# Presentation: 657321

## 
by
 Andrew Bartoszyk, Tim Carnahan, Steve Hendricks,
John Johnston, Jonathan Kuhn, Cengiz Kunt, Ben Rodini
NASA/GSFC Code 542 & Swales Aerospace

Acknowledgements
ISIM Mechanical Team is gratefully acknowledged with special thanks to
Eric Johnson, Gurnie Hobbs, Acey Herrera, Emmanuel Cofie,
 Kannan Kesarimangalam, John Ryskewich, Dan Young,
Charles Kaprielian, & Joel Proebstle.

FEMCI Workshop - May 5, 2005

**by**
-  Andrew Bartoszyk, Tim Carnahan, Steve Hendricks,
- John Johnston, Jonathan Kuhn, Cengiz Kunt, Ben Rodini
- NASA/GSFC Code 542 & Swales Aerospace
**Acknowledgements**
- ISIM Mechanical Team is gratefully acknowledged with special thanks to
- Eric Johnson, Gurnie Hobbs, Acey Herrera, Emmanuel Cofie,
-  Kannan Kesarimangalam, John Ryskewich, Dan Young,
- Charles Kaprielian, & Joel Proebstle.
**FEMCI Workshop - May 5, 2005**

**Integrated Science Instrument Module (ISIM) Primary Metering Structure**

**Design and Analysis of the JWST**

## Outline

- Introduction
- JWST, OTE, & ISIM
- ISIM Structure Design Status
- ISIM Structural Requirements & Challenges
- Description & Evolution of the Primary Structure
- Finite Element Models
- Baseline Structure Performance Predictions
- Normal Modes
- Structural Integrity under Launch Loads
- Further Improvements
- Summary & Conclusion

## JWSTJames Webb Space Telescope

- Courtesy of John Nella, et al. Northrop Grumman Space Technology

## ISIM and OTE Backplane

**Notes:**
Let’s start with the Optical Telescope Element (OTE).  The OTE structure is primarily composed of the Backplane (brown, which supports the optical elements) and the Backplane Support Frame (green, which stiffens the BP and provide the structural connection to the S/C).

The ISIM Envelope (shown in blue wireframe) is defined by the BP and BSF.  ISIM is integrated [this way].  Consequently, [these BSF tubes] are removable.

ISIM is composed of the SIs (MIRI, NIRCam, NIRSpec, and FGS), the Dewar, and the ISIM Structure.  This picture shows the SI and Dewar Envelopes only.

## ISIM Overview

- ISIM Structure is being designed by GSFC.
- Swales Aerospace substantially contributing to ISIM design and analysis.
- ISIM Instruments are being provided by different agencies.
- ISIM Structure successfully passed PDR (Preliminary Design Review) in January 2005 and meets all design requirements.
- Detailed Design & Analysis of the Structure is in progress.
- Critical Design Review is scheduled for December 2005.

- Total Mass =1140 kg

**Notes:**
This picture shows the SIs and the Dewar.

The SIs and the Dewar are kinematically mounted to the ISIM Structure.  MIRI is integrated [this way], and the MIRI KMs are [here].  NIRCam is integrated [this way], and the NIRCam KMs are [here].  The Dewar is integrated [this way], and the Dewar KMs are [here].

## Scientific Instrument (SI) Accommodations
Volumes & Access
SI & OTE Interfaces
Total Supported Mass of 1140 kg
Structure Mass Allocation of 300 kg
Minimum Fundamental Frequency
25 Hz with margin
Structural Integrity under Launch
Thermal Survivability
Survival Temp= 22 K
Operating Temp= 32 K
Alignment/Dimensional Performance
Launch & Cool-Down to 32 K
Operational Stability at 32 K

- Volumes & Access
- SI & OTE Interfaces
- Total Supported Mass of 1140 kg
- Structure Mass Allocation of 300 kg
- Minimum Fundamental Frequency
- 25 Hz with margin
- Structural Integrity under Launch
- Thermal Survivability
- Survival Temp= 22 K
- Operating Temp= 32 K
- Alignment/Dimensional Performance
- Launch & Cool-Down to 32 K
- Operational Stability at 32 K

**ISIM Structure Critical Requirements****& Major Challenges**

**Challenge#1**
**Launch Stiffness & Strength**
**Topic of this Presentation**

- Design a Structure that satisfies these Constraints and meets the following Challenging Requirements:

