The Magnetospheric Multiscale (MMS) mission is the fourth mission of the Solar Terrestrial Probes (STP) program. The MMS mission, consisting of four identically instrumented spacecraft, will use Earth’s magnetosphere as a laboratory to study magnetic reconnection, a fundamental plasma-physical process that taps the energy stored in a magnetic field and converts it — typically explosively — into heat and kinetic energy in the form of charged particle acceleration and largescale flows of matter.
The Command and Data Handling (C&DH) subsystem on the MMS mission is one of several key components of the MMS spacecraft. It provides the computing power necessary to execute stored or uplinked commands, and distribute the commands to the Instrument Suite (IS) and other spacecraft components. The C&DH collects spacecraft telemetry from the IS and other spacecraft components, and sends the data to the ground via the Radio Frequency (RF) Communication subsystem. The C&DH only provides encoding to the science data prior to sending it to the ground. It is also responsible for spacecraft time management and distribution and hosts the flight software. SpaceWire (SpW) is used as the primary spacecraft bus, providing communication paths for commands and telemetry, including science data. SpW is also used as the main interface between the various components of the C&DH.
The C&DH interfaces to the IS through the Central Instrument Data Processor (CIDP) as well as other hardware components such as the S-band Transponder, the Accelerometer, the Digital Sun Sensor (DSS), and the Star Sensor. The C&DH subsystem consists of one box with two of each card [Backplane, Low Voltage, and Power Services (LVPS) Card; Communication Card; Processor Card; and Analog Card]. One side is designated as Side A, or the primary side, and the other as Side B, or the redundant side. Only one side (primary side) is active (fully powered on) at a given time. However, the other side (redundant side) has a warm front end where the interface to the RF Communication subsystem (Com muni - cation Card) is on for command decoding and is also capable of downlinking data. The computing part of the redundant side is powered off.
This work was done by David Raphael, Robert Stone, Damaris Guevara, and James Fraction of Goddard Space Flight Center. GSC-17223-1