The JEM-EUSO mission: An introduction
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The Extreme Universe Space Observatory on board the Japanese Experiment Module of the International Space Station, JEM-EUSO, is being designed to search from space ultra-high energy cosmic rays. These are charged particles with energies from a few 1019 eV to beyond 1020 eV, at the very end of the known cosmic ray energy spectrum. JEM-EUSO will also search for extreme energy neutrinos, photons, and exotic particles, providing a unique opportunity to explore largely unknown phenomena in our Universe. The mission, principally based on a wide field of view (60 degrees) near-UV telescope with a diameter of ∼ 2.5 m, will monitor the earth’s atmosphere at night, pioneering the observation from space of the ultraviolet tracks (290-430 nm) associated with giant extensive air showers produced by ultra-high energy primaries propagating in the earth’s atmosphere. Observing from an orbital altitude of ∼ 400 km, the mission is expected to reach an instantaneous geometrical aperture of Ageo ≥ 2 × 105 km2 sr with an estimated duty cycle of ∼ 20 %. Such a geometrical aperture allows unprecedented exposures, significantly larger than can be obtained with ground-based experiments. In this paper we briefly review the history of space-based search for ultra-high energy cosmic rays. We then introduce the special issue of Experimental Astronomy devoted to the various aspects of such a challenging enterprise. We also summarise the activities of the on-going JEM-EUSO program.
KeywordsUltra-high energy cosmic rays Neutrinos
1 Introduction and history
JEM-EUSO, the Extreme Universe Space Observatory on board the Japanese Experiment Module (JEM) of the International Space Station (ISS), is a pioneer mission designed to observe the most energetic particles in our universe, the ultra-high energy (UHE) cosmic rays with energies from a few E ∼ 1019 eV to well beyond the threshold of the Greisen-Zatsepin-Kuzmin effect and up to the energy decade above E ∼ 1020 eV , , .
The MASS idea evolved in 1996, in the US, into the Orbiting Wide Angle Light Concentrator (OWL), while the first Airwatch symposium was organised in Europe, in Catania (Italy), in 1996. The OWL mission study proposal was accepted by NASA in 1996 and entered into NASA’s Structure and Evolution of the Universe Mid-Term strategic plan in 2010. The OWL mission concept consists of two satellites observing in stereo configuration from an initial orbit at ∼ 1000 km that will reduce to ∼ 550 km at the end of the mission. The baseline OWL-eye instrument is a large f/1 Schmidt camera with a 45-degree full field of view and a 3.0 m entrance aperture. The entrance aperture is filled with a Schmidt corrector. The deployable primary mirror is 7 m in diameter. The focal plane has an area of 4 m2 segmented into about 1,300 multi-anode photomultiplier tubes for approximately 500,000 pixels. However, the mission has not yet been developed.
In 2006, the Japanese and US teams, under the leadership of Yoshiyuki Takahashi, redefined the mission as an observatory attached to KIBO, the Japanese Experiment Module (JEM) of the ISS. They renamed the mission JEM-EUSO and started a new phase-A study targeting launch in 2013 in the framework of the second utilisation phase of the JEM/EF . The kick-off meeting of the renewed EUSO mission was held in RIKEN in 2006. In 2010 the EUSO mission was also included in the European Life and Physical Sciences in Space Programme (ELIPS) of ESA.
The Phase A/B1 study of JEM-EUSO led by JAXA continued with extensive simulations, design, and prototype developments, that significantly improved the JEM-EUSO mission profile, targeting eventually a launch in 2016 , , , .
This special issue of Experimental Astronomy comprises a series of papers which summarize all these efforts.
