ISS Utilization: ASIM (Atmosphere-Space Interactions Monitor)
ASIM is an ESA science instrument assembly to be flown on the Columbus External Platform Facility (CEPF) of the ISS (International Space Station). The ASIM concept has been proposed by DNSC [Danish National Space Center, formerly DSRI (Danish Space Research Institute)], with the objective to observe TLEs (Transient Luminous Events) that occur in the Earth's upper atmosphere accompanied by thunderstorms in the lower atmosphere. These events are known as blue jets, sprites and elves, the phenomena were first observed in 1989. The ISS is considered a perfect platform from which to enhance our knowledge of them. 1) 2) 3) 4) 5) 6) 7)
The mission is realized throughESA. In January 2007, DNSC of Copenhagen, Denmark (formerly DSRI) became DTU-Space, an institute at the Technical University of Denmark. DTU-Space provides the scientific leadership, and the Danish company, Terma, the technical leadership. Other major partners include the University of Valencia in Spain, and the University of Bergen in Norway, who are both involved in the development of the instruments.
ASIM has a number of cameras, specially designed for the International Space Station, that will observe the Earth's atmosphere. ASIM will give new insights into climate processes that will improve climate models by quantifying the effect of electrical and chemical processes at the atmosphere/space boundary. DTU Space is responsible for delivering a package of instruments (2 cameras, 3 photometers and one X- and gamma-ray detector) which will be mounted on the International Space Station. 8) 9)
ASIM will study the Earth's atmosphere as one system, from the surface of the Earth to the edge of space. The atmosphere is the thin layer that covers the planet's crust, and protects life as we journey through space. ASIM will observe extreme thunderstorms, water vapor, clouds, aerosols and their interplay in the atmosphere.
The nature of the electrical phenomena (Figure 1) and their discharges are linked to violent storms in the tropics and inject water vapor, NOx and other greenhouse gases into the stratosphere where they become part of the climate moderators. ASIM will study these effects, as well as the electrical influence on the ionosphere and the atmospheric interactions with the particle radiation from the sun. Both of which also have a direct bearing on the Earth's climate.
ASIM, an approved ESA project, was selected in response to a call for flight opportunity issued by the Directorate of Human Spaceflight in December 2002 for external payloads to be flown to and operated onboard Columbus external platforms. The ASIM payload is planned to be taken to the ISS in the time frame 2014.
The ASIM project has been a Danish initiative, from the very start, headed in the initial phase by the Danish National Space Centre (DNSC) with participation of the universities of Valencia (Spain) and Bergen (Norway). As of 2007, the project is in Phase B planned to complete in 2009. The ASIM development is lead by TERMA, a high-tech company of Denmark. The consortium includes DNSC, Damec Research Aps, the University of Valencia, the University of Bergen, the University of Ferrara, and the University of Bologna. The production Phase C of ASIM was started in August 2010. 10) 11) 12)
The primary research objectives of the mission require the following measurements:
• Study the physics of TLEs (Transient Luminous Events). Optical detection of TLEs with high spatial- and time resolution in selected spectral bands - a comprehensive global survey
• Study the physics of TGFs (Terrestrial Gamma-ray Flashes) and their relationship with TLEs and thunderstorms. X-ray and γ-ray detection of TGFs with high time resolution and at photon energies reaching down to 10 keV
• Simultaneous optical detection of thunderstorm- and TLE activity with TGF activity. The optical instruments must view with the X- and γ-ray detector towards the nadir
• Study the coupling to the mesosphere, thermosphere and ionosphere of thunderstorms and TLEs
• Observations from space during a minimum of one year at all local times to observe seasonal and local time variations in thunderstorm-, TLE-, and TGF activity.
Secondary objectives based on observations:
- Spectroscopic studies of the aurora
- Studies of greenhouse gas concentrations above thunderstorms (NOx, O3)
- Studies of meteor ablation in the mesosphere and thermosphere.
Optical and X-ray measurements are used to study aurora, differential absorption of light emissions from lightning-illuminated thunderstorm clouds measured by photometers defines ozone column densities, NOx production in TLEs is to be monitored by photometer 5, and optical imaging, and photometers will be used to study meteor ablation.
