# Presentation: 554163

## TPF Mirror Technology Assessment		September 28, 2006

- Gary Matthews
- Director of Business Development
- _[gary.matthews@itt.com](mailto:gary.matthews@itt.com)_
- Phone: 585-269-6511

## Planet Finding Concepts Continue to Emerge and to Redefine What TPF May Be

- Several new baseline concepts have been developed recently that provide alternatives to the traditional TPF-C mission architecture

**TPF-C Concept**

**Phase-Induced Amplitude Apodization (PIAA) Telescope Concept**
**(Paper by Olivier Guyon)**

**New Worlds Observer Concept**
**(Paper by Webster Cash)**

**Visible Nulling Interferometer Concept**
**(Paper by Michael Shao)**

## Mission Concepts Will Drive the Mirror Requirements and the Need for Technology Development

- Current concepts span a wide range of configurations and technologies

## A Top Level Requirements Comparison Provides Some Keys to Required Technology Development

|  | TPF-C(Baseline) | New World Observer
(NWO) | Phase-Induced Amplitude Apodization
(PIAA) | Visible Nulling Interferometer
(VNI) |
| --- | --- | --- | --- | --- |
| PM Size Range | 3m x 6m
3.5m x 8m | 2m  ---  4m | 4m | 4m |
| PM Configuration | Off-axis | On-axis | Off-axis | On-axis |
| PM Actuation
 | Low Authority | Passive | High Authority | Passive |
| Quality
 | Corona-graphic | Visible | Visible | Visible |

- No Technology Development (TRL 6 Minimum)
- Engineering Process Development (TRL 5)
- Technology Development Needed (TRL 4 or Less)

## Mirror Configurations for the Various Sizes of Primary Mirrors Under Consideration

**Note:****	****Design details are available **
**	****No contingency is included in these estimates**

## Mirror Technology Maturity

## Primary Mirror Size and Areal Density	Space Flight Designs

- Based on previous efforts by ITT and Corning, any of the mirrors under consideration by TPF can be manufactured
- There are several breakpoints in facilities that would require some investment
- Demonstrations and risk reduction recommended for mirrors larger than 3m
- Significant technology development required for the very large, active 3.5mx8m primary mirror configuration
- Based on previously reported LMM (Large Monolithic Mirror) study conducted by ITT

## Evolution of Lightweight Mirror Technology

**200**
**100**
**50**
**25**

**1980**

**1990**

**2000**

**Hubble Space Telescope**
**Primary Mirror**
**2.5 meter**

**ITT SSD AOSD Telescope**
**Segmented Primary Mirror**
**2.6 meters**

**ATT**
**LTF/Pocket-milled**
**2.5 meter**

**AMSD - Class Technology**
**1.4 meter (scaled to 2.5 meter)**

**Aerial Density (kg/m****2****)**

**2m-class primary mirrors can be manufactured and processed routinely in the 40-60 kg/m****2**** range**
**TRL > 6**

## Facility Break Points have been identified

|  | 2m - 2.5m | 2.5m – 3.0m | 3.0m – 4.0m | 3.5mx8m |
| --- | --- | --- | --- | --- |
| ULE® Glass Manufacturing | No issues. Raw glass manufacturing has been demonstrated to 8m diameter at Corning |  |  |  |
| Mirror Blank Manufacturing | Facilities in place at Corning | Facilities in place between Corning and ITT | New furnace required | Segmented manufacturing process requires development |
| Mirror Processing and Coating | Facilities in place | Minor upgrades required for final finishing and test. Coating chamber required. | Some modifications required for finishing and test. Coating chamber required | Major facility upgrades required. |
| Recommendation | No issues.Pathfinder will reduce schedule risk. | Pathfinder suggested to harden processes | Qualification model recommended to verify processes | Subscale pathfinder and full scale pathfinder recommended |

## Passive Primary Mirror Model

**PM Model**

**Front Plate Model with pocket milling included**

- ITT has done detailed modeling of large passive and active systems

**In order to achieve acceptable areal density goals for very large primary mirrors, pocket milled face sheets will most likely by required**
**This technique has been demonstrated on demonstration mirrors**

## Mirror Pocketmilling Details	Typical of 2.4m, 3.2m and 4.0m

**Front plate pocket milling**
**68%-72% plate lightweighting**
**Back plate pocket milling**
**72%-74% plate lightweighting**
**Reduces faceplate and core mass while minimizing processing induced quilting **

**Glass Mirror Construction**

**Pocket milled detail**

**Notes:**
Description of Baseline Sandwich Design (cont’d)
The manufacturing technologies needed to produce and finish the lightweight mirror designs described on charts 7 and 8 are have all been demonstrated.  
Note that the sandwich mirrors have segmented cores.  This feature significantly reduces schedule and manufacturing risk during core fabrication since any one core segment can be quickly replaced if it becomes unusable.
Significant lightweighting of the front and back plates is accomplished by pocket milling the inside surfaces of the plates.  The pictures above show isolated portions of the front and back plates.  Milling is performed quickly, safely, and accurately using an existing low pressure abrasive water jet process.  The dark ribs shown in the pictures above provide surfaces to which the mirror core is fused during final mirror blank assembly and firing operations.  The intercell ribs stiffen the thin plate skin over each cell in order to limit local gravity quilting of the frontplate to acceptable levels during 1g ground optical testing.  The ribs also allow the mirrors to be polished in acceptable time frames by reducing polishing quilting during mirror processing.

## Ultra Lightweight 2m class Passive Primary Mirror Technology has been Demonstrated

**Advanced Technology Testbed (ATT) 2.4-meter Primary Mirror**

**ATT Pocket Milled Facesheet**

- Abrasive waterjet lightweight segmented core reduces risk
- Pocket milled facesheets reduces weight to about 1/3  the areal density of HST with comparable stiffness
- Low Temperature Fusion (LTF) process eliminates the effects of Frit-bonding
- Directly scalable to 4m size

## Corning Has the Capacity to Produce Any of the TPF Mirror Blanks With Some Facilitization

**Deep Core Cutting for Lightweight Mirrors**

**Very large water jet cutting facility**

**8m Furnace Facility with 4m mirror**

## Primary Mirror Configuration	On and Off-Axis Designs

- No major difference in making the various designs given today’s processing technology
- The development of large, off-axis, lightweight mirrors has been demonstrated
- Quality and clear aperture need to be considered
- TDM was a key step in demonstrating coronagraphic quality mirrors in a lightweight, off-axis configuration

## Passive and Active Mirror Designs	Flight Qualification and TRL

- No flight qualified active primary mirrors have been developed to TRL 6
- Several demonstrations have been completed
- Technology development will be required to achieve required maturity level prior to flight

**ITT’s Advanced Optical System Demonstrator showed the viability of phase and figure control of an active primary mirror**

## Mirror Quality	Processing Capability of Lightweight Mirrors

- Lightweight mirrors have been processed that approach coronagraphic quality
- If required, a qualification program would be needed to assure that the quality aspects of the mirrors in the flight configuration could be met

**TDM Spec**

**AFRL DOT Mirror Figure**

**TDM Spec**

**Highly aspheric processed mirror**

## Summary

- All TPF Primary Mirror concepts appear feasible to manufacture, process, and test
- Some designs will require technology development to achieve
- Pathfinder/Back-up mirror recommended for all configurations to reduce schedule risk
- For modest sized systems (<3.0m), the primary mirror will not be the critical path of the observatory