Illumination system (ILL) for an EUV projection exposure apparatus (WSC) for receiving EUV radiation (LR) of an EUV radiation source (LS) and for shaping illumination radiation (ILR) from at least one portion of the received EUV radiation, wherein the illumination radiation is directed into an illumination field in an exit plane (ES) of the illumination system during exposure operation, wherein the EUV radiation source is arranged in a source module (SM) separate from the illumination system, said source module generating a secondary radiation source (SLS) at a source position (SP) in an entrance plane (IS) of the illumination system, comprising: an alignment state determining system (ADS) for determining an alignment state of the secondary radiation source in relation to the illumination system, wherein the alignment state determining system comprises an alignment detector (AD) configured to receive a portion of the EUV radiation emerging from the secondary radiation source and to generate therefrom an alignment detector signal (AS) representative of the alignment state, and a mirror module (MM) comprising a used mirror element (UM) and an alignment mirror element (AM), wherein during exposure operation the used mirror element contributes to the shaping of the illumination radiation incident on the illumination field and the alignment mirror element reflects a portion of the EUV radiation of the secondary radiation source in the direction of the alignment detector, characterized in that the mirror module (MM) is embodied as a structurally exchangeable mirror module, and an optical alignment auxiliary component (AAC) is assigned to the illumination system (ILL), wherein with the aid of the optical alignment auxiliary component an alignment auxiliary signal (AAS, AAS') is generatable which allows a checking of the alignment state of the secondary radiation source (SLS) or of an alignment state of an alignment mirror element (AM) after an exchange of the mirror module. an alignment state determining system (ADS) for determining an alignment state of the secondary radiation source in relation to the illumination system, wherein the alignment state determining system comprises an alignment detector (AD) configured to receive a portion of the EUV radiation emerging from the secondary radiation source and to generate therefrom an alignment detector signal (AS) representative of the alignment state, and a mirror module (MM) comprising a used mirror element (UM) and an alignment mirror element (AM), wherein during exposure operation the used mirror element contributes to the shaping of the illumination radiation incident on the illumination field and the alignment mirror element reflects a portion of the EUV radiation of the secondary radiation source in the direction of the alignment detector, characterized in that the mirror module (MM) is embodied as a structurally exchangeable mirror module, and an optical alignment auxiliary component (AAC) is assigned to the illumination system (ILL), wherein with the aid of the optical alignment auxiliary component an alignment auxiliary signal (AAS, AAS') is generatable which allows a checking of the alignment state of the secondary radiation source (SLS) or of an alignment state of an alignment mirror element (AM) after an exchange of the mirror module. <EOS>