Download Solar Physics, Space Weather, and Wide-field X-ray

CREOL & FPCE: The College of Optics and Photonics
Solar Physics, Space Weather, and
Wide-field X-ray Telescopes
James E. Harvey
Optical Design and Image Analysis Laboratory
[email protected]
Presented at
CREOL Industrial Affiliates Day
“Optics & Photonics for
Space-Based and Medical Applications”
April 21, 2006
Abstract
The sun is essentially a giant thermonuclear fusion reactor (105 x
the size of the Earth). The detrimental effects of solar storm induced
“space weather” ranges from disruption of our space communication
systems to astronaut health hazards to power grid overloads and
blackouts. The National Oceanic & Atmospheric Administration
(NOAA) and NASA are cooperating on a Solar X-ray Imager (SXI)
program intended to allow NOAA to monitor and predict space
weather. Four flight models and a spare of the SXI telescope have
been designed and fabricated. The first is scheduled to be launched
on the next-generation Geosynchronous Operational Environmental
Satellite (GOES-N) in 2006.
After briefly reviewing solar physics and space weather, this talk
will discuss a new class of wide-field grazing incidence X-ray
telescopes developed at CREOL specifically for the SXI program.
This new design differs significantly from the classical Wolter Type I
designs previously built and used as X-ray stellar telescopes.
Outline
• High-Energy Solar Physics
• Space Weather and its Detrimental Effects
• X-ray Astronomy and Grazing Incidence X-ray Telescopes
• The Solar X-ray Imager (SXI) Telescope
• Summary and Conclusions
Solar Physics: The Photosphere
The Visible Sun (Photosphere)
● Sun is a ball of gas ~ 700,000 km radius.
● Photosphere is the sun’s visible surface.
● Actually a layer about 100 km thick
● Easily observable features include:
Ο
Ο
sunspots.
“limb darkening”
The Sunspot Cycle
● Galileo
made
the
first
European
observations of Sunspots in 1610.
● Daily observations were started at the Zurich
Observatory in 1749.
● Continuous observations since 1849.
● Detailed records indicate a dramatic periodic
variation (factor > 100) in the number of
sunspots, with a period of about 11 years.
● The nature and causes of the sunspot cycle
constitute one of the great mysteries of solar
astronomy.
Solar Physics: The Solar Corona
The White-light Corona
● Corona is the Sun's outer atmosphere.
● Visible during total eclipses of the Sun as a
pearly white crown surrounding the Sun.
● Displays a variety of features including
streamers, plumes, and loops.
● Coronal
gases
are
super-heated
temperatures greater than 1,000,000ºC.
to
● Hydrogen and helium are stripped of their
electrons, producing spectral emission lines.
● The highest temperature regions of the
corona produce intense X-ray emissions.
Emission-line Corona (Green Line)
The X-ray Corona
Solar Physics: The Sun as a Laboratory
● Serves an important role in helping
to understand the rest of the
astronomical universe.
The Sun as a Star
Star-birth Clouds (M16) recorded by HST
● Only star close enough to us to
reveal details about its surface.
● Sun is thus the key to understanding
the birth and evolution of other stars.
The Solar Core
● Sun is a giant thermonuclear fusion
reactor (105 X size of Earth).
● Sun produces its energy by nuclear
fusion of four hydrogen nuclei to form
single helium nuclei deep within the
Sun's core.
● This energy diffuses outward by
radiation and by convective fluid
flows.
Magnetism: the Key to Understanding the Sun
● Magnetic fields are produced on the
Sun by the flow of electrically charged
ions and electrons.
Magnetic Loops and Solar Flares
● Sunspots are places where very intense
magnetic lines of force break through
the Sun's surface.
● Streamers, flares, and loops seen in the
corona are shaped by magnetic fields.
Coronal Mass Ejections
July 1, 2002
Soft X-ray Image
Solar Environment
● Solar Wind: low energy charged
particles created by magnetic storms
propagate from the sun (v < c/1000).
● Sunspots (X-ray hot spots).
