1. 1 Mirror subsystem: telescope structure Functions: Functions: Support mirrors subsystem to S/C Support mirrors subsystem to S/C Accommodate cryostat Accommodate cryostat Connect mirrors to cryostat mechanically within alignment requirements Connect mirrors to cryostat mechanically within alignment requirements Support cryostat radiator TBD (not drawn) Support cryostat radiator TBD (not drawn) Goals: Goals: Current designs of mirrors and cryostat shall be kept unchanged to a maximum extend Current designs of mirrors and cryostat shall be kept unchanged to a maximum extend

2. 2 Telescope structure requirements (1/2) Mechanically decoupled from cryostat (minimum interference with current cryostat design) Mechanically decoupled from cryostat (minimum interference with current cryostat design) Mechanical launch loads, stiffness requirements, shock loads Mechanical launch loads, stiffness requirements, shock loads Mechanical alignment sufficient (build tolerances, need for alignment cubes ?, ≤ 1 mm total) Mechanical alignment sufficient (build tolerances, need for alignment cubes ?, ≤ 1 mm total) Thermal stability during mission operations (≤ 1 mm total, T gradients not known) Thermal stability during mission operations (≤ 1 mm total, T gradients not known) Operational temperature: 20 ± 5 deg (or as low as -100 deg), coupling to dewar, MLI at satellite level Operational temperature: 20 ± 5 deg (or as low as -100 deg), coupling to dewar, MLI at satellite level Light tight, venting (not vacuum tight) but no dust Light tight, venting (not vacuum tight) but no dust No cold trap foreseen No cold trap foreseen X-ray shielding (possibly at cryostat flange) X-ray shielding (possibly at cryostat flange) Access to the cryostat Access to the cryostat

3. 3 Mirror and cover/door requirements (2/2) Cover on mirror (one shot) Cover on mirror (one shot) Operating temperature mirror 20 ± 5 deg C (could be lower?) Operating temperature mirror 20 ± 5 deg C (could be lower?) Gradient mirror: < 4 deg / mirror assembly (lateral) Gradient mirror: < 4 deg / mirror assembly (lateral) Avoidance angles for bright light: 45° (sun and earth albedo) Avoidance angles for bright light: 45° (sun and earth albedo) Thermal control (separate unit) Thermal control (separate unit)

4. 4 Design options telescope structure (1/3) Satellite I/F: mid-plane or bottom plane configurations Satellite I/F: mid-plane or bottom plane configurations 1a/ Tube (bottom plane S/C I/F) 1b/ Tube (mid plane) Pro’s tube design: Structure also serves as light tight baffle Structure also serves as light tight baffle Con’s tube design: One piece production (risk, cost) One piece production (risk, cost) Spare part needed? Spare part needed? Non iso-static mounting to S/C Non iso-static mounting to S/C Thermal expansion of tube w.r.t. end flanges (thermo-mechanical stress) Thermal expansion of tube w.r.t. end flanges (thermo-mechanical stress)Remarks: Cryostat accessibility: good for mid-plane S/C I/F, less for bottom-plane configuration Cryostat accessibility: good for mid-plane S/C I/F, less for bottom-plane configuration Lighter & rigid telescope design for mid- plane configuration Lighter & rigid telescope design for mid- plane configuration

5. 5 Design options telescope structure (2/3) 2a/ Hexapod (small light shield) 2b/ Hexapod (large light shield) Pro’s: Iso-static support of mirror (independent from S/C panel stiffness and flatness) Iso-static support of mirror (independent from S/C panel stiffness and flatness) Non-sensitive to delta thermal expansion between S/C panel and mirror Non-sensitive to delta thermal expansion between S/C panel and mirror Manufacturing and spare spare parts philosophy: Manufacturing and spare spare parts philosophy: Good accessibility of cryostat Good accessibility of cryostatCon’s: Extra light tight baffle needed Extra light tight baffle needed Angle of struts requires (possibly) more rigidity at mirror I/F Angle of struts requires (possibly) more rigidity at mirror I/F Production costs likely to be smaller than for tubular design Production costs likely to be smaller than for tubular design Each strut can be proof tested after production before integration to FM Each strut can be proof tested after production before integration to FM Limited number of spare parts Limited number of spare parts

