Xray Cryogenic Test Facility

1
X-ray / Cryogenic Test Facility

• Jeff Kegley, et.al.
• [phone]
• jeff.kegley_at_msfc.nasa.gov

2
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

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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

4
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

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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

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Helium Refrigerator

• 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

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

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Typical Helium Shroud Cooling
----- Empty ----- SBMD
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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 mirrors
  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

9
NGST Mirror System Demonstrator (NMSD) Mirror
Mounted on 5DOF Table
10
Sub-scale Beryllium Mirror Demonstrator
(SBMD) Mirror Inside Helium Shroud
11
Optical Test System

• Teamed with University of Alabama Huntsville
  Center for Applied Optics

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

12
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
• lt 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

13
Facility Dynamic Stability

• Recent dynamic characterization tests
• A note on XRCFs coordinate system (xoptical
  axis, ynorth/south, zup/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)

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AMSD Test Configuration
1.4 meter circumscribed hex
Existing shroud module 1
New, cooled aperture extension
10 meters
15
NGST Full-Scale Segment / Petal Test
Configuration Concept
New, larger shroud module
3 meter diameter
Existing shroud modules 2,3
16 meters