The measurements include imaging in 4 auroral bands simultaneously, coupled with high time-resolution photometer observations and X-ray and γ-ray observations. The inclination of the ISS orbit at 51.6º brings the instruments over the auroral oval during periods of high solar (geomagnetic) activity when the auroral oval expands to lower latitudes. These are also periods with high auroral activity.
Figure 3: Illustration of a TGF. Terrestrial gamma ray flashes are high energetic discharges in the Earth atmosphere, but the origin of events is unclear. This is why ASIM aims to study the correlation between the TGF with lightning and TLE (image credit: ASIM collaboration)
A space window to electrifying science: 14)
Lightning triggers powerful electrical bursts in Earth's atmosphere almost every second. The inner workings of these magnificent forces of nature are still unknown, but a rare observation by an ESA astronaut gave a boost to the science community. A European detector will take on the challenge of hunting for thunderstorms from space next week.
As he flew over India at 28 800 km/h on the International Space Station in 2015, astronaut Andreas Mogensen directed a high-resolution camera towards a gigantic thunderstorm. He caught a blue jet repeatedly shooting up into space towards the upper layers of the atmosphere – as high as 40 km.
Figure 4: For years, their existence has been debated: elusive electrical discharges in the upper atmosphere that sport names such as red sprites, blue jets, pixies and elves. Reported by pilots, they are difficult to study as they occur above thunderstorms. ESA astronaut Andreas Mogensen on the International Space Station in 2015 was asked to take pictures over thunderstorms with the most sensitive camera on the orbiting outpost to look for these brief features (image credit: ESA/NASA) 15)
Figure 5: ESA astronaut Tim Peake took this image circling Earth 400 km up in the International Space Station. He commented: "Sometimes looking down on Earth at night can be kinda spooky." The image shows lightning strikes illuminating clouds over Western Australia during a thunderstorm (image credit: ESA/NASA) 16)
Legend to Figure 5: Although this picture was taken in Tim's free time, the Station is used for research into elusive phenomena in the upper atmosphere during thunderstorms – red sprites, blue jets and elves. Some of the most violent electric discharges are very difficult to capture from the ground because of the atmosphere's blocking effect. From space, astronauts can judge for themselves where to aim the camera, where to zoom in and follow interesting regions for researchers.
Astronauts often spot thunderstorms and are impressed by how much lightning they observe.
ASIM payload elements and accommodation:
The ASIM optical instruments make up the MMIA (Miniature Multispectral Imaging Array) consisting of 3 modules, each housing 2 video-rate cameras and two photometers. Two modules view in the ram-direction towards the limb and one module towards the nadir. The MXGS (Miniature X-ray and Gamma-ray Sensor) is pointed towards nadir.
In addition, there are the following subsystems:
• DHPU (Data Handling and Power Unit). The DHPU handles all electrical interfaces between ASIM and ISS. The DHPU receives two 120 V supplies, one for operational power and one for heaters. During the Dragon flight and robotic installation, a third 120 V heater supply is utilized. The DHPU converts the 120 V operational supply to 28 V instrument supplies. The 120 V heater supplies are distributed to two separate heater sets in the instruments and DHPU itself. Two sets are used since the necssary power for thermal conditioning is different in the Dragon and robotics phases compared to the mission life on Columbus.
- Apart from the 120 V supplies, the DHPU implements an ethernet connection for data link, MIL-BUS for monitored data and time synchronization with ISS, and finally a serial line which allows the ISS crew to patch the firmware of the DHPU.
Figure 6: Photo of the DHPU (image credit: ASIM collaboration)
• CEPA (Columbus External Payload Adapter). The CEPA is a standard structural item designed by Boeing for Columbus. It implements a standard interface to ISS called the FRAM (Flight Releasable Attachment Mechanism), which allows payloads and standard cargo like battery assemblies, to be attached on the ISS FRAM location like the Columbus External Payload Facility. The FRAM interface includes connectors which routes the electrical connections from the ISS through the FRAM system connectors on the top side of the CEPA. It is these connectors that are routed through the ASIM harness to DHPU and then distributed to the instruments.
