TWINS

This article is about the NASA instruments on Earth satellites. For the meteorological instruments on NASA's InSight Mars lander, seeTemperature and Winds for InSight.For other uses of "Twins", seeTwins (disambiguation).

TWINS

TWINS 1 and TWINS 2 in simultaneous Molniya orbits, obtain stereo images of the Earth's ring current, including signals from both trapped ions and precipitating ions.
Operator	NASA
Instrument type	Spectrometer
Function	Magnetospheric
Mission duration	2 years (planned)
Website	http://twins.swri.edu/index.jsp
Properties
Number launched	2
Host spacecraft
Spacecraft	USA-184 USA-200
Operator	NRO
Orbit	Molniya

Two Wide-Angle Imaging Neutral-Atom Spectrometers(TWINS) are a pair ofNASAinstruments aboard twoUnited StatesNational Reconnaissance Office(NRO) satellites inMolniya orbits.TWINS was designed to provide stereo images of the Earth'sring current.The first instrument,TWINS-1,was launched aboardUSA-184on 28 June 2006.TWINS-2followed aboardUSA-200on 13 March 2008.

Each instrument consists of anenergetic neutral atomimager and aLyman Alphadetector. The ENA imager provides indirectremote sensingof the ring current ions, and the Lyman Alpha detector gives a measure of the neutralhydrogencloud about theEarth,known as thegeocorona.The TWINS prime mission lasted two years, from 2008 to 2010, and has been followed by an extended mission which is ongoing.

Mission

Launched as missions of opportunity (MoO) aboard classified, non-NASA U.S. government spacecraft, TWINS conductsstereoscopicimaging of Earth'smagnetosphere.By imaging the charge exchange neutral atoms over a broad energy range (~1-100keV) using two identical instruments on two widely spaced high-altitude, high-inclination spacecraft, TWINS enables the 3-dimensional visualization and the resolution of large scale structures and dynamics within the magnetosphere for the first time. In contrast to traditional space experiments, which make measurements at only one point in space, imaging experiments provide simultaneous viewing of different regions of the magnetosphere. Stereo imaging, as done by TWINS, takes the next step of producing 3-D images, and provides a leap ahead in our understanding of the global aspects of the terrestrial magnetosphere.

The ENA imagers observe energetic neutrals produced from the global magnetospheric ion population, over an energy range of 1 to 100 keV with high angular (4°) and time (about 1-minute) resolution. A Lyman- Alpha geocoronal imager is used to monitor cold exospherichydrogenatomsthat produce ENAs from ions viacharge exchange.Complementing these imagers are detectors that measure the local charged particle environment around the spacecraft. The offset in the orbital phases (apogeesat different times) of TWINS 1 and TWINS 2 means that in addition to stereo ENA imaging for several hours twice per day, the two TWINS instruments also obtain essentially continuous magnetospheric observations. The TWINS instrumentation is essentially the same as the MENA instrument on theIMAGEspacecraft. This instrumentation consists of a neutral atom imager covering the ~1-100 keV energy range with 4° x 4° angular resolution and 1-minute time resolution, and a simple Lyman- Alpha imager to monitor the geocorona.

TWINS provides stereo imaging of the Earth's magnetosphere, the region surrounding the planet controlled by its magnetic field and containing theVan Allen radiation beltsand other energetic charged particles. TWINS enables three-dimensional global visualization of this region, leading to greatly enhanced understanding of the connections between different regions of the magnetosphere and their relation to thesolar wind.

Operation and storm events

This is a first-light stereo ENA image of the terrestrial ring current obtained by TWINS on 15 June 2008 for 10 keV energy. Visible in each image are both low-altitude emissions (LAE) from precipitating ions, and high-altitude ring current emissions (RCE). For reference, the Earth's limb is drawn in, along with dipole magnetic field lines at four cardinal local times (noon=red, dusk=lavender, midnight, and dawn) and two L-values (L=4 and L=8).

Routine stereo imaging by TWINS began on 15 June 2008, during an extremely weak geomagnetic storm whoseDst indexnever fell below -40nT,as compared to a nominal Dst of -100 nT for classification as a storm. During the TWINS prime mission (2008–2010), an extended and unprecedented solar minimum (from solar cycle 23) prevailed, bringing with it very calm magnetospheric conditions ranging from dead quiet to mildly disturbed. During this time period TWINS observed numerous weak storms, roughly once every 27 days (corresponding to the solar rotation period and triggered by solar corotating interaction regions (CIRs). The strongest storm (which was still very mild) observed by TWINS during its prime mission was on 22 July 2009, with Dst reaching a moderate -79 nT. Throughout these extended quiet conditions TWINS images contained ENA signals from both high-altitude (ring current) and low-altitude emission (LAE) regions.

The TWINS Mission of Opportunity maintains a library of selected storm events.

Instruments

Name	Launch name	Spacecraft	Launch date (UTC)	Launch site	Rocket	Orbit	Remarks
TWINS-1	TWINS-A	USA-184	28 June 2006 03:30:00	VAFB,SLC-6	Delta IV-M+(4,2)	1,138 × 39,210 km (707 × 24,364 mi) x 63.2°
TWINS-2	TWINS-B	USA-200	13 March 2008 10:02	VAFB,SLC-3E	Atlas V411	1,652 × 38,702 km (1,027 × 24,048 mi) x 63.4°

See also

• STEREOTwo spacecraft launched into heliocentric orbit in 2006 to provide stereographic imagery of the Sun
• List of heliophysics missions
• Temperature and Winds for InSight(TWINS, sensor package onInSightMars lander)

External links

• TWINS,official site
• TWINSArchived12 October 2020 at theWayback Machine,SwRIversion
• LAD,LAD/TWINS instrument