A payload-centric integration and test approach on the Wide-field Infrared Survey Explorer Mission

NASA's Wide-field Infrared Survey Explorer (WISE) mission was successfully launched on December 14, 2009. All spacecraft subsystems and the single instrument consisting of four imaging bands from 3.4 to 22 microns, a 40 cm afocal telescope, reimaging optics, and a two-stage solid hydrogen cryostat have performed nominally on orbit, enabling the trouble-free survey of the entire infrared sky. Among the many factors that contributed to the WISE post-launch success is the thorough pre-launch system integration and test (I&T) approach tailored to the cryogenic payload. The simple and straightforward interfaces between the spacecraft and the payload allowed the payload to be fully tested prior to integration with the spacecraft. A payload high-fidelity thermal, mass and dynamic simulator allowed the spacecraft I&T to proceed independently through the system-level thermal vacuum test and random vibration test. A payload electrical simulator, a high-rate data processor and a science data ingest processor enabled very early end-to-end data flow and radio-frequency testing using engineering model payload electronics and spacecraft avionics, which allowed engineers to identify and fix developmental issues prior to building flight electronics. This paper describes in detail the WISE I&T approach, its benefits, challenges encountered and lessons learned.