Designing for ESPA: The Challenges of Designing a Spacecraft for a Launch Accommodation Still in Development

The Evolved Expendable Launch Vehicle (EELV) Secondary Payload Adapter (ESPA) is a joint program developed by the DoD Space Test Program and the Space Vehicles Directorate of the Air Force Research Laboratory. It is designed to carry six small satellites as secondary payloads, weighing up to 400 pounds each, as well as a 15,000-pound primary payload into space on the next generation of expendable US launch vehicles. The purpose of this paper is to present the small spacecraft user community with its first insight into the unique challenges of launching on the Delta-IV/ESPA configuration, based on experiences from the Space Test Program Mission 1 (STPSat-1) mission. Specifically, this paper addresses the issues associated with designing a spacecraft while the launch vehicle system is still under development, and the launch conditions and environments have not been completely characterized. It also explores the design approaches used to accommodate a cantilevered launch configuration. The paper also discusses how the STPSat-1 spacecraft design has been optimized for this launch vehicle, including specific design elements that minimize support requirements from the launch vehicle, both during the pre-launch integration phase and during launch itself. Lessons learned and recommendations for future payloads are also included