# Presentation: 750339

## Constellation-X Mirror Development: Achievements, Problems, and Prospects

- Will Zhang
- Laboratory for X-Ray Astrophysics
- NASA Goddard Space Flight Center

## Mirror Development Team

**GSFC:**
- David Content
- John Lehan
- Rob Petre
- Timo Saha
- Will Zhang

**MSFC:**
- Bill Jones
- Mikhail Gubarev
- Steve O’Dell

**SAO:**
- Paul Reid

**Technology Development Manager:**
- Scott Owens
**Laboratory Manager:**
- Curtis Odell
**Technical Support:**
- James Mazzarella,
- Marton Sharpe,
- Melinda Hong,
- John Kearney

## Fabrication

- Start with a sheet of commercially available borosilicate glass, 0.4mm thick
- Place it on a fused quartz mandrel whose surface has been treated to prevent sticking and provide other necessary properties for slumping
- Start a temperature cycle between between 20 and 600 degrees C

**Goal: Make every mirror look exactly like the mandrel and prove it**

**Metrology**

- Mirror segment held at 3 points
- 25 axial scans for each mirror, one every 2 degrees
- Verification of the fabrication process
- Feedback to the fabrication process

## Development Strategy

- Start with a technique that meets **three** (effective area, mass, and production cost) of the **four** requirements, work on the fourth one (**angular resolution**)
- Pursue **reproducibility**, or process determinism: making all the mirrors look alike
- Pursue **traceability**: making all the mirrors look like the mandrels

## Apparent Surface Map(including both fabrication error and gravity distortion)

## Mirror Apparent Axial Figure Error

## Distribution of Apparent Mirror Quality(all mirrors produced between Jan and Apr 2006)

## Repeatability: Slumping is a deterministic process

- Forming has to be good
- Metrology registration has to be good
- Distortion has to be very small or nearly identical

**Best: 21nm RMS     Typical: 50nm RMS**
- These numbers are most likely dominated by a lack of accurate cross registration, therefore should be considered as upper limits

**Necessary Conditions to Have Repeatability**

## Comparison between Mandrel and Mirror Black=Mirror; Blue=Mandrel

## Result from a new mirror support

**Black: with new support**
**Blue: with 3-point support**

**Mandrel**

## Error Decomposition Estimate

**Potential of this technology**

**No. 1 Issue**

**Easy to solve**

**Relatively easy**

## Summary of Status and Issus

- We have achieved excellent repeatability in slumping substrates
- Typical: 50nm RMS
- Best: 20nm RMS
- These mirrors, when properly integrated, are expected to perform better than 20 arcsec  (HPD, 2 reflections)
- We need to address the following issues
- Metrology
- Use better reference optics: commission of a new 10-in interferometer
- Construct better mirror holding fixture: mattress
- Understand, reduce/eliminate the mid-frequency error

## Mid-frequency Problem and Its Solution

- Cause: dust from the slumping environment and detritus resulting from the release layer
- Solution:
- Better slumping environment: clean oven
- Improved mandrel surface release layer

## Prospects

- Almost all technological aspects of the mirror fabrication are understood and going very well:
- Problems are well defined
- Solutions are being implemented
- In all likelihood, we will be able to do significantly better than the SXT baseline requirements. By the end of this year we should be able to quantitatively gauge
- whether the present technology can achieve the SXT goal of 5 arcsec
- What specific things we need to do to reach the goal

## AcknowledgementsThis work has been supported in part byThe Constellation-X Project OfficeGSFC Core Competence FundA NASA Astronomy and Physics Analysis GrantGSFC Internal R&D FundGSFC Technical Equipment FundGSFC Director’s Discretionary Fund

## SXT Mandrel Challenge in Perspective

|  | Con-X | XMM | Chandra | JWST |
| --- | --- | --- | --- | --- |
| No. of Assy. | 4 | 3 | 1 | 1 |
| No. of Shells per Assy. | 216 | 58 | 4 | NA |
| Total Mirror Area (m2) of the Observatory | 883 | 158 | 19 | 36 |
| Total Mandrel Area (m2) | 28 | 53 | 19 | 36 |

**Manufacture of SXT mandrels is NOT challenging in historic terms. **
**  ****Comparable to,  or easier than,  XMM’s mandrels because of smaller area**
**  ****Much easier than Chandra’s mirrors because of much less stringent figure requirements**
**  ****Much easier than JWST mirrors because there are no lightweighting or cryogenic requirements**

## Mirror Segment Description

**By definition/convention, all the Delta terms (azimuth dependent) have zero means. So does also the R(z,phi) term.**

- Coordinate Measuring Machine

- Interferometer

## Mirror Parameters

## Application to Normal Incidence Optics