Relativity, a rocket startup with roots at Blue Origin and SpaceX, says it has been awarded an exclusive 20-year lease to use a 25-acre engine test complex at NASA’s Stennis Space Center in Mississippi.

The arrangement furthers Relativity’s plans to develop its 3-D-printed Aeon 1 rocket engine as the heart of its low-cost Terran rocket, with an eye toward starting commercial launches in 2021.

Relativity got its organizational start in Seattle two years ago, thanks in part to CEO Tim Ellis’ background as a propulsion engineer for billionaire Jeff Bezos’ Blue Origin space venture in Kent, Wash. Relativity’s chief technology officer, Jordan Noone, interned at Blue Origin and worked at SpaceX.

Since its founding, Relativity’s base of operations has shifted to Los Angeles, where it has a production facility that boasts the world’s largest metal 3-D printer.

The company has used Stennis as an engine testing ground for more than a year, but the lease for the space center’s E-4 Test Complex kicks the relationship up a notch. In addition to four 32-foot-tall engine test cells, the facility includes a shop area, control rooms and a nearly 13,000-square-foot high bay.

“Relativity pays maintenance and utilities out of pocket, but there are no direct lease or building fees,” Ellis said in an email. “There is a 225-acre expansion option surrounding the initial 25-acre E4 test site, resulting in a 250 acre total contiguous site area.”

Ellis estimated that it’d cost Relativity $30 million to build a comparable facility as an independent test site.

“Thus, the public-private partnership with NASA over this extended time frame represents a strong value addition by enabling Relativity to privately invest in proprietary automation and 3-D printing technologies instead of fundamental infrastructure,” he wrote.

Ellis said Relativity’s infrastructure footprint size will rise from 10,000 square feet of manufacturing and office space in January to more than 40,000 square feet, thanks to the Stennis deal as well as an expansion of its L.A. headquarters.

Relativity aims to bring down the cost of rocket production by automating 95 percent of the manufacturing process.

The two-stage Terran rocket is designed to send up to 2,750 pounds (1,250 kilograms) of payload into low Earth orbit at a cost of $10 million per launch. Relativity’s development plan calls for the first test launch to take place in late 2020, with commercial service beginning in 2021.

The company says it’s nearing 100 test firings of its Aeon 1 rocket engine, and is holding hundreds of millions of dollars’ worth of tentative launch commitments in the form of memorandums of understanding and letters of intent.

In addition to his CEO role, Ellis serves as a member of the National Space Council’s Users Advisory Group.