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)
Figure 1: Red sprites, blue jets and elves above thunderstorms (image credit: ESA)
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 2013.
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 the fall of 2008. The ASIM development is lead by TERMA 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. 7) 8)
The primary research objectives of the mission require the following measurements:
• Study the physics of TLEs. 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.
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:
• PSE (Payload Support Equipment)
- Mechanical support structure
- Payload Power Distribution Unit
- ASIM Payload Computer
• CEPA (Columbus External Payload Adapter)
- The CEPA provides the mechanical and electrical interface between the instrument and respectively the Columbus External Payload Facility (CEPF) and the carrier (LCC).
ASIM is designed to be accommodated on the starboard deck location of the CEPF (Columbus External Payload) platform (Figure 2).
Figure 2: ASIM allocation at the Columbus External Platform Facility (image credit: ESA)
The overall power consumption of ASIM is expected not to exceed 420 W with a mass, including CEPA and the active FRAM (Flight Releasable Attachment Mechanism) of about 330 kg. The on-orbit lifetime is expected to be 2 years.
Launch: ASIM is designed for launch in the timeframe 2013 with the HTV (H-II Transfer Vehicle), the automated unmanned transport system developed by JAXA as cargo transportation system for the International Space Station. ASIM will be mounted in the FRAM-compatible ULC (Unpressurized Logistics Carrier) module of the HTV. 9)
ASIM instrument assemblies:
ASIM scientific instruments include 6 cameras, 6 photometers and one X- and gamma-ray detector. The 4 cameras with 4 companion photometers are directed forward towards the horizon (ram, limb). Two cameras, two photometers and the X- and gamma-ray detectors are directed downwards (nadir).
The cameras and the photometers constitute the MMIA (Modular Multispectral Imaging Array). Each module includes two cameras and two photometers, such that there are 3 MMIA modules in all, two pointing forward and one downward. The MMIA instruments observe in different optical spectral bands. The two MMIA modules which are directed forward towards the horizon observe thunderstorms from the side, where it is possible directly to identify the effects on the atmosphere as a function of altitude.
Figure 3: Payload elements of ASIM and system configuration (image credit: DNSC)
The X- and gamma-ray detector is called the MXGS (Modular X- and Gamma-Ray Sensor). 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).
Figure 3 provides an overview of the ASIM instruments which are grouped in two assemblies:
1) a limb-looking ISS ram-direction assembly consisting of 4 cameras and 4 photometers (a detailed view is in Figure 4)
2) a nadir-looking assembly consisting of 2 cameras, 2 photometers, and MXGS. (a detailed view is in Figure 7).
The limb-looking assembly, dedicated to the observation of TLEs, includes two MMIA modules. The nadir-looking assembly, dedicated to the observation of TGFs, includes one MMIA module and the MXGS (Miniature X-ray and Gamma-ray Sensor). The nadir-looking assembly field of view is 80º and the limb-looking assembly is 20º.
The overall objectives are:
• To study thunderstorms and their relation to atmospheric processes and a changing climate
• Focus on the region of discharges above thunderstorms.
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):
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).
Table 2: Optical parameters of the MMIA instruments
Legend: *extension under consideration – will allow also day time observations of lightning
Figure 4: Block diagram of the MMIA photometers (TNO Science and Industry)
Figure 5: 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 6: Overview of system data and signal interfaces (image credit: DNSC)
Figure 7: The nadir-viewing assembly (MMIA) of 2 cameras + 2 photometers + MXGS, image credit: DNSC
MXGS (Modular X-ray and Gamma-ray Sensor):
The MXGS is designed to detect bremsstrahlung from TGFs (Terrestrial Gamma Flashes) and from lightning induced electron precipitation (LEP). The detector is based on a CZT (Cadmium Zinc Telluride) semiconductor detection plane of 1032 cm2 (32 cm x 32 cm) with possible imaging capabilities. This detector is characterized by a large stopping efficiency for X and gamma rays up to a few hundred keV. The detector energy sensitivity ranges from 7 to 500 keV with an energy resolution of < 10% @ 60 keV. 17) 18) 19) 20) 21) 22)
Table 3: Technical parameters of MXGS 23)
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 9).
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 8: Schematic view of the MXGS instrument elements (image credit: MAPRAD)
Figure 9: Photo of the detector module (image credit: DNSC, University of Bergen)
Figure 10: 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).