● Solar Flares (solar-magnetic storms)
Solar and Heliospheric Observatiory (SOHO)
● Coronal mass ejections (CME’s) are
explosions in the sun’s corona that
spew out tons of high-energy charged
particles (v < c/100).
Outline
• High-Energy Solar Physics
• Space Weather and its Detrimental Effects
• X-ray Astronomy and Grazing Incidence X-ray Telescopes
• The Solar X-ray Imager (SXI) Telescope
• Summary and Conclusions
Solar Storm Induced “Space Weather”
● Earth’s magnetic field provides protection
from the brunt of solar flares and CME’s.
Sun-Earth Electromagnetic Connection
● However, the Sun-Earth electromagnetic
connection serves to funnel residual
charged particles into the Van Allen belts
where they become trapped and initiate
various geomagnetic instabilities.
● These geomagnetic instabilities constitute a
type of space weather that can result in a
variety of detrimental effects.
Sun-Earth Electromagnetic Connection ● If the Earth’s position happens to coincide
with one of these plasma “hurricanes”
caused by a coronal mass ejection, it
becomes a detrimental geomagnetic storm.
● Solar storm induced “space weather” erodes
our space communications technological
infrastructure.
● Although auroras are a pleasing side-affect
of this extra-terrestrial phenomenon, they
are outweighed many times over by the
dangerous and costly consequences.
Detrimental Effects of “Space Weather”
● Communication satellites and scientific
spacecraft are vulnerable to the ravages of
severe space weather which can jeopardize
Ο Cell phone service
Ο GPS systems
Ο Scientific data links
Communication Satellite Failure
Synchronous
Orbit
Low earth
Orbit
● Also, fluctuating electro-jet currents high in
the atmosphere can produce magneticallycoupled current overloads in terrestrial
power lines resulting in electrical blackouts.
Power Grid Overloads
Detrimental Effects
● Geomagnetic Storms (compass / GPS malfunction)
● Power Grid Overloads (blackouts)
● Ionospheric Expansion (satellite deorbit)
● Electromagnetic Interference (communications
failure)
● Radiation Overdose (astronaut health hazard)
● Single Event Upsets (satellite electronics
malfunction)
Outline
• High-Energy Solar Physics
• Space Weather and its Detrimental Effects
• X-ray Astronomy and Grazing Incidence X-ray Telescopes
• The Solar X-ray Imager (SXI) Telescope
• Summary and Conclusions
Deterrents to the Development of X-ray Astronomy
● Adequate X-ray detectors have not always been available.
● No suitable refractive material exists for fabricating X-ray
lenses.
● Normal incidence mirrors exhibit extremely low reflectance
at X-ray wavelengths, thus the development of grazing
incidence optical designs.
● Grazing incidence optical designs are cumbersome and
difficult to fabricate and align.
● Surface scatter effects (even from our smoothest mirrors)
severely degrade X-ray image quality.
● Atmospheric absorption requires a spaced-based telescope.
X-ray Astronomy is a Relatively New Science
● 1948: First 2-D X-ray imager (Kirkpatrick and
Grazing Incidence Mirrors Required
Baez).
● 1952: X-ray Telescope Designs (Wolter).
● 1962: First X-ray telescope launched into
Kirkpatrick-Baez
space (no mirrors); discovered Sco-X1 in the
constellation Scorpius (Giacconi).
● 1970: First satellite, Uhuru, dedicated to the
discovery
of
X-ray
(Giacconi, Tananbaum).
cosmic
sources
● 1978: First X-ray telescope with mirrors, the
Einstein Observatory (Giacconi, Tananbaum).
Barrel, not Dish Shaped Mirrors
Einstein Observatory
(Wolter Type I)
2002 Nobel Prize in Physics
Riccardo Giacconi
For pioneering
contributions to
astrophysics, which
have led to the
discovery of cosmic
X-ray sources.
X-ray Astronomy and High-energy Solar Physics
Grazing Incidence Imaging Systems
•
•
•
•
•
•
•
The Einstein Observatory (HEAO B) 1978
The European ROSAT Telescope
1990
Japanese Yohkoh Solar Telescope
1991
UC Berkeley EUVE Telescope
1992
The Chandra Observatory (AXAF)
1999
ESA X-ray Spectrum Mission (XMM) 2000
The Solar X-ray Imager (SXI)
Solar Cycle
200
Sunspot Number
2006
150
100
50
0
1987
1991
1995
1999
2003
2007
August 1999
Classical Wolter Type I X-ray Telescope Design
(Ideal for Stellar Telescopes)
rp2 = 2 Rp ( z − zp )
2
2
Hyperboloid: (z − 2zh ) − rh2 = 1
● Three independent parameters: Rp, a, b.
Paraboloid:
a
r
● Equalizing grazing angle: two remain.
b
● ro and f ’ completely defines system.
Lh
Lp
Gap
Paraboloid
Hyperboloid
ro
z = 0 z1
.
.
Rp
x2
a(ε -1)
f’
z
2aε
● Co-aligned and confocal grazing incidence paraboloid and hyperboloid mirror.
● Corrected for spherical aberration.
● Can only balance defocus against field curvature by displacing the focal plane.
● Ideal for small-field stellar telescopes, not for wide-field staring solar telescopes.
Outline
• High-Energy Solar Physics
• Space Weather and its Detrimental Effects
• X-ray Astronomy and Grazing Incidence X-ray Telescopes
• The Solar X-ray Imager (SXI) Telescope
• Summary and Conclusions
National Oceanic & Atmospheric Administration
(NOAA)
• Operating unit of the U.S. Department of Commerce.
– National Weather Service
– National Satellite and Information Service
• NOAA’s charter has historically been to monitor and predict
terrestrial and atmospheric weather and climatic changes.
• NOAA operates the Geosynchronous Operational Environmental Satellites (GOES) whose down-looking telescopes
produce the weather maps we see on TV each night.
• NOAA’s charter has recently been changed to include
monitoring and predicting of Space Weather.
• The Solar X-ray Imager (SXI) Instrument is intended to help
NOAA accomplish that goal.
The Solar X-ray Imager (SXI) Contract
● NASA/GSFS was the contract monitor for the SXI program.
● Lockheed Martin’s Solar and Astrophysics Laboratory
(LMSAL) was the prime contractor responsible for
designing and building the SXI instrument.
● Raytheon Optical Systems, Inc. of Danbury, CT was the
subcontractor responsible for fabricating the precision
grazing incidence X-ray mirrors.
● CREOL also had a small subcontract from LM on the SXI
program (primarily because of our surface scatter
expertise).
CREOL’s Role in the SXI Program
(Perform a Complete Systems Engineering Analysis of Image Quality)
● Include Surface Scatter Effects, and
● and Misc. Errors from
Manufacturer’s Error
Budget Tree
*
*
Aperture Diffraction PSF
*
Geometrical PSF
Surface Scatter PSF
Residual Misc. Error PSF
Intensity
1.0
Hsystem = Hdiffraction Haberrations Hscattering Hmisc
0.5
0.0
F
-20
Az
i
m -10
ut
ha
lA
n
F
-20
gl
0
e
(a
r
-10
c
0
10
se
c)
10
20
20
di
Ra
ng
al A
ar
le (
cs
e c)
PSFsys = PSFdiff PSFaberr PSFscat PSFmisc
Resulting System PSF (or Aerial Image) of SXI Telescope
(Six arc min Field Angle, λ = 44.7 Å)
*
*
*
Determined the Need for an Alternative
Optical Design for SXI
● Kick-off meeting in Palo Alto with NOAA, NASA, Lockheed Martin, Raytheon,
and CREOL representatives present.
● Bi-monthly optical fabrication progress reviews at Raytheon Optical Systems,
Inc. in Danbury, CT.
● Graduate student Patrick Thompson and I started developing our image
analysis MatLab code.
● Quickly came to realize that the top level image quality requirement was
inappropriate for a staring solar telescope, and the classical Wolter Type I was
a non-optimum design.
● Tried to raise a question concerning the optical design at a general SXI
meeting (with customers present). Nobody wanted to hear it!