- Challenge#2

- Challenge#3

## Launch Design Limit Load (DLL) Factors

**ISIM Primary Structure Launch DLL Factors, g’s**

_**Instrument & Instrument Interfaces Launch DLL**_
- Based on an Enveloping Mass-Acceleration Curve and weight of instrument:
-   MIRI: ±13.5 g one axis at a time
-   All other SIs: ±12.0 g one axis at a time

| Load Case | Thrust (V3) | Lateral (V1,V2)a  |
| --- | --- | --- |
| Max Compression | -6.44 | 1.5 |
| Max Tension | +3.25 | 1.5 |
| Max Lateral | -3.65 | 3.0 |
| a - Lateral loads are swept in the V1-V2 plane |  |  |

## Factors of Safety (FS) for Flight Hardware Strength Analysis

- 1

- 2

- 3

- 4

- FS listed apply to both mechanically and thermally induced loads.
- Strength Margin of Safety, MS= Allowable/(FS * Applied) - 1

- Use of an additional fitting factor (typically 1.15) is at the discretion of the analyst.

- For tension fasteners, use an FS of 1.0 on torque preload tension. Maintain a minimum

- gapping FS of 1.25.

- Localized yielding of adhesive that does not undermine performance is acceptable.

- Notes:

## ISIM Baseline Structure Overview

**ISIM Baseline Structure Overview**

- 	_Frame type construction selected_
- provides good access to SIs
- structurally more efficient than plate construction for supporting discrete mounting points of SIs. Verified this through early concept studies.

- _Kinematic Mounts to OTE_
- 2 Bipods (Ti-6Al-4V)
- 2 Monopods (Tubes+Ti-6Al-4V Post Flexures)
- Total Mass~25 kg

- 	_Carbon Fiber Composite Materials used for Primary Structure Members_
- Biased Laminate with
- High specific stiffness
- Near-zero CTE
- 75 mm square tubes with 4.6 mm wall thickness
- Length~75 m, Mass~130 kg

## Baseline Structure OverviewMetal Joints

**Baseline Structure Overview****Metal Joints**

- Use of metal minimized due to structure weight limitations
- Metal parts used where absolutely necessary to make joints strong and stiff enough such as Plug Joints and Saddle Mounts (at SI interfaces)
- All metal parts bonded to composite tubes have to be INVAR for thermal survivability
- Adhesive: EA 9309

- Plug Joint

- Saddle Mount

- _Total Mass of_
- Metal Plug Joints ~40 kg
- Saddles ~45 kg

## Baseline Structure OverviewGusseted & Clipped Joints

- Square Tubes used to make light weight joints possible with gussets and shear clips
- Gussets and clips sized to result in joints with good strength provided that
-  a pair of gussets and a pair of clips are used, and
-  gussets are not notched to undermine the joint load paths
- Gussets: 4.5 mm thick QI (Quasi-Isotropic) Laminate
- Clips: 1.9 mm thick INVAR
- Adhesive: EA 9309

- _Total Mass of_
- Gussets ~20 kg
- Shear Clips ~10 kg
- Adhesive~2 kg

## Evolution of Structure Topology &OTE Kinematic Mount Configuration

- An exhaustive study of structure topology has been performed to arrive at an efficient structure lay-out. Selected intermediate results are displayed.
- ISIM/OTE interface configuration is also very critical to ISIM frequency & mass.
- Started with 3 point Kinematic Mount (KM) interface and considered many options.

- KM constraints

## Arriving at the Final Structure Topology &OTE Kinematic Mount Configuration

- Monopod Load Lines
- Intersection Point

- Found that a lateral (V2) constraint at the +V3 end is very effective
- if it is at or close to the projected CG of ISIM
- Because it provides an essential V3 torsional stiffness
- Finally evolved to a split Bipod (pair of Monopods) as shown below.
- At the –V3 end, two bipods are oriented optimally for maximum stiffness.
- The resulting structure topology is discussed in detail on the next slide.

**Arriving at the Final Structure Topology &****OTE Kinematic Mount Configuration**

- Split Bi-pod (Monopod)  Evolution

- Baseline Structure
- & KM Configuration

## Baseline StructureLoad Paths Discussion

**Baseline Structure****Load Paths Discussion**

- Structure lay-out is close to a 3D truss but deviates from it due to need to have open bays for SI integration and stay-out zones

- Open bays are for
- NIRCam & Light Cones
- FGS
- AOS stay-out zone
- Open bays stiffened through adjacent trusses and “wings.”
- No removable members used to stiffen the open bays in view of distortion risk.
- All primary load lines intersect at joints.
- Trusses in different planes are staggered to simplify some joints, for example:

- with the removal of the dewar, plug fittings at the two lower +V3 corners are also removed and members properly offset and joined through lighter gussets and shear clips.

