ELECTROMAGNETIC COMPATIBILITY REQUIREMENTS FOR EQUIPMENT AND SUBSYSTEMS

1.0 INTRODUCTION
1.1 Background
Marshall Space Flight Center – Specification (MSFC-SPEC)-521 was initially published in 1978 to (1) interpret and integrate the various electromagnetic compatibility (EMC) requirements found in Shuttle, Spacelab, and payloads system documentation, and (2) document them for payload subsystems and equipment. The requirements of this specification, from its basic revision through revision B, were primarily derived from the Spacelab Payload (SLP) Accommodation Handbook, SLP-2104; the Orbiter/Spacelab Interface Control Document (ICD), 2-05301; Military Standard (MIL-STD)-461; National Space Transportation System (NSTS)-SL-E-0002; the Material Science Laboratory (MSL) User's Handbook, JA655; and the Space Shuttle Payload Accommodations Handbook, Volume XIV of NSTS 07700.
Although written specifically for Spacelab payloads, the specification became a de facto EMC standard for MSFC hardware where equipment and system level requirements did not exist or were unknown at the beginning of the development process.
Currently, MIL-STD-461, Requirements for the Control of Electromagnetic Interference Characteristics of Subsystems and Equipment; and MIL-STD-464, Electromagnetic Environmental Effects Requirements for Systems; are the engineering standards endorsed by the National Aeronautics and Space Administration (NASA) Office of Chief Engineer for electromagnetic interference (EMI) control and system-level EMC. MIL-STD-461 and MIL-STD-464 are applicable to all activities and agencies of the Department of Defense (DoD). Because of the broad applicability of these standards, the documents allow for tailoring of requirements commensurate with the intended installation and operation of the equipment and subsystems.
Because MIL-STD-461 and MIL-STD-464 are intended for all DoD activities, the scope of requirements exceeds those generally required for spaceflight programs and projects. Blind compliance with these standards frequently results in over-specification and excessive costs.
In accordance with NASA Procedural Requirements (NPR) 7120.10, Technical Standards for NASA Program and Projects; MSFC-SPEC-521D, presented herein, is a tailored version of MIL-STD-461, MIL-STD-464, and GP11461, Gateway Requirements for the Control of Electromagnetic Interference Characteristics of Subsystems and Equipment. The scope of the specification is intended to meet the needs of a substantial majority of MSFC Programs and Projects to prevent over-specification of requirements, yet still maintain EMC.
The NASA Office of Primary Responsibility (OPR) for this document is the Marshall Space Flight Center (MSFC) Engineering Directorate (ED), ES31, Electromagnetic Effects discipline lead organization.

1.2 Purpose
The basic EMC requirement for a system is that all included subsystems shall be able to operate compatibly during the mission. To accomplish this, requirements are imposed at two levels: one at the system level, the other at the equipment or subsystem level. While some system-level requirements are outlined here, the primary objective of this document is to define equipment-level requirements to which the equipment developer shall adhere.

1.3 Scope
This document defines the minimum EMC requirements to be imposed on any electrical and/or electronic equipment to be transported by launch vehicle or spacecraft carrier systems. This includes experiment equipment and flight support equipment subsystems that are payload elements of the launch vehicle, spacecraft, or free-flying satellite.
Since this specification is intended to provide, at low cost, reasonable confidence that equipment can operate compatibly within the operating environment, only the most important emission and susceptibility requirements have been chosen. Some requirements have been converted into more usable terms, and some have been modified to be more easily verified.
The intent of this specification is to address the EMC needs of 80 percent of equipment and subsystems developed for small MSFC projects. As such, for example, not all requirements of MIL-STD-461 are represented in Section 3 of this document. Other requirements, necessary to achieve EMC on previous NASA Programs and Projects, are contained in Section 3. Information is provided in the Appendices to aid the Program, Project manager, and Electromagnetic Environmental Effects (E3) engineer in developing these requirements. In addition, this document serves as an equipment level specification for the Commercial Low Earth Orbit Development Program (CLDP).
Recognizing that a discussion of EMC requirements at the hardware equipment level also brings into focus certain system-level requirements, some system-level aspects of an EMC program are referred to in this specification: for example, the design and arrangement of hardware equipment enclosure connectors must be in concert with the compatible development of the system’s interconnecting wiring and cabling; and proper attention must be paid to the development of an electrical bonding plan that will be compatible with the bonding provisions being designed into the hardware items that are within the scope of this document. These and other higher-level considerations may be examined in the system E3 Control Plan.