SPRITESAT Project mission for sprites and TGFs studies

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SPRITE-SAT Project mission for sprites and TGFs
studies
2008 TLE Workshop, Corte, 26 Jun. 2008

• Yukihiro Takahashi1, Mitsuteru Sato2,
• Umran Inan3, David Smith4, Sparite-Sat team
• 1 Tohoku University, Japan
• 2 Hokkaido University, Japan
• 3 Stanford University, U.S.A.
• 4 University of California, Santa Cruz, U.S.A

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0. Scientific background -- sprites
Occurrence probability of sprites
Sprite ? QE Model
Optical energy of sprites and CMC
Hu et al. 2002
Hu et al., 2002
Takahashi et al. 2008 (this workshop)
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VLF
ELF
CG
Adachi et al., 2003 (GRL)
Ohkubo et al., 2005 (GRL)
of columns is determined not by CMC, but by
EMP.
Sprites appear in the period of sferics cluster,
not at CG.
suggesting the important roles of - EMP -
intra-cloud (including horizontal) currents in
sprites generation/formation processes
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1. TLEs (Transient Luminous Events)
TLEs transient optical emission in the
stratosphere, mesosphere and lower thermosphere
caused by lightning discharges.

• Issues to be answered
• time delay and horizontaldisplacement from
  parent lightning
• CM deviations from QE-model predictions
• what determines number of columns and
  locations

Nadir Obs. from Space!
Figs. Horizontal lightning current plays crucial
role. Valdivia et al., 1997
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2. TGFs (Terrestrial Gamma-ray Flashes)

• Observational results from CGRO satellite and
  RHESSI satellite.
• Discovery of terrestrial gamma-ray flash
• High occurrence rate (1 event/2 day)
• Associated with lightning discharges?
• Timing between TGF and lightning is important

TGF and Lightning
Smith et al. 2005
Runaway Electron

• Which lightning process generates TGFs?
• Relationship between TLEs and TGFs?

Simultaneous Obs. from a Satellite!
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Outline of the SPRITE-SAT project
The first university satellite in Japan dedicated
to the geoscience under collaboration of Science
and Eng. faculties History 2003 Oct. applied
for grant-in-aid for 7 kg satellite with 1
camera and 1 (MeV) electron sensor (failed)
2004 Oct. applied for grant-in-aid again2004
RHESSI results presented in AGU fall meeting2005
Apr. 0.35 M USD for 4 years adopted (0.24M USD
used) modified to 10-kg satellite with 1 camera
and 1 TGF counter (TGC)2006 Apr. modified to
40-kg satellite with 4 cameras, 1 TGC2006 Dec.
chosen as one of the candidates for piggyback
launch of JAXA2007 May chosen as a piggyback
satellite2007 Jun. funded by grant-in-aid (3.5
M USD/4years) for scientific research in the
highest category for individual groups, not by
space agency, JAXA.
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Total cost 3.8 M USD - including fundamental
development and ground measurements/facilities
- 1 M USD for satellite manufacturingLaunch
Jan. 2009Lifetime 5 years expectedTelemetry
UHF(up), S-band at 9600bps (down) Ground
facilities 2.4 m S-band dishes at Sendai (Japan)
and Kiruna gt 5 MB/day 5-10 events/day
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3. Objects of SPRITE-SAT

• Achievement of the first synthetic observation of
  lightning, TLEs and TGFs from a satellite

• To investigate,
• