Transcript PPT

Solar Polar Orbit Radio Telescope (SPORT):
A Mission Concept for Interplanetary CMEs
Imaging
WU Ji, LIU Hao, SUN Weiying, ZHENG Jianhua, FENG
Xueshang, ZHANG Cheng, YANG Xuan, etc
National Space Science Center, Chinese Academy of
Sciences (NSSC, CAS)
Contents
• Background & Motivation
− Objective: CME observation
− How? Synthetic aperture imaging
• Mission Overview
− Frequency selection
− System design
− Orbit design
− Other payloads
− Current status & development plan
• Summary
1. Background
Coronal Mass Ejections (CMEs) are expulsions of coronal
plasmas and magnetic fields from the Sun.
CME
The detection of CMEs between the Sun and the Earth is
important for understanding and ultimately predicting space
weather conditions.
CME observations:
Ground-based observation
Mark IV coronagraph
MLSO, Hawaii, Sep.7, 2005
Nancay Radioheliograph
CME observations:
Spaceborne observation
1.Background
Due to the latitude effect and the rotation of the Sun,
most of the CME’s are propagate near the ecliptic plane.
1. Background
To observe the CME’s from solar polar orbit is
expected in order to have an overall view of it and
predict the direction of its propagation.
SPORT
SPORT
SPORT
Sun
Earth
1. Background
• In order to observe the ICMEs (plasma clouds),
radio frequency band is then proposed with the
brightness temperature as the main physical
parameter to measure
• However, to image at radio frequency need a very
large antenna aperture and also to scan it.
• We need to select an accepted physical aperture
of the antenna by a minimum spatial resolution
How can we get required spatial
resolution from Solar Polar Orbit at
radio frequency?
• Synthetic Aperture Imaging Technology
Original Scene
Its spatial Frequency
Domain Representation
Synthetic Aperture Radio Telescope
• 1980, VLA (Very Large Array)
• ALMA
Advantage: to get very high angular resolution
that can not be achieved by traditional real
aperture reflector antenna system due to
physical aperture size restriction!
Microwave Synthetic Aperture Radiometer:
for Earth Observation
• from 1980’s, L-band, for soil moisture & ocean salinity
obsvation
• from 2000~, millimeter wave, 50~56GHz, for geostationary
atmospheric sounding
Difference between Radio
Astronomy & Earth Observation
Radio Astronomy
Earth Observation
Target Field Of View
Small Scale Target
Distributed Target
(several tens degree)
Spatial Resolution
Arc-seconds
Degrees, minutes
Sampling requirement in
spatial frequency domain
Sparse sampling
Full sampling
SPORT is more like an earth observation system, which is
intended for extended targets observation from space.
SPORT Overview
•
System Specifications
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Frequency:
150MHz
Bandwidth:
20MHz
Polarization:
Circular
Angular Resolution：
2º
Radiometric Sensitivity： ~1K
Imaging Period：
30~60 mins
FOV：
±25º
SPORT
SPORT
SPORT
Sun
Earth
Observing Geometry
2.1 Frequency selection
Interplanetary CMEs may exhibit three relevant radio emission
mechanisms: bremsstrahlung, gyrosynchrotron emission and
plasma emission.
Bremsstrahlung is produced by Coulomb collisions between
charged particles in plasmas.
Gyrosynchrotron emission is the electromagnetic emission
generated by mildly relativistic electrons moving in a magnetic field.
Plasma emission is generated by plasma instabilities, wavewave and/or wave-particle interactions.
2.1 Frequency selection
Thermal free-free emission:
2.1 Frequency selection
0.12
140
f=70MHz
f=90MHz
f=110MHz
f=130MHz
f=150MHz
f=170MHz
emission brightness temperature(K)
0.1
0.08
0.06
0.04
0.02
0
0.2
f=70MHz
f=90MHz
f=110MHz
f=130MHz
f=150MHz
f=170MHz
120
emission brightness temperature(K)
(a)
100
80
60
40
20
0.25
0.3
R
0.35
Background solar wind
0.4
0
0.2
0.25
0.3
R
0.35
With Interplanetary CMEs
0.4
2.1 Frequency selection
Background brightness temperature
2.1 Frequency selection
Background brightness temperature
2.2 System design
• Using the clock scan scheme, the main telescope will have two groups
of element antennas and their receiving channels, each composed of
four elements
• Clock Scan can realize uniform sampling of the spatial frequency
domain
SPORT Artistic View
Stowed
Dimension of the
“seconds boom”
group: 35.76m
Dimension of the
“minutes boom”
group: 31.76m
Deployed
2.2 System design
Front-end
Antenna
Digital Correlator
I
0 ~ 10 MHz
Q
0 ~ 10 MHz
Central
Unit
IQ Mixer
ADC
140±10MHz
LNA
PMS
(Power Measurement System)
Element
Antenna/Receiver
Power
Divider
LO（f=140MHz）
• Antennas: to receive the of radio emissions of the CME & galactic background
• Receivers: to amplify the received noise IQ down-conversion
• Digital Correlators: to get the visibilities
• PMS: total power measurement
• LO & Power Divider: to provide a common LO
2.2 System design
2.2 System design
2.2 System design
Antenna: “Umbrella”
Deployment
2.2 System design
2.2 System design – imaging simulation
Case 1:
Case 2:
2.3 Orbit design
The orbit of SPORT is designed to follow the Ulysses orbit
with a swing by Jupiter to get enough energy to escape from
the ecliptic plane:
2.3 Orbit design
2AU
2.3 Orbit design
2.4 Other payloads
•
Optical instruments:
– such as chronographer, X-EUV imagers, Heliospheric
Imager, etc
•
In situ measurement package:
– solar wind plasma detectors, both ion and electrons,
energetic particle detector, fluxgate magnetometer, low
frequency wave detector, solar radio burst
spectrometer
2.4 Current study and development Schedule
 The concept of SPORT was proposed in 2004.
 Enhanced key technology and engineering feasibility
studies 2008-2011，with the support from CNSA.
 Frequency issues, sensitivity v.s. background
 Main telescope (element channels)design and ground
test
 Image retrieval algorithms
 Orbit injection studies
 ICMEs propagation numerical simulation and theories
2.4 Current study and development Schedule
• Background engineering study (ongoing): 2011~2015,
with the support from “Strategic Priority Research
Program - Space Science” of the CAS
• Engineering development may start 2016
• Launch date: March 2020
• In orbit observation start 2023-2024
Summary
 SPORT will be probabaly the first mission taking image
of the interplanetary CME from the solar polar orbit (>38
degrees)
 It will provide unique overall view of the interplanetary
CME not only on the Sun – Earth line but all around
using radio frequency band and optical instruments
 International participation is welcome
Thank You