1. SPICA / FPI Mechanical /Optical Issues
Nov. 19, 2009 prepared by
T. Kotani, H. Matsuhara, T. Yamawaki et al.

2. Current Status of FPIA & IOB design
For ESA study, preliminary design of 200cmf, 7cm thick (ribbed) Al plate was proposed but found to be so fragile – SiC is thus currently considered
Real FPI design: current optical design of MIRACLE, SCI, & FPC has been delivered and focal-plane cold-hardware arrangement is now being investigated.
In parallel, SHI started to design the structure of Japanese-led FPIs

3. Common Pick-off Module (PoM): Motivation
Pick-off location at the telescope focus has been investigated.
If the pick-off mirror for each FPI belongs to the cold hardware volume of the FPI, assembling of the whole FPIs on IOB is really difficult / impractical.
We decide to consider a common pick-off module (PoM) separated from each FPI, but mechanically I/F to IOB
PoM is a subsystem of IOBA

4. FOV allocation

5. Pick Off Mirrors

6. SCI
FPC-G-2
MIRACLE-2
MIRACLE-1
FPC-G-1&S
SAFARI

7. 3D View of FPI Optics
FPC-G-1&S
SAFARI
MIRACLE-2
MIRACLE-1
SCI
FPC-G-2

8. 3D View of FPI Optics
SCI
MIRACLE-2
FPC-G-2
FPC-G-1&S
SAFARI
MIRACLE-1

9. Interference between FPIs
FPC-G&S
SAFARI

10. Interference between FPIs
FPC-G&S
SAFARI

11. IOB & PoM: Basic concepts
FPIA should satisfy the stringent stiffness requirement (150Hz axial, 100Hz lateral) within the 200kg weight limit. Two options (trade-off shall be made):
IOB made of SiC (or CFRP)
MIRACLE (& MIRMES, MIRHES) housing will be a part of IOB structure (made of Aluminum)
PoM : no moving parts, such as “beam provider” mechanism

12. FPI footprint on IOB
Envelopes of FPIs are very preliminary

13. FPIA & IOB: Important A/Is & short-term Scenario (1)
Is the Scenario below OK for SAFARI team?
JAXA will release preliminary envelopes for each FPI on IOB on Dec 10, 2009
Each FPI should answer if the proposed envelope is acceptable by TBD date
Thermal control : location of contact point of the heat straps for 1.7K (&4.5K) cooler
Each FPI should answer (based on the current location on the IOB) by TBD date

14. FPIA & IOB: Important A/Is & short-term Scenario (2)
JAXA will release preliminary design of PoM in Early January 2010
Stray-light control :
feedthrough (or baffle) in the IOB – STA or PoM – FPI
Each FPI should check the PoM design, and answer their requirements by TBD date
“Co-focus” required for MIRACLE,MIRHES, SCI (& other FPIs)
stringent accuracy requirements in their back-focus location : Alignment control in the assembly process
Each FPI should answer by TBD date

15. Q & A: Optical (1)
What are the advantages and disadvantages to have a common pick off mirror on the IOB?
common pick-off module (PoM) enables us to relax the handling requirement in the FPIA assembly process.
Disadvantages are
1) mass allocation of the PoM (under strict pressure of 200kg for the whole FPIA + IOBA)
2) alignment I/F control is required

16. Q & A : Optical (2)
Need, location, and design of stray-light baffles for IOB feedthroughs – thermal and electrical.
See the slide #10 above.

17. Q & A: Mechanical (1)
What is the impact of a common pick off mirror with respect to instrument envelope? The interface, envelope of the FPU on the IOB should be reviewed.
same as the answer above related to ``Optical" the outer envelope of the FPIs are under consideration.

18. Q & A : Mechanical (2)
Launch loads – very high at the moment and driving design – what is the justification for these? Exchange of models.
More realistic level at the FPI or IOB is under investigation using CLA by SHI. However, based on the current STA+FPI concept, the level of random vibration cannot be relaxed.
Format for data exchange?

19. Q & A : Mechanical (3)
What are the acceptable loads into the IOB from the instrument static and dynamic – during launch - during cool down – at operating temperature.
Launch & “cool-down (cruising)” phases: no attention has been paid for the loads from FPIs into the IOB, so far “zero” was assumed. Loads in the operation phase should be controlled under ICS-SAFARI (& ICS-FPI), like heat dissipations, mechanical disturbance sources
Loads in the Launch & Cruising phases should be also discussed, such as ``launch lock for the FTS mechanism?