Stratolaunch, the Seattle-based space venture created by Microsoft co-founder Paul Allen seven years ago, says it’s discontinuing its programs to develop a new type of rocket engine and a new line of rockets.

The company said it would continue work on the world’s largest airplane, which is designed to serve as a flying launch pad for rockets. Last week, Stratolaunch put its 385-foot-wide, twin-fuselage plane through a high-speed taxi test that many saw as a precursor for its first test flight at Mojave Air and Space Port.

“Stratolaunch is ending the development of their family of launch vehicles and rocket engine. We are streamlining operations, focusing on the aircraft and our ability to support a demonstration launch of the Northrop Grumman Pegasus XL air-launch vehicle,” the company said in an emailed statement. “We are immensely proud of what we have accomplished and look forward to first flight in 2019.”

The dramatic turn of events comes three months after Allen’s death.

Employees were told today that more than 50 people were being laid off as a result of the streamlining strategy, according to two sources who aren’t employed by Stratolaunch but are familiar with the operation. The sources, speaking on condition of anonymity, told GeekWire that about 20 employees were staying on to work on the plane and prepare for the flight test.

Stratolaunch’s statement didn’t provide specifics on the layoffs, and efforts to get further details were not immediately successful.

The company’s development plan has called for getting its giant plane certified to carry rockets by as early as 2020, with the capacity to launch up to three of Northrop Grumman’s Pegasus XL launch vehicles from an altitude in the neighborhood of 35,000 feet.

Air-launch capability has the advantage of allowing payloads to be sent into orbit on a variety of trajectories, from any base of operation that’s big enough to accommodate the plane. Such flexibility may be attractive to certain types of commercial, governmental and military customers.

It’s not clear how the streamlining effort announced today will affect the company’s timeline or its long-term business plan.

Stratolaunch had been working on a hydrogen-fueled rocket engine that was named the “PGA,” in honor of Paul G. Allen. It also laid out a plan for building a variety of launch vehicles, including a space plane, with the first in-house rocket targeted for launch in 2022. Those parts of the Stratolaunch program have now been canceled.

Paul Allen passed away in October at the age of 65, after a struggle with non-Hodgkin’s lymphoma. Control of Stratolaunch as well as Allen’s many other ventures passed to his sister, Jody Allen, as executor of his estate.

Jody Allen has not said much about Stratolaunch or her late brother’s space aspirations. However, the cost of pursuing a private space effort would give anyone pause, even billionaires and their heirs. Amazon billionaire Jeff Bezos, for example, has said he is spending $1 billion or more annually on his Blue Origin space venture. Last month, British billionaire Richard Branson said he’s “personally invested about a billion dollars” in Virgin Galactic and Virgin Orbit.

In the absence of any more definitive information, the likeliest motivation for cutting back on Stratolaunch’s agenda would be to reduce the program’s costs and risks, thus freeing up resources for other priorities.