# Presentation: 266738

## X-ray / Cryogenic Test Facility

- Jeff Kegley, et.al.
- (256) 544-2291
- jeff.kegley@msfc.nasa.gov

## X-ray / Cryogenic Test Facility

- History
- Originally built in 1975-76 for the ground test and calibration of the HEAO B/Einstein Observatory
- Rebuilt during 1990 and upgraded in 1996 for the x-ray optical performance testing of the optics and science instruments for the Chandra Observatory
- Recent Modification for NGST
- Modified in 1999 to add the capability to cryogenically test large, lightweight, normal incidence, space optics at visible wavelengths
- Have successfully completed 12 cryo/optical tests to date

## Chamber Description

- Optically clean, horizontal, polished stainless steel cylinder 24 ft (7.3 m) in diameter and 75 ft (22.9 m) in length
- Chamber test volume to an approximately cylindrical shape that is 20 ft (6.1 m) in diameter by 60 ft (18.3 m) in length
- Has full liquid nitrogen shroud.  Inboard of the shroud are electrically heated aluminum panels which can be precisely controlled in 55 zones from –160 F to 160 F.
- Pumped with cryogenic pumps and oil-free turbomolecular pumps.  Vacuum levels in the 10-7 Torr range are routinely attainable.  Extremely low levels of both molecular and particulate contamination are maintained within the test volume

## Clean Room Description

- Clean Rooms
- Chamber opens into a 6000 square foot clean room
- Operates at better than class 1000 and is equipped with a 20-ton crane specially designed for clean room operations and with slow speeds for handling delicate optics
- Optics and equipment to be tested are mounted on benches using the overhead crane.  The benches (and optics) are then loaded into the chamber via a rail system that extends from the clean room into the chamber.  Once in place, the benches can be offloaded onto thermally/dimensionally controlled, vibration isolated columns
- A 2000 square foot, class 10,000 clean room serves as an anteroom for the class 1000 clean room

## Cryogenic Shroud

- Helium-cooled thermal enclosure capable of less than 20 Kelvin
- Rectangular box 3.3 m (10.8 ft) wide, 2.7 m (8.9 ft) tall, and 10.0 m (32.8 ft) long

- Three sections to facilitate handling and installation, and to provide for flexibility in configuring tests
- Free-molecular conductivity methods are employed using helium at low pressures to augment heat transfer

## Helium Refrigerator

- Closed-loop, reverse Brayton cycle (gas expansion w/ regeneration)

- Control selectable to 0.1K
- Stable to +/- 0.2K
- Programmable rates are possible
- Test article rates and gradients monitored
- Capacity = 940 Watts at 20 Kelvin

## Typical Helium Shroud Cooling

- -----  Empty
- -----  SBMD

## Cryogenic Optical Test Configuration

- Mirror to be tested is mounted in the optical test chamber within the cryogenic shroud with the optical axis horizontal and with an Optical Testing System (OTS) located at the mirror’s center of curvature
- Mirrors up to 2-meters in diameter with base radii of curvatures from 10 to 20 meters can be tested from ambient to temperatures below 30 K
- Mirror systems and the OTS are mounted to precision remotely controlled support structures that can each be adjusted in five degrees of freedom

## NGST Mirror System Demonstrator (NMSD)

- Mirror Mounted on 5DOF Table

## Sub-scale Beryllium Mirror Demonstrator (SBMD)

- Mirror Inside Helium Shroud

## Optical Test System

- Teamed with University of Alabama – Huntsville Center for Applied Optics

- Available primary instruments
- Wave Scope® by Adaptive Optics Associates, Inc.
- PhaseCamTM Interferometer by 4D Vision Technology
- Instantaneous Phase-shifting Interferometer (IPI) by ADE Phase Shift
- Details of OTS to follow

## Facility Dynamic Stability

- Some past dynamic characterization tests
- 12/91 MSFC seismometers on test benches in chamber
- Peak-hold averaging from 0.1 to 100 Hz
- < 100 μG peaks (10-40 Hz) in all axes
- 10/98 MSFC accelerometers
- Instrumented facility floor and chamber isolation pad to search for vibration input:  Clean room fans, air handlers, cooling towers shutdown – no significant driver found
- Instrumented interferometer isolation column pit to select isolation medium (concrete alone, sand, corkboard, and combinations) – sand and corkboard on concrete was selected
- PSDs are available

## Facility Dynamic Stability

- Recent dynamic characterization tests
- A note on XRCF’s coordinate system (x=optical axis, y=north/south, z=up/down)
- 8/00 UAH position sensitive detector (Geary)
- Measured relative motion (y,z) between OTS platform and mirror mount
- Magnitude of motion = 35 - 76.6 μm PV (15-20Hz)
- 10/00 GSFC quad-cell (Fitzmaurice)
- Quad-cell measured relative motion (y,z) between OTS platform and mirror mount
- Magnitude of motion =  70 - 130 μm PV (15-35Hz)
- 10/00 MSFC laser vibrometer
- Measured relative motion (x) between OTS platform and mirror
- Magnitude of motion =  4 - 17 μm PV (9.5-12.5Hz)

## AMSD Test Configuration

- 1.4 meter circumscribed hex

- 10 meters

- Existing shroud module 1

- New, cooled aperture extension

## NGST Full-Scale Segment / Petal Test Configuration Concept

- 3 meter diameter

- 16 meters

- New, larger shroud module

- Existing shroud modules 2,3