubbing system. Unlike last time, there'll won't be any satellites flying as a secondary payload on the Dragon, Shotwell said.

Anomalies addressed
In October, the previous Dragon mission failed to deploy its secondary payload, an Orbcomm communications satellite, because of an engine problem that occurred during the Falcon 9's ascent. Shotwell said the problem was traced to "a material flaw that went undetected" in the sheathing around one of the nine Merlin engines on the Falcon's first stage. The failure of that material resulted in a breach that caused the engine to lose pressure, signaling the rocket's flight computer to shut down the engine.

Despite the engine shutdown, the rocket was able to reach the required altitude for the space station delivery. It couldn't deliver the Orbcomm OG2 satellite to its proper orbit, however. Days later, the satellite fell out of the sky.

Shotwell said the engine assembly for the rocket to be launched on Friday has gone through extensive testing, using a procedure called non-destructive evaluation, or NDE. She said half-jokingly that engineers skilled in NDE procedures were more valued in the wake of last October's anomaly. "We're hiring you at SpaceX," she said.

She also discussed another anomaly that came to light after the previous Dragon's splashdown: The spacecraft sat in Pacific waters off the coast of California for hours, and it turned out that the water may have shorted out the power supply for the research freezer shipped down from the space station. NASA space station manager Mike Suffredini told reporters that the freezer was "fine, even with the loss of power." Since then, the Dragon for Friday's mission has been retrofitted to make the power supply more watertight, Shotwell said.

Suffredini said he was satisfied with the way that SpaceX followed up on the anomalies. "There's nothing that we would have done that they have chosen not to do," he said.

NASA has had its own share of problems crop up: Last week, the space station's main communication system went out for several hours during a software upgrade, but Suffredini said the outage "was never really a big concern." The software was eventually upgraded successfully, he said.

"Over a million lines of code were upgraded, including the software for the [robotic] arm that's going to capture the Dragon," Suffredini said.

A fast flight
The flight plan calls for the Falcon 9 to send the Dragon capsule on an orbital trajectory that will bring it to the station less than 24 hours after launch. That's a significant faster trip than the previous Dragon flights, due to a favorable orbital geometry, Shotwell said. When the Dragon comes within 10 meters (33 feet), astronauts will use the station's robotic arm to latch onto the spacecraft and pull it in for its berthing at a port on the Harmony module. The hatch would be opened on Sunday. Then the astronauts would unload the supplies and fill the Dragon back up with cargo to be returned to Earth.

The Dragon is due to be unberthed on March 25, and will head down to a Pacific splashdown and recovery.

SpaceX's cargo flights are meant to fill the gap left by the retirement of NASA's space shuttle fleet in 2011. Another company, Orbital Science Corp., has a separate NASA contract to begin deliveries to the space station later this year. Cargo can also be delivered to the space station on Russian, Japanese and European transports, but only SpaceX currently has the capability to bring cargo back down.

SpaceX and two other companies, Sierra Nevada Corp. and the Boeing Co., are developing crew-capable spacecraft under a separate NASA program. Those spaceships could be ready for NASA's use as early as 2017. In the meantime, U.S. astronauts have to ride on Russian Soyuz capsules at a cost of about $60 million per seat.

Extra credit:

• The previous mission included a shipment of vanilla-chocolate swirl ice cream for the crew, stored inside a research freezer. This time, the Dragon will be bringing snacks that are "a little bit healthier," Shotwell said. She said the goodies would be coming from the orchard of a SpaceX employee's father — but she wasn't more specific.
• When Shotwell was asked about millionaire space tourist Dennis Tito's plan to send a married couple to Mars and back in 2018, she replied that SpaceX was not currently participating in the mission. "I think his plan is very ambitious," she said. Shotwell didn't slam he door on Tito, however. "We are a launch service provider, and if he can come up with the funding to execute this mission, I'd be happy to have him as a customer," she said.

More about SpaceX:

• Falcon 9 rocket passes pre-launch test
• 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.

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.

NASA

Among the spaceship projects receiving NASA support are Boeing Co.'s CST-100 capsule (left), Sierra Nevada Corp.'s Dream Chaser space plane (middle) and SpaceX's Dragon capsule (right).

Americans could be flying into orbit on U.S.-built spaceships again as early as 2015 — but the first fliers won't be NASA astronauts or millionaire space tourists. Instead, they'll be commercial test pilots, employed by the Boeing Co., Sierra Nevada Corp., SpaceX or maybe even a dark-horse company like Blue Origin, the venture funded by Amazon.com billionaire Jeff Bezos.

Those four companies provided updates on their efforts to build new spaceships capable of carrying astronauts to and from the International Space Station during a Wednesday news briefing at NASA's Kennedy Space Center. One of the companies, Blue Origin, is wrapping up its work for NASA and is no longer receiving money through the Commercial Crew Program, or CCP. But SpaceX, Boeing and Sierra Nevada are splitting more than $1 billion that's to be paid out through 2014.