● Back at CREOL Patrick and I continued to evaluate other designs.
● Finally, I got LM to give me 30 min on the agenda at one of the bi-monthly
optical fabrication meetings (without NOAA and NASA customer present).
Image Quality Criterion for Wide-field Applications
(Desire Fine Detail in Extended Object)
● SXI is a wide-field staring X-ray
telescope pointed at the center of the
sun.
● The total information content in a given
image is maximized if we minimize the
field
weighted
average
resolution
element as degraded by all error
sources.
HPR fwa = 1
AT
where
Solar X-ray Imager (SXI)
Wide-field X-ray Imaging Applications
θy
dθ
θ dθ dϕ
dϕ
θx
OFOV
∫ HPR(θ ) 2πθ dθ ,
θ =0
AT = π (OFOV ) 2
● Since scattering effects are a significant
error source at these wavelengths, the
field weighted average half power radius
(HPRfwa) of the point spread function
(PSF) as degraded by all error sources is
an appropriate image quality criterion for
the SXI mission.
Solar Disc
(15 arc min radius)
OFOV
N = # of Res. Ele. = 2π
θ
∫ π HPR (θ ) dθ
θ =0
2
Hyperboloid-Hyperboloid Grazing Incidence
X-ray Telescope Design
● Five parameters (Rvp, εp, Rvs, εs, and svv) are required to completely characterize the
hyperboloid-hyperboloid optical prescription.
● In addition, the primary and secondary mirror lengths and the gap separating them
must be specified (Lp, Ls , and gap).
y
Ls
Lp
Primary
Gap
Secondary
rj
f’
z = 0 z1
zj
svv
z•sf1 zsv1 zf
Δf
zcs
2asεs
Δps
x
zsv2z•sf 2 zpf 1 zpv1
z
Extra design variables allow us to balance various aberrations over a given OFOV.
Geometrical Performance of a Family of Optimal
Hyperboloid-Hyperboloid Designs
12
θB = 1.5
θB = 3.8
θB = 7.9
θB = 10.5
θB = 12.1
θB = 14.3
θB = 16.1
θB = 17.2
θB = 20.0
RMS Image Radius (arc sec)
10
8
6
4
2
Linear Component (coma) Cannot be Corrected!
0
0
3
6
9
12
15
18
21
Field Angle (arc min)
Defocus, field curvature, SA3, astigmatism, and oblique spherical aberration
are all balanced at a different field angle for each design! This leaves only a
residual linear coma aberration at that unique field angle.
Optical Design Methodology
● Choose the desired OFOV, and plot the
field-weighted average rms image size vs.
optical design parameter θB . This yields
optimum parameter θB.
● Go to ZEMAX Optical Design Code with that
parameter to obtain the optimum optical
prescription of the telescope.
● Perform exhaustive ray trace analysis at
various field angles (geometrical PSF).
Finding Optimum Design Parameter
Field-weighted average HPR vs OFOV
14
Field-Weighted-Average RMS Image Radius (arc sec)
● 2-D integration of previous curves yield the
field-weighted average rms image size
versus the OFOV.
θB
θB
θB
θB
θB
θB
θB
θB
θB
12
10
= 1.5
= 3.8
= 7.9
= 10.5
= 12.1
= 14.3
= 16.1
= 17.2
= 20.0
= 22.5
8
6
4
2
0
0
3
6
9
12
15
18
21
24
27
H-T#17 Optical Design Prescription
Field-Weighted-Average RMS Image Radius (arc sec)
5.0
OFOV = 18 arc min
4.5
SXI Telescope System Parameters
4.0
3.5
3.0
2.5
0
2
4
6
8
10
12
14
16
Angle at which rms Image size is Minimized (θB in arc min)
18
30
Operational Field Of View (arc min)
Complete Systems Engineering Analysis
of Image Quality
6 arc min Field Angle, λ = 44.7Å
*
*
Aperture Diffraction PSF
*
Geometrical PSF
Surface Scatter PSF
Residual Misc. Error PSF
Intensity
1.0
Hsystem = Hdiffraction Haberrations Hscattering Hmisc
0.5
0.0
F
-20
Az
i
m -10
ut
ha
lA
n
-20
gl
0
e
(a
r
-10
c
0
10
se
c)
10
20
20
d ia
Ra
ng
lA
ar
le (
c
)
se c
F
PSFsys = PSFdiff PSFaberr PSFscat PSFmisc
Resulting System PSF (or Aerial Image) of SXI Telescope
*
*
*
Image Evaluation of the Optimum Design
● Insight concerning the relative effect of the
various image degradation mechanisms
obtained by plotting the fractional encircled
energy of the aerial image and its four main
contributors.
