EChO, the Exoplanet Characterisation Observatory, has been one of the five M-class mission candidates competing for the M3 launch slot within the science programme Cosmic Vision 2015-2025 of the European Space Agency (ESA). As such, EChO has been the subject of a Phase 0/A study that involved European Industry, research institutes and universities from ESA member states and that concluded in Exp Astron EChO is a concept for a dedicated mission to measure the chemical composition and structure of hundreds of exoplanet atmospheres using the technique of transit spectroscopy. With simultaneous and uninterrupted spectral coverage from the visible to infrared wavelengths, EChO targets extend from gas giants (Jupiter or Neptune-like) to super-Earths in the very hot to temperate zones of F to M-type host stars, opening up the way to large-scale, comparative planetology that would place our own solar system in the context of other planetary systems in the Milky Way. A review of the performance requirements of the EChO mission was held at ESA at the end of 2013, with the objective of assessing the readiness of the mission to progress to the Phase B1 study phase. No critical issues were identified from a technical perspective, however a number of recommendations were made for future work. Since the mission was not selected for the M3 launch slot, EChO is no longer under study at ESA. In this paper we give an overview of the final mission concept for EChO as of the end of the study, from scientific, technical and operational perspectives.
Since its launch in 2002, ESA's INTErnational Gamma-Ray Astrophysics Laboratory(INTEGRAL) has been observing astronomical objects simultaneously in gamma-rays, Xrays and visible light. Using its four instruments, it provides insight into the nature of sources of extremely high-energy radiation, and 9 years after its launch the scientific interest is still very high. The performance of INTEGRAL has far exceeded design specifications. To date, it is still the most sensitive gamma ray observatory in space, all prime units are still in use, no major failures have occurred and the degradation of spacecraft components is minimal. Last but not least, the nominal lifetime of two years has already been far exceeded, and the remaining fuel on board still allows for another decade of operations.Major challenges the mission faces are the orbital evolution and the aging of spacecraft components: on October 25th 2011, INTEGRAL reached the lowest perigee altitude since its launch. This resulted in both increased exposure to proton radiation during perigee passage and an increased heating of the spectrometer's cryocooler due to the Earth albedo, leading to a small reduction in payload performance. Furthermore, all electrical components will have reached their total dose qualification limit soon. This paper summarizes the effects of the period of low perigee altitude on the degradation of the materials and spacecraft components. Furthermore, it presents the associated countermeasures, operational strategies as well as the impact on the fuel consumption and the science. Finally, the prospects for future INTEGRAL operations are summarized along with the lessons learned from the period of low perigee.
Cosmic rays interacting with the Earth's atmosphere can generate photons with energies up to the gamma regime. This effect has only been studied marginally from space. In 2006, four short Earth occultation observations were performed successfully with INTEGRAL during a solar minimum, where the gamma-ray flux of the Earth's atmosphere was at a maximum due to cosmic ray bombardment. These observations demonstrated the technical feasibility of the Earth occultation observation method with INTEGRAL and its high scientific potential. Exploiting further this scientific potential, another set of occultation observations is planned for AO-9 (2012-2013) to further probe the three distinct soft gamma-ray diffuse components: the cosmic X-ray background (CXB), the galactic background emission and the Earth atmospheric emission due to both the reflection of the CXB and cosmic-ray interactions. The total exposure time of the AO-9 observations will be longer than in 2006. In order to follow the evolution of the soft gamma-ray diffuse components towards the solar maximum, the upcoming observations will be spread over a period of two years. This paper summarises the scientific objectives of the planned Earth occultation observation campaign with INTEGRAL as well as the associated operational strategies and challenges, such as the need to use a non-standard INTEGRAL pointing mode.
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