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THEMIS (satellite)
Encyclopedia
The Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission was originally a constellation of five NASA
satellite
s to study energy releases from Earth
's magnetosphere
known as substorm
s, magnetic phenomena that intensify aurora
s near Earth's poles. The name of the mission is an acronym for Time History of Events and Macroscale Interactions during Substorms, alluding to the Titan
, Themis
.
Now three of the original satellites remain in the magnetosphere, while two have been moved into orbit near the moon. Those two have been renamed ARTEMIS
for Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun, but are also referred to as ARTEMIS P1 (THEMIS B) and ARTEMIS P2 (THEMIS C).
The THEMIS satellites were launched February 17, 2007 from Cape Canaveral Air Force Station Space Launch Complex 17 aboard a Delta II
rocket
. Each satellite carries identical instrumentation, including a fluxgate magnetometer (FGM), an electrostatic analyzer (ESA), a solid state telescope (SST), a search-coil magnetometer (SCM) and an electric field instrument (EFI). Each has a mass of 126 kg, including 49 kg of fuel.
THEMIS was originally scheduled to launch on October 19, 2006. Owing to delays caused by workmanship problems with Delta II second stages—an issue that also affected the previous mission, STEREO
—the THEMIS launch was delayed to Thursday, February 15, 2007. Due to weather conditions occurring on Tuesday, February 13, fueling of the second stage was delayed, and the launch pushed back 24 hours. On February 16, the launch was scrubbed in a hold at the T-4 minute point in the countdown due to the final weather balloon reporting a red, or nogo condition for upper level winds. A 24-hour turnaround procedure was initiated, targeting a new launch window between 23:01 and 23:17 UTC
on February 17.
Favorable weather conditions were observed on February 17, and the countdown proceeded smoothly. THEMIS successfully launched at 6:01 p.m. EST. The spacecraft separated from the launch vehicle approximately 73 minutes after liftoff. By 8:07 p.m. EST, mission operators at the Space Sciences Laboratory
(SSL) of the University of California, Berkeley, commanded and received signals from all five spacecraft, confirming nominal separation status.
The launch service was provided by the United Launch Alliance
through NASA Launch Services Program (LSP).
. On December 4, 2007 the first tail science phase of the mission began. In this segment of the mission scientists will collect data from the magnetotail of the Earth's magnetosphere
. During this phase the satellites' orbits are in apogee inside the magnetotail. The scientists hope to observe substorms and magnetic reconnection events. During these events charged particles stored in the Earth's magnetosphere
are discharged to form the aurora borealis. Tail science is performed in the winter of the northern hemisphere
because the ground magnetometers that Themis scientists correlate the satellite data with have relatively longer periods of night. During the night, observations are not interrupted by charged particles from the Sun.
In 2007, THEMIS "found evidence of magnetic ropes connecting Earth's upper atmosphere directly to the sun," reconfirming the theory of solar-terrestrial electrical interaction (via "Birkeland current
s" or "field-aligned currents") proposed by Kristian Birkeland
circa 1908. NASA also likened the interaction to a "30 kiloVolt battery in space," noting the "flux rope pumps 650,000 Amp current into the Arctic!"
On 26 February 2008, THEMIS probes were able to determine, for the first time, the triggering event for the onset of magnetospheric substorms. Two of the five probes, positioned approximately one third the distance to the Moon, measured events suggesting a magnetic reconnection
event 96 seconds prior to Auroral intensification. Dr. Vassilis Angelopoulos
of the University of California, Los Angeles, who is the principal investigator for the THEMIS mission, claimed, "Our data show clearly and for the first time that magnetic reconnection is the trigger."
(SSL) at Berkeley
announced NASA had extended the THEMIS mission to the year 2012. NASA has officially approved the movement of THEMIS B and THEMIS C into Lunar orbit
under the mission name ARTEMIS
(Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun).
On June 22, 2011, ARTEMIS P1 began firing its thrusters to move out of its kidney-shaped "libration" orbit on one side of the moon, where it had been since January. As of July 2, 12:30 p.m. EDT, ARTEMIS P1 has achieved lunar orbit. The second spacecraft, ARTEMIS P2, moved into lunar orbit as of July 17, 2011. Along the way, the two spacecraft were the first to ever achieve orbit around the moon's Lagrangian points.
simultaneously monitor aurora
s. Ground station mission and science operations are being managed by the University of California Space Sciences Laboratory
.
) manufactured all five probes for this mission. Each was built-up and tested at the Beltsville facility, before being delivered to the University of California, Berkeley
for instrument integration. Swales was responsible for integrating the BAU, IRU, Solar Arrays, Antenna, Battery, and other components necessary for functionality. This was the second major satellite built by Swales, the first being the EO-1 spacecraft, which continues to orbit the Earth. Swales was also responsible for designing and building the Electrical Ground Support Equipment (EGSE) used for monitoring the probes during all phases of pre-launch activities, including use at the launch site.
