The EELV Secondary Payload Adapter (ESPA) is an adapter for launching secondary payloads on orbital launch vehicles. Originally developed for US launch vehicles in the 2000s to launch secondary payloads on space missions of the United States Department of Defense that used the Atlas V and Delta IV, the adapter design has become a de facto standard and is now also used for spaceflight missions on non-governmental private spacecraft missions as well. For example, multiple ESPA rings were used on a non-DoD launch of the SpaceX Falcon 9 that carried the Orbcomm OG-2 constellation of communication satellites. The use of ESPA ring technology reduces launch costs for the primary mission and enables secondary and even tertiary missions with minimal impact to the original mission. History Development was funded by the Air Force Research Laboratory Space Vehicles Directorate (AFRL/RV) for the United States Department of Defense (DoD) Space Test Program (STP) under a Small Business Innovative Research (SBIR) grant in the late 1990s. Moog CSA Engineering teamed with AFRL to design, build and qualify the ring in the early 2000s. Additional studies have been done on ESPA applications for lunar and science missions under an SBIR from NASA Ames Research Center. , the ring is produced by Moog CSA Engineering. A number of missions have used the ESPA ring. The ESPA ring's maiden mission was on STP-1 in 2007. , the ESPA ring had been used on all 3 EELV-class rockets (Atlas V, Delta IV and Falcon 9). Multiple ESPA rings may be used on a single launch, stacked to increase the satellite carrying capacity. Two ESPA Grande rings were used on Orbcomm OG-2 flight 1 in 2014 and three stacked Grande rings for the 11-satellite Orbcomm OG-2 flight 2 deployment in 2015. Technical characteristics The initial ESPA ring was designed to support a primary payload and up to six secondary payloads. Each secondary spacecraft is mounted radially on a diameter port and is allocated × × volume. This has led to the colloquial designation of ESPA-class payloads. The design includes a standard electrical interface for the attached payloads; however mission-specific requirements may preclude each secondary payload from receiving more than a single, non-redundant payload separation signal. ESPA Grande ports are in diameter, and can support payloads. Moog's version of the ESPA Grande supports up to payloads. Derivatives Derivatives of the ESPA ring include satellite dispensers, space tugs and satellite buses.