NASA's manager for the Commercial Crew Program, Ed Mango, said the agency and its commercial partners are already talking about "Phase 2" for the program. The certification requirements and timetable for Phase 2 are expected to be set this year, with contracts awarded by May 2014, Mango said. "We believe that there’ll be more than one, probably two, three, maybe others, that will be ready to compete for Phase 2," he said.

That phase would move the program forward to 2017, by which time NASA expects to be flying its astronauts on U.S. launch vehicles for the first time since the shuttle fleet was retired in 2011. In the meantime, NASA will be paying the Russians more than $60 million per seat for round trips to the space station.

"Our target was to repatriate that industry back to the United States, and that's what we're doing," said Mark Sirangelo, chairman of SNC Space Systems at Sierra Nevada.

Here's how the companies' plans are shaping up:

SpaceX: Former NASA astronaut Garrett Reisman, SpaceX's commercial crew project manager, said his company is working toward a launch pad abort test by the end of the year at Kennedy Space Center. An in-flight test that would demonstrate the ability to abort a launch safely during ascent, "at the worst possible moment," is planned for April 2014, he said. If SpaceX sticks to its schedule, it would use its Falcon 9 rocket and Dragon capsule for a manned test flight in mid-2015, and would send test pilots to the space station by the end of 2015. "We're not selling tickets. Don't call our toll-free number," Reisman joked.

Sierra Nevada Corp.: Sirangelo said his company was planning to drop its Dream Chaser mini-shuttle from a carrier airplane for its first autonomous, free-flying glide test in the first quarter of this year. That would be followed by a series of autonomous and crewed aerodynamic test flights, similar to the tests conducted by NASA using the prototype shuttle Enterprise in the late 1970s. Then Sierra Nevada's team would launch the Dream Chaser into space — first on suborbital test flights, and eventually into orbit. Last year, the company said manned orbital flights could begin in 2016.

The Boeing Co.: John Mulholland, vice president and program manager for Boeing's commercial crew program, said his company proposed conducting a three-day orbital spaceflight with a Boeing crew in 2016. The head of Boeing's flight test program is former NASA astronaut Chris Ferguson, who commanded Atlantis' crew during the final flight of the shuttle program. "He is defining crew requirements," Mulholland said. Before the test pilots fly, Boeing will conduct an unmanned orbital trial of its CST-100 space capsule, plus an altitude abort test.

NASA / Blue Origin

An artist's conception shows Blue Origin's orbital space vehicle.

Blue Origin: The company that Bezos founded in 2000 is not receiving NASA funding during the current phase of the agency's spaceship development program — but Blue Origin's president and program manager, Rob Meyerson, said he's still doing business with the space agency. "We're working with NASA to extend our Space Act Agreement in an unfunded manner," Meyerson said. The company is continuing to test its BE-3 rocket engine and work on its next prototype propulsion vehicle. Eventually, Blue Origin aims to launch crews on suborbital as well as orbital spaceflights.

The plans for future flights are dependent on continued NASA support — and Phil McAlister, NASA's commercial spaceflight development director, acknowledged that "the budget is going to be an extremely challenging topic."

If NASA's funding is reduced, Reisman said his company would continue to move toward manned flights, but at a slower pace. "Human spaceflight is our reason for being. We are in this for the long haul," Reisman said. "There will be impacts to cost and schedule, should funding dry up. But we're going to get there eventually."

More about the commercial space race:

• Blue Origin aces pad-escape test
• Boeing looks for test pilots
• Sierra Nevada's mini-shuttle passes first flight test
• SpaceX capsule splashes down after space station delivery

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.

SpaceX's prototype Grasshopper rocket took one giant leap last week, rising to a 12-story height and settling back down safely on its landing legs at the company's Texas rocket test facility. Just for fun, the engineers let a dummy cowboy go along for the ride.

The Dec. 17 test flight at the pad in McGregor, Texas, was documented in a YouTube video released today — and discussed in a series of lighthearted tweets from SpaceX's billionaire founder, Elon Musk.

"To provide a little perspective on the size of Grasshopper, we added a 6-ft cowboy to the rocket. ... Then we took him for a ride," Musk wrote. So how did the cowboy fare? "No problemo," said Musk.

The 10-story-tall Grasshopper rocket is designed to take off and land vertically, as part of Musk's plan to develop a rocket capable of returning itself to a launch pad for rapid reusability. Today's vertical-takeoff launch systems generally rely upon expendable lower stages — although the space shuttle's solid rocket boosters could be recovered from the Atlantic Ocean and refurbished for reuse. If a rocket stage can return to its launch facility intact and ready to go again, that could significantly lower the cost of spaceflight. That's what Musk is shooting for.