(FAST) mission supported THEMIS in 2008 and 2009 before being retired. FAST was a Small Explorer program
(SMEX) mission launched in 1996.
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
s to study energy releases from Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
's magnetosphere
Magnetosphere
A magnetosphere is formed when a stream of charged particles, such as the solar wind, interacts with and is deflected by the intrinsic magnetic field of a planet or similar body. Earth is surrounded by a magnetosphere, as are the other planets with intrinsic magnetic fields: Mercury, Jupiter,...
known as substorm
Substorm
A substorm, sometimes referred to as a magnetospheric substorm or an auroral substorm, is a brief disturbance in the Earth's magnetosphere that causes energy to be released from the "tail" of the magnetosphere and injected into the high latitude ionosphere. Visually, a substorm is seen as a sudden...
s, magnetic phenomena that intensify aurora
Aurora (astronomy)
An aurora is a natural light display in the sky particularly in the high latitude regions, caused by the collision of energetic charged particles with atoms in the high altitude atmosphere...
s near Earth's poles. The name of the mission is an acronym for Time History of Events and Macroscale Interactions during Substorms, alluding to the Titan
Titan (mythology)
In Greek mythology, the Titans were a race of powerful deities, descendants of Gaia and Uranus, that ruled during the legendary Golden Age....
, Themis
Themis
Themis is an ancient Greek Titaness. She is described as "of good counsel", and is the embodiment of divine order, law, and custom. Themis means "divine law" rather than human ordinance, literally "that which is put in place", from the verb τίθημι, títhēmi, "to put"...
.
Now three of the original satellites remain in the magnetosphere, while two have been moved into orbit near the moon. Those two have been renamed ARTEMIS
Artemis
Artemis was one of the most widely venerated of the Ancient Greek deities. Her Roman equivalent is Diana. Some scholars believe that the name and indeed the goddess herself was originally pre-Greek. Homer refers to her as Artemis Agrotera, Potnia Theron: "Artemis of the wildland, Mistress of Animals"...
for Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun, but are also referred to as ARTEMIS P1 (THEMIS B) and ARTEMIS P2 (THEMIS C).
The THEMIS satellites were launched February 17, 2007 from Cape Canaveral Air Force Station Space Launch Complex 17 aboard a Delta II
Delta II
Delta II was an American space launch system, originally designed and built by McDonnell Douglas. Delta II is part of the Delta rocket family and was in service from 1989 until November 1, 2011...
rocket
Rocket
A rocket is a missile, spacecraft, aircraft or other vehicle which obtains thrust from a rocket engine. In all rockets, the exhaust is formed entirely from propellants carried within the rocket before use. Rocket engines work by action and reaction...
. Each satellite carries identical instrumentation, including a fluxgate magnetometer (FGM), an electrostatic analyzer (ESA), a solid state telescope (SST), a search-coil magnetometer (SCM) and an electric field instrument (EFI). Each has a mass of 126 kg, including 49 kg of fuel.
Launch
STEREO
STEREO is a solar observation mission. Two nearly identical spacecraft were launched into orbits that cause them to respectively pull farther ahead of and fall gradually behind the Earth...
—the THEMIS launch was delayed to Thursday, February 15, 2007. Due to weather conditions occurring on Tuesday, February 13, fueling of the second stage was delayed, and the launch pushed back 24 hours. On February 16, the launch was scrubbed in a hold at the T-4 minute point in the countdown due to the final weather balloon reporting a red, or nogo condition for upper level winds. A 24-hour turnaround procedure was initiated, targeting a new launch window between 23:01 and 23:17 UTC
Coordinated Universal Time
Coordinated Universal Time is the primary time standard by which the world regulates clocks and time. It is one of several closely related successors to Greenwich Mean Time. Computer servers, online services and other entities that rely on having a universally accepted time use UTC for that purpose...
on February 17.
Favorable weather conditions were observed on February 17, and the countdown proceeded smoothly. THEMIS successfully launched at 6:01 p.m. EST. The spacecraft separated from the launch vehicle approximately 73 minutes after liftoff. By 8:07 p.m. EST, mission operators at the Space Sciences Laboratory
Space Sciences Laboratory
The Space Sciences Laboratory is an Organized Research Unit of the University of California, Berkeley. It is located in the Berkeley Hills above the university campus...
(SSL) of the University of California, Berkeley, commanded and received signals from all five spacecraft, confirming nominal separation status.
The launch service was provided by the United Launch Alliance
United Launch Alliance
United Launch Alliance is a joint venture of Lockheed Martin and Boeing. ULA was formed in December 2006 by combining the teams at these companies which provide spacecraft launch services to the government of the United States. U.S...
through NASA Launch Services Program (LSP).
