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Mirror subsystem: telescope structureMirror 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 Connect mirrors to cryostat

mechanically within alignment mechanically within alignment requirementsrequirements

• Support cryostat radiator TBD (not Support cryostat radiator TBD (not drawn)drawn)

• Goals:Goals:• Current designs of mirrors and Current designs of mirrors and

cryostat shall be kept unchanged cryostat shall be kept unchanged to a maximum extend to a maximum extend

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Telescope structure requirements Telescope structure requirements (1/2)(1/2)

• Mechanically decoupled from cryostat (minimum interference Mechanically decoupled from cryostat (minimum interference with current cryostat design)with current cryostat design)

• Mechanical launch loads, stiffness requirements, shock loadsMechanical launch loads, stiffness requirements, shock loads• Mechanical alignment sufficient (build tolerances, need for Mechanical alignment sufficient (build tolerances, need for

alignment cubes ?, ≤ 1 mm total)alignment cubes ?, ≤ 1 mm total)

• Thermal stability during mission operations (≤ 1 mm total, T Thermal stability during mission operations (≤ 1 mm total, T gradients not known)gradients not known)

• Operational temperature: 20 ± 5 deg (or as low as -100 deg), Operational temperature: 20 ± 5 deg (or as low as -100 deg), coupling to dewar, MLI at satellite levelcoupling to dewar, MLI at satellite level

• Light tight, venting (not vacuum tight) but no dustLight tight, venting (not vacuum tight) but no dust• No cold trap foreseenNo cold trap foreseen• X-ray shielding (possibly at cryostat flange)X-ray shielding (possibly at cryostat flange)

• Access to the cryostatAccess to the cryostat

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Mirror and cover/door requirements Mirror and cover/door requirements (2/2)(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 Avoidance angles for bright light: 45° (sun and earth albedoand earth albedo))• Thermal control (separate unit)Thermal control (separate unit)

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Design options telescope structure Design options telescope structure (1/3)(1/3)

• Satellite I/F: mid-plane or bottom plane configurationsSatellite I/F: mid-plane or bottom plane configurations

1a/ Tube1a/ Tube(bottom plane S/C I/F)(bottom plane S/C I/F)

1b/ Tube1b/ Tube(mid plane)(mid plane) Pro’s tube design:Pro’s tube design:

•Structure also serves as light tight baffleStructure also serves as light tight baffle

Con’s tube design: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/CNon iso-static mounting to S/C•Thermal expansion of tube w.r.t. end Thermal expansion of tube w.r.t. end flanges (thermo-mechanical stress)flanges (thermo-mechanical stress)

Remarks:Remarks:•Cryostat accessibility: good for mid-plane Cryostat accessibility: good for mid-plane S/C I/F, less for bottom-plane configurationS/C I/F, less for bottom-plane configuration•Lighter & rigid telescope design for mid-Lighter & rigid telescope design for mid-plane configurationplane configuration

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Design options telescope structure Design options telescope structure (2/3)(2/3)

2a/ Hexapod2a/ Hexapod(small light shield)(small light shield)

2b/ Hexapod2b/ Hexapod(large light shield)(large light shield) Pro’s:Pro’s:

•Iso-static support of mirror (independent Iso-static support of mirror (independent from S/C panel stiffness and flatness)from S/C panel stiffness and flatness)•Non-sensitive to delta thermal expansion Non-sensitive to delta thermal expansion between S/C panel and mirrorbetween S/C panel and mirror•Manufacturing and spare spare parts Manufacturing and spare spare parts philosophy:philosophy:

•Good accessibility of cryostatGood accessibility of cryostat

Con’s:Con’s:•Extra light tight baffle neededExtra light tight baffle needed•Angle of struts requires (possibly) more Angle of struts requires (possibly) more rigidity at mirror I/Frigidity at mirror I/F

•Production costs likely to be smaller than for Production costs likely to be smaller than for tubular designtubular design•Each strut can be proof tested after production Each strut can be proof tested after production before integration to FMbefore integration to FM•Limited number of spare partsLimited number of spare parts

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Design options telescope structure Design options telescope structure (3/3)(3/3)

Baseline designBaseline design Remarks:Remarks:•Connection cryostat support to mirror support. Goal: direct Connection cryostat support to mirror support. Goal: direct mechanical mounting as to: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 structurecon: Hexapod in angled position w.r.t. mirror structure

•Light tight baffle is not vacuum tight (labyrinth connection to Light tight baffle is not vacuum tight (labyrinth connection to mirror and cryostat)mirror and cryostat)•Baffle stiffness may not dictate mirror position: this can be Baffle stiffness may not dictate mirror position: this can be resolved by an isostatic baffle mountingresolved by an isostatic baffle mounting•Baffle needs to accommodate cryostat doorBaffle needs to accommodate cryostat door

•The shown cryostat support to S/C panel (current design?) is The shown cryostat support to S/C panel (current design?) is non iso-static: panel (stiffness and flatness) and cryostat non iso-static: panel (stiffness and flatness) and cryostat support mechanically influence each other. Need this to be support mechanically influence each other. Need this to be avoided? Can it?avoided? Can it?

