chandra x-ray center chandra x-ray observatory overview roger brissenden smithsonian astrophysical...

Chandra X-ray Center

Chandra X-ray Observatory Overview

Roger Brissenden

Smithsonian Astrophysical Observatory

CIAO Workshop

23 April 2001


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


NASA Great Observatories

CHANDRA


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


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


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


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

sssssssssssssssssssssss


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


2. Mission and Observatory Description


Focusing X-rays


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


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


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


Aspect Camera and Fiducial Transfer System


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


HRMA and Associated Structures


HRMA Effective Area HRMA Encircled Energy


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+


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


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


Advanced CCD Imaging Spectrometer (ACIS)


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


High Resolution Camera


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


Chandra Grating Spectrometers

m=2

m=1

m=0

m=-1

m=-2

IncomingRadiation

m = d sin

d

6. Chandra X-ray Center Architecture

chandra x-ray center chandra x-ray observatory overview roger brissenden smithsonian astrophysical...

Documents

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chandra xray center

chandra xray center

chandra mission summary

chandra uxray events

telemetry units

shuttle orbit

final orbit