## ISIM Finite Element Models

_**ISIM Loads FEM with ideal SI Representations**_** **
- used for quick turn around concept and trade studies

_**ISIM Loads FEM with full-up SI Representations**_
- used for final analysis and delivered to project for JWST Integrated Modeling

## ISIM Loads FEMwith ideal SI Models

- Intentionally kept simple for quick turn around concept and trade studies
- provides good accuracy for normal modes and launch reaction analysis
- Beam, Mass, and Spring elements used with joints assumed rigid
- Total mass adjusted to the allocation of 1140 kg
- SI Representations include mass and mass moments of inertia
- Mounted with ideally kinematic attachments hence conservative for normal modes and stress analysis
- tuned to have a fixed base fundamental frequency of ~50 Hz per requirement

- Comparison of its fundamental frequency results with those from
- Distortion FEM demonstrated it to be accurate within 5%,
- Loads FEM with full-up SIs confirm that it is slightly conservative as expected.

## ISIM Normal Modes Summary &Fundamental Mode

**Fundamental frequency is predicted to be 27.7 Hz and meets the requirement of 25 Hz with sufficient margin.**

- Fundamental Frequency Mode Shape dominated by KM and SI support structure flexibilities

## Maximum Deformations & Stresses Under Launch Loads 

- Results shown for the envelope of all launch load cases
- Max deformation is under 3.5 mm
- Max tube stress is ~54 MPa which is well under the allowable

- Primary Tube Stress Contours (Pa) Under Enveloping Load Case
- Deformed & Undeformed Shapes Shown

## Tube Max Reactions & Min MSUnder Launch Loads

-  Most highly loaded tubes listed and highlighted
-  **All MS for tube net-section stress are high**
-  Away from the joints
-  Calculated in spreadsheet under launch limit reactions recovered from loads model
-  **All MS for tube column buckling are high**

## Joint Reactions & MS under Launch LoadsGussets

-  Joint reactions under launch loads are recovered from loads model.  Selected results shown here for gussets.
-  Stresses and MS are calculated by hand analysis for:
-  Gusset net-section failure
-  Gusset-tube bonded joint shear failure
-  Summarized below and highlighted in the FEM plot

- Highly loaded gusset-tube joints highlighted

## ISIM structure meets launch Strength Requirement. All MS under launch loads calculated here as well as in detailed stress analysis (reported elsewhere) are positive. 

Following limit reactions predicted by the Loads FEM are used in detailed stress analysis.

- Following limit reactions predicted by the Loads FEM are used in detailed stress analysis.

**Summary of All-Up Structure****Reactions & MS under Launch Loads**

## Further Improvements

- Considering improvements in the inspectability and reparability of our joints
- Structure mass margin is low, hence we are looking at ways of reducing structure mass
- Removal of shear clips that do not carry significant transverse shear loads
- Tube wall thickness optimization
- 	(one page summary follows)

## Sample Tube Wall Thickness Optimizationusing 2 different wall thicknesses of 2.9 & 5.8 mm

**Sample Tube Wall Thickness Optimization**using 2 different wall thicknesses of 2.9 & 5.8 mm

- NASTRAN optimizer used to assign either 2.9 or 5.8 mm thickness to each tube element to minimize structure weight while maintaining fundamental frequency at ~27.5 Hz
- As binned results are not practical and cleaned-up to have one thickness for every continuous member. Some member thicknesses are bumped up to maintain frequency.
- Substantial tube mass reduction (~28 kg) is predicted.

- 2.9 mm (green)
- 5.8 mm (red)

- as binned

## Summary & Conclusion

- ISIM primary structure has been designed and sized to meet the challenging requirements of Launch Stiffness & Strength given:
- Difficult design constraints including;
- SI integration access,
- SI and OTE Interfaces,
- Tight structure weight budget
- And the other conflicting Structural Requirements namely;
- Thermal Survivability under cryogenic cool-down cycles to 22 K
- Alignment Performance under cool-down to and during operation at 32 K
- Simple Loads FEM proved to be very effective & efficient in guiding structure design
- Concept & Trade Studies
- Tube wall thickness optimization