"What's next?"

Work is quietly underway in the South Bay on a massive 22-story rocket whose power is rivaled in the U.S. only by the mighty Saturn V rocket, which took man to the moon, in a risky private venture that could herald a new era in space flight.

Dubbed Falcon Heavy, the 27-engine booster is being assembled by rocket maker Space Exploration Technologies Corp., or SpaceX, at its sprawling complex in Hawthorne where it has about 1,100 workers.

The rocket, which has twice the lifting capability of the next largest launcher built by a U.S. company, is being announced Tuesday at the National Press Club in Washington.

"We're embarking on something that's unprecedented in the space industry," Elon Musk, the company's chief executive, told The Times. "This is territory that has only belonged to the U.S. government — with its tens of billions of dollars."

Musk's company is building the 227-foot-tall Falcon Heavy even though there are no guarantees that the military or NASA will step forward to pay for the rocket to lift its payloads — or even astronauts — into space someday.

SpaceX hopes to launch it in a demonstration flight from Vandenberg Air Force Base, northwest of Santa Barbara, at the end of next year.

The undertaking to be announced by Musk was hyped all last week on the Internet with a video laden with fiery blast-offs proclaiming "Something new is coming. 4.5.11." The 30-second clip highlighted SpaceX's recent launches, boasted that the work was done "at a fraction of the cost" and asked "What's next?"