PACS IIDR 01/02 Mar 2001 PACS  -ISVR 1  -ISVR Recommendations Introduction and Close-out A. Poglitsch

PACS IIDR 01/02 Mar 2001 PACS  -ISVR 2 Board Findings and PACS Response (1) The Board is satisfied to note that significant progress has been made in the PACS FPU design since the ISVR and the implementation of the bolometers as shown by the amount and quality of the documentation provided to the reviewers. 

PACS IIDR 01/02 Mar 2001 PACS  -ISVR 3 Board Findings and PACS Response (2) The Board notes that the draft instrument specification has been updated in line with the recommendation given at the ISVR. The specification, however, at present concentrates on the optical definition of PACS, and the Board expects that the draft specification will be further extended to cover explicitly further engineering requirements on PACS. The scope of the PACS Instrument Requirements Document (PIRD) is a compilation of high-level requirements on implementation and performance of the instrument to meet the scientific requirements. With the exceptions described in the PIRD, all derived or additional requirements are addressed in separate documents, a list of which has been added to the PIRD in response to the Board’s request.

PACS IIDR 01/02 Mar 2001 PACS  -ISVR 4 Board Findings and PACS Response (3) The Board was impressed by the work performed on the optical design of the focal plane unit, i.e. a complete redesign of the FPU in 6 months. The implementation of the bolometer arrays greatly simplifies the instrument and also allows for an improved straylight rejection/baffling. The Board considered the optical design to be completed, however, to be accompanied by a detailed alignment plan and an instrument straylight analysis that is to be completed by the time of IIDR. A straylight analysis has been performed of the "entrance optics" subunit for straylight sources placed on the rear of the primary mirror, near the central hole (KT-AN-004). Already at the end of the entrance optics the straylight fulfills the requirements at the detector level. A detailed alignment plan has been prepared (KT-PL-007) which describes the tasks for FPU subunit internal alignment, subunit- subunit alignment, and also a proposal for FPU-Telescope alignment.

PACS IIDR 01/02 Mar 2001 PACS  -ISVR 5 Board Findings and PACS Response (4) The Board takes note that the Cryogenic Readout Electronics (CRE’s) for the Ge:Ga detectors has made real progress. It appears that the managerial problems have been resolved since the ISVR, while the technical problems, i.e. demonstration of feasibility, have not been solved yet. The development remains technically extremely critical and is in addition also becoming schedule critical. The Board asks PACS to identify possible ways forward for the Ge:Ga detector arrays in case the CRE technology will not be demonstrated in time and thus not be available when needed. The technical feasibility of the CREs has been demonstrated in the meantime, i.e., all functional blocks of the CRE have been implemented and tested separately, and either already meet the requirements, or the modifications necessary to make them meet the requirements have been identified. (See IIDR presentation by IMEC)

PACS IIDR 01/02 Mar 2001 PACS  -ISVR 6 Board Findings and PACS Response (5/1) The Board notes little progress in the development of the grating mechanism. Although it does not appear to be on the critical path yet, the Board would clearly like PACS to accelerate the activities. The Board notes with concern little exchange of information between PACS system engineering and the grating responsibles and would like PACS to improve on communication exchange. The Board asks PACS to already now consider means of recovery for the case that the design does not mature in time as needed. On CM #12 CSL presented the current AIV schedule and confirmed the delivery dates for the AVM and CQM First functional tests at 4K on the cryogenic prototype will take place in March Selection of lubricants / lifetime tests (bearings) are foreseen for April and May Launch-lock breadboard is available, a grating sample will be available in April-Mai 2001

PACS IIDR 01/02 Mar 2001 PACS  -ISVR 7 Board Findings and PACS Response (5/2) Actuator EM available, CQM/PFM procurement will be released in March 2001, Position Sensor procurement for the CQM/PFM will be released in March 2001 Drive mechanism: ITT for CQM/PFM on EMITS since 23-Jan-01 Diffraction Grating procurement for CQM/PFM will be released in June 2001 The ICD with respect to FPU has been issued