Mission status
From February 15, 2007 until September 15, 2007 the five Themis satellites coasted in a string of pearls orbital configuration. From September 15, 2007 until December 4, 2007 the satellites were moved to more distant orbits in preparation for data collection in the magnetotail. This phase of the mission was called the "Dawn Phase" because the satellites' orbits were in apogee on the dawn side of the magnetosphereMagnetosphere
A magnetosphere is formed when a stream of charged particles, such as the solar wind, interacts with and is deflected by the intrinsic magnetic field of a planet or similar body. Earth is surrounded by a magnetosphere, as are the other planets with intrinsic magnetic fields: Mercury, Jupiter,...
. On December 4, 2007 the first tail science phase of the mission began. In this segment of the mission scientists will collect data from the magnetotail of the Earth's magnetosphere
Magnetosphere
A magnetosphere is formed when a stream of charged particles, such as the solar wind, interacts with and is deflected by the intrinsic magnetic field of a planet or similar body. Earth is surrounded by a magnetosphere, as are the other planets with intrinsic magnetic fields: Mercury, Jupiter,...
. During this phase the satellites' orbits are in apogee inside the magnetotail. The scientists hope to observe substorms and magnetic reconnection events. During these events charged particles stored in the Earth's magnetosphere
Magnetosphere
A magnetosphere is formed when a stream of charged particles, such as the solar wind, interacts with and is deflected by the intrinsic magnetic field of a planet or similar body. Earth is surrounded by a magnetosphere, as are the other planets with intrinsic magnetic fields: Mercury, Jupiter,...
are discharged to form the aurora borealis. Tail science is performed in the winter of the northern hemisphere
Northern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...
because the ground magnetometers that Themis scientists correlate the satellite data with have relatively longer periods of night. During the night, observations are not interrupted by charged particles from the Sun.
In 2007, THEMIS "found evidence of magnetic ropes connecting Earth's upper atmosphere directly to the sun," reconfirming the theory of solar-terrestrial electrical interaction (via "Birkeland current
Birkeland current
A Birkeland current is a set of currents which flow along geomagnetic field line connecting the Earth’s magnetosphere to the Earth's high latitude ionosphere. They are a specific class of magnetic field-aligned currents. Lately, the term Birkeland currents has been expanded by some authors to...
s" or "field-aligned currents") proposed by Kristian Birkeland
Kristian Birkeland
Kristian Olaf Birkeland was a Norwegian scientist. He is best remembered as the person who first elucidated the nature of the Aurora borealis. In order to fund his research on the aurorae, he invented the electromagnetic cannon and the Birkeland-Eyde process of fixing nitrogen from the air...
circa 1908. NASA also likened the interaction to a "30 kiloVolt battery in space," noting the "flux rope pumps 650,000 Amp current into the Arctic!"
On 26 February 2008, THEMIS probes were able to determine, for the first time, the triggering event for the onset of magnetospheric substorms. Two of the five probes, positioned approximately one third the distance to the Moon, measured events suggesting a magnetic reconnection
Magnetic reconnection
Magnetic reconnection is a physical process in highly conducting plasmas in which the magnetic topology is rearranged and magnetic energy is converted to kinetic energy, thermal energy, and particle acceleration...
event 96 seconds prior to Auroral intensification. Dr. Vassilis Angelopoulos
Vassilis Angelopoulos
Vassilis Angelopoulos is a Greek American physicist. He is a specialist on Space and Astrophysical Plasmas. He is THEMIS principal investigator at the University of California, Berkeley's Space Sciences Laboratory, in Berkeley, California...
of the University of California, Los Angeles, who is the principal investigator for the THEMIS mission, claimed, "Our data show clearly and for the first time that magnetic reconnection is the trigger."
Extended mission
On May 19, 2008 the Space Sciences LaboratorySpace Sciences Laboratory
The Space Sciences Laboratory is an Organized Research Unit of the University of California, Berkeley. It is located in the Berkeley Hills above the university campus...
(SSL) at Berkeley
University of California, Berkeley
The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...
announced NASA had extended the THEMIS mission to the year 2012. NASA has officially approved the movement of THEMIS B and THEMIS C into Lunar orbit
Lunar orbit
In astronomy, lunar orbit refers to the orbit of an object around the Moon.As used in the space program, this refers not to the orbit of the Moon about the Earth, but to orbits by various manned or unmanned spacecraft around the Moon...
under the mission name ARTEMIS
Artemis
Artemis was one of the most widely venerated of the Ancient Greek deities. Her Roman equivalent is Diana. Some scholars believe that the name and indeed the goddess herself was originally pre-Greek. Homer refers to her as Artemis Agrotera, Potnia Theron: "Artemis of the wildland, Mistress of Animals"...
(Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun).
ARTEMIS
As of Spring 2010, ARTEMIS P1 (THEMIS B) has performed two Lunar flybys and one Earth flyby, and was approaching insertion into a Lissajous orbit around a Lunar Lagrange point. Lunar orbit insertion is targeted for April 2011. ARTEMIS P2 (THEMIS C) completed a Lunar flyby and was on the inbound leg of the first of three deep space excursions on its way to a Lissajous orbit and was targeted for Lunar orbit in April 2011.On June 22, 2011, ARTEMIS P1 began firing its thrusters to move out of its kidney-shaped "libration" orbit on one side of the moon, where it had been since January. As of July 2, 12:30 p.m. EDT, ARTEMIS P1 has achieved lunar orbit. The second spacecraft, ARTEMIS P2, moved into lunar orbit as of July 17, 2011. Along the way, the two spacecraft were the first to ever achieve orbit around the moon's Lagrangian points.
Aboard the spacecraft
- Instrument Data Processing Unit (IDPU): The IDPU houses most of the electronics for the instruments on the THEMIS spacacraft.
- Electric Field Instruments (EFI): The EFI is designed and built to sense the electric field in Earth's ever-changing magnetosphere
- Fluxgate magnetometer (FGM): The FGM measures the background magnetic field to identify and time the abrupt reconfigurations of the magnetosphere during substorm onset.
- Search-coil magnetometer (SCM): The SCM measures low frequency magnetic field fluctuations and waves in three directions in Earth's magnetosphere.
- Electrostatic AnalyzerElectrostatic analyzerAn electrostatic analyzer or ESA is an instrument used in ion optics that employs an electric field to allow the passage of only those ions or electrons that have a given specific energy. It usually also focuses these particles into a smaller area...
(ESA): The ESA measures thermal electrons and ions to identify and track high-speed flows through the magnetotail and identify pressure pulses. - Solid State Telescope (SST): The SST measures energetic particle distribution functions.
- Digital Fields Board (DFB): The DFB uses an FPGA to perform configurable on board band pass processing and fast Fourier transformations(FFT) on instrument data.
Ground based
As the satellites monitor the magnetosphere from orbit, twenty ground stations in North AmericaNorth America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
simultaneously monitor aurora
Aurora (astronomy)
An aurora is a natural light display in the sky particularly in the high latitude regions, caused by the collision of energetic charged particles with atoms in the high altitude atmosphere...
s. Ground station mission and science operations are being managed by the University of California Space Sciences Laboratory
Space Sciences Laboratory
The Space Sciences Laboratory is an Organized Research Unit of the University of California, Berkeley. It is located in the Berkeley Hills above the university campus...
.
- Ground-Based All-Sky Imager (ASI) Array: The ground-based All-Sky Imager (ASI) array observes the aurora over the Northern American continent from Canada to Alaska in order to determine where and when the auroral substorm onset occurs.
- Ground-Based Magnetometer (GMAG) Array: The GMAG Measure changes in Earth’s magnetic field near Earth’s surface due to substorm onset to help determine the timing of substorm events.
Swales Aerospace
Swales Aerospace, now Alliant Techsystems Inc., (Beltsville, MarylandMaryland
Maryland is a U.S. state located in the Mid Atlantic region of the United States, bordering Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware to its east...
) manufactured all five probes for this mission. Each was built-up and tested at the Beltsville facility, before being delivered to the University of California, Berkeley
University of California, Berkeley
The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...
for instrument integration. Swales was responsible for integrating the BAU, IRU, Solar Arrays, Antenna, Battery, and other components necessary for functionality. This was the second major satellite built by Swales, the first being the EO-1 spacecraft, which continues to orbit the Earth. Swales was also responsible for designing and building the Electrical Ground Support Equipment (EGSE) used for monitoring the probes during all phases of pre-launch activities, including use at the launch site.
JPL
Testing after the installation of instruments at SSL, Berkeley, including vacuum testing, was done at NASA's Jet Propulsion Laboratory in Pasadena, California.FAST
The Fast Auroral Snapshot ExplorerFast Auroral Snapshot Explorer
The Fast Auroral Snapshot Explorer was launched from Vandenberg Air Force Base on board a Pegasus XL rocket on August 21, 1996. One in the series of NASA's Small Explorer spacecraft, FAST was designed to observe and measure the plasma physics of the auroral phenomena which occur around both poles...
(FAST) mission supported THEMIS in 2008 and 2009 before being retired. FAST was a Small Explorer program
Small Explorer program
The Small Explorer program is an effort within NASA to fund space exploration missions that cost no more than $120 million.- Program history :...
(SMEX) mission launched in 1996.