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Design options baffle/door Design options baffle/door (1/4)(1/4)

• Optical baffle avoidance angle 45° from direct sunlight/earth Optical baffle avoidance angle 45° from direct sunlight/earth albedoalbedo

• Accommodates sieve slitAccommodates sieve slit• Door design:Door design:

• Spring loaded hingeSpring loaded hinge• Hold-down and release mechanism Hold-down and release mechanism (e.g. pyro, thermal knife, (e.g. pyro, thermal knife,

memory metal)memory metal)

• Not vacuum tight to baffle Not vacuum tight to baffle (no sealing necessary, thus avoiding high (no sealing necessary, thus avoiding high spring loads to open door)spring loads to open door)

• Shock damper at end of stroke TBD Shock damper at end of stroke TBD (as to limit shock to mirror) (as to limit shock to mirror)

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Design options baffle/door Design options baffle/door (2/4)(2/4)

• eRosita optical baffle design: eRosita optical baffle design: • No door foreseen on mirror module levelNo door foreseen on mirror module level• Baffle is (probably) not able to carry cover mass loadsBaffle is (probably) not able to carry cover mass loads

• Two options:Two options:• 1/ Keep baffle eRosita: create extra support structure for door1/ Keep baffle eRosita: create extra support structure for door• 2/ New baffle design integrated with door support2/ New baffle design integrated with door support

DM – Mirror design

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Design options baffle/door Design options baffle/door (2/3)(2/3) Option 1: Option 1: eRositaeRosita baffle kept baffle kept

Support on mirror spiderSupport on mirror spider

Pro: Pro: •Short strutsShort struts•Small envelopeSmall envelope

Con:Con: •Mech.loads mirror spider Mech.loads mirror spider (launch, door shock) (launch, door shock) •Struts not in triangular Struts not in triangular configurationconfiguration

Supported on mirror I/FSupported on mirror I/F

Pro:Pro: • Small envelopeSmall envelope• No mechanical loads No mechanical loads

on mirror spideron mirror spider

Con:Con: • Long strutsLong struts• Struts not in triangular Struts not in triangular

configurationconfiguration

Supported on mirror I/FSupported on mirror I/F

Pro:Pro:•Struts in triangular Struts in triangular configurationconfiguration•No mechanical loads on No mechanical loads on mirror spidermirror spider

Con:Con:•Long strutsLong struts•Larger envelopeLarger envelope

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Design options baffle/door Design options baffle/door (3/3)(3/3) Option 2: Option 2: Door support is integrated in baffleDoor support is integrated in baffle

Support on mirror spiderSupport on mirror spider

Pro: Pro: •Small envelopeSmall envelope

Con: Con: •Mechanical loads on Mechanical loads on mirror spider (launch, mirror spider (launch, door shock) door shock)

Supported on mirror I/FSupported on mirror I/F

Pro: Pro: • No mechanical loads No mechanical loads

on mirror spideron mirror spider

Con: Con: • Larger envelopeLarger envelope• MassMass

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ResourcesResources• Power: 32 W Power: 32 W (see next slide)(see next slide)

• Mass: 61 kg Mass: 61 kg (incl. hexapod, appendages, mirror (incl. hexapod, appendages, mirror cover, cryostat-to-mirror baffle, etc)cover, cryostat-to-mirror baffle, etc)

• Volume:Volume:• Diameter hexapod I/F to S/C 1300 mm Diameter hexapod I/F to S/C 1300 mm

approx. approx. (determined by mirror diameter and (determined by mirror diameter and cryostat size)cryostat size)

• Mirror ext. diameter 430 mm (max.)Mirror ext. diameter 430 mm (max.)• Height 3000 mm Height 3000 mm (incl. eRosita baffle, door)(incl. eRosita baffle, door)

• Electronics: operating 10-30°C, non-Electronics: operating 10-30°C, non-operating 0-40°Coperating 0-40°C

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Thermal resources: mirror heatersThermal resources: mirror heaters