SpaceX says the Grasshopper consists of a Falcon 9 rocket first stage, a Merlin 1D engine, four steel landing legs with hydraulic dampers, and a steel support structure. During the prototype's first flight test on Sept. 21, the Grasshopper rose 6 feet into the air. The second test, on Nov. 1, lasted 8 seconds and lifted the Grasshopper 17.7 feet (5.4 meters) off the pad. The company said last week's third test went for 29 seconds, during which the Grasshopper rose 131 feet (40 meters) into the air, hovered and landed safely back on the pad, using closed-loop thrust vector and throttle control.

SpaceX

A dummy cowboy is perched on SpaceX's Grasshopper rocket for a Dec. 17 test.

In addition to the Grasshopper, SpaceX is sending its Dragon capsules to resupply the International Space Station, working on a version of the Dragon that could carry astronauts into orbit sometime soon, and developing a Falcon Heavy rocket that could conceivably power flights to the moon. But Musk's long-range goal is even more ambitious: getting settlers to Mars. He has said Grasshopper-style rocket reusability is a key part of that long-term strategy.

"If it does works, it'll be pretty huge," he said last year during a speech at the National Press Club in Washington.  

More on the commercial space race:

• SpaceShipTwo straps on its engine
• Golden Spike wants to fly you to the moon ... for $1.4 billion
• Blue Origin's spaceship prototype aces pad-escape test
• Gallery: Ten players in the commercial space race
• Cosmic Log archive on the new space race

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.

SpaceX

SpaceX's Falcon 9 rocket fires its engines on a Cape Canaveral launch pad during Saturday's successful static fire test, in preparation for an Oct. 7 launch to the International Space Station.

SpaceX says it successfully test-fired the engines on its Falcon 9 rocket today in preparation for Oct. 7's scheduled liftoff of the California-based company's first official cargo delivery to the International Space Station.

The static-fire test at Cape Canaveral Air Force Station in Florida was considered the "last major test" in advance of the launch, SpaceX said in a Twitter update. The rocket was held down while its nine Merlin engines blazed for a couple of seconds on the pad, at the end of a computer-controlled fueling sequence. Data from the test will be analyzed in advance of the scheduled launch at 8:34 p.m. ET on Oct. 7.

This will be the first launch under the terms of a 12-flight, $1.6 billion NASA contract to resupply the space station. In May, a SpaceX Falcon 9 rocket sent an unmanned Dragon capsule to its first space station hookup, during a NASA-funded demonstration flight. The success of that mission cleared the way for cargo flights to begin in earnest.

Another company, Orbital Sciences Corp., is working on its own launch system for supplying the space station: The first stage of Orbital's Antares rocket is due to roll out next week in preparation for a hold-down test on its Virginia launch pad.

SpaceX is also working on a modified version of the Dragon capsule that could be used to transfer NASA astronauts to and from the space station, beginning in the 2015-2017 time frame. That effort falls under a separate NASA program that is also funding spaceship development efforts by the Boeing Co. and Sierra Nevada Corp.

Watch this brief video of today's static-fire test:

More about SpaceX:

• Cargo launch to space station set for Oct. 7
• Why SpaceX is setting the pace in space race
• Gallery: Ten players in commercial space race
• Cosmic Log archive on the new space race

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.

NASA

Among the spaceship projects receiving NASA support are Boeing Co.'s CST-100 capsule (left), Sierra Nevada Corp.'s Dream Chaser space plane (middle) and SpaceX's Dragon capsule (right).

NASA has committed $1.1 billion over the next 21 months to support spaceship development efforts by the Boeing Co., SpaceX and Sierra Nevada Corp., with the aim of having American astronauts flying once more on American spacecraft within five years. 

The lineup of companies matches what sources told NBC News on Thursday, but today NASA laid out the details, including the outlays for each of the teams involved. The space agency is setting aside $460 million for Boeing, $440 million for SpaceX and $212.5 million for Sierra Nevada.

The next phase of NASA's commercial spaceflight effort — known as Commercial Crew Integrated Capability, or CCiCap — calls for these three companies to take their design and testing program through a series of milestones by May 2014. Optional milestones could lead to crewed demonstration flights in later years.

NASA wants to have at least one commercial space taxi carrying astronauts to and from the International Space Station by 2017. The three companies say they can meet or beat that schedule, provided that they continue to receive NASA support.

NASA Administrator Charles Bolden told reporters that the space taxi program "is a top priority of the Obama administration." In the wake of last year's retirement of the shuttle fleet, the space agency has had to depend on the Russians to fly American astronauts at a cost of roughly $60 milllion a seat. Bolden said the move to U.S. commercial transport would guarantee "that we never find ourselves in the situation where we find ourselves today," at the mercy of a sole provider.

