The NIRSpec Critical Design Review Oct 8th 2008 - Dec 11th 2008


The NIRSpec Critical Design


Oct 8th 2008 - Dec 11th 2008

T. Beck (& M. Stiavelli)


• Quick NIRSpec instrument overview

• Brief Overview of ESA’s CDR process and goals

• NIRSpec CDR Results

• Next Steps & Schedules

• Some Operational “Issues” of interest

NIRSpec Instrument Overview

“The most complicated instrument ever to fly in space”


Spectrograph Mode

(MOS) with an MSA

• Integral Field Unit (IFU)

• 4 Fixed Slits + 1 Broad


JWST Focal Plane, NIRSpec tilted by 41.5


R~100, 1000 and 3000 spectroscopy over 3


I = 0.7 - 1.8mm

II = 1.7 - 3.0mm

III = 2.9 - 5.0mm

NIRSpec Instrument Overview

Reflective Surfaces -


FOR Filter RMA (MSA/IFU/FS) COLL Grating CAM Detector



NIRSpec Instrument Overview

MSA Focal Plane

• 4 MSA Quadrants

• IFU Entrance


• Fixed Slits

• New, 1.”6x1.”6 sq aperture

• (IFU “Virtual Slit”


ESA’s CDR Goals

• Verify that the instrument system performance will meet both the scientific and functional requirements

• Verify that the instrument detailed design is robust, shows adequate margins, and is compliant with product assurance reqs

• External and internal interfaces are defined/documented in the relevant ICDs

• Instrument verification/test plans are realistic and adequate

• The instrument level qualification plan is complete, satisfactory and complies with the subsystem qualification plans.

• The instrument schedule is realistic with adequate margin

• The identified risks are thoroughly assessed with clearly defined mitigation plans

• PA practices are fully implemented

• Ops concept is defined and is consistent with Flight SW architecture

• Commanding and control of the instrument is properly defined in FSW

• Critical technologies have been identified and performance demonstrated.

ESA’s CDR Process

• CDR Board + 5 “Panels”

• Document Delivery to Panel and Board members (late September 2008)

• CDR “Kickoff” Meeting = 1 day of instrument presentations, 1 day of face-toface meeting with the panels (Oct. 8-9, 2008)

• Panel members are tasked with identifying “Review Item Discrepancies”

(RIDs) = discrepancies/inconsistencies/errors in documentation, design or instrument performance vs. requirements

• One month of document reading with weekly telecons between panel members - RIDs continuously input into online tracking system.

• Colocation Meeting - All RIDs from all panels discussed among the large group and actions determined

• Board Meeting - Final presentations on findings, issues from RIDs flagged with actions noted. (Dec. 11th 2008).

• Final Board Report released to team (yesterday!)

ESA’s CDR Process

ESA’s CDR Process and Goals

Board (T. Beck) (M. Stiavelli)

Panel # 1


R. Meynart

G. Bagnasco



R. Bureo

J.C. Salvignol



B. Harnish

M. Te Plate



F. Marliani

P. Rumler/P. Strada



M.v. Eesbeek

M. Falcolini

System Design

Overall Science & Func Perfo






Overall AIV

Structure Design

Mechanicms Design

Thermal Design

Relevant Perfo


Relevant AIV

Optical Design

Relevant Perfo


Relevant AIV

Electrical Design

Harness Design

SW Design

Relevant Perfo


Relevant AIV

Quality Assurance

Product Assurance

Cleanliness & Contamination

Risk Management


• ESA led review, co-chaired by NASA Independent Review Office

• 18 Board members from ESA , NASA and STScI

• 60 Panel members from ESA , NASA, IST, and STScI

NIRSpec CDR Results

• During the Reviews, Panels came up with a total of:

– 192 RIDS

• 70 RIDS Classified as “Major”

• 92 RIDS Classified as “Minor”

• ALL RIDS have either been Closed or accepted with a well defined action

• NO Items were elevated to the Board for Resolution

• (At the time of the NIRSpec Instrument CDR, the MSS subsystem had not had it’s CDR - this is taking place


NIRSpec CDR Results

• Issues Highlighted by the CDR Board:

