Stratolaunch

Stratolaunch says its air-launch system will incorporate a three-stage rocket built by Orbital Sciences Corp., as shown in this artist's conception.

Stratolaunch has solidified its partnership with Orbital Sciences Corp. to develop a new rocket capable of launching payloads into orbit from what will be the world's widest airplane.

"We've been together now for nine months and working well as a team ... so we're really excited to see Orbital get started," Gary Wentz, Stratolaunch's CEO and president, told NBC News.

Founded by software billionaire Paul Allen, Stratolaunch aims to send payloads into orbit — and eventually, people as well — using rockets that are carried up to high altitude on a 385-foot-wide (117-meter-wide) carrier plane incorporating components from two Boeing 747s. The rocket would be released into the air and then would fire its engines to complete the ascent.

When the project was announced in December 2011, the rocket was supposed to be a modified version of SpaceX's Falcon 9 — but as time went on, Stratolaunch and SpaceX decided that wasn't the right fit. SpaceX dropped out late last year, and Stratolaunch engaged Orbital to study alternatives for the rocket design. Now the engagement has turned into a marriage of sorts.

"We have assembled a first-class team of professionals, with decades of experience, and we are ready to support the program as it moves from concept into design and production," Frank Culbertson, Orbital's executive vice president and general manager of its Advanced Programs Group, said Monday in a news release.

For more than two decades, Orbital has used its solid-fueled, air-launched Pegasus rocket to put payloads weighing up to 1,000 pounds (450 kilograms) into orbit. In April, the Virginia-based company conducted the first test launch of its Antares rocket, which is designed to deliver 11,000 pounds (5,000 kilograms) to the International Space Station.

Wentz said the new three-stage rocket could put up to 13,500 pounds (6,100 kilograms) into low Earth orbit. The first two stages would be solid-fueled, and the third stage would rely on liquid propellant. Advance reports have referred to the rocket as a "Pegasus 2," but Wentz said the rocket has not yet been named.

While Orbital works on the rocket and system integration, California-based Scaled Composites is working on the mothership. The plane looks like a scaled-up version of Virgin Galactic's WhiteKnightTwo, which was also built by Scaled. Wentz said the development plan calls for the first flight test of the airplane to take place in 2016, with the first demonstration of the entire launch system coming in 2018.

"It is similar to what Virgin Galactic has done with Scaled, based on a building-block approach," Wentz said.

Stratolaunch says its system will be able to provide "any orbit, anytime, almost anywhere" launch services for medium-size payloads.

"Stratolaunch is introducing an innovative solution unlike anything ever before attempted, with convenient, airport-like operations to launch commercial and government payloads, and eventually, human missions," Wentz said in Monday's news release. "With the rocket design and operational methodology well understood, we are now positioned to bring this vision to fruition."

More about frontier space ventures:

• SpaceShipTwo goes supersonic
• Planetary Resources looks to crowdfunding
• Cosmic Log archive on new space ventures

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the NBC News Science Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with NBCNews.com's 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.

Steve Helber / AP

The Antares rocket is illuminated by lights on Tuesday night, waiting for launch from a Virginia spaceport.

Orbital Sciences Corp. postponed the maiden launch of its Antares rocket on Wednesday when an umbilical data cable was disconnected prematurely from the launch vehicle's second stage.

The launch abort came at about 4:48 p.m. ET, just minutes before the Antares was due to lift off from the Mid-Atlantic Regional Spaceport on Wallops Island, Va. Orbital said the 5 p.m. ET liftoff would be rescheduled for Friday at the earliest.

"We are still examining all of the data, but it appears that the issue is fairly straightforward," Frank Culbertson, Orbital’s executive vice president and mission director for the Antares test flight, said in a company statement. "With this being the first launch of the new system from a new launch facility we have taken prudent steps to ensure a safe and successful outcome. Today, our scrub procedures were exercised and worked as planned.  We are looking forward to a successful launch on Friday."

Imagery posted to the independent NASASpaceFlight.com website showed a tower on the launch pad twisting in a motion that could have dislodged the data cord from its connector.

Orbital is giving the Antares rocket its first in-flight test in preparation for trips to the International Space Station later this year. This time around, the rocket is carrying merely a dummy payload, along with some secondary satellites that are to be deployed in orbit. But if the practice run is successful, Orbital could start providing a second line of made-in-the-USA commercial vehicles for resupplying the space station.

The Virginia-based company is following in the footsteps of California-based SpaceX, which began cargo runs to the space station last year.

