Mirror subsystem telescope structure Functions Support mirrors subsystem

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

Telescope structure requirements (1/2) Mechanically decoupled from cryostat (minimum interference with current cryostat design) • Mechanical launch loads, stiffness requirements, shock loads • Mechanical alignment sufficient (build tolerances, need for alignment cubes ? , ≤ 1 mm total) • 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 • Light tight, venting (not vacuum tight) but no dust • No cold trap foreseen • X-ray shielding (possibly at cryostat flange) • • Access to the cryostat 2

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

Design options telescope structure • (1/3) Satellite I/F: mid-plane or bottom plane configurations 1 a/ Tube 1 b/ Tube (bottom plane S/C I/F) (mid plane) Pro’s tube design: • Structure also serves as light tight baffle Con’s tube design: • One piece production (risk, cost) • Spare part needed? • Non iso-static mounting to S/C • 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 • Lighter & rigid telescope design for midplane configuration 4

Design options telescope structure 2 a/ Hexapod 2 b/ Hexapod (small light shield) (large light shield) (2/3) Pro’s: • 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 • Manufacturing and spare parts philosophy: • Production costs likely to be smaller than for tubular design • Each strut can be proof tested after production before integration to FM • Limited number of spare parts • Good accessibility of cryostat Con’s: • Extra light tight baffle needed • Angle of struts requires (possibly) more rigidity at mirror I/F 5

Design options telescope structure Baseline design (3/3) Remarks: • Connection cryostat support to mirror support. Goal: direct mechanical mounting as to: -rule out any influence of S/C panel on telescope alignment -facilitate alignment and verification at instrument level • Presented design includes Mirror Interface Structure (MIS) pro: Quasi-isostatic mirror support con: Hexapod in angled position w. r. t. mirror structure • 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 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? 6

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

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

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

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

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

Thermal resources: mirror heaters Thermal model: • Mirror Ø 407 mm, temperature 20°C, full frontal area: ε=1 • Outer baffle Ø 407 mm, inner baffle Ø 66 mm, length 300 mm • Baffle conductively coupled to mirror (one node only, Tbaffle= -47°C) • Baffle outer surface thermally decoupled from S/C and space by MLI • No sieve slit • No temporal gradients (sun, earth albedo on baffle) • Required heater power 32 W • Ways of heater power reduction: • Mirror temp of 0°C reduces to approx. 24 W • Application of sieve slit (thermal decoupling from mirror provided) • 12

Interfaces 13

Open items SXC to S/C (1/4) Mech I/F of SXC to satellite • Present baseline: bottom-plane I/F to S/C • Launch loads, shock loads, stiffness requirements • SXC mechanical I/F needs to be checked against: • Hexapod mirror support • Platform size and location of other SI • Position of Stirling coolers on cryostat (does not fit presently) • 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 • 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) 14

Open items SXC to S/C (2/4) Thermal • 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 • 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) • A start will be made for a S/C Thermal Math Model by delivering preliminary SXC thermal data to IKI 15

Open items SXC to S/C (3/4) Location of electronics boxes • Mounting surface area for 8 boxes: CAP 30 x 30 cm; CDP 30 x 22 cm; PSU 5 x 38 cm; • CDE 1 10 x 38 cm; CDE 2 28 x 38 cm; ADR ? ; IDC 18 x 22 cm • TAC ? • Total area: 3590 cm 2 (excl. ADR, TAC and cable harness routing) At lower side of S/C panel? • Beneath cryostat? • • Available under cryostat 13000 cm 2 (Ø 130 cm) • drawbacks: • radiated heat towards cryostat • • Telescope Center-of-Gravity 30 -40 cm higher Elsewhere? 16

Payload configurations 17

Open items SXC internally • • • (4/4) Electron deflector (not needed? ) Sieve slit (may also reduce required mirror heater power) Thermal control of e. ROSITA mirrors (power level, control unit) 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) Optical refs mirror-to-detector/cryostat: alignment cube or dowel pins? 18