- The CEPA provides the mechanical and electrical interface between the instrument and respectively the Columbus External Payload Facility (CEPF) and the carrier (LCC).
Figure 7: Photo of the CEPA (image credit: ASIM collaboration)
ASIM is designed to be accommodated on the starboard deck location of the CEPF (Columbus External Payload) platform (Figure 8).
The overall power consumption of ASIM is expected not to be 500 W (including 200W for thermal heaters). The mass of ASIM, including CEPA and the active FRAM (Flight Releasable Attachment Mechanism) is about 314 kg. The on-orbit lifetime is expected to be 2 years. ASIM has a downlink allocation of 200 kbit/s continuous data, which will be fully utilized since the instruments collect a wast amount of data, and low prioritized data cannot be fully downlinked.
Development status of ASIM:
• Due to a failure of the Columbus External Payload Adapter (CEPA), ASIM had to go through a complete de-integration from the failed CEPA and has started integration onto the new one sent by NASA. The ASIM schedule is still compatible with a handover to NASA at the end of November 2017, in time for launch on SpaceX CRS-14 (scheduled for early 2018). 17)
This flight delivers scientific investigations looking at severe thunderstorms on Earth, the effects of microgravity on production of high-performance products from metal powders, and growing food in space. Dragon also carries cargo for research in the National Laboratory, operated by CASIS (Center for the Advancement of Science in Space), including testing the effects of the harsh space environment on materials, coatings and components; identifying potential pathogens aboard the station; and investigating an antibiotic-releasing wound patch.
Dragon is packed with 2625 kg of research, crew supplies and hardware to be delivered to the station:
ASIM (Atmosphere-Space Interactions Monitor), an ESA science instrument (314 kg) to be installed on the Columbus External Platform Facility (CEPF). ASIM surveys severe thunderstorms in Earth's atmosphere and upper-atmospheric lightning, or transient luminous events. These include sprites, flashes caused by electrical break-down in the mesosphere; the blue jet, a discharge from cloud tops upward into the stratosphere; and ELVES, concentric rings of emissions caused by an electromagnetic pulse in the ionosphere.
RemoveDebris is an EU Framework 7 (FP7) funded research microsatellite (100 kg), low cost in-orbit demonstrator mission for future ADR (Active Debris Removal) missions. The project is a partnership of SSC (Surrey Space Center) and NanoRacks. SSC leads a consortium of partners [Airbus, Ariane Group, SSTL, ISIS (Netherlands), CSEM (Switzerland), Inria (France), Stellenbosch University (South Africa)]. This project will use the NanoRacks RemoveDEBRIS satellite platform to deploy two CubeSats as artificial debris targets to demonstrate four technologies for debris removal (net capture, harpoon capture, vision-based navigation). RemoveDebris will be deployed, via the NanoRacks Kaber system. Once in orbit the ADR experiments on board the spacecraft will be performed. 20)
MISSE-FF (Materials ISS Experiment Flight Facility) with MSCs (MISSE Sample Carriers) in the fully open position exposing samples/experiments to the harsh environment of space in LEO (Low Earth Orbit). Designed by Alpha Space and sponsored by CASIS, MISSE-FF provides a platform for testing how materials react to exposure to ultraviolet radiation, atomic oxygen, ionizing radiation, ultrahigh vacuum, charged particles, thermal cycles, electromagnetic radiation, and micro-meteoroids in the low-Earth orbit environment. MISSE-FF has a mass of ~435 kg.
The MSL SCA-GEDS-German (NASA Sample Cartridge Assembly-Gravitational Effects on Distortion in Sintering) experiment focuses on determining the underlying scientific principles to forecast density, size, shape, and properties for liquid phase sintered bodies over a broad range of compositions in Earth-gravity (1g) and microgravity (µg) conditions.
Wound Healing. NanoRacks Module 74 Wound Healing tests a patch containing an antimicrobial hydrogel that promotes healing of a wound while acting as a scaffold for regenerating tissue. Reduced fluid motion in microgravity allows more precise analysis of the hydrogel behavior and controlled release of the antibiotic from the patch.
