Download - Chandra X-ray Observatory Overview
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Chandra X-ray Center
Chandra X-ray Observatory Overview
Roger Brissenden
Smithsonian Astrophysical Observatory
CIAO Workshop
23 April 2001
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Chandra X-ray Center
Overview
1. Mission Summary, Launch and Architecture
2. Mission and Observatory Description
3. Spacecraft Subsystems
4. High Resolution Mirror Assembly
5. Science Instruments
6. Chandra X-ray Center Architecture
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Chandra X-ray Center
NASA Great Observatories
CHANDRA
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Chandra X-ray Center
Launch July 23, 1999– STS-93/ Inertial Upper Stage / Integral Propulsion System– 10,000 km x 140,000 km, 28.4o Inclined Orbit
Design Lifetime > 5 Years 10-m Focal Length Wolter -1 Mirror: 4 nested Mirror Pairs Energy Range: 0.1-10 KeV 2 Imaging Focal Plane Science Instruments
– ACIS (Advanced CCD Imaging Spectrometer) – HRC (High Resolution Camera)
2 Objective Transmission Gratings for Dispersive Spectroscopy– LETG (Low-Energy Transmission Grating)– HETG (High-Energy Transmission Grating)
1. Chandra Mission Summary
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Chandra X-ray Center
Chandra Launch Launched on Space Shuttle
Columbia 7/23/99 on the third attempt
Shuttle placed Chandra and IUS in 150 mile orbit
Chandra was the longest and heaviest payload launched on the Shuttle
Payload bay doors open 1.5 hours after launch
Chandra/IUS deployed 7.5 hours after launch
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Chandra X-ray Center
Chandra Deployment and Orbit Inertial Upper Stage (IUS)
boosted Chandra from shuttle orbit to transfer orbit. Two stage rocket with two 2 minute burns.
Chandra separated from the IUS 9.5 hr into mission with orbit of 300km x 74,000km
Chandra’s Integral Propulsion System fired 5 times over 15 days to reach final orbit: 10,000 km x 140,000 km. Orbit of 64 hrs and going 1/3 of way to moon
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Chandra X-ray Center
Chandra Operations Mission science plan
converted to command loads and uplinked to Chandra
X-ray events collected and stored on Solid-State Recorders (SSR)
Ground contact established every ~8 hours through Deep Space Network– SSR data downlinked
– new command load uplinked (up to 72 hours of stored commands)
Data transferred to OCC through JPL for science processing
CXO
CXCOCC
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Chandra X-ray Center
S/C Support &Eng Analysis
Attitude Det. &Sensor Cal
Mission Planning& Scheduling
Command Management
Data Capture
TelemetryProcessing
CommandProcessing
Communication
Ops Simulator
OperationsDatabase
Off-Line System On-Line System
Flight S/W Maint Fac
IPIs, Guest Observers
CXC
Observation RequestMission Schedules
Telemetry
Proposed ObservationScience Data
S/W Changes
TelemetryCommands
DSN SchedulingState Vector
TelemetryCommands
Deep Space NetworkDeep Space Network
TelemetryCommands(Via Shuttle) Telemetry
Commands
OCC
Chandra
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Chandra X-ray Center
2. Mission and Observatory Description
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Chandra X-ray Center
Focusing X-rays
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Chandra X-ray Center
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Chandra X-ray Center
Electrical Integration Assy
A B
On-Board Computer
A B
Solid State Recorder
A B
Ultra-Stable Oscillator
A B
InterfaceUnit
A
B
Command & Telemetry Unit
A B
PCADRCTU
A B
EPSRCTU
A B
Science Instrument
RCTU A B
TelescopeRCTU
A B
Transmitter A
Receiver A
Receiver B
Transmitter B
Mechanism Control Elec.