According to the JAXA study, the JEM-EUSO instrument shall be transferred to the ISS by the HTV (H2 transfer vehicle). To accommodate JEM-EUSO into the volume of the HTV transfer vehicle, a contractible/extendable structure has been adopted. After the HTV docks in the ISS Docking Port, the Space Station Remote Manipulator System (SSRMS) takes out JEM-EUSO and passes it to the JEM Remote Manipulator System (JEMRMS). JEM-EUSO shall be attached to the Exposed Facility Unit #2 of the JEM External Facility and then expanded to the operational configuration using the deploying mechanism. The principal components of the Ground Segment are the ISS ground station, the JEM Mission Control Room (MCR) in Tsukuba and the JEM-EUSO Science Data Centre (SDC). The end-to-end communication is established via NASA’s Tracking and Data Relay Satellite (TDRS). The ground based calibration facility, equipped with Xenon flashers and lasers, is also an essential element of the ground segm- ent.
Recently, a new study based on the Space-X Falcon 9 launching rocket and using Dragon as the transfer vehicle has been performed.
2 Why a space-based mission to study UHE cosmic rays?
The requirements, the expected performance, and the main features of JEM-EUSO are summarized in , , , , , . The observational technique and exposure of JEM-EUSO is described in .
Another advantage is the large and well constrained distance between the instrument and the location of the extensive air shower (EAS). EASs are in fact constrained to a track length of ∼ 10−20 km, rather small compared with the height (∼ 400 km) of the ISS orbit. In addition, space-based observatories have the possibility of observing in cloudy conditions since, in most cases, the maximum of the shower occurs above the cloud-top .
Assuming a duty cycle of ∼ 20 %, the currently expected trigger efficiencies, and an operation time of about five years, JEM-EUSO can reach an annual exposure close to an order of magnitude larger than the currently operating ground-based observatories. More details can be read in , .
3 The JEM-EUSO pathfinders
In parallel with the development of the main mission concept, the JEM-EUSO program has been enlarged to include a series of “pathfinders” (which are experiments to test the observational technique, and to validate the specific technologie).
3.1 The EUSO-Balloon
The EUSO-Balloon has been developed by the JEM-EUSO collaboration as a demonstrator for the specific technologies and methods featured in the main instrument. The mission was proposed by the French laboratories involved in JEM-EUSO and is led by the balloon division of the CNES, the French Space Agency. The instrument has been built by the JEM-EUSO collaboration. EUSO-Balloon is an imaging UV telescope, a scaled version of the EUSO telescope, pointing towards the nadir from a float altitude of ∼ 40 km. Using Fresnel Optics and a Photo-Detector Module, a prototype of the ones designed for the main mission, the instrument monitors a 12° × 12° wide field of view in the wavelength range between 290 and 430 nm, at a rate of 400,000 frames/s .
3.2 The EUSO-TA
EUSO-TA is currently taking data in a series of rather successful measurement campaigns. At the time of writing, EUSO-TA has already properly detected artificial EAS tracks simulated with the portable laser system from the Colorado Mines school and has detected its first cosmic ray events.
4 What comes next?
Unfortunately the JEM-EUSO mission in its baseline configuration, as designed in the phase A/B1 study, has been frozen by JAXA due to the restructuring of the space station program of Japan. In addition, the HTV launch program will most likely be reduced.
The US team is currently pursuing, with the support of the collaboration, the goal of reorienting the mission using the Falcon 9 launcher and the Dragon transport vehicle to accommodate the mission on the JEM module. The so-called “Dragon” option also impacts the design of the instrument since a circular optics and focal surface can now be used, instead of the side-cut design needed for HTV. Preliminary simulations show that the JEM-EUSO performances summarised in the special issue of Experimental Astronomy can be reached with the new configuration, and in some cases improved.
A different parallel approach is also being actively studied by the JEM-EUSO collaboration: an improved version of the Russian KLYPVE mission, defined as KLYPVE-EUSO or K-EUSO for short. The KLYPVE project, already included into the ROSCOSMOS long term program of experiments on board the Russian segment of the ISS, uses a compound mirror concentrator instead of Fresnel lenses, reaching a better efficiency but a smaller field of view. Major improvements of the KLYPVE-EUSO mission are the use of a Fresnel corrector lens to significantly reduce the size of the reflected spot on the focal surface, and new elements of the structure and electronics. The mission is planned to be launched in 2020. More details can be found in .