The Canadian Space Agency's study Bone Marrow Adipose Reaction: Red or White (MARROW) will look at the effects of microgravity on bone marrow and the blood cells it produces – an effect likened to that of long-term bed rest on Earth. The extent of this effect, and bone marrow's ability to recover when back on Earth, are of interest to space researchers and healthcare providers alike.
Understanding how plants respond to microgravity also is important for future long-duration space missions and the crews that will need to grow their own food. The PONDS (Passive Orbital Nutrient Delivery System) arriving on Dragon uses a newly-developed passive nutrient delivery system and the Veggie plant growth facility currently aboard the space station to cultivate leafy greens. These greens will be harvested and eaten by the crew, with samples also being returned to Earth for analysis.
Orbit: Near-circular orbit of the ISS, altitude of ~400 km, inclination = 51.6º.
ASIM will be transported to ISS in the external trunk of Dragon. Once Dragon is docked to ISS Node 2, the SSRMS (Space Station Remote Manipulator System) will install ASIM in its final location on Columbus. The SSRMS will utilize the SPDM (Special Purpose Dexterous Manipulator) to grab ASIM in the Dragon trunk for extraction. The SPDM can operate the FRAM (Flight Releasable Attachment Mechanism) to detach ASIM from the trunk. The same mechanism is installed on the SPDM iteself in case ASIM needs to be fixed to the SPDM in order receive power for thermal heaters during the seven hour transfer to Columbus. On the CEPF (Columbus External Payload Facility ), ASIM will be attached to the starboard facing deck location, named EPF SDX, which also suppports the FRAM.
Figure 9: ESA's ASIM instrumentation, the center-bottom box in this image, is seen here after its installation in SpaceX Dragon's open cargo carrier ahead of next week's launch. On 2 April, a Falcon 9 rocket will deliver this instrument to the International Space Station to begin its mission of chasing down elusive electrical discharges in the atmosphere (image credit: 2018 Space Exploration Technologies Corp. All rights reserved) 21)
Additional CubeSat missions of CRS-14.
Irazú, a 1U CubeSat of ACAE and ITCR (Costa Rica Institute of Technology). Irazu is a technology demonstration mission (1 kg) of ITCR.
UBAKUSAT, a joint Turkish and Japanese 3U Cubesat (4 kg) technology demonstration mission, built by ITU (Istanbul Technical University), Istanbul, Turkey in cooperation with JPF (Japan Space Forum), and KIT (Kyushu Institute of Technology).
Overview-1A, a 3U CubeSat (4.2 kg) of SpaceVR (Space Virtual Reality), a crowd-funded mission based on a Pumpkin platform, USA. The goal is to allow users to ‘experience space firsthand' using any mobile, desktop, or virtual reality device.
1KUNS-PF (1st Kenyan University NanoSatellite-Precursor Flight), a 1U CubeSat developed at the University of Nairobi, Kenya in collaboration with "La Sapienza" University of Rome and ASI (Italian Space Agency). A technology demonstration mission.
• May 23, 2018: As the International Space Station flew over the Indonesian coast of Sumatra on an April night, lightning from a thunderstorm reached the upper layers of the atmosphere and its light show was captured by ESA's latest observatory in space. 22)
- ASIM (Atmosphere-Space Interactions Monitor), also known as the Space Storm Hunter, is completing its initial tests a month after it was installed outside Europe's Columbus laboratory. "We collected 100,000 measurements per second of this amazing force of nature," explains Torsten Neubert, science team coordinator at the Technical University of Denmark, "this is a fantastic example of how powerful our photometers are".
