ECSS-E-70 PART 2A, SPACE ENGINEERING-GROUND SYSTEMS AND OPERATIONS -PART 2: DOCUMENT REQUIREMENTS DEFINITIONS (DRDS) (2 APR 2001)., Part 2 of ECSS-E-70 “Space engineering - Ground systems and operations” defines the content of the document requirements definitions (DRDs) which are called up by other ECSS Standards and specifically referenced in ECSS--E--70 Part 1: “Principles and requirements”.