• Thermal model:Thermal model:• Mirror Ø407 mm, temperature 20°C, full frontal area: Mirror Ø407 mm, temperature 20°C, full frontal area: εε=1 =1 • Outer baffle Ø407 mm, inner baffle Ø66 mm, length 300mmOuter baffle Ø407 mm, inner baffle Ø66 mm, length 300mm• Baffle conductively coupled to mirror Baffle conductively coupled to mirror (one node only, (one node only,

TTbafflebaffle= -47= -47°C°C))

• Baffle outer surface thermally decoupled from S/C and space Baffle outer surface thermally decoupled from S/C and space by MLIby MLI

• No sieve slitNo sieve slit• No temporal gradients (sun, earth albedo on baffle)No temporal gradients (sun, earth albedo on baffle)• Required heater power 32 WRequired 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 Application of sieve slit (thermal decoupling from mirror provided)(thermal decoupling from mirror provided)

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InterfacesInterfaces

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Open items SXC to S/C Open items SXC to S/C (1/4)(1/4)

Mech I/F of SXC to satellite Mech I/F of SXC to satellite • Present baseline: bottom-plane I/F to S/CPresent baseline: bottom-plane I/F to S/C• Launch loads, shock loads, stiffness requirementsLaunch 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 supportHexapod mirror support• Platform size and location of other SIPlatform size and location of other SI• Position of Stirling coolers on cryostat (does not fit Position of Stirling coolers on cryostat (does not fit

presently)presently)• Cryostat support Cryostat support (issues: S/C panel stiffness, flatness, CTE)(issues: S/C panel stiffness, flatness, CTE)

• Preferred by SXC : one combined mech. I/F to S/C as to rule Preferred by SXC : one combined mech. I/F to S/C as to rule out ‘un’-alignment by thermo-mechanical issues out ‘un’-alignment by thermo-mechanical issues

• Co-alignment to other instruments Co-alignment to other instruments (initial assembly; thermal in-flight (initial assembly; thermal in-flight warp of S/C panel, can be solved after S/C thermal analysis has been at higher warp of S/C panel, can be solved after S/C thermal analysis has been at higher level)level)

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Open items SXC to S/C Open items SXC to S/C (2/4)(2/4)

ThermalThermal• Location and size of cryostat radiatorsLocation and size of cryostat radiators

(issues: radiator size; electronics need to be cooled as well?; view factor (issues: radiator size; electronics need to be cooled as well?; view factor to solar panels; shielding from sun, earth albedo?) to solar panels; shielding from sun, earth albedo?)

• Spacecraft temperature, stability and spatial gradientsSpacecraft temperature, stability and spatial gradients• Electronics: operating 10-30°C, non-operating 0-40°CElectronics: operating 10-30°C, non-operating 0-40°C• Any mechanical I/F’s to S/C thermal system? Any mechanical I/F’s to S/C thermal system? (e.g. S/C MLI to (e.g. S/C MLI to

mirror subsystem)mirror subsystem)

• A start will be made for a S/C Thermal Math Model by A start will be made for a S/C Thermal Math Model by delivering preliminary SXC thermal data to IKIdelivering preliminary SXC thermal data to IKI

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Open items SXC to S/C Open items SXC to S/C (3/4)(3/4)

Location of electronics boxesLocation 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 cmCDE1 10 x 38 cm; CDE2 28 x 38 cm; ADR ?; IDC 18 x 22 cm• TAC ?TAC ?

Total area: 3590 cmTotal area: 3590 cm22 (excl. ADR, TAC and cable harness routing)(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 cmAvailable under cryostat 13000 cm2 2 (Ø130 cm)(Ø130 cm) • drawbacks:drawbacks:

• radiated heat towards cryostatradiated heat towards cryostat• Telescope Center-of-Gravity 30-40cm higherTelescope Center-of-Gravity 30-40cm higher

• Elsewhere? Elsewhere?

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Payload configurationsPayload configurations

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Open items SXC internally Open items SXC internally (4/4)(4/4)

• Electron deflector (not needed?)Electron deflector (not needed?)• Sieve slit (may also reduce required mirror heater Sieve slit (may also reduce required mirror heater

power)power)• Thermal control of eROSITA mirrors (power level, control Thermal control of eROSITA mirrors (power level, control

unit)unit)• Thermal load on telescope structure (alignment issues, Thermal load on telescope structure (alignment issues,

thermo-mechanical stress)thermo-mechanical stress)• Structural support of cryostat and fixation to hexapod Structural support of cryostat and fixation to hexapod

and S/C and S/C (issues S/C Panel stiffness, flatness)(issues S/C Panel stiffness, flatness)

• Optical refs mirror-to-detector/cryostat: alignment cube Optical refs mirror-to-detector/cryostat: alignment cube or dowel pins?or dowel pins?