WASHINGTON — Rocket maker and NASA commercial spaceflight hopeful Space Exploration Technologies (SpaceX) has raised $50.19 million in new equity financing from 16 investors, according to a Nov. 9 filing with the U.S. Securities and Exchange Commission.

The investors were not named in the filing, and SpaceX spokeswoman Kirstin Brost would only identify them as existing shareholders. “Our existing investors are bullish on the future of SpaceX and asked if they could invest more,” Brost said via e-mail Nov. 10.

Elon Musk, SpaceX’s founder and chief executive, is the company’s largest shareholder. Other shareholders include fellow PayPal co-founder Luke Nosek, managing partner of the Founders Fund of San Francisco, and venture capitalist Steve Jurvetson of Menlo Park, Calif.-based Draper Fisher Jurvetson.

One of two U.S. companies under contract with NASA to deliver cargo to the international space station, SpaceX of Hawthorne, Calif., is on the hook to complete three increasingly sophisticated test flights of its new Falcon 9 rocket and Dragon spacecraft over the next several months. Pending successful completion of those demonstrations, SpaceX would begin routine supply runs to the orbiting outpost under a separate, fixed-price agreement.

SpaceX has received more than $360 million from NASA since it signed on to the agency’s Commercial Orbital Transportation Services (COTS) demonstration program in 2006. Of that amount, $248 million has come from COTS milestone payments and about $115 million has come from progress payments on the company’s $1.6 billion Commercial Resupply Services contract the company won in 2008.

In February NASA proposed boosting its COTS funding line by $300 million in 2011 in part to keep SpaceX and the agency’s other COTS partner, Dulles, Va.-based Orbital Sciences Corp., on track. The request was authorized in the 2010 NASA Authorization Act that U.S. President Barack Obama signed into law Oct. 11, but congressional appropriators have yet to enact spending legislation to fund it.

Although SpaceX’s first COTS demo was originally slated to occur in September 2008, the company’s COTS agreement was later modified to reflect a June 2009 date. Routine resupply runs to the space station were expected to begin as early as December of this year, but development of the medium-class rocket and cargo vessel has taken longer than planned.

SpaceX’s first COTS demonstration flight is now slated to occur no earlier than Dec. 7.