Figure 10: Eyes on the storm. The two cameras of ASIM captured the strong signature of lightning with unprecedented accuracy 400 kilometers above Earth. As the International Space Station flew over the Indonesian coast of Sumatra on an April night, lightning bursts from a thunderstorm reached the upper layers of the atmosphere. Even with the clouds partly blocking the lightning, the instruments show powerful electrical discharges high in the atmosphere. Scientists believe it is an elve. Elves are the highest of all the ‘transient luminous events' known to date. In the blink of an eye concentric rings appear as a dim, expanding glow hundreds of kilometers wide formed by electrons colliding and excited nitrogen molecules (image credit: DTU)
• April 13, 2018: The ASIM (Atmosphere-Space Interactions Monitor) instrumentation, also known as the Space Storm Hunter, was installed today outside the European space laboratory Columbus. Operators in Canada commanded the International Space Station's 16 m long robotic arm (Canadarm2) to move ASIM from a Dragon spacecraft's cargo hold to its place of operation on Columbus. 23)
- Pointing straight down at Earth, the storm hunter will observe lightning and powerful electrical bursts in the atmosphere that occur above thunderstorms, the so-called transient luminous events. The inner workings of these magnificent forces of nature are still unknown. The ISS offers a great vantage point to gather information about such events – it circles 400 km above Earth and covers the areas where most thunderstorms appear.
- Setting up: The first part to getting data is checking the communication channels. The storm hunter will send data over the International Space Station network beamed via communication satellites to a ground station in White Sands, USA, then on to the Space Station mission control in Houston, under the Atlantic Ocean to the Columbus Control Center in Oberpfaffenhofen, Germany, and finally to the Belgian user operations and support center in Brussels.
- The observatory has two suites of instruments to capture optical images in infrared and ultraviolet, and X-ray and gamma-ray detectors. The sensors will measure light levels to determine if an image should be taken and the data sent back to Earth.
- Setting the levels will be a matter of trial and error – setting the trigger too low will flood the network with images that are of no use, too high and some thunderstorms will not be recorded. The operators will collaborate with scientists at the Technical Institute of Denmark who are eagerly awaiting readings from the observatory, in order to find the best solution.
- Visual cameras will pinpoint areas of interest while photomultiplier tubes record the details of the lightning and transient luminous events. Other sensors are included to learn more about terrestrial gamma-ray flashes, for high and low energy X-ray and gamma-ray bursts.
- Each element of the storm hunter will be activated in turn and tested to ensure they are working as expected. This is expected to take up to six weeks, during which the user control center will be run continuously.
- Anuschka Helderweirt, operations engineer at the Belgian operations center, says: "We are thrilled to start operating these instruments in space, this is what the hours spent training, developing procedures and preparing for anomalies was for. We are ready to deliver some fascinating new scientific data."
Figure 11: Atmospheric zoo of light and energy: ASIM observes a wide variety of phenomena in Earth's upper atmosphere. The inner working of these magnificent forces of nature are still unknown, but lightning affects the concentration of atmospheric gases that are important for the climate. New data will improve our understanding of the effect of thunderstorms on the atmosphere and contribute to more accurate climate models (image credit: ESA)
• On April 4, 2018, the SpaceX Dragon CRS-14 arrived at the International Space Station to deliver more than 2630 kg of research investigations, cargo and supplies, including NASA's Materials International Space Station Experiment (MISSE). This is the ninth MISSE mission in the program's long history of testing material samples in space. 24)
Figure 12: The MISSE Flight Facility is shown here, as manufactured by Alpha Space Test and Research Alliance. The new configuration offers multiple sides, allowing material specimens to be exposed to the space environment from all four orientations (ram, wake, zenith, and nadir), image credit: Alpha Space Test & Research Alliance
• April 4, 2018: The SpaceX Dragon capsule has arrived at the International Space Station (ISS) after a two-day orbital chase. Astronauts aboard the ISS snagged the uncrewed Dragon at 10:40 GMT using the orbiting lab's huge Canadarm2 robotic arm. The cargo vehicle had launched Monday afternoon (April 2) aboard a SpaceX Falcon 9 rocket, on a contracted mission for NASA. 25)
Figure 13: Astronauts aboard the ISS snagged the uncrewed Dragon today (April 4) at 10:40 GMT using the orbiting lab's huge Canadarm2 robotic arm (image credit: NASA TV)
- ISS crewmembers will soon start unloading the 2,630 kg of cargo Dragon, which includes a number of scientific experiments. Among them is a study designed to help optimize plant growth in space, and an investigation into how bone marrow produces red blood cells in a microgravity environment.
