By Nancy Atkinson
Universe Today

SpaceX's Grasshopper flew 250 meters (820 feet) straight up, tripling the height flown on its previous leap. The video provides a great overhead view from SpaceX’s hexacopter.

Via Twitter, SpaceX CEO said the Grasshopper was able to remain steady in its flight even on a windy day, hover and then land.

Grasshopper is a 10-story Vertical Takeoff Vertical Landing (VTVL) vehicle that SpaceX has designed to test the technologies needed to return a rocket back to Earth intact. While most rockets are designed to burn up in the atmosphere during re-entry, SpaceX's rockets are being designed to return to the launch pad for a vertical landing.

This is Grasshopper's fifth in a series of test flights, with each test demonstrating dramatic increases in altitude. Last September, Grasshopper flew to 2.5 meters (8.2 feet). In November, it flew to 5.4 meters (17.7 feet). In December, it flew to 40 meters (131 feet), and then 80.1 meters (262.8 feet) in March.

Grasshopper consists of a Falcon 9 rocket's first-stage tank, a Merlin 1D engine, four steel and aluminum landing legs with hydraulic dampers, and a steel support structure.

Nancy Atkinson is Universe Today's Senior Editor. She also is the host of the NASA Lunar Science Institute podcast and works with the Astronomy Cast and 365 Days of Astronomy podcasts. Nancy is also a NASA/JPL Solar System Ambassador.

This report was originally published on Universe Today as "SpaceX Grasshopper Flies High." Copyright 2013 Universe Today. Reprinted with permission.

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

Two of SpaceX's Merlin 1D engines sit on a test stand at the company's rocket development facility in Texas.

By Mike Wall
Space.com

SpaceX's next-generation rocket engine is ready to fly and will probably power a commercial space launch for the first time this summer, company officials announced Wednesday.

The Merlin 1D engine was judged flight-ready after firing for a total of nearly 33 minutes over the course of 28 different tests at SpaceX's rocket-development facility in McGregor, Texas. The new engine will soon be incorporated into the company's Falcon 9 rocket, officials said.

"The Merlin 1D successfully performed every test throughout this extremely rigorous qualification program," SpaceX's CEO and chief designer, Elon Musk, said in a statement. "With flight qualification now complete, we look forward to flying the first Merlin 1D engines on Falcon 9’s Flight 6 this year."

The Falcon 9 has flown five times to date, most recently on March 1, when it blasted the robotic Dragon capsule toward the International Space Station on California-based SpaceX's second contracted supply run for NASA. According to the company's launch manifest, flight No. 6 will launch a Canadian communications satellite, probably in mid-June. [Photos: SpaceX's Amazing Rockets & Spaceships]

Company officials say the Merlin 1D will provide a big boost for the Falcon 9, which has been using nine Merlin 1C engines to power its first stage.

"The Merlin 1D has a vacuum thrust-to-weight ratio exceeding 150, the best of any liquid rocket engine in history," SpaceX officials wrote in a press release Wednesday. "This enhanced design makes the Merlin 1D the most efficient booster engine ever built, while still maintaining the structural and thermal safety margins needed to carry astronauts."

SpaceX indeed plans to launch astronauts using the Merlin 1D. The company is working on a manned version of its Falcon 9/Dragon transportation system, in the hopes of scoring a NASA contract to ferry astronauts to and from the space station.

SpaceX will also incorporate the 1D into its Falcon Heavy booster, a huge rocket still in development that will use 27 engines in its first stage. The Falcon Heavy will be capable of carrying payloads weighing 53 metric tons to low-Earth orbit, company officials say, and it is also being designed to meet NASA human-rating standards.

The Merlin 1D already powers SpaceX's Grasshopper rocket, an experimental booster that the company hopes will pave the way for a fully reusable launch system. Earlier this month, the Grasshopper lifted off on its fourth test flight, rising 263 feet (80 meters) into the Texas skies before returning to Earth and making a soft landing.

Follow Mike Wall on Twitter @michaeldwall. Follow us @Spacedotcom, Facebook or Google+. Originally published on Space.com.

• SpaceX Dragon's 2nd Space Station Cargo Delivery (Photos)
• SpaceX's Quest For Rocketry's Holy Grail - Space.com Exclusive Video
• Quiz: How Well Do You Know SpaceX's Dragon Spaceship?

Copyright 2013 Space.com, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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.

NASA TV

The International Space Station's robotic arm unloads grapple-bar assemblies from the unpressurized "trunk" of SpaceX's Dragon cargo capsule on Wednesday.

By Miriam Kramer
Space.com

NASA engineers used a robotic arm on Wednesday to unpack the first exterior cargo ever delivered to the International Space Station by an American-built commercial supply ship.

A robotics team at NASA Mission Control in Houston remotely controlled the space station's 58-foot (17-meter) Canadarm2 robotic arm to unload two so-called grapple bars from the unpressurized "trunk" of the privately built unmanned Dragon space capsule. The Dragon's trunk is a cylindrical cargo section beneath the spacecraft's re-entry module.

The Dragon spacecraft, built by California-based SpaceX, was launched to the space station on Friday and arrived two days later, delivering about 1,200 pounds (544 kilograms) of supplies to the orbiting lab. It's the second of 12 scheduled SpaceX cargo deliveries for NASA under a $1.6 billion agreement.

SpaceX launched a demonstration flight to the space station last May and made its first cargo delivery in October. But both of those missions only carried items inside the Dragon's pressurized capsule, which is accessible to astronauts on the station through a docking hatch. [See photos of Dragon's space station arrival]

The current mission marks the first time SpaceX has ever delivered gear meant for the outside of the space station using the Dragon's trunk. SpaceX built the support hardware holding the grapple bars in place on the Dragon capsule, company officials said.

The six astronauts living aboard the space station finished unloading the pressurized cargo section on Monday, leaving only the grapple bars to be retrieved. "These bars, which together weigh about 600 pounds [272 kilograms], can be used to remove failed radiators on the station’s S1 and P1 truss segments, should that ever be deemed necessary," NASA officials said in a statement.

The grapple bars will be stored in a temporary spot on the International Space Station exterior for now, but will eventually be mounted to a permanent storage point, NASA officials said.

With the Dragon capsule empty, the station crew will soon start loading the capsule with 2,668 pounds (1,210 kilograms) of experiments and unneeded items for the spacecraft's return to Earth on March 25. The Dragon is expected to splash down off Baja California in the Pacific Ocean so it can be retrieved by recovery teams.

Various space agencies are expecting items to return to Earth onboard Dragon. For example, stem cells and hair that are currently being used in experiments on the station will be sent down with Dragon for the Japan Aerospace Exploration Agency.

Empty food containers will also be delivered back to Earth, according to a NASA manifest. And some science experiments are making a round trip with the capsule.

SpaceX is one of two companies with billion-dollar-plus contracts to supply cargo missions to the space station for NASA. The other company, Orbital Sciences Corp. of Virginia, has a $1.9 billion contract with the agency for eight resupply missions to the station using the new Antares rocket and Cygnus spacecraft.

NASA is relying on privately built spacecraft to ferry cargo — and ultimately astronaut crews — to and from the International Space Station. With the retirement of its space shuttle fleet in 2011, NASA is currently dependent on Russia's Soyuz spacecraft to launch American astronauts to the space station.

Follow Miriam Kramer @mirikramer and Google+. Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com.

• SpaceX to Space Station: Complete Coverage
• 6 Fun Facts About Private Rocket Company SpaceX
• Dragon Docked To ISS After Glitched Launch | Video

Copyright 2013 Space.com. All rights reserved.

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