Virgin Galactic envisions future variants of its passenger-carrying suborbital space vehicle being propelled by derivatives of a liquid-fueled engine the company is developing for its small-satellite launcher, which is slated to debut in 2016, a company official said.

But Virgin Galactic is sticking with a hybrid-engine for its SpaceShipTwo suborbital tourism vehicle, now in testing and scheduled to begin commercial operations late this year.

Asked at the 2014 Space Tech Expo conference whether the engines being developed in house for the LauncherOne rocket would be used in future crewed spacecraft, William Pomerantz, Virgin Galactic’s vice president of special projects, replied, “That’s why we’re doing it. When we are eventually fulfilling all of [Virgin Galactic founder] Sir Richard Branson’s wild dreams about flying from London to Los Angeles in 45 minutes, we’re doing that off the LauncherOne propulsion architecture, not the SpaceShipTwo propulsion architecture.” 

That day, Pomerantz acknowledged, is a long way off.

Virgin Galactic is developing the restartable NewtonOne upper-stage engine and the larger NewtonTwo core-stage propulsion system for its LauncherOne system, which could carry 225 kilograms to a low-inclination, low Earth orbit, or 100 kilograms to a sun-synchronous orbit, Pomerantz said. Unlike SpaceShipTwo, which is built by Scaled Composites of Mojave, Calif., and uses hybrid rocket engines made by Sierra Nevada Space Systems of Louisville, Colo., LauncherOne is being developed almost entirely in house. 

“We’re the prime developer on the entire system: aircraft, spacecraft, avionics, propulsion systems, tanks,” Pomerantz said.

Developing LauncherOne is Virgin Galactic’s way of learning how to build progressively larger space systems, Pomerantz said. An early example, he added, will be a bigger orbital rocket.

“There will be one, someday,” Pomerantz said at the expo, held April 1-3 in Long Beach, Calif. 

In the meantime, Pomerantz said Virgin Galactic has signed up new customers, whom he declined to identify, for LauncherOne. He also said four LauncherOne customers Virgin signed in 2012 —Skybox Imaging, GeoOptics Inc., Spaceflight Inc. and Planetary Resources Inc. — are still planning to use the small rocket.