PARIS — Small launch vehicle developer Relativity Space announced Sept. 11 a contract with Momentus to carry a set of small satellites to geostationary orbit.

The launch agreement, announced during Euroconsult’s World Satellite Business Week here, covers one launch of Relativity’s Terran 1 rocket in 2021 with an option for up to five additional launches. The companies did not disclose the terms of the agreement, but Relativity offers the Terran 1 for a list price of $10 million.

The 2021 launch will fly Momentus’ Vigoride Extended tug, capable of carrying up to 350 kilograms of satellites. The tug will transport the satellites from an initial low Earth orbit to geostationary orbit using its water plasma thruster technology.

Tim Ellis, chief executive of Relativity, said Momentus helps Relativity address a wider range of potential customers. “It really opens up not just low Earth orbits and medium Earth orbits, which we can currently do with the baseline Terran 1,” he said during a panel discussion at the conference. “It lets us do things like phasing of satellites in LEO, geosynchronous launches and beyond Earth orbit.”

Momentus joins several other customers announced by Relativity in recent months, including Telesat, Thai startup mu Space and smallsat aggregator Spaceflight. Ellis said that development of Terran 1 was progressing well, with commercial launches set to begin in 2021 after one or more test launches planned for late 2020. Relativity plans to establish one launch site at Cape Canaveral’s Launch Complex 16, and Ellis said the company was in discussions for a launch site at Vandenberg Air Force Base in California.

Momentus is developing a range of tugs, starting with the Vigoride, which can accommodate payloads of up to 250 kilograms. Three Vigoride missions are planned for 2020, said Negar Feher, vice president of product and business development at Momentus, at the conference Sept. 11. Two of those will be on launches to sun-synchronous orbit and one will be deployed from the International Space Station.

The company has billed the tugs as a way for smallsats flown on rideshare missions to reach their desired orbits. Momentus announced Aug. 22 it will fly a Vigoride tug on a Falcon 9 as part of SpaceX’s new dedicated rideshare smallsat launch effort.

Momentus launched its first satellite, a 16-unit technology demonstration cubesat called El Camino Real, as a secondary payload on a Soyuz rocket in July. Feher said that engineers have recently completed post-launch commissioning of the satellite and started firing its water plasma thrusters. Those thruster tests will continue for the next six months, she said.