A B
Low Energy Transmission
Grating
High EnergyTransmission
Grating
InstrumentProcessor
A B
Power Control Unit
Control Elec. Assy
A B
Earth Sensor
A B
Inertial Reference Unit
A B
Drive Elec. Assy
A B
Solar Array Drive Assy
+Y -Y
Wheel Drive Assy
(6 wheels)=
Reaction Wheels
SupportElec. Assy
A B
Secondary Elec. Assy
A B Focus Motion
Translation Motion
Commandand DataBusses
Local RCTU
Sequencer
Processing Elec. Assy
A B
Aspect Camera
A B
Fine Sun Sensor
A B
Coarse Sun Sensor
A B
CPE
MUPSThrusters
A B
Optical Bench Heaters
Fid LightController
A B
Solar Arrays
Batteries
Chandra System Level Block Diagram
Switched to B components during Safe Mode Transition
EIA Sequencer performs Core Unit Swap
CPE-A Control in Safe Mode
Safe ModeEnable
Sequencer Complete
EIO / EPHIN (Radiation
Monitor) A
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Chandra X-ray Center
3. Spacecraft Systems
Command, Control and Data Management– 2 low gain antennas, 2 S-band transponders
– Two solid state recorders, each 1.8 GB
– Redundant 16-bit On Board Computers (OBC), interface units, command and telemetry units, remote command and telemetry units
– 32 kbps telemetry with usual 24 kbps science and 8 kbps engineering
Electrical Power– Generates, stores and distributes electrical power to the spacecraft
– 2 solar wings provide 2112 watts
– 3 Ni Hydride batteries capacity 120 Amp hours for eclipses Thermal Control
– Passive elements include multi-layer insulation and radiators
– Active elements include thermostats and sensors
– OBC controls HRMA at 70 +/- 2.5 deg with active elements
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Chandra X-ray Center
Spacecraft Subsystems
Propulsion– Integral propulsion system used for transfer orbit, deactivated– Momentum unloading propulsion system for unloading momentum
from reaction wheels Pointing Control and Attitude Determination
– Sensors and control hardware to point, slew, solar array positioning and momentum unloading
– Pointing requirements a modest ~30” due to photon counting nature of the science instruments
– Pointing direction determined from aspect camera tracking 5-8 stars and gyroscopes
– Photon positions are reconstructed using aspect camera data during ground processing
– Performance of aspect system gives ~3” absolute pointing, 0.3” image reconstruction and 0.6” celestial location
– System includes 6 reaction wheels for attitude control, coarse and fine sun sensors for pointing without aspect camera
– Spacecraft dithered during observations with ~16 arcsec Lissajous
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Chandra X-ray Center
Aspect Camera and Fiducial Transfer System
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Chandra X-ray Center
4. High Resolution Mirror Assembly 4 pairs of concentric thin-walled, grazing
incidence Wolter Type-I mirrors Fabricated from Zerodur, polished to 3A
and coated with Ir Diameters range from 0.65 to 1.23m
and total weight 1484 Kg Characteristics
– Focal length 10m
– Plate Scale 48.8 microns/arcsec
– PSF (FWHM) 0.5 arcsec
– Ghost-free FOV 30’ diameter
– Effective Area
@ 0.25 keV 800 cm^2
@ 5.0 keV 400 cm^2
@ 8.0 keV 100 cm^2
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Chandra X-ray Center
HRMA and Associated Structures
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Chandra X-ray Center
HRMA Effective Area HRMA Encircled Energy
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Chandra X-ray Center
5. Chandra Science Instruments
Advanced CCD Imaging Spectrometer (ACIS)– CCD array with 16’x16’ field of view (ACIS-I)– high energy grating readout array (ACIS-S)
High Resolution Camera (HRC)– microchannel plate imager with 31’x31’ field of view (HRC-I)– low energy grating readout array (HRC-S)
High Energy Transmission Grating Spectrometer (HETG)– transmission grating pairs for medium and high energy
Low Energy Transmission Grating Spectrometer (LETG)– transmission grating for low energy
ACIS-I
ACIS-S
HRC-I
HRC-S
b b
Z+
Y+
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Chandra X-ray Center
Science Instrument Module
ACIS and HRC mounted on SIM along the Z axis
SIM provides 20 inches of motion in Z to select ACIS-I, ACIS-S, HRC-I or HRC-S
Provides 0.8 inches of motion in X to adjust focus
ACIS Sun Shade
ACIS
ACIS Radiator Shade
HRC
Optical Bench
Top Hat and Lean-to
TSC
PSMC
BTU
RCTU
FLCA
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Chandra X-ray Center
Advanced CCD Imaging Spectrometer (ACIS)
Ten 1024x1024 pixel CCDs– 2x2 array for imaging: ACIS-I labeled I0-I3– 1x6 array for imaging or spectroscopy: ACIS-S labeled S0-S5– 6 chips can be operated simultaneously– Array Size 16.9x16.9 arcmin (ACIS-I), 8.3x50.6 arcmin (ACIS-S)– Pixel Size 0.49 arcsec
8 Front-illuminated and 2 back-illuminated chips– BI chips are S1 and S3– BI response extends lower that FI– Average energy resolution of BI chips better than FI
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Chandra X-ray Center
Advanced CCD Imaging Spectrometer (ACIS)
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Chandra X-ray Center
High Resolution Camera (HRC)
Microchannel plate device with imaging and spectroscopy detectors
Time resolution 16 microseconds Energy Range 0.08 – 10 keV Pixel readout size 6.4 microns = 0.13 arcsec/pix Detection sequence for X-ray
– Passes through UV-ion shield– Through photocathode yields photo emission– Photoelectrons accelerated by electric field– Pass through second microchannel plate for additional gain– Electron cloud (2e7 electrons/photon) detected with wire
cross grid detector
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Chandra X-ray Center
High Resolution Camera
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Chandra X-ray Center
Grating Spectrometers
HETG– Designed for use with ACIS-S providing E/delta(E) to 1000
between 0.4 and 10.0 keV– Two sets of gratings– Medium Energy Gratings (MEG) for use with outer 2 mirrors– High Energy Gratings (HEG) for use with inner 2 mirrors– Mounted at different angles to form an “X” dispersed pattern
LETG– Provides highest resolving power at low energies– Designed for use with HRC-S with 0.07 – 7.29 keV– E/delta(E) > 1000 for 0.07 < E < 0.15 keV– E/delta(E) < 1000 for E > 0.15 keV
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Chandra X-ray Center
Chandra Grating Spectrometers
m=2
m=1
m=0
m=-1
m=-2
IncomingRadiation
m = d sin
d
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6. Chandra X-ray Center Architecture
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Chandra X-ray Center