- Also aboard Dragon is an experimental spacecraft called RemoveDebris, which will be deployed from the ISS in the near future to test ways to clean up space junk. Once it's flying freely, the RemoveDebris mothership will practice hitting an onboard target with a harpoon, and it will also jettison a small piggyback satellite and then try to bag it up with a net.
- The Dragon will remain at the ISS until next month, when crewmembers will load it up with about 1,800 kg of cargo from the station, SpaceX representatives have said. The capsule will depart and maneuver its way to a splashdown in the Pacific Ocean off Baja California, where SpaceX personnel will retrieve it by boat.
ASIM instrument assemblies (MMIA, MXGS):
ASIM consists of two optical cameras, 3 photometers, and one large X- and Gamma ray detector. The instruments will be installed on the Columbus External Pallet to be mounted on the exterior of the Columbus module, housing ESA's laboratory on the ISS. 26) 27) 28) 29) 30) 31) 32) 33)
The optical assembly, referred to as MMIA (Modular Multispectral Imaging Array), comprises two optical narrow band cameras and three photometers with related optical and signal processing capabilities, including autonomous event detection algorithms to identify and prioritize events for download to Earth.
The MMIA instrument will be combined with the MXGS (Modular X- and Gamma-ray Sensor) into the Nadir Viewing Assembly looking directly down on top of thunderstorms according above the Earth.
MXGS is designed to detect radiation from TGF (Terrestrial Gamma Flashes) and from lightning induced electron precipitation. The detector is built around a BiGe (Bismuth Germanium) as well as a CZT (Cadmium Zinc Telluride) semiconductor detection plane of 32 cm x 32 cm with possible imaging capabilities.
Fast electronic circuitry used in the MXGS will provide time history and spectra over the course of the expected lifetime of 1-5 ms for each TGF. Also, a TGF burst trigger signal is passed to the adjacent MMIA module (and visa versa) for synchronization of the two types of observation.
X- and gamma-rays are strongly absorbed in the atmosphere. This is why the detector points directly downwards, such that a minimum of atmosphere is between the detector and the thunderstorms within its field of view. Most of the atmosphere is below the altitude where giant lightning and terrestrial gamma-ray flashes are generated. Therefore, space is particularly well suited to observe these phenomena in the band reaching from gamma-rays to UV, which is difficult to observe from the ground. ASIM is measuring in these bands (colors).
The ASIM mission will address a variety of important scientific and technological aspects which will include:
• Understanding of the processes involved in thunderstorm initiated electrical discharges
• Understand their impact on atmospheric processes and possible links to climate determining factors
• Development of new technologies with spin-off into terrestrial applications for advanced process control and optical instrumentation
• Demonstration of the fruitful utilization of the collaborative investments in the International Space Station.
In view of the unique observation point, the advanced instrumentation set, and the long duration of the mission, it is expected that ASIM will produce scientific data of high quality which will give an unprecedented contribution to the understanding of interaction mechanisms between the atmosphere and space.
MMIA (Modular Multispectral Imaging Array):
ASIM uses optical observiations in carefully selected bands in order to filter out data with TLEs from the lightning data. Since the data downlink is limited, the algorithms are implemented in the on-board software. The ASIM MMIA instrument is capable of observing 12 frames/s continuously in the 777.4 nm and 337 nm bands, both only 5 nm wide. Combined with the 100 kHz photometer data from the same two bands in addition to a 180-230 nm band, data is filtered in realtime to optimize the available downlink capability allocated to ASIM on ISS.
Figure 15: Illustration of the MMIA assembly (image credit: ASIM collaboration)
The optical instruments are grouped into two) groups, each composed of two optical narrow band cameras and 2 photometers with related optical and signal processing capabilities including autonomous event detection algorithms to identify and prioritize events for download.
• 4 cameras and 4 photometers look forward towards the limb
• 2 cameras and 2 photometers look downwards towards the nadir
The cameras and photometers are equipped with baffles for stray light protection. The camera sampling is 12 bit 1024 x 1024 pixel frames at a maximum of 25 Hz.
