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PACS – IHDR PhFPU Design. J. Martignac CEA/DSM/DAPNIA Service d’Astrophysique. INTRODUCTION. PhFPU Requirements BFP & PhFPU : - Design -Thermal & Grounding Scheme - Validation & Qualification Critical Items. PhFPU Requirements. Mass around 7 kg.

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Pacs ihdr phfpu design


J. Martignac


Service d’Astrophysique


  • PhFPU Requirements

  • BFP & PhFPU :

    - Design

    -Thermal & Grounding Scheme

    - Validation & Qualification

  • Critical Items

Phfpu requirements
PhFPU Requirements

  • Mass around 7 kg.

  • External Envelope & Mechanical I/F according to the Doc. : PACS-KT-ID-005-iss.4

  • Admissible Load according to the Doc : PACS-KT-AN-005-iss.2

  • Thermal Consumption :

  • -  to 12µW at 300mK

  • -  to 4,3mW at 2K without the Cooler

Bfp design
BFP : Design

  • The BFP is mainly composed by 5 Sub-assemblies:

  • the mechanical structure,

  • the focal plane at 300 mK,

  • the 300mK thermal strap

  • the 2K circuit buffer,

  • the envelope.

Phfpu design

Cooler Harness Holder

Connector Panel

4K Structure

PhFPU : Design

  • The PhFPU is mainly composed of 8 Sub-assemblies:

  • the 4K Structure,

Phfpu design1

R & B BFPs Holder

Stainless Steel

Insulating Tubes


Insulating Spacers

PhFPU : Design

  • the 2K Structure,

Phfpu design2



Filters Boxes

R&B 2K/4K

Ribbon Cables


PhFPU : Design

  • the two BFPs Red & Blue ,

Phfpu design3

3He Cooler Harness

3He Cooler

L0 Straps Baffling

Shield Covers

PhFPU : Design

  • the 3He sorption Cooler

Phfpu design4

R&B Copper



Thermall I/F

300mK Thermal Strap

Kevlar wires suspension

to the 2K

Stray light Baffling

Copper Braid

Kevlar wires suspension

to the 4K

3He Cooler Thermal Interface

PhFPU : Design

  • the PhFPU 300mK Thermal Strap from the cooler to the BFPs

Phfpu design5


2K Feedthrough (by KT)

Copper Braids

Stray Light Baffle

L0 Strap I/F

PhFPU : Design

  • the 2K Thermal Strap,

Phfpu design6

2K Baffle

4K Baffle

PhFPU : Design

  • & the Baffles.

Phfpu design7
PhFPU : Design

PhFPU assembly

  • Status:

  • Mechanical I/F: OK

  • Optical I/F: SOAM (KT)

  • Parts Manufacturing: OK

  • Integration Tools: OK

  • Black Paint: in progress

  • Full Assembly: First Time

  • Thermal: to be validated

Phfpu thermal equivalent scheme

élec=2,8mW (B&R BFP)







4K Structure







Evap. Switch I/F

T  2K





Pump Switch I/F




PhFPU Thermal Equivalent Scheme

Global Thermal budget on the L0 level:

- 4,1mW + 0,5mW*

*:(TBC by KT)

L0 Straps manufacturing is under responsibility of Astrium

Phfpu grounding scheme

PhFPU Structure @ 4K

BFP Housing @ 2K



Cooler Structure @ 4K

Optical Bench

Space Scraft L0 Thermal Straps

He Tank

PhFPU Grounding scheme

  • The PhFPU grounding configuration is like represented:

  • one shield @ 2K close to the bolometers and signal

  • one shield @ 4K performed by the outer PhFPU and Cooler Structure

  • the electrical insulation between the two shields are performed by:

    • Voltalef parts at the Structure level

    • 0,1mm layer of STYCAST 1266 between copper foils at the Thermal Strap level (300mK & 2K)

Validation qualification
Validation & Qualification

  • Succesful Warm vibrations have been done :

    • on a BFP Structure alone

    • at the PhFPU level

    • & at the Instrument level

A new PhFPU SM has been build for the Cold vibration campaign at CSL.

The BFP Kevlar suspensions only survived to the first two axis (Y & Z), and a breakage occured at the beginning of the third run (X).

But higher input levels than specified in the IIDA was applied.

Bfp validation qualification future tests
BFP : Validation & Qualification – Future Tests

New stiffness measurements at 4K will be done on a BFP Structure in two directions :

- axial (applied load  to the focal plane)

- transverse ( // to the focal plane)

These tests should be repeated 2 or 3 times on the same Structure to study the thermal cycling influence on the Kevlar wire suspensions.

  • Cold vibrations are planed :

    • on a BFP Structure alone

    • on a BFP equiped with detectors and its complete readout circuit to validate all the interconnections from the detectors to the end of the 2K/4K Ribbon Cable.

Phfpu validation qualification future tests
PhFPU : Validation & Qualification – Future Tests

  • A complete PhFPU FEM is complete now with the Cooler & the BFP Kevlar suspensions

  • Warm vibrations will be done at the PhFPU level to investigate potential coupling between the PhFPU 4K Structure and 3He Cooler:

  • Cooler SM refurbished with a Titanium core and a functionnal switch linked to a representative L0 Strap: TBC!).

  • New cold vibrations campaign under negociation (ESA/Inst).

Phfpu critical items
PhFPU Critical Items

  • Critical:

  • Qualification at Cold temperature

  • BFP Kevlar wire suspension

  • Mechanical load on the Cooler thermal switches I/F

  • To be validated:

  • 0,3K Strap thermal behaviour (without & with electrical insulating parts.

  • Cooler behaviour mounted on the PhFPU (thermal environment)

Progress since ibdr
Progress since IBDR

  • 3 models of the PhFPU have been built: SMKT, SMKT2 & SOAM

  • Warm vibrations done succesfully passed at sub-assembly and at instrument level

  • BFP assembly & integration is now completely stabilised

  • 2K/4K ribbon cables manufacturing is now under control

  • PhFPU design is complete, all the parts for the QM are manufactured