Fractional Encircled Energy of on-axis PSF
HT#17
Fractional Encircled Energy
● Detailed systems engineering analysis of
image quality is very computationally
intensive.
Scatter Effects
Dominate
Geo. Aberrations
for Small Field Angles
θ = 0.0 arc min
λ = 13.3Å
ADPSF
GPSF
SSPSF
HPR
● Plot HPR of aerial image vs. field angle for
different wavelengths (or X-ray energies).
RMEPSF
Aerial Image
Radius of Circle (arc sec)
Fractional Encircled Energy of off-axis PSF
Graphical Display of Systems Performance
9
Wavelength = 44.7 A
Geo. Aberrations
Dominate
Scatter Effects
For Large Field Angles
HT#17
θ = 20.0 arc min
λ = 13.3Å
ADPSF
HPR
GPSF
SSPSF
RMEPSF
Aerial Image
Wavelength = 8.34 A
7
Half Power Radius (arc sec)
Fractional Encircled Energy
8
6
5
4
3
2
1
0
0
Radius of Circle (arc sec)
3
6
9
12
Field Angle (arc min)
15
18
21
H-T#17 Design yields an 80% Increase in the Number of
Spatial Resolution Elements over the Solar Disc
Percent increase of the H-T#17 design (over NOAA baseline design) in the number
of spatial resolution elements versus the radius of the operational field-of-view.
% Increase in # of Spatial Res. Ele.
100
90
87% Increase
80
76% Increase
70
60
50
18 arc min radius OFOV
40
30
Wavelength = 44.7 A
20
OFOV
N = # of Res. Ele. = 2π
10
Wavelength = 8.34 A
θ
∫ π HPR (θ ) dθ
θ =0
2
0
12
13
14
15
16
17
18
19
Radius of Operational Field-of-View (arc min)
20
21
CREOL X-ray Telescope Design Adopted by NOAA
for GOES Series N-P Missions
● Solar X-ray Imager (SXI) is a complimentary,
add-on instrument designed primarily for
use on the GOES next generation satellites.
SXI Engineering Model
● Modular design is suitable for installation on
many other spacecraft platforms.
● Four flight models and a spare of the
grazing incidence X-ray mirrors were
fabricated to the CREOL HT#17 design by
Goodrich Optical & Space Systems, Inc.
● The Engineering Model underwent vibration
and electrical testing at LMSAL in Palo Alto.
Fabricating Grazing Incidence Mirrors
CREOL’s Role in GOES/SXI
● Developed a systems engineering analysis
capability to include the effects of surface
scatter and other manufacturing errors.
● Continued to provide general technical support
by modeling the “as manufactured” mirrors and
optimizing final detector plane position.
● Re-defined image quality requirem’t appropriate
for wide-field X-ray imaging applications.
● Developed new X-ray telescope design to yield
an 80% increase in performance over the NOAA
Baseline Design.
Conclusion
● GOES-N is the first of the next generation weather satellites that will include a
Solar X-ray Imager (SXI) instrument to provide full solar disc images of the sun
at X-ray wavelengths.
● The first model was incorporated into the GOES-N satellite and scheduled for
launch in May 2005 (launch was scrubbed due to computer glitch).
● GOES-N was re-scheduled for launch in June, and
again in July. It was cancelled each time, and is
currently awaiting the installation of new batteries
before being re-scheduled for launch.
GOES-N