Table 1: Parameters of the MMIA optical instruments
The photometers are used to measure rapid time variations, which cannot be done by the imaging cameras. They view the exact same region but measure only the total photon flux from the region - but with high time resolution. The photometer FOVs are identical to those of the cameras: 20º x 20º (limb or ram direction) and 80º x 80º (nadir direction).
Legend: *extension under consideration – will allow also day time observations of lightning
Figure 16: Block diagram of the MMIA photometers (TNO Science and Industry)
Figure 17: View of the MMIA limb assembly with 4 cameras and 4 photometers (image credit: DNSC)
Data handling subsystem: Time synchronizing of instrument measurements with a relative time accuracy < 10 µs and with an accuracy of 100 µs compared to GPS/UTC.
Figure 18: Overview of system data and signal interfaces (image credit: DNSC)
MXGS (Modular X-ray and Gamma-ray Sensor):
The MXGS instrument carries two set of detectors for TGFs (Terrestrial Gamma-ray Flashes). The low energy detector is senstive in the spectral band from 15 keV to 400 keV and the high energy detector is sensitive from 200 keV to 40 MeV. The low energy detector is pixellated in 128 by 128 channels, which, in combination with a high mass density coded mask in front of the detector, allows advanced post-processing algorithms to pin point the direction to the TGF source. Overlaying the TGF direction with the optical imaging by the MMIA instrument, the correllation with lightning and TLE is possible. 34) 35) 36) 37) 38) 39) 40) 41) 42)
Table 3: Technical parameters of MXGS 43)
The MXGS detector plane consists of a 1024 cm2 array of CZT detector crystals. It is protected against the background radiation by a passive graded shield surrounding the detector housing. A hopper shaped collimator defines the 80º x 80º field of view for MXGS and shields the detector plane against the Cosmic X-ray Background. The DFEE (Detector Front End Electronics) is mounted in the housing below the detectors. The electronics contains also the HVPS (High Voltage Power Supply) and LVPS (Low Voltage Power Supply) as well as the DPU (Data Processing Unit).
The DFEE design consists of 4 DAUs (Detector Assembly Units), and each DAU consists of 16 DM (Detector Modules) and one DAB (Detector Assembly Board). The DAB holds the read-out electronics and the RCU (Readout Control Unit). The RCUs interface to the DPU. The purpose of the DAU is to read out the events and transfer the data to the DPU.
The DM consists of two separable units, a CZT sensor and an ASIC. The sensor comprises four 20 mm x 20 mm x 5 mm CZT detectors tiled together on a PCB. Each detector is pixelated into 64 pixels (2.5 mm pixel pitch), making a 16 x 16 pixel array in total. The detector unit is stacked onto the ASIC unit via three connectors (Figure 22).
The MXGS uses fast ASICs to provide the time history and spectra over the course of the expected TGFs lifetime of 1-5 ms and a TGF burst trigger signal is passed to the companion MMIA module (and visa versa). The observation plane is protected from background radiation by a passive shield and the field of view is defined by a hopper shaped collimator.
Figure 20: Illustration of the MXGS instrument (image credit: University of Bergen)
Figure 21: Schematic view of the MXGS instrument elements (image credit: MAPRAD)
Figure 23: Illustration of the MXGS instrument (image credit: ASIM collaboration)
ASIM is controlled from a ground USOC (User Operator Center) connected to the ISS ground stations. When USOC sends a command to ASIM, it is routed to theCOL-CC ( Columbus Control Center), then to the ISS ground station in Houston responsbile for uplinking the command to ISS, which eventually reaches ASIM through Columbus. The DHPU will process all commands and it also supports a command schedule for autonomous observation timelines. The ASIM science and housekeeping data follow the same route in reverse back to the USOC.
Figure 24: Overview of the ground segment elements for ASIM operations (image credit: ESA)
Ground observations are important parts of the ASIM and TARANIS missions (observe from space what is best observed from space and from ground what is best observed from ground).
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The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).