6. 6 Design options telescope structure (3/3) Baseline design Remarks: Connection cryostat support to mirror support. Goal: direct mechanical mounting as to: Connection cryostat support to mirror support. Goal: direct mechanical mounting as to: -rule out any influence of S/C panel on telescope alignment -rule out any influence of S/C panel on telescope alignment -facilitate alignment and verification at instrument level -facilitate alignment and verification at instrument level Presented design includes Mirror Interface Structure (MIS) Presented design includes Mirror Interface Structure (MIS) pro: Quasi-isostatic mirror support pro: Quasi-isostatic mirror support con: Hexapod in angled position w.r.t. mirror structure con: Hexapod in angled position w.r.t. mirror structure Light tight baffle is not vacuum tight (labyrinth connection to mirror and cryostat) Light tight baffle is not vacuum tight (labyrinth connection to mirror and cryostat) Baffle stiffness may not dictate mirror position: this can be resolved by an isostatic baffle mounting Baffle stiffness may not dictate mirror position: this can be resolved by an isostatic baffle mounting Baffle needs to accommodate cryostat door Baffle needs to accommodate cryostat door The shown cryostat support to S/C panel (current design?) is non iso-static: panel (stiffness and flatness) and cryostat support mechanically influence each other. Need this to be avoided? Can it? The shown cryostat support to S/C panel (current design?) is non iso-static: panel (stiffness and flatness) and cryostat support mechanically influence each other. Need this to be avoided? Can it?

7. 7 Design options baffle/door (1/4) Optical baffle avoidance angle 45° from direct sunlight/earth albedo Optical baffle avoidance angle 45° from direct sunlight/earth albedo Accommodates sieve slit Accommodates sieve slit Door design: Door design: Spring loaded hinge Spring loaded hinge Hold-down and release mechanism (e.g. pyro, thermal knife, memory metal) Hold-down and release mechanism (e.g. pyro, thermal knife, memory metal) Not vacuum tight to baffle (no sealing necessary, thus avoiding high spring loads to open door) Not vacuum tight to baffle (no sealing necessary, thus avoiding high spring loads to open door) Shock damper at end of stroke TBD (as to limit shock to mirror) Shock damper at end of stroke TBD (as to limit shock to mirror)

8. 8 Design options baffle/door (2/4) eRosita optical baffle design: eRosita optical baffle design: No door foreseen on mirror module level No door foreseen on mirror module level Baffle is (probably) not able to carry cover mass loads Baffle is (probably) not able to carry cover mass loads Two options: Two options: 1/ Keep baffle eRosita: create extra support structure for door 1/ Keep baffle eRosita: create extra support structure for door 2/ New baffle design integrated with door support 2/ New baffle design integrated with door support DM – Mirror design

9. 9 Design options baffle/door (2/3) Option 1: eRosita baffle kept Support on mirror spider Pro: Short struts Short struts Small envelope Small envelopeCon: Mech.loads mirror spider (launch, door shock) Mech.loads mirror spider (launch, door shock) Struts not in triangular configuration Struts not in triangular configuration Supported on mirror I/F Pro: Small envelope Small envelope No mechanical loads on mirror spider No mechanical loads on mirror spiderCon: Long struts Long struts Struts not in triangular configuration Struts not in triangular configuration Supported on mirror I/F Pro: Struts in triangular configuration Struts in triangular configuration No mechanical loads on mirror spider No mechanical loads on mirror spiderCon: Long struts Long struts Larger envelope Larger envelope

10. 10 Design options baffle/door (3/3) Option 2: Door support is integrated in baffle Support on mirror spider Pro: Small envelope Small envelopeCon: Mechanical loads on mirror spider (launch, door shock) Mechanical loads on mirror spider (launch, door shock) Supported on mirror I/F Pro: No mechanical loads on mirror spider No mechanical loads on mirror spiderCon: Larger envelope Larger envelope Mass Mass

11. 11 Resources Power: 32 W (see next slide) Power: 32 W (see next slide) Mass: 61 kg (incl. hexapod, appendages, mirror cover, cryostat-to-mirror baffle, etc) Mass: 61 kg (incl. hexapod, appendages, mirror cover, cryostat-to-mirror baffle, etc) Volume: Volume: Diameter hexapod I/F to S/C 1300 mm approx. (determined by mirror diameter and cryostat size) Diameter hexapod I/F to S/C 1300 mm approx. (determined by mirror diameter and cryostat size) Mirror ext. diameter 430 mm (max.) Mirror ext. diameter 430 mm (max.) Height 3000 mm (incl. eRosita baffle, door) Height 3000 mm (incl. eRosita baffle, door) Electronics: operating 10-30°C, non- operating 0-40°C Electronics: operating 10-30°C, non- operating 0-40°C

