It's been five months since Virgin Galactic's SpaceShipTwo rocket plane broke up in flight, killing one of its pilots and injuring the other. The results of the investigation have not yet been released, and for that reason the company's executives are reluctant to say much about the lessons learned. But there's one lesson they're willing to share: Don't say too much about what you're planning to do before you do it.

Before the accident, company founder Richard Branson issued statements saying SpaceShipTwo would fly paying passengers to the edge of space within one to three years — whether that translated into 2007, or 2008, 2012, 2013, 2014 or 2015.

"Sometimes people misinterpreted those as firm dates or promises," said Will Pomerantz, Virgin Galactic's vice president for projects, "so we don't want to repeat that mistake."

About 700 customers have been waiting to get a ride on SpaceShipTwo, putting down as much as $250,000 for their reservation. But they shouldn't expect to hear a firm date for their flight. Instead, Pomerantz will say only that "we are making steady progress" on building a second SpaceShipTwo to replace the first.

Milestones ahead

The next big milestone is called "weight on wheels," when the rocket plane is complete enough that its weight can be supported on its own wheels rather than the construction framework around it. Then there's the rollout, and ground testing, and glide tests, and rocket-powered tests, and finally commercial operations.

If all proceeds according to plan, the new SpaceShipTwo craft is "on track" to begin ground testing this year in Mojave, California, Pomerantz said.

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Some new customers have signed up since the accident, to show solidarity with the teams at Virgin Galactic and at The Spaceship Company, the sister subsidiary that's in charge of building the hardware. Meanwhile, some old customers have asked for their money back. "The overwhelming majority of that group said, 'I believe you will fly, and I believe it's safe to fly, but I just don't know when and I want to do something else with that money," Pomerantz said.

The net effect "has evened itself out," he said.

Pomerantz paid tribute to the customers who have stayed the course: "They totally get how challenging this is, and they understand that there is some risk involved. ... Their level of satisfaction has been really astounding. That's something that has a wonderful feedback effect."

LauncherOne on the rise

Virgin Galactic is also getting a lift from its other space program: LauncherOne, a system that's being developed to put small satellites into orbit using an air-launched rocket. LauncherOne will employ the same WhiteKnightTwo mothership used for SpaceShipTwo air launches, but the rocket will be equipped with a new kind of liquid-fueled engine called the Newton.

"Stay tuned for some updates from that team," Pomerantz said.

In February, the LauncherOne operation moved into a new 150,000-square-foot manufacturing facility in Long Beach. Last month's job fair in Long Beach was expected to draw about 1,000 applicants. Instead, more than 6,000 showed up.

About 65 people are now working full-time on LauncherOne, and another 40 to 50 would be added in the months ahead. "We've got this great mix of people who have been involved in basically every American rocket that's been launched in the past 40 or 50 years," Pomerantz said.

LauncherOne is slated to play a role in deploying hundreds of satellites for OneWeb, a venture that aims to provide low-cost, global Internet access by 2019. But Virgin Galactic has other customers for LauncherOne, including Planetary Resources, Skybox Imaging, Spaceflight Inc., GeoOptics — and other companies that haven't yet announced they're customers.

So when will LauncherOne start launching? Once again, Pomerantz was cautious in his response. He noted that when the program was unveiled in 2012, Virgin Galactic said blastoffs would begin by the end of 2016.

"I think we're still more or less on schedule for that," Pomerantz said.

Virgin Galactic's Will Pomerantz will discuss the future of private-sector spaceflight with NBC News' Alan Boyle on Wednesday's installment of "Virtually Speaking Science," an hourlong talk show airing at 8 p.m. ET via BlogTalkRadio. You can also watch the show as part of a live virtual audience in the Exploratorium's Second Life auditorium. If you miss the live show, never fear: You can always catch up with the podcast in BlogTalkRadio's archive or on iTunes. March's show featured a discussion of the UFO phenomenon with Seth Shostak, senior astronomer at the SETI Institute; and Fermilab physicist Don Lincoln, author of "Alien Universe."

NBCUniversal has established a multi-platform partnership with Virgin Galactic to track the development of SpaceShipTwo.