ESPA from Concept to Flight Hardware

Abstract : In August of 2003, flight hardware for the EELV Secondary Payload Adapter "ESPA" will be delivered to Cape Canaveral. The ESPA Ring and five spacecraft will launch on an Air Force Delta IV mission scheduled for March 2006. This flight, STP-1, will be the maiden voyage for a payload adapter that was conceived by the Air Force in 1995 to provide a secondary payload capability for Evolved Expendable Launch Vehicles "EELVs". ESPA was designed and flight qualified during the period of 1999 to 2002, for use with both Atlas V and Delta IV launch vehicles. The ESPA Ring provides an American counterpart to the Ariane adapter that has been exploited for European launches since 1990. It is now feasible for up to six secondary spacecraft to be placed in orbit whenever a Delta IV Medium or Atlas V "400 or 500 series" launch is configured with excess payload capacity. Since the majority of EELV launches in the foreseeable future have significant excess capacity, the small satellite community has a significant new option for access to space. This paper tells the story of ESPA from conception to the first flight unit. Early discussions on EELV secondary payloads led to formation of a development team by the Air Force Space Test Program "STP". The Air Force Research Laboratory "AFRL" directed the team for STP with contractor support and guidance from Boeing and Lockheed Martin. A design mandate adopted from the beginning demanded no added risk for the primary payload. An early composite/aluminum design was abandoned in favor of a single-piece aluminum structure. Qualification testing at Kirtland Air Force Base added a new capability for STP and the AFRL. "No added risk to the primary" led to including environment mitigation technology such as lowshock separation systems and whole-spacecraft vibration and shock isolation.