Orbital and SpaceX have received hundreds of millions of dollars from NASA to develop their transports, as part of the space agency's strategy to replace the space shuttle fleet. The shuttles were retired in 2011 to make way for a new generation of spaceships capable of going beyond Earth orbit. NASA wants private companies to take over the role of getting cargo — and eventually astronauts as well — to low Earth orbit.

Orbital won NASA's contract for the Antares rocket and the Cygnus cargo capsule in 2008.

A simulated Cygnus payload is to be lofted into orbit during a 10-minute ascent, and is expected to remain in orbit for several weeks before plunging to its fiery doom in Earth's atmosphere. Four tiny satellites are to be deployed from the simulator, including three smartphone-equipped PhoneSats for NASA (Alexander, Graham, and Bell) and the commercial Dove-1 remote-sensing nanosatellite. The main point of the mission, however, is to check whether Antares is ready to send cargo to the space station.

"This is a big event for the Eastern Shore, for Wallops and for everybody in the surrounding area, but also, I think, for the country," Frank Culbertson, executive vice president and general manager of Orbital's Advanced Program Group, said during Tuesday's pre-launch briefing.

He cautioned journalists not to expect a perfect test flight. "That first word is 'test,' so if things don't go exactly as planned, we will learn what we need to learn and press on," he said.

If the test is successful, another Antares is due to send a real Cygnus capsule to the space station as early as this June. And if that demonstration flight succeeds, Orbital could proceed with a series of eight resupply flights to the station under the terms of a $1.9 billion contract with NASA. SpaceX is already two flights into its own 12-mission, $1.6 billion resupply contract.

Phil McAlister, NASA's director of commercial spaceflight development, said Orbital would play an important role in providing "assured cargo access" to the space station. The idea is that if SpaceX's Falcon 9 rocket and Dragon capsule are grounded for technical reasons, Orbital's Antares and Cygnus would serve as a backup — and vice versa. That wasn't the case during the space shuttle program, when NASA's only Plan B was to rely on other countries' spaceships.

"We are in such a better situation today, and [it's] about to be even better with the debut of this new capability," McAlister said.

NASA is following a similar approach for the development of U.S.-made spaceships for crew transport. Three companies — SpaceX, the Boeing Co. and Sierra Nevada Corp. — are splitting more than a billion dollars of NASA's money during the current phase of work. NASA expects commercial crew transports to start flying to the space station by 2017. 

Correction for 6:55 p.m. ET April 17: I've cleaned up a couple of errors, including the date when Orbital won NASA's nod in the Commercial Orbital Transportation Services program (2008, not 2007) and the SpaceX contract amount under NASA's Commercial Resupply Services program ($1.6 billion, not $1.6 million).

More about the Antares rocket:

• Five things you didn't know about Antares
• Watch as Antares rises into orbit

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 is basking in the glow of last month's successful cargo mission to the International Space Station, but it's also celebrating the glow of its next-generation Merlin 1D rocket engine, which has now gone through a full mission duration firing of 185 seconds.

The California-based company said today that the engine firing took place at its rocket development facility in McGregor, Texas, on a test stand near the building where the recently returned Dragon cargo capsule is being kept. The test reached 147,000 pounds of thrust, satisfying the duration and power requirements for a Falcon 9 launch. SpaceX also tested the Merlin 1D's capability for multiple restarts.

"This is another important milestone in our efforts to push the boundaries of space technology," SpaceX CEO and chief designer Elon Musk said in today's announcement. "With the Merlin 1D powering the Falcon 9 and Falcon Heavy rockets, SpaceX will be capable of carrying a full range of payloads to orbit."

The Merlin 1D represents an enhancement of the Merlin 1C engines that are being used on the Falcon 9's first flights. SpaceX said the 1D should open the way for "improved manufacturability by using higher-efficiency processes, increased robotic construction and reduced parts count." The new engine's structural and thermal safety margins play a key part in SpaceX's plans to start launching astronauts into space as early as 2015.

SpaceX says the Merlin 1D's should see their first flight on Falcon 9 Flight 6, due for liftoff next year.

Also today, Aerojet's AJ26 rocket engine was test-fired at NASA's Stennis Space Center in Mississippi, according to a Twitter update from the space agency's rocket test complex. The AJ26 is to be used on Orbital Sciences Corp.'s Antares rocket. Like SpaceX, Orbital has been receiving hundreds of millions of dollars from NASA to support the development of a launch system capable of resupplying the space station. Orbital says the first Antares test flight will be launched later this summer.

NASA

A picture from NASA's Stennis Space Center shows the test firing of Aerojet's AJ26 rocket engine.

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