PACS IIDR 01/02 Mar 2001 PACS  -ISVR 8 Board Findings and PACS Response (6) The option of a parallel mode of PACS and SPIRE was not fully addressed in the presentation, and the Board would like PACS to perform a critical trade-off for the IIDR, taking due consideration of the lifetime impact of the parallel operation of the 3 He sorption coolers for PACS and SPIRE and the scientific benefit of such mode. The full impact (lifetime + resulting level 1 and 2 temperatures, including dynamics) can only be answered by detailed thermal modeling at system level (PACS + SPIRE + Herschel cryostat). A trade-off of scientific benefits vs. “side effects”, therefore, has to be delayed until the latter ones have been quantified. The development of PACS is not affected by this issue being left open.

PACS IIDR 01/02 Mar 2001 PACS  -ISVR 9 Board Findings and PACS Response (7) The Board notes that the selection for a black paint for straylight reduction in the FPU is not yet completed, however, supports the approach to consider this a commonality issue among the three FIRST instruments. BRDF measurements on test samples confirmed that NEXTEL Black Suede (Germany) and DeSoto Gunship (USA) paint with SiC grain layers are both suitable candidates. Results and a preliminary procedure are summarized in test report PACS-ME- MP-001. Further tests with larger SiC grains and glass micro- spheres are in preparation. Independent from these ongoing activities a detailed preliminary coating procedure was defined and procurement of the black paint has started. A qualification of the coating is required. For evaluation, PACS will provide a sample to ESA and ask Project to get support for the qualification program.

PACS IIDR 01/02 Mar 2001 PACS  -ISVR 10 Board Findings and PACS Response (8) The Board notes that the instruments’ development plan has been significantly improved since the ISVR. However, the delivery dates show little or no margins w.r.t. the need dates defined by ESA and agreed to by the instrument. The Board asks PACS to critically review the development plan and to optimise it in order to demonstrate adequate margin to the specified need dates. Further, the late qualification of the CQM, and in general the parallel activities of the CQM and the PFM plan should be addressed and potential conflicts be resolved. A more detailed break-down of the AIV phase for all PACS models in the development plan is defined in the PACS Test Plan, which was issued recently. In its present version, only during QM ILT a little margin could be identified, FM and FS test schedules and delivery dates remain not showing adequate margin.

PACS IIDR 01/02 Mar 2001 PACS  -ISVR 11 Board Findings and PACS Response (9) The Board is satisfied with the structure of the PACS system engineering team and the definition of responsibilities and reporting lines. However, the Board recognises room for improvement for the communication between the subsystem engineering managers and the subsystems. As one aspect of this, the role of Kayser-Threde, as industrial architect for the Focal Plane Unit, is not fully clear to the Board. The nominally large influence of Kayser-Threde in the system engineering decision making is not apparent in the system engineering team set-up and should be revisited by the PACS project. The FPU and the Optics System Engineers are in nearly daily contact with KT. In addition we have status meetings with KT every two to three weeks.

PACS IIDR 01/02 Mar 2001 PACS  -ISVR 12 Board Findings and PACS Response (10/1) The Board is concerned about the mass increase presented for the focal plane unit, and urges PACS to carry out the detailed design work and mechanical analysis and to find ways to reduce the mass. The Board is confident that PACS will be able to present at the time of the IIDR an instrument mass budget within the allocation and with adequate margins. One element in the design of the FPU is the structure support system. This is designed to minimise the head load onto the unit. However, since this is only a small fraction of the total heat load the board suggested to PACS the option of a less optimised, but simpler support system (similar to the concept used on SPIRE). In the IID-A, the maximum allocated mass for the three FPU instruments on the optical bench is 179 kg. On the last technical FPU meeting with Project the following numbers where given by the instrument teams (without margins):

PACS IIDR 01/02 Mar 2001 PACS  -ISVR 13 Board Findings and PACS Response (10/2) HIFI46kg SPIRE 45kg + 7.2kg + 3 kg = 55.2kg (different from ESA minutes: 51kg) PACS71kg Total172.2kg The mass of PACS is still TBC as long as the structural analysis is not completely finalized and as long as the detailed light weighting tasks on the main structure have not been performed. PACS will carefully look into all possibilities and make all efforts to reduce the mass of the FPU and to get adequate margins. In the new design of the PACS FPU structure also a modified structure support system is included. The suspension concept has been simplified, the thermal load increase to the FPU is acceptable.

