COLORADO SPRINGS — Orbital ATK says it is well positioned to win a U.S. Air Force competition early next year to support continued development of a new large launch vehicle to serve government and commercial users.

The company announced April 3 that it was making progress on what it calls the Next Generation Launch (NGL) program, on which the company and the Air Force have spent a combined $200 million to date through awards made as part of an effort to develop a replacement for United Launch Alliance’s workhorse Atlas 5 rocket.

In an interview during the 33rd Space Symposium here, Mike Laidley, vice president of the NGL program at Orbital ATK, said the next major milestone for the program is the release this summer of a request for proposals from the Air Force Space and Missile Systems Center (SMC) on the next phase of that effort, called the Launch Service Agreement (LSA).

The Air Force plans to make up to three LSA awards in early 2018 to complete prototype vehicle development, including certification test flights. “I think we’re pretty confident we’re going to make the LSA downselect,” Laidley said. “We have a high degree of confidence that we provide value to the Air Force.”

That confidence is based on the progress Orbital ATK has made to date on elements of the NGL system, including through a Rocket Propulsion System award the company won from SMC in January 2016.

Laidley said the combined investment in the NGL program to date is about $200 million, with the Air Force providing two thirds of the investment and Orbital ATK one third. The NGL vehicle uses a combination of solid- and liquid-propellant stages. The lower two stages are solid motors, based in part on solid rocket motors the company built for the space shuttle and NASA’s Space Launch System heavy-lift rocket.

The NGL motors are similar in size to the shuttle and SLS motors, Laidley said, but use a composite case and a different propellant formulation to meet the performance requirements of the EELV program. One version of the NGL would use a two-segment solid motor, called the Castor 600, as the first stage, while a heavier version would use a four-segment motor, the Castor 1200.

Both would use a single-segment Castor 300 motor as the rocket’s second stage, and have the option to use solid strap-on boosters. The rocket’s upper stage will be powered by liquid oxygen and liquid hydrogen. “We’re in the process now of evaluating a couple of different engine options,” Laidley said, with a decision “in the next month or so” on the engine the company will include in its proposal to the Air Force this summer. He declined to identify the specific engines under consideration.

“I think it’s pretty clear what engine options are out there in the liquid oxygen/hydrogen realm,” he said.

That would likely include Aerojet Rocketdyne’s RL10 and Blue Origin’s BE-3U, the only American engines using those propellants and designed for use on upper stages. Orbital ATK’s 2016 award included funding for developing an extendable nozzle for the BE-3U.

NGL launches from the East Coast would take place from Launch Complex 39B at NASA’s Kennedy Space Center, a former shuttle launch pad converted into a multi-user pad for the SLS and other vehicles.

Laidley said they will be able to use other facilities there, including the Vehicle Assembly Building and a mobile launch platform. The company is evaluating potential West Coast sites for launches into polar orbits.

Orbital ATK is assuming a mix of government and commercial customers for the NGL vehicles. “We’ve taken a really hard look at our business case for this vehicle, because it’s a significant amount of investment for Orbital ATK,” said Mark Pieczynski, vice president of business development and strategy. “We close our business case with three to four launches a year.”

That would include a mix of Air Force, NASA and commercial missions, he said. Company officials declined to say whether they would continue the NGL program if it does not win an Air Force award next year. “The company is heavily committed to this,” Laidley said. “But, obviously, government selection and having those missions as kind of our anchor tenant is kind of important to us.”