# Presentation: 111072

## JOSEPH HOWARDa, GARY MOSIERa, KEITH PARRISHa, SHAUN THOMSONa, MARK MCGINNISb, JEREMY REDDENb, KONG Hac, CARL BLAUROCKda NASA-GODDARD SPACE FLIGHT CENTER, GREENBELT, MDbSWALES AEROSPACE, BELTSVILLE, MDc SGT, GREENBELT, MDdNIGHTSKY SYSTEMS, RALEIGH, NC 

**JOSEPH HOWARD****a****, GARY MOSIER****a****, KEITH PARRISH****a****, SHAUN THOMSON****a****, MARK MCGINNIS****b****, JEREMY REDDEN****b****, KONG Ha****c****, CARL BLAUROCK****d****a**** NASA-GODDARD SPACE FLIGHT CENTER, GREENBELT, MD****b****SWALES AEROSPACE, BELTSVILLE, MD****c**** SGT, GREENBELT, MD****d****NIGHTSKY SYSTEMS, RALEIGH, NC**** **

**THE JAMES WEB SPACE TELESCOPE (JWST) IS A LARGE, INFRARED-OPTIMIZED, SPACE TELESCOPE SCHEDULED FOR LAUNCH TO L2 IN 2014.**
**IT MUST MEET RIGOROUS THERMAL STABILITY REQUIREMENTS, ALMOST ALL OF WHICH WILL BE VERIFIED THROUGH ANALYSIS.  TERRESTRIAL TESTING WILL BE PERFORMED BUT EVEN THAT WILL REQUIRE SIGNIFICANT ANALYTICAL INTERPRETATION OF RESULTS. **
**PRELIMINARY ANALYSIS INDICATES THAT TRADITIONAL THIRD-ORDER EFFECTS COULD CAUSE THE TELESCOPE TO EXCEED ESTABLISHED PERFORMANCE REQUIREMENTS.  THIS LEADS TO VERY LARGE DETAILED MODELS. PRIMARILY SINCE COMPOSITE TUBES ARE BEING MODELED USING SOLID ELEMENTS. **
**TO MINIMIZE DIFFERENCES BETWEEN THE CURRENT BASELINE AND THE MODEL THE PROJECT IS USING A NUMBER OF RAPID ANALYSIS CYCLES THE LARGE SIZE OF THE TELESCOPE MODELS AND THE SHORT CYCLE TIME CREATES A DEMANDING MULTI-DISCIPLINARY ANALYSIS ENVIRONMENT.**

**Optical Performance Modeling of the James Webb Space Telescope ****- An Update -**

***Science Requirements***
- Measure the luminosities, morphologies, and environments of galaxies within the spectral band 0.6 – 10 μm
- Measure the spectra of 2500 galaxies over the redshift range 1 < *z* < 5
- 5-year lifetime.

***Constraints ***
- Launch by 2014
- Cost capped
- Significant International Contributions
- Spacecraft from Prime Contractor

***Key Mission Trades***
- Launch Vehicle
- Filled vs. Partially-Filled Apertures
- Thermal Management
- Sky Coverage
- Communications Strategy

***Science Instruments***
** ****NIR Imaging Camera [NIRCam]**** **
-  8 square arc minutes field of view
-  Spectral resolution R (λ/Δλ) ≤ 100
-  Wavelength range 0.6-5 μm
** ****Multi-object spectrograph**** [****NIRSpec****]**
-  Observing > 100 objects at once
-  9 square arc minutes field of view
-  *R *~1000 over λ from 1-5 μm
-  *R *~100 over λ from 0.6-5 μm
**MIR instrument [MIRI]**
-  Imaging and spectroscopy
-  2 square arcminutes field of view
-  *R *~1500 spectroscopy over λ from 5-28 μm.

***Design Cycles***

***Current Generation JWST FEM***
***for Thermal Distortion***

- Major analyses of current baseline design are repeated during each cycle
- On-orbit Thermal Distortion
- Perform two cooldown analyses and take the difference of displacements
- Compare results to budgeted wavefront error allotments
- On-orbit Jitter
- Calculate normal modes and modal damping based on strain energy
- Apply reaction wheel and cryocooler disturbances in DOCS for optical performance calculation
- Design cycles are approximately 3 months from model receipt to completion

- MATLAB & FEMAP

- NASTRAN &MATLAB

*Semi-automated *
*Mapping of Backplane*

**ISIM**

**Backplane**

**SDR3 Hot-to-cold Slew ****Wavefront Error**

**Current Thermal Distortion Model Size**
**	****3.8 million GRIDS**
**	****2.0 million solid elements**
**	****260 thousand plate elements**

***JWST Project Summary***

*Linear Optical Model*

**Closeup of Backplane ****& Mirror Segment**

**Models assembled by NGST**
**from subassemblies created ****by various subcontractors**

**Previously documented use of optical sensitivities to predict wavefront error in MATLAB from NASTRAN punch file inputs**
- Added decomposition of wavefront error by source and budget category
- Will soon add Zernicke coefficient calculation
**Addition of field distortion upcoming**
- Previously considered the errors in transmitting a point source through the system
- Now adding the changes in the shape of an extended body
- A slight distortion in one axis is inherent in the design but will be removed in post-processing
- The *change *in this calibrated distortion becomes very important for NirSpec as it observes the spectrum of many objects simultaneously through an array of micro-shutters: Too much distortion prevents observation of the correct science targets
- We are tracking this distortion stability by keeping track of multiple field points and evaluating their relative separations after thermal/structural events, such as repointing the observatory so that the sun strikes at a different angle