– Grating Wheel Assembly (GWA) Wavefront Error is significantly out of spec - continued troubleshooting, updates in budgets

– Refocus Mechanism Assembly (RMA) deforms at cryogenic temperatures causing WFE (coated on back, have SiC backups)

– Board requests a report by February 2009 on the recent failure of the RMA gearbox lifetime testing

– HAWAII 2RG performance - Detector Noise and sensitivity degradation due to radiation damage still not established

– MSS CDR delayed until January - after NIRSpec CDR, which resulted in a lack of proper documentation on the MSS. Board requests a report by Feb. 2009 on conclusions from the MSS CDR incl. clear analysis of MSS problems and qualification plans/status.

– Schedule delays in some elements (e.g., GWA) will impact flight model tests - now planned to perform FM cryo tests in two phases.

NIRSpec CDR Results

• Issues Highlighted by the CDR Board:

– Stray light reduction mask - out of field stray light may be blocked by a static, oversized pupil mask positioned in front of the FWA, board endorsed feasibility study for implementing such a mask.

– Concern regarding software validation flow from ICE/MSS/DS through to ISIM level, recommends that the project define and describe in detail an appropriate NIRSpec FSW validation process based on top-level requirements.

– Performance Budgets are not yet consolidated and verified with measurement values - requests that budgets are maintained and updated systematically as new data become available. (incl.

GWA WFE, FOR WFE, Detector noise/sensitivity/dark current).

– Total of 70 actions assigned to Astrium, ESA and NASA on

“Major” RID items - (many = updates to qual plans and verification matrix for consistency with test plans)

NIRSpec CDR Results

• Total of 70 actions assigned to Astrium, ESA and NASA on “Major” RID items, including:

– many = updates to qual plans and verification matrix for consistency with test plans, error budgets

– Report from NASA on Prasedymium-Iron-Boron for use in the

MSS magnet arm, risk due to corrosion, brittleness, contamination and loss of magnetic strength

– Confirmation that acrylic adhesive Y966 can be used at cryotemperature (reports of risk due to lack of adhesion)

NIRSpec CDR Results

• CDR Board Conclusions:

– The NIRSpec CDR will be satisfactorily concluded when the recommendations highlighted (previously) and actions from the CDR panel teams have been addressed and concluded.

– The board requests a report on the status of the identified major issues and

RID actions by May 2009.

NIRSpec - The Future

• DM (Demonstration Model) ambient tests ongoing, cryotests in

Spring 2009 (Focal plane detector at MSA plane)

• FM (Flight Model) plan with schedule mitigation has been developed

– Main deliveries: grating wheel assembly, filter wheel assembly, microshutter subsystem, detector subsystem

– Plan for dual cryogenic test with intermediate refurbishing

– Likely to be implemented for grating wheel

• The PLAN:

• NIRSpec DM (ETU) Delivery in

July 2009 (26d contingency)

• NIRSpec FM mid 2010 delivery to GSFC (40d contingency)

NIRSpec Operational “Issues” of Interest

• MSA = A complicated component!

– Stuck open/closed shutters

From T. Boker’s presentation at CDR Kickoff

NIRSpec Operational “Issues” of Interest

NIRSpec Operational “Issues” of Interest

NIRSpec Operational “Issues” of Interest

NIRSpec Operational “Issues” of Interest

• “Plugging” moves quadrants into useable space -

(NOTE: most of the MSA quads considered for flight aren’t quite as bad as the ENG-grade images presented in images here)

NIRSpec Operational “Issues” of Interest

• MSA Quad lifetime tests show that shutters can become stuck open/closed during operations, after many moves of the MSA magnet arm

– MSA open/closed shutters may change over time!

– MSA Quadrant heating (heat to ~270K) unsticks the shutters and returns the MSA to it’s nominal performance

– MSA Quadrant heating may need to take place after every ~2000 moves (TBD/TBR!)

– NIRSpec will be unusable during the heating process

(nominal duration TBR!, but on order of ~15hrs).

– We may need an updatable map of stuck open/closed shutters that can be updated in the APT MSA planning tool