The Magnetospheric Multiscale (MMS) Mission is a

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...

robotic space mission to study the Earth's magnetosphere, using four identical spacecraft flying in a

tetrahedral In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all the ...

formation. The spacecraft were launched on 13 March 2015 at 02:44 UTC. The mission is designed to gather information about the microphysics of

magnetic reconnection Magnetic reconnection is a physical process occurring in highly conducting plasmas in which the magnetic topology is rearranged and magnetic energy is converted to kinetic energy, thermal energy, and particle acceleration. Magnetic reconnecti ...

, energetic particle acceleration, and

turbulence In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between ...

⁠ — processes that occur in many astrophysical plasmas. As of March 2020, the MMS spacecraft have enough fuel to remain operational until 2040.

Background

The mission builds upon the successes of the ESA Cluster mission, but will surpass it in spatial resolution and in temporal resolution, allowing for the first time measurements of the critical electron diffusion region, the site where magnetic reconnection occurs. Its orbit is optimized to spend extended periods in locations where reconnection is known to occur: at the dayside magnetopause, the place where the pressure from the

solar wind The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sol ...

and the planets' magnetic field are equal; and in the magnetotail, which is formed by pressure from the solar wind on a planet's magnetosphere and which can extend great distances away from its originating planet. Magnetic reconnection in Earth's magnetosphere is one of the mechanisms responsible for the

aurora An aurora (plural: auroras or aurorae), also commonly known as the polar lights, is a natural light display in Earth's sky, predominantly seen in high-latitude regions (around the Arctic and Antarctic). Auroras display dynamic patterns of bri ...

, and it is important to the science of controlled

nuclear fusion Nuclear fusion is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles ( neutrons or protons). The difference in mass between the reactants and products is manife ...

because it is one mechanism preventing magnetic confinement of the fusion fuel. These mechanisms are studied in outer space by the measurement of motions of matter in stellar atmospheres, like that of the Sun. Magnetic reconnection is a phenomenon in which energy may be efficiently transferred from a magnetic field to the motion of charged particles.

Spacecraft

The MMS mission consists of four spacecraft. Each has a launch mass of . In their stowed launch configuration, each are approximately , and when stacked together they have a total height of . After being deployed in orbit, a total of eight axial and wire booms are deployed, including four Spin-Plane Double Probe (SDP) wire booms each long. The MMS spacecraft are spin stabilized, turning at a rate of three revolutions per minute to maintain orientation. Each spacecraft contains 12 thrusters connected to four hydrazine fuel tanks. Position data is provided by highly sensitive GPS equipment, while attitude is maintained by four

star tracker A star tracker is an optical device that measures the positions of stars using photocells or a camera. As the positions of many stars have been measured by astronomers to a high degree of accuracy, a star tracker on a satellite or spacecraft may ...

s, two

accelerometer An accelerometer is a tool that measures proper acceleration. Proper acceleration is the acceleration (the rate of change of velocity) of a body in its own instantaneous rest frame; this is different from coordinate acceleration, which is acce ...

s, and two

sun sensor A sun sensor is a navigational instrument used by spacecraft to detect the position of the sun. Sun sensors are used for attitude control, solar array pointing, gyro updating, and fail-safe recovery. In addition to spacecraft, sun sensors fin ...

s. The mission is broken into three phases. The commissioning phase will last approximately five and a half months after launch, while the science phases will last two years. The first science phase will focus on the magnetic boundary between the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's sur ...

and

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

(day side operations) for one and a half years, with the spacecraft formation orbiting the Earth at . The second science phase will study reconnection in Earth's magnetic tail (night side operations) for half a year, increasing the orbit to .

Instruments

Each spacecraft carries several experiments, divided into three suites: the Hot Plasma Suite, the Energetic Particles Detector Suite, and the Fields Suite.

Hot Plasma Suite

The Hot Plasma Suite measures plasma particle counts, directions, and energies during reconnection. It consists of two instruments: * Fast Plasma Investigation (FPI), a set of four dual electron

spectrometer A spectrometer () is a scientific instrument used to separate and measure spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomenon where the ...

s and four dual ion spectrometers. * Hot Plasma Composition Analyzer (HPCA), detects particle speed in order to determine its mass and type.

Energetic Particles Detector

The Energetic Particles Detector Suite detects particles at energies far exceeding those detected by the Hot Plasma Suite. It consists of two instruments: * Fly's Eye Energetic Particle Sensor (FEEPS), a set of silicon solid state detectors to measure electron energy. Between two FEEPS per spacecraft, the individual detectors are arranged to provide 18 different view angles simultaneously; hence the term "fly's eye". * Energetic Ion Spectrometer (EIS), measures energy and total velocity of detected ions in order to determine their mass. The EIS can detect helium and oxygen ions at energies higher than that of the HPCA.

