The first mission under the agreement will launch no sooner than November 2022 on a SpaceX Falcon 9.
The new version of the Antares, called the Antares 330, will feature the first stage using seven Miranda engines under development by Firefly.
This is a follow-up to the non-binding memorandum of understanding for cooperation between the two companies at the Mobile World Congress in March.
The company has raised its projected revenues for 2022 to at least $420m, keeping the upper end of the range unchanged at $440m.
NASA awarded a contract to SpaceX in February 2021 for the Falcon 9 launch for SPHEREx alone, valued at $98.8m.
Space for Humanity, a nonprofit group, has sponsored the seat of Sara Sabry, the first Egyptian to go to space.
News of the potential tie-up comes as SES has announced its first half results.
In order to bridge the digital divide, SkyEdge II-c will connect rural villages to government networks.
Hyundai and Kia will contribute to the mission with their robotic technologies and software and hardware design expertise.