© Didier Barret et authorsBarret, DidierAlbouys, VincentHerderm Jan-Willem denPiro, LuigiCappi, MassimoHuovelin, JuhaniKelley, RichardMas-Hesse, J. MiguelPaltani, StéphaneRauw, GregorRozanska, AgataFiore, FabrizioBonny, PatrickBoorman, PeterBoreux, CharlesBounab, AyoubCuttaia, FrancescoGabici, StefanoBoutelier, MartinBoyce, KevinMolin, AlexeïEtcheverry, ChristopheBrienza, DanieleBruijn, MarcelBandler, SimonPuccio, ElenaBulgarelli, AndreaCalarco, SimonaCallanan, PaulD'Ai, AntoninoCamus, ThierryCanourgues, FlorentBranduardi-Raymont, GraziellaCavazzuti, ElisabettaGant, FlorentCapobianco, VitoCardiel, NicolásCastellani, FlorentCheatom, OscarPascale, RamonChervenak, JamesD'anca, FabioGastaldello, FabioEttori, StefanoDadina, MauroBarbera, MarcoDaniel, ChristophePeille, PhilippeGloaguen, EmilieDeNigris, NatalieDercksen, JohannesDiPirro, MichaelDoumayrou, EricDubbeldam, LucFinoguenov, AlexisBozzo , EnricoDupieux, MichelMonestes, DavidGenolet, LudovicGhizzardi, SimonaPlaa, Jelle deAlcacera Gil, María ÁngelesDupourqué, SimonGiovannini, ElisaDurkin, MalcomGrosso, NicolasCharles, IvanGodet, OlivierGómez Elvira, J.Montinaro, NicolaGonzález, ManuelGonzález, RaoulGottardi, LucianoArdellier, FlorenceGranat, DolorèsGros, MichelPinsard, FredericRioland, GuillaumeGuignard, NicolasHieltjes, PaulFioretti, ValentinaMot, BaptisteHurtado, Adolfo JesusCostantini, ElisaIrwin, KentJacquey, ChristianArgan, AndreaVan der Kuur, JanJaniuk, AgnieszkaJaubert, JeanRodriguez, LouisJolly, AntoineSmith, StephenJourdan, ThierryJulien, SabineGeoffray, HervéKedziora, BartoszKaastra, JelleKorb, AndrewVan Leeuwen, Bert-JoostDauser, ThomasKreykenbohm, IngoKönig, OleLanger, MathieuMurat, DavidRoig, AntonLaudet, PhilippeLaurent, PhilippeMazzotta, PasqualeLaurenza, MonicaLesrel, JeanJacques, LionelBellouard, EliseLigori, SebastianoLorenz, MaximilianLuminari, AlfredoNagayoshi, KenichiroDecourchelle, AnneMaffei, BrunoColonges, StéphaneRollet, BertrandMaisonnave, OcéaneMarelli, LorenzoMassonet, DidierMaussang, IrwinCarron, JérômeNazé, YaëlRoudil, GillesNoguès, LoïcKirsch, ChristianPailot, DamienChiarello, FabioFossecave, HervéDuval, Jean-MarcPanessa, FrancescaParodi, LuigiPetit, PascalPiconcelli, EnricoAdams, JosephPinto, CiroMiller, JonRudnicki, TomaszGatti, FlavioClerc, NicolasSanisidro, JulienEncinas Plaza, José MiguelSciortino, LuisaDurand, Jean LouisHoogeveen, RuudSilva, VitorSordet, MichaelMiniutti, GiovanniSoto Aguilar, JavierSpizzi, PierreSurace, ChristianClerc, LaurentFernández Sánchez, MiguelTaralli, EmanueleFiorini, MauroGoldwurm, AndreaHartog, Roland denEckert, DominiqueNicastro, FabrizioJackson, BrianSvoboda, JiriJonker, PeterKilbourne, CarolineCobo, BeatrizKorpela, SeppoMacculi, ClaudioMendez, MarianoKhosropanah, PouryaMitsuda, KazuhisaFinkbeiner, FredMolendi, SilvanoPajot, FrançoisEiriz, ValvaneraPointecouteau, EtiennePorter, FrederickGao, Jian-RongVan der Hulst, PaulPratt, Gabriel W.Prêle, DamienRavera, LaurentSciortino, SalvatoreMartin, SylvainSato, KosukeSchaye, JoopShinozaki, KeisukeSkup, KonradErcolani, EricCoeur-Joly, OdileSoucek, JanThibert, TanguyVink, JaccoYamaguchi, HiroyaKiviranta, MikkoWebb, NataliePerry, JamesChaoul, LaurenceRaulin, DesiSimionescu, AuroraTorrejón, José MiguelColeiro, AlexisAcero, FabioBeaumont, SophiePradines, AliceCucchetti, EdoardoD'Andrea, MatteoLe Mer, IsabelleReina, M.Ledot, AurélienEckart, MeganFerrando, PhilippeKammoun, EliasLotti, SimoneFiocchi, Maria