Fields Suite

The Fields Suite measures magnetic and electric field characteristics. It consists of six instruments: * Analog Fluxgate

magnetometer A magnetometer is a device that measures magnetic field or magnetic dipole moment. Different types of magnetometers measure the direction, strength, or relative change of a magnetic field at a particular location. A compass is one such device, ...

(AFG), determines the strength of magnetic fields. * Digital Fluxgate magnetometer (DFG), determines the strength of magnetic fields. * Electron Drift Instrument (EDI), measures electric and magnetic field strength by sending a beam of electrons into space and measuring how long it takes the electrons to circle back in the presence of these fields. * Spin-plane Double Probe (SDP), consists of

electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials ...

s on the end of four wire booms that extend from the spacecraft to measure electric fields. * Axial Double Probe (ADP), a set of electrodes on two antennas mounted axially on the spacecraft. * Search Coil Magnetometer (SCM), an induction magnetometer used to measure magnetic fields.

Personnel and development

The

principal investigator In many countries, the term principal investigator (PI) refers to the holder of an independent grant and the lead researcher for the grant project, usually in the sciences, such as a laboratory study or a clinical trial. The phrase is also often u ...

is James L. Burch of

Southwest Research Institute Southwest Research Institute (SwRI), headquartered in San Antonio, Texas, is an independent and nonprofit applied research and development (R&D) organization. Founded in 1947 by oil businessman Tom Slick, it provides contract research and devel ...

, assisted by an international team of investigators, both instrument leads and theory and modeling experts. The project scientist is Thomas E. Moore of

Goddard Space Flight Center The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory located approximately northeast of Washington, D.C. in Greenbelt, Maryland, United States. Established on May 1, 1959 as NASA's first space flight center, GSFC empl ...

. Education and public outreach is a key aspect of the mission, with student activities, data sonification, and planetarium shows being developed. The mission was selected for support by NASA in 2005. System engineering, spacecraft bus design, integration and testing has been performed by

Maryland Maryland ( ) is a state in the Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware and the Atlantic Ocean t ...

. Instrumentation is being improved, with extensive experience brought in from other projects, such as the

IMAGE An image is a visual representation of something. It can be two-dimensional, three-dimensional, or somehow otherwise feed into the visual system to convey information. An image can be an artifact, such as a photograph or other two-dimensio ...

Cluster may refer to: Science and technology Astronomy * Cluster (spacecraft), constellation of four European Space Agency spacecraft * Asteroid cluster, a small asteroid family * Cluster II (spacecraft), a European Space Agency mission to study th ...

and Cassini missions. In June 2009, MMS was allowed to proceed to Phase C, having passed a Preliminary Design Review. The mission passed its

Critical Design Review In the United States military integrated acquisition lifecycle the Technical section has multiple acquisition "Technical Reviews". Technical reviews and audits assist the acquisition and the number and types are tailored to the acquisition. Over ...

in September 2010. The spacecraft launched on an

Atlas V Atlas V is an expendable launch system and the fifth major version in the Atlas launch vehicle family. It was originally designed by Lockheed Martin, now being operated by United Launch Alliance (ULA), a joint venture between Lockheed Mart ...

421 launch vehicle, in March 2015.

Formation flying

In order to collect the desired science data, the four satellite MMS constellation must maintain a tetrahedral formation through a defined region of interest in a highly elliptical orbit. The formation is maintained through the use of a high altitude rated GPS receiver, ''Navigator'', to provide orbit knowledge, and regular formation maintenance maneuvers. Through ''Navigator'', the MMS mission broke the

Guinness World Record ''Guinness World Records'', known from its inception in 1955 until 1999 as ''The Guinness Book of Records'' and in previous United States editions as ''The Guinness Book of World Records'', is a reference book published annually, listing world ...

twice for highest altitude fix of a GPS signal (at and above the surface in 2016 and 2019 respectively).

Discoveries

In 2016, the MMS mission was the first to directly detect

, the phenomenon which drives

space weather Space weather is a branch of space physics and aeronomy, or heliophysics, concerned with the time varying conditions within the Solar System, including the solar wind, emphasizing the space surrounding the Earth, including conditions in the ...

in the Earth's magnetosphere. MMS has since detected magnetic reconnection occurring in unexpected places. In 2018, MMS made the first-ever detection of magnetic reconnection in the magnetosheath, a region of space previously thought to be too chaotic and unstable to sustain reconnection. Magnetic flux ropes and Kelvin–Helmholtz vortices are other phenomena where MMS has detected reconnection events against expectations. In August 2019, astronomers reported that MMS made the first high-resolution measurements of an interplanetary shock wave from the Sun.

References

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