WASHINGTON (Reuters) - Boeing ( BA ) and Lockheed Martin ( LMT ) are in talks to sell their rocket-launching joint venture United Launch Alliance to Sierra Space, two people familiar with the discussions said.

A deal to sell ULA, a major provider of launch services to the U.S. government and a top rival to Elon Musk's SpaceX, would mark a significant shift in the U.S. space launch industry as ULA separates from two of the largest defense contractors to a smaller, privately held firm.

The potential sale comes after years of speculation about ULA's future and failed attempts to divest the joint venture over the past decade. In 2019, Boeing ( BA ) and Lockheed Martin ( LMT ) reportedly explored selling ULA but couldn't agree on terms with potential buyers.

The negotiations could end without a deal, the sources said.

ULA referred Reuters to Boeing ( BA ) and Lockheed for comment. The two companies said they do not comment on market speculation. Sierra did not immediately return a request for comment.