WASHINGTON — Small launch vehicle developer Relativity announced May 6 it has signed an agreement with Spaceflight for a series of smallsat rideshare launches.

The launch services agreement between the two companies includes an order for one launch of Relativity’s Terran 1 rocket in the third quarter of 2021, with an option for an unspecified number of additional launches. Terms of the deal were not disclosed, although Relativity has publicized a list price of $10 million for the rocket.

Spaceflight will use those launches for dedicated rideshare missions, aggregating a set of small satellites to fly on the rocket. Spaceflight is best known for arranging secondary payload accommodations on launches of larger vehicles for small satellites, but performed a dedicated rideshare mission last December, launching 64 satellites on a single Falcon 9.

“We consistently look for innovative new technologies that provide flexible, reliable and low-cost access to space for our customers,” Curt Blake, chief executive and president of Spaceflight, said in a statement. Relativity’s Terran 1 rocket “delivers key advantages in launching rideshare payloads.”

In an interview last month, Blake said the Falcon 9 mission last year, known as SSO-A, was at the “upper limit” of what the company thought was feasible for a rideshare mission. The large number of customers created what he called “constant churn” as some customers dropped out of the mission while others sought to join.

“Getting a smaller number of payloads makes sense because you don’t have as much churn,” he said. “If you’re talking 15 customers, 20 customers, that’s a lot easier.”

The Terran 1 should provide that better fit. The vehicle can place up to 1,250 kilograms into low Earth orbit and 900 kilograms into a 500-kilometer sun-synchronous orbit.

“With Spaceflight’s leadership in rideshare launch solutions, state-of-the-art integration infrastructure, and experience, we are excited to work together to offer industry-defining lead time, flexibility, and cost for smallsats and cubesats and meaningfully expand the total launch capacity available through Spaceflight’s offering,” said Tim Ellis, chief executive of Relativity, in a statement.

The Spaceflight deal adds to a growing order book for Relativity. The company announced April 5 a contract with satellite operator Telesat for an unspecified number of launches of that company’s proposed broadband satellite constellation. Relativity followed that up April 23 with a deal with Thai startup mu Space for the launch of a low Earth orbit satellite.

Relativity is best known for making use of additive manufacturing, or 3D printing, technologies to build its rocket. That approach, the company believes, will allow it to produce rockets quickly while minimizing labor and other costs.

The first launch of the Terran 1 is scheduled for the “very end of 2020,” Ellis said in an interview last month. The company is working with the U.S. Air Force to develop launch facilities for the rocket at Cape Canaveral’s Launch Complex 16, while also looking for a second site that can support launches to sun-synchronous and other high-inclination orbits.