TeresaMesnager, Jean-MichelRigano, ManuelaVan Loon, DennisMichalski, LeaRoelfsema, PeterNatalucci, LorenzoSchwander, DenisPoyatos Martínez, D.Ceballos, Maria TeresaTorrioli, GuidoUllom, JoelMedinaceli Villegas, EduardoZuchniak, MonikaMillerioux, Jean-PierreBrachet, FrankLo Cicero, UgoCorcione, LeonardoLyautey, BertrandParot, YannProuvé, ThomasSakai, KazuhiroDoriese, WilliamWeers, Henk vanWilms, JoernMineo, TeresaAbdoelkariem, ShariefaAdam, ThomasAdami, ChristopheCoriat, MickaelAicardi, CorinneAkamatsu, HirokiMerino Alonso, Pablo EleazarPtak, AndyAmato, RobertaAndré, JérômeRoncarelli, MauroFranssen, PhilippeAngelinelli, MatteoAñón Cancela, M.Yamasaki, NorikoCoynel, AlexandreAnvar, ShebliAtienza, R.Attard, AnthonyAuricchio, NataliaPuccetti, SimonettaDuband, LionelBalado, A.Bancel, FlorianFerrari Barusso, LorenzoFrericks, MartinBernard, VivianBarcons, XavierBerrocal, A.Blin, SylvieAudard, MarcBonino, DonataMinervini, GabrieleBonnet, FrançoisJiménez, MaríaGonzalo Melchor, AlejandroVERA TRALLERO, ISABEL2023-01-172023-01-172022-08-30Experimental Astornomy 54(2): --preprint--0922-6435https://arxiv.org/abs/2208.14562http://hdl.handle.net/20.500.12666/83448 pages, 29 figures. *Accepted for publication in Experimental Astronomy with minor editing.The Athena X-ray Integral Unit (X-IFU) is the high resolution X-ray spectrometer, studied since 2015 for flying in the mid-30s on the Athena space X-ray Observatory, a versatile observatory designed to address the Hot and Energetic Universe science theme, selected in November 2013 by the Survey Science Committee. Based on a large format array of Transition Edge Sensors (TES), it aims to provide spatially resolved X-ray spectroscopy, with a spectral resolution of 2.5 eV (up to 7 keV) over an hexagonal field of view of 5 arc minutes (equivalent diameter). The X-IFU entered its System Requirement Review (SRR) in June 2022, at about the same time when ESA called for an overall X-IFU redesign (including the X-IFU cryostat and the cooling chain), due to an unanticipated cost overrun of Athena. In this paper, after illustrating the breakthrough capabilities of the X-IFU, we describe the instrument as presented at its SRR, browsing through all the subsystems and associated requirements. We then show the instrument budgets, with a particular emphasis on the anticipated budgets of some of its key performance parameters. Finally we briefly discuss on the ongoing key technology demonstration activities, the calibration and the activities foreseen in the X-IFU Instrument Science Center, and touch on communication and outreach activities, the consortium organisation, and finally on the life cycle assessment of X-IFU aiming at minimising the environmental footprint, associated with the development of the instrument. Thanks to the studies conducted so far on X-IFU, it is expected that along the design-to-cost exercise requested by ESA, the X-IFU will maintain flagship capabilities in spatially resolved high resolution X-ray spectroscopy, enabling most of the original X-IFU related scientific objectives of the Athena mission to be retained.engAttribution-NonCommercial-NoDerivatives 4.0 Internationalhttps://creativecommons.org/licenses/by-nc-nd/4.0/Astrophysics of GalaxiesHigh energyAstrophysical phenomenaSolar and stellar astrophysicsinfo:eu-repo/semantics/article1572-9508info:eu-repo/semantics/openAccess