1) G. G. Reibaldi, R. Nasca, T. Neubert, O. Hartnack, “The Atmosphere-Space Interactions Monitor (ASIM) Payload Facility on the ISS,” 58th IAC (International Astronautical Congress), International Space Expo, Hyderabad, India, Sept. 24-28, 2007, IAC-07- B1.1.09
3) P. L. Thomsen, “ASIM Payload System Overview,” ASIM Topical Team Meeting-1, ESA/ESTEC, June 26-27, 2006
4) T. Neubert, I. Kuvvetli, C. Budtz-Jorgensen, N. Ostgaard, V. Reglero, N. Arnold, “The Atmosphere-Space Interactions Monitor (ASIM) for the International Space Station,” ILWS (International Living With a Star) Workshop 2006, Goa, India, Feb. 19-20, 2006, URL: http://cdaw.gsfc.nasa.gov/publications/ilws_goa2006/448_Neubert.pdf
5) G. Reibaldi, R. Nasca, H. Mundorf, P. Manieri, G. Gianfiglio, S. Feltham, P. Galeone, J. Dettmann, “The ESA Payloads for Columbus- A bridge between the ISS and exploration,” ESA Bulletin, No 122, May 2005, pp. 60-70
6) Torsten Neubert, “The Atmosphere-Space Interactions Monitor (ASIM) for the International Space Station,” Workshop on Coupling of Thunderstorms and Lightning Discharges to Near-Earth Space, June 23-27, 2008, University of Corsica, Corte, France
7) Torsten Neubert, Lundgaard Rasmussen, “Atmosphere-Space Interactions Monitor (ASIM) on the International Space Station,” URL: http://www.iapg.bv.tum.de/mediadb/15094/15095/05_080526-asim.pdf
8) Torsten Neubert, Christos Haldoupis, “European Studies of Coupling of Thunderstorms to the Upper Atmosphere,” URL: http://nova.stanford.edu/~vlf/IHY_Test/TunisTalks/Denmark_Neubert.pdf
9) Rosario Nasca, “The Columbus External Payload Facility (CEPF) and the ESA observation Payloads (SOLAR and ASIM),” Dec. 7, 2009, URL: http://esamultimedia.esa.int/docs/hsf_research/Climate_change_ISS_presentations/CEPF_Nasca.pdf
11) C. Budtz-Jorgensen, I. Kuvvetli, I. L. Rasmussen, T. Neubert, N. Ostgaard, A. Spilde, J. Stadsness, G. A. Johansen, V. Reglero, A. R. Berlanga, P. H. Connell, C. Eyles, J. M. Rodrigo, “The Miniature X- and Gamma-Ray Sensor (MXGS) on ASIM,” EDCE Workshop, Rome, Italy, Dec. 21, 2006, URL: http://projects.iasf-roma.inaf.it/EdgeGMPresentations/52_Budz_ASIM_ROME.ppt
14) P. J. Espy, T. Neubert, N. Ostgaard, “A Nitric Oxide Photometer for ASIM,” Workshop on Coupling of Thunderstorms and Lightning Discharges to Near-Earth Space, June 23-27, 2008, University of Corsica, Corte, France, URL: http://www.oma.be/TLE2008Workshop/Session5/Espy.ppt
15) Andy J. Court, “Fast Photometer Design for the ASIM ISS >Mission,” Proceedings of the 60th IAC (International Astronautical Congress), Daejeon, Korea, Oct. 12-16, 2009, IAC-07-B1.3.06
16) Torsten Neubert and the ASIM Team, “Status of the Atmosphere-Space Interactions Monitor (ASIM) for the International Space Station and plans for Ground Campaigns in 2009 and beyond,” URL: http://www.costp18-lightning.org/Publications/Symposium2009/Release/S4/02_Neubert.pdf
17) M. Marisaldi, “A High Energy gamma-ray detector for the ASIM mission,” AAE Workshop, Jan. 21, 2009, Rome, Italy, URL: http://projects.iasf-roma.inaf.it/aae/Meeting20-21Jan09/13-Marisaldi_ASIM_AAE2009.pdf
18) Francesca Renzi, “Background estimation in MXGS apparatus on ISS,” 6th Geant 4 (GEometry ANd Tracking) Space Users' Workshop,Madrid, Spain, May 19-22, 2009, URL: http://www.inta.es/.../Renzi_BackgroundEstimationInMXGS.pdf
19) C. Budtz-Jorgensen, I Kuvvetli, Y. Skogseide, K. Ullaland, N. Ostgaard, “Characterization of CZT Detectors for the ASIM Mission,” 2008, URL: http://ipy-icestar.uib.no/~nikost/papers/R04-5_MIC08.pdf
20) Irfan Kuvvetli, “X- and Gamma Ray Detector Development at DNSC,” First International Workshop of the Astrophysics of Neutron Stars Project (ASTRONS), July 2-6, 2007, Istanbul, Turkey, URL: http://astrons.sabanciuniv.edu/workshop2007/PDFs/Kuvvetli.pdf
22) Carl Budtz-Jorgensen, Irfan Kuvvetli, Ib Lundgard Rasmussen, Torsten Neubert, Nikolai Ostgaard, Asbjorn Spilde, Johann Stadsness, Geir Anton Johansen, Victor Reglero, Andrés R. Berlanga, Paul H. Connell, Chris Eyles, Juana M. Rodrigo, “The Miniature X- and Gamma-Ray Sensor (MXGS) on ASIM,” Toledo, Sain, June 29, 2006, URL: http://projects.iasf-roma.inaf.it/EdgeGMPresentations/52_Budz_ASIM_ROME.ppt
23) Mark R. Drinkwater, “Remote Sensing Observations of the Mesosphere-Lower Thermosphere Region by Earth Observation Satellites,” QB50 Workshop, Nov. 17, 2009, URL: http://www.vki.ac.be/QB50/download/workshop/papers_17nov/drinkwater.pdf
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.