The JEM-EUSO collaboration is also developing and actually building a new pathfinder mission: Mini-EUSO. Mini-EUSO, already included in the ISS science programs of ROSCOSMOS and the Italian Space Agency (ASI), is a small, compact UV telescope to be inside the Russian Module of the ISS. It will measure the UV background from earth. Mini-EUSO will be placed in the nadir looking UV window in the Russian segment of the ISS. In addition to measuring and monitoring the UV emission of night-time earth, Mini-EUSO will study UV atmospheric and bioluminescence phenomena. It will also observe several meteors. Launch is foreseen in 2017.
5 The special issue of experimental astronomy on JEM-EUSO
The special issue on JEM-EUSO summarises many of the efforts of the JEM-EUSO collaboration to develop the science case as well as the experimental, technological, and engineering aspects of such a challenging pioneer mission. The expected performance, obtained by careful end to end simulations, are also an important contribution to the special issue.
The science aspects of the exploratory objectives, UHE photons and neutrinos are discussed in , while the science of the atmospheric phenomena is presented in , with a focus on meteors and exotic nuclearites in . Two papers are devoted to the JEM-EUSO observation technique, also discussing observations in cloud conditions (, ). The instrument is summarised in , while details on the photo-detector module are presented in  and its calibration in . The other key element of the JEM-EUSO instrument, the AM system, is presented in , while the details of the IR camera are discussed in . The angular and energy resolution (obtained with end to end simulations) are discussed in  and . Finally, the pathfinders, including the TUS mission onboard the Lomonosov satellite, are presented in ,  and .
The JEM-EUSO collaboration includes, as of today, 16 Countries1, 80 Institutions, and more than 300 researchers.
It is always difficult to predict the future. We do not know exactly how or when this mission will be launched. Hopefully it will be launched in the next few years. There are no doubts that the corpus of the papers included in this issue constitutes an invaluable base for any future studies in the field.
This special issue is dedicated to the memory of John Linsley, Livio Scarsi, and Yoshi Takahashi, whose relentless efforts and creative, contagious enthusiasm opened the field of space-base exploration of the Ultra High Energy Univ- erse.
Countries member of the JEM-EUSO collaboration are: Algeria Bulgaria, France, Germany, Italy, Japan, Korea, Mexico, Poland, Romania, Russia, Slovakia, Spain, Sweden, Switzerland and USA
The work on JEM-EUSO and its pathfinders has been supported by the Basic Science Interdisciplinary Research Projects of RIKEN and JSPS KAKENHI Grant (22340063, 23340081, and 24244042), by the Italian Ministry of Foreign Affairs, General Direction for the Cultural Promotion and Cooperation, by the Deutsches Zentrum für Luft- und Raumfahrt, by the Helmholtz Alliance for Astroparticle Physics HAP funded by the Initiative and Networking Fund of the Helmholtz Association (Germany), and by Slovak Academy of Sciences MVTS JEM-EUSO as well as VEGA Grant agency Project 2/0076/13. The Spanish Consortium involved in the JEM-EUSO Space Mission is funded by MICINN under Projects AYA200906037-E/ESP, AYA-ESP 2010 19082, AYA201129489-C0301, AYA201239115-C03 01, CSD200900064 (Consolider MULTIDARK) and by Comunidad de Madrid (CAM) under Project S2009/ ESP-1496. The EUSO Balloon has been supported by the French CNES and IN2P3. The US is supported by the NASA grants NNX13AH55G, NNX13AH53G. Russia is supported by the Russian Foundation for Basic Research Grant No 13-02-12175-ofi-m. Moreover, studies for JEM-EUSO have been partly funded by the European Space Agency (ESA) through the ”EUSO” Topical Team Fund.
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