12. 12 Thermal resources: mirror heaters Thermal model: Thermal model: Mirror Ø407 mm, temperature 20°C, full frontal area: ε=1 Mirror Ø407 mm, temperature 20°C, full frontal area: ε=1 Outer baffle Ø407 mm, inner baffle Ø66 mm, length 300mm Outer baffle Ø407 mm, inner baffle Ø66 mm, length 300mm Baffle conductively coupled to mirror (one node only, T baffle = -47 °C ) Baffle conductively coupled to mirror (one node only, T baffle = -47 °C ) Baffle outer surface thermally decoupled from S/C and space by MLI Baffle outer surface thermally decoupled from S/C and space by MLI No sieve slit No sieve slit No temporal gradients (sun, earth albedo on baffle) No temporal gradients (sun, earth albedo on baffle) Required heater power 32 W Required heater power 32 W Ways of heater power reduction: Ways of heater power reduction: Mirror temp of 0°C reduces to approx. 24 W Mirror temp of 0°C reduces to approx. 24 W Application of sieve slit (thermal decoupling from mirror provided) Application of sieve slit (thermal decoupling from mirror provided)

13. 13 Interfaces

14. 14 Open items SXC to S/C (1/4) Mech I/F of SXC to satellite Present baseline: bottom-plane I/F to S/C Present baseline: bottom-plane I/F to S/C Launch loads, shock loads, stiffness requirements Launch loads, shock loads, stiffness requirements SXC mechanical I/F needs to be checked against: SXC mechanical I/F needs to be checked against: Hexapod mirror support Hexapod mirror support Platform size and location of other SI Platform size and location of other SI Position of Stirling coolers on cryostat (does not fit presently) Position of Stirling coolers on cryostat (does not fit presently) Cryostat support (issues: S/C panel stiffness, flatness, CTE) Cryostat support (issues: S/C panel stiffness, flatness, CTE) Preferred by SXC : one combined mech. I/F to S/C as to rule out ‘un’-alignment by thermo-mechanical issues Preferred by SXC : one combined mech. I/F to S/C as to rule out ‘un’-alignment by thermo-mechanical issues Co-alignment to other instruments (initial assembly; thermal in-flight warp of S/C panel, can be solved after S/C thermal analysis has been at higher level) Co-alignment to other instruments (initial assembly; thermal in-flight warp of S/C panel, can be solved after S/C thermal analysis has been at higher level)

15. 15 Open items SXC to S/C (2/4) Thermal Location and size of cryostat radiators Location and size of cryostat radiators (issues: radiator size; electronics need to be cooled as well?; view factor to solar panels; shielding from sun, earth albedo?) Spacecraft temperature, stability and spatial gradients Spacecraft temperature, stability and spatial gradients Electronics: operating 10-30°C, non-operating 0-40°C Electronics: operating 10-30°C, non-operating 0-40°C Any mechanical I/F’s to S/C thermal system? (e.g. S/C MLI to mirror subsystem) Any mechanical I/F’s to S/C thermal system? (e.g. S/C MLI to mirror subsystem) A start will be made for a S/C Thermal Math Model by delivering preliminary SXC thermal data to IKI A start will be made for a S/C Thermal Math Model by delivering preliminary SXC thermal data to IKI

16. 16 Open items SXC to S/C (3/4) Location of electronics boxes Mounting surface area for 8 boxes: Mounting surface area for 8 boxes: CAP 30 x 30 cm; CDP 30 x 22 cm; PSU 5 x 38 cm; CAP 30 x 30 cm; CDP 30 x 22 cm; PSU 5 x 38 cm; CDE1 10 x 38 cm; CDE2 28 x 38 cm; ADR ?; IDC 18 x 22 cm CDE1 10 x 38 cm; CDE2 28 x 38 cm; ADR ?; IDC 18 x 22 cm TAC ? TAC ? Total area: 3590 cm 2 (excl. ADR, TAC and cable harness routing) At lower side of S/C panel? At lower side of S/C panel? Beneath cryostat? Beneath cryostat? Available under cryostat 13000 cm 2 (Ø130 cm) Available under cryostat 13000 cm 2 (Ø130 cm) drawbacks: drawbacks: radiated heat towards cryostat radiated heat towards cryostat Telescope Center-of-Gravity 30-40cm higher Telescope Center-of-Gravity 30-40cm higher Elsewhere? Elsewhere?

17. 17 Payload configurations

18. 18 Open items SXC internally (4/4) Electron deflector (not needed?) Electron deflector (not needed?) Sieve slit (may also reduce required mirror heater power) Sieve slit (may also reduce required mirror heater power) Thermal control of eROSITA mirrors (power level, control unit) Thermal control of eROSITA mirrors (power level, control unit) Thermal load on telescope structure (alignment issues, thermo-mechanical stress) Thermal load on telescope structure (alignment issues, thermo-mechanical stress) Structural support of cryostat and fixation to hexapod and S/C (issues S/C Panel stiffness, flatness) Structural support of cryostat and fixation to hexapod and S/C (issues S/C Panel stiffness, flatness) Optical refs mirror-to-detector/cryostat: alignment cube or dowel pins? Optical refs mirror-to-detector/cryostat: alignment cube or dowel pins?