ESPA

Comtech AeroAstro's STPSat-1 is the first microsatellite built to specifically exploit the Evolved Expendable Launch Vehicle (EELV) Secondary Payload Adapter (ESPA) multi-mission launch capability. ESPA is a structural ring placed between a launch vehicle and primary payload which mechanically supports up to six small secondary spacecraft. This capability allows for significantly improved space access for secondary payloads.
Comtech AeroAstro has developed a family of vehicles including the Astro 200 and Astro 200AS that are designed to provide maximum performance in the highly constrained ESPA envelope. These vehicles support payload masses in the 60–100 kg range and can provide optional propulsive capability.