The Magnectorspheric MultiScale Mission (MMS) is a Solar-Terrestrial Probe mission consisting of four identically instrumented spacecraft. The goal is that the spacecraft will use the Earth’s magnetosphere as a laboratory to study the microphysics of three fundamental plasma processes: magnetic reconnection (Magnetic reconnection is the fundamental mechanism by which magnetic energy is dissipated.), energetic particle acceleration, and turbulence. The four MMS spacecraft are being developed at NASA’s Goddard Space Flight Center. The mission is set to launch August 14, 2014.
Mission Description
In the first phase of the mission, The MMS spacecraft will probe reconnection sites at the mid-latitude dayside magnetopause. Here the interplanetary magnetic field (IMF) merges with the geomagnetic field, transferring mass, momentum, and energy to the magnetosphere. The solar wind flow transports the merged IMF/geomagnetic field lines toward the nightside, causing a build up of magnetic flux in the magnetotail. In the second phase of the mission, the MMS constellation will investigate reconnection sites in the nightside magnetotail, where reconnection releases the magnetic energy stored in the tail in explosive events known as magnetospheric substorms and allows the magnetic flux stripped away from the dayside magnetopause by the solar wind/magnetosphere interaction to return to the dayside.
Spacecraft Formation
The sketches used in scientific papers and textbooks to illustrate the concept of reconnection are generally two-dimensional. Yet reconnection, like other natural phenomena, occurs in three dimensions, not two, and unraveling its physics requires simultaneous observations of the magnetic field and plasma at, ideally, a minimum of four locations. Thus, MMS is being implemented with four spacecraft, which will be launched together on a single launch vehicle and inserted sequentially into Earth orbit. As they explore the dayside and nightside reconnection regions, the spacecraft will fly in a tetrahedron formation, allowing them to capture the three-dimensional structure of the reconnection sites they encounter. Onboard propulsion will be used to adjust the separation among the spacecraft, from hundreds of kilometers to as close as 10 kilometers, to achieve the optimum interspacecraft separation for probing the diffusion region.
Orbital Structure
The four MMS spacecraft will be placed into a low-inclination (28 degree) elliptical orbit with a perigee (geocentric) of 1.2 Earth radii and a perigee during Phase 1 of 12 Earth radii. (1 Earth radius = 6371 km.) As the orbit evolves during Phase 1, the spacecraft will sample reconnection sites at different locations on the dayside magnetopause. During Phase 2, the tail reconnection campaign, perigee will remain at 1.2 Earth radii, but apogee will increased in stages to a final distance of 25 Earth radii. The science operations phase of the mission begins after instrument commissioning is complete and will last two years, with data analysis continuing for another year after the end of the prime mission.
Proposed Payload
The SMART payload comprises three instrument groups: Hot Plasma, Energetic Particles, and Fields. In addition, the payload includes two Active Spacecraft Potential Control Devices (ASPOC) and a Central Instrument Data Processor (CIDP).
Instrument description:
Hot Plasma
- Fast Plasma Instrument (FPI): The FPI consists of Dual Ion Sensors and Dual Electron Sensors and measures 3D ion and electron flux distributions over the energy range ~10 eV to 30 keV with an energy resolution of 20%. Electrons will be measured with a time resolution of 30 ms, ions with a time resolution 150 ms. FPI development is led by Co-I T. E. Moore (GSFC).
- Hot Plasma Composition Analyzer (HPCA): The HPCA employs a novel RF technique to measure minor ions such as oxygen and helium in regions of high flux. Energy range = ~10 eV to 30 keV; energy resolution = 20%; time resoluton = 15 s. HPCA development is led by Co-I D. T. Young (SwRI).
Energetic Particles
- Fly’s Eye Energetic Particle Sensor (FEEPS): The two FEEPS will measure 3D energetic ion and electron flux distributions over the energy ranges ~25 keV to 500 keV (electrons) and ~45 keV to 500 keV (ions). Time resolution = 10 s. FEEPS development is led by Co-I J. B. Blake (Aerospace Corporation).
- Energetic Ion Spectrometer (EIS): EIS uses a time-of-flight/pulse-height sensor to provide ion composition measurements (protons vs. oxygen ions) and angular distributions over the energy range ~45 keV to 500 keV and with a temporal resolution of 30 s. EIS development is led by Co-I B. H. Mauk (Applied Physics Laboratory), who also heads the Energetic Particle investigation as a whole.
FIELDS: The FIELDS investigation is an advanced suite of six sensors to measure critical electric and magnetic fields in and around reconnection regions. The investigation is led by Co-I R. B. Torbert (University of New Hampshire).
Analog Fluxgate (AFG) and Digital Fluxgate (DFG) Magnetometers: The AFG and DFG sensors are provided by UCLA and the Technical University of Braunschweig, respectively. C. T. Russell (UCLA) has overall responsibility for fluxgate development. The two different kinds of magnetometers will provide redundant measurements of the magnetic field and current structure in the diffusion region.
Electron Drift Instrument (EDI): The EDI determines the electric and magnetic fields by measuring the drift of ~1 keV electrons emitted from the Gun Detector Unit (GDU). Each GDU sends (receives) a coded beam to (from) the other EDI-GDU. The EDI gun is being developed at the Institut fuer Weltraumforschung of the Austrian Academy of Sciences; EDI optics are being developed at the University of Iowa.
Double Probes: MMS requires two sets of double-probe instruments. The Spin-plane Double Probe (SDP) consists of four 48-meter wire booms with spherical sensors at the end. The Axial Double Probe (ADP) consists of two 10-meter antennas deployed axially near the spacecraft spin axis. The SDP and ADP provide full 3D electric field measurements over a range from DC to 100 kHz with an accuracy of 0.5 mV/m (SDP) and 1 mV/m (ADP).
Search Coil Magnetometer (SCM): The SCM will measure the 3-axis AC magnetic field up to 6 kHz and will be used together with the ADP and SDP to determine the contribution of plasma waves to the turbulent dissipation that occurs in the diffusion region. The SCM is being developed in France at the Centre d’etude des Environnements Terrestre et Planetaires.
ASPOC: The ASPOOCs neutralize the electrical potential of the spacecraft, allowing measurement of low-energy ions and electrons by the plasma instruments and eliminating spurious electric fields that can contaminate double-probe measurements.The ASPOCs are being developed at the Institut fuer Weltraumforschung of the Austrian Academy of Sciences.
CIDP: The CIDP provides the interface between the instruments and the spacecraft C&DH subsystem. The CIDP is being developed at Southwest Research Institute.
Atlas V Rocket
MMS will launch August 14, 2014 using the Atlas V rocket. This trusty rocket is the latest member of the Atlas family and has been used to launch many payloads including: the Mars Reconnaissance Orbiter and New Horizons, among many others.
MMS Team
The MMS mission is a major scientific undertaking, involving a number of institutions in the United States as well as partners in Europe and Japan. The SMART Team is led by Southwest Research Institute, San Antonio, Texas, and consists of an Instrument Team and a Theory and Modeling Team. In addition, NASA has selected three Interdisciplinary Science (IDS) teams to participate in the mission as members of the MMS Science Working Group. The four spacecraft are being built, integrated, and tested at NASA’s Goddard Space Flight Center, Greenbelt, Maryland, which is also responsible for mission operations. Science operations planning and instrument command sequence development will be performed at the MMS Science Operations Center (SOC) located at the University of Colorado’s Laboratory for Atmospheric and Space Physics, Boulder, Colorado.= References and external links =