THIS IS A PROPOSAL FOR A COOPERATIVE AGREEMENT BETWEEN NASA GODDARD SPACE FLIGHT CENTER (GSFC) AND THE SMITHSONIAN ASTROPHYSICAL OBSERVATORY (SAO) OF CAMBRIDGE MASSACHUSETTS. THE AGREEMENT WILL CONTINUE AND EXPAND THE EXTREMELY PRODUCTIVE TEAMING RELATIONSHIP BEGUN WITH THE DEVELOPMENT OF THE CONSTELLATION X-RAY OBSERVATORY FOLLOWED BY THE INTERNATIONAL X-RAY OBSERVATORY AND THEN ATHENA OVER THE PAST TWENTY YEARS. THE PROPOSED AGREEMENT WHEN PUT IN PLACE WILL ENSURE THAT THE UNIQUE EXPERTISE AND INSIGHT OF THE SAO TEAM WILL BE MADE AVAILABLE TO NASA AS THE US PARTICIPATION IN ATHENA EVOLVES.