PACS IIDR 01/02 Mar 2001 PACS  -ISVR 14 Board Findings and PACS Response (11) The Board takes note that the FPU thermal model has been established to a level of detail to allow for proper analysis and prediction of the static and dynamic thermal behaviour of PACS. This analysis should be pursued and completed. PACS thermal analyses, based on an upgraded PACS TMM and using the Simplified Thermal Model of the Herschel cryostat (Optical Bench) have been performed. Steady state temperatures and transients were predicted. During the last technical FPU Meeting at ESTEC (21 Feb 01) it was agreed that further detailed analyses should be performed with the PACS TMM based on the full ESATAN thermal model of the optical bench. PACS will deliver its thermal model to ESA for integration with the existing ESATAN cryostat model.

PACS IIDR 01/02 Mar 2001 PACS  -ISVR 15 Board Findings and PACS Response (12) The Board would like to emphasise the importance of EMC design and analysis, specifically for the bolometers and recommends to PACS to initiate related analysis and design work. Terry Bax who has a lot of experience from ISO will get a contract of one year to work on EMC matters, especially in the FPU area. This contract will be funded by DLR.

PACS IIDR 01/02 Mar 2001 PACS  -ISVR 16 Board Findings and PACS Response (13) The Board notes a potential mechanical problem of the Chopper w.r.t. the random vibration specification and asks PACS to provide a detailed assessment to the ESA project for consideration. The final modified design of the FPU structure has been achieved recently, and the SMM has been adapted correspondingly. A structural analysis is in progress, KT will provide vibration loads/ resonance amplifications on the chopper until mid March PACS will provide a detailed assessment to the ESA Project for consideration right after the values were derived.

PACS IIDR 01/02 Mar 2001 PACS  -ISVR 17 Board Recommendations and PACS Response (1) The Board recommends to the PACS project team to implement improvements in the communication of the system engineering team with the subsystem responsibles. The PACS consortium has adopted this recommendation and introduced a regular exchange of information between the responsibles at system and subsystem level as well as a better co-ordination within the system engineering team. The Board requests that PACS completes the open analyses tasks for the instrument, specifically the straylight, alignment, mechanical and thermal analysis of the FPU. The status of these analyses is presented as part of the IIDR.

PACS IIDR 01/02 Mar 2001 PACS  -ISVR 18 Board Recommendations and PACS Response (2) The Board notes progress in all areas of concern identified during the last review. However, it is recommended that PACS places specific emphasis on the following identified critical areas: –Cryogenic Readout Electronics for the photoconductors –The grating mechanism –The bolometer arrays The PACS consortium fully agrees with this assessment and is making all possible efforts to achieve the necessary progress in these areas. The CRE development has made a qualitative step from uncertainty of technical feasibility to optimisation of circuit implementation. Concrete solutions for the grating drive bearings are in the process of evaluation. The first round of bolometer focal plane processing is near completion.

PACS IIDR 01/02 Mar 2001 PACS  -ISVR 19 Board Recommendations and PACS Response (3) The Board recommends to PACS to continue working on the development philosophy and plan in order to gain margins in the delivery dates and to reduce the parallel activities in CQM and PFM AIV. PACS is actively working, in co-ordination with Project (and in the future with the satellite Prime Contractor), on a development philosophy and schedule which will allow the delivery of a well- characterised instrument and be compatible with a launch in Feb This has been agreed upon during the Herschel-FPU Technical Meeting on Feb 21.

PACS IIDR 01/02 Mar 2001 PACS  -ISVR 20 Board Conclusions and PACS Response The Board is satisfied that PACS achieved all objectives of the Delta Instrument Science Verification Review set before the meeting. It is, however, also realised that PACS has a number of critical areas that need specific attention, and a significant amount of work has to be carried out in the time up to the IIDR. We can tell!! But we also appreciate the open, supportive atmosphere in which the PACS consortium, ESA and the funding agencies are working together towards a success of this project.