Flying crew by 2015, 2016, 2017?
This is actually the third phase of NASA's Commercial Crew Program. All three companies have received NASA support adding up to hundreds of millions of dollars during earlier phases. Boeing is working on a capsule called the CST-100, SpaceX is upgrading its Dragon capsule to be capable of flying astronauts safely, and Sierra Nevada is testing its Dream Chaser space plane, which looks like a miniaturized version of the space shuttle.

The CST-100 and Dream Chaser would be sent into orbit on United Launch Alliance's Atlas 5 rocket, while SpaceX would launch the crew-capable Dragon on its own Falcon 9 rocket. The Dragon and Falcon 9 are already being used for robotic cargo resupply missions to the space station. 

The three companies say their spacecraft will be capable of flying seven astronauts to the space station, at a per-seat cost that's less than what NASA is paying the Russians.

NASA and congressional leaders made a deal that called for two commercial partners to receive full funding, with one additional backup partner receiving half funding. That would imply that Sierra Nevada Corp. is the halfway partner, but Mark Sirangelo, chairman of SNC Space Systems, said he didn't see it that way.

"We're very happy with the award," Sirangelo told me. "Obviously more money would have been great." He said NASA's funding, plus Sierra Nevada's own resources, would keep the program on track for the start of operations in 2016 or 2017. Sierra Nevada's milestones stop just short of a critical design review, while SpaceX and Boeing could be funded through that phase.

In a statement, Elon Musk, SpaceX's billionaire founder, CEO and chief designer, hailed the CCiCap award as "a decisive milestone in human spaceflight" that would set "an exciting course for the next phase of American space exploration."

"SpaceX, along with our partners at NASA, will continue to push the boundaries of space technology to develop the safest, most advanced crew vehicle ever flown," Musk said.

Boeing also welcomed today's announcement. "Today’s award demonstrates NASA's confidence in Boeing's approach to provide commercial crew transportation services for the ISS," John Elbon, Boeing vice president and general manager of space exploration, said in a statement. "It is essential for the ISS and the nation that we have adequate funding to move at a rapid pace toward operations so the United States does not continue its dependence on a single system for human access to the ISS."

SpaceX projects being able to launch a crewed demonstration flight in 2015, and Boeing anticipates achieving that feat by late 2016, said Phil McAlister, director of NASA's commercial spaceflight development program. However, he said those timetables come with a "big asterisk": optimal funding from NASA, which McAlister said almost never happens.

Musk told me that the 2015 demonstration flight would go into orbit, but not to the space station. He estimated that the first space station flight could take place a year later. Getting to that point would require NASA funding to the tune of $1 billion, he said — which implies that SpaceX would be roughly halfway there with the CCiCap funding.

A PDF file from NASA summarizes the details for the CCiCap agreements.

Who didn't win?
Four other companies submitted proposals for CCiCap funding, said Bill Gerstenmaier, NASA's associate administrator for human exploration and operations. Three of the also-rans — Space Operations, American Aerospace and Space Design — didn't meet the requirements for consideration, he said.

The fourth company was ATK, which has been working with Lockheed Martin and Astrium on the Liberty launch system. ATK has said that it will continue work on Liberty, which would use adapted versions of the space shuttle's solid rocket booster and a second stage from Astrium's Ariane 5 rocket. But without NASA support, the pace of development would be slower.

Gerstenmaier said ATK's development plan didn't come up to the level of the three companies that were selected, but held off on providing details about the decision process. "The stronger proposals were really the three that we talked about," he said.

Additional companies could negotiate unfunded agreements for NASA's advice, McAlister said. ATK and two other companies, United Launch Alliance and Excalibur Almaz, had such agreements during earlier phases of the commercial crew program. Another company, Blue Origin, has been received NASA funding for the development of its orbital space vehicle but did not apply for continued CCiCap support.

Looking ahead
NASA says the reliance on commercial transport to low Earth orbit would free up the space agency to concentrate on exploration beyond Earth orbit.

"For 50 years American industry has helped NASA push boundaries, enabling us to live, work and learn in the unique environment of microgravity and low Earth orbit," Gerstenmaier said in a statement. "The benefits to humanity from these endeavors are incalculable. We're counting on the creativity of industry to provide the next generation of transportation to low Earth orbit and expand human presence, making space accessible and open for business."

NASA is spending billions of dollars to develop the Orion multipurpose crew vehicle for deep-space exploration, as well as a heavy-lift rocket known as the Space Launch System. Those spacecraft are being designed to send astronauts to a near-Earth asteroid by 2025, and to Mars and its moons in the 2030s.

More about the space race:

• NASA backs Boeing, SpaceX, Sierra Nevada in space race
• Follow the money in the commercial space race
• Why SpaceX is setting the pace in the space race
• Cosmic Log archive on commercial space

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 dwarf planet and the search for new worlds.