WASHINGTON — A combination of scientific breakthroughs and technical accomplishments are making astronomers optimistic the European Space Agency will proceed with development of a space-based gravitational wave observatory.

A European consortium submitted to ESA in January a proposal for the development of the Laser Interferometer Space Antenna (LISA) mission for ESA’s third large mission, or L3, competition. LISA is widely considered the leading candidate to be selected for that mission for launch likely in the early 2030s.

LISA, as proposed, will consist of three spacecraft in a triangular formation, each 2.5 million kilometers from the other two in an orbit around the sun trailing the Earth. The spacecraft would shine lasers at each other, with interferometers on each spacecraft detecting minute distance changes caused by passing gravitational waves.

The three spacecraft, with a combined mass of about 6,000 kilograms, including payload adapter, would launch on an Ariane 6 and drift to their planned orbit over the course of a year and a half. LISA would have a planned mission lifetime of four years, but with sufficient propellant on each spacecraft to operate for up to a decade.

“LISA looks like it’s going to happen. It looks like it’s on a pretty firm track,” said David Shoemaker, a senior research scientist at the Massachusetts Institute of Technology’s Kavli Institute for Astrophysics and Space Research, during a meeting of the American Physical Society (APS) here Jan. 29.

Shoemaker is chairman of the L3 Study Team, a NASA group looking at contributions NASA can make to the LISA mission. The LISA proposal submitted to ESA assumes NASA will cover 20 percent of the mission’s cost through instruments and other technologies.

Parth of the confidence of Shoemaker and other scientists is linked to the announcement a year ago of the first detection of gravitational waves, by the Laser Interferometer Gravitational-Wave Observatory (LIGO), ground-based gravitational wave detectors in Louisiana and Washington. That discovery removed any doubt that gravitational waves exist, creating confidence that a mission like LISA could also successfully detect and study gravitational waves, and do so at frequencies not possible with LIGO.

Another factor is the technical success of ESA’s LISA Pathfinder mission, a single small spacecraft launched in December 2015 to test technologies that could be used in a later LISA mission. The performance of the spacecraft, including a thruster system provided by NASA, exceeded expectations.

Those tests not only exceeded the stability expectations of the LISA Pathfinder mission, but also approached the requirements for the full-fledged LISA mission. “This was a successful demonstration of drag-free control at a level necessary for a LISA-type gravitational wave observatory,” said Charles Dunn of JPL, project technologist for the disturbance reduction system flown on LISA Pathfinder, at the APS meeting Jan. 28.

Despite the failure of one the thrusters on LISA Pathfinder in October, the spacecraft will go through additional testing in an extended mission in mid-March for about a month. After that, the spacecraft will fire its thrusters to move out of the Earth-sun L-1 Lagrange point, ending its mission, project scientist Paul McNamara said.

With the LISA proposal submitted, scientists are working to refine the science case for the mission and, in the case of the L3 Study Team, identify the specific contributions NASA would make. Shoemaker said that involves making a case for LISA for inclusion in the next astrophysics decadal survey, to be published in late 2020.

“It looks like we can achieve a very good, solid science mission through this combined European-U.S. effort,” Shoemaker said.

He added that while ESA’s plans for the L3 mission project a launch in the early 2030s, scientists would like to be able to move that up by several years. “The objective of all of this activity is to enable the earliest possible launch date,” he said. “Studies have shown there’s a high likelihood that we could launch earlier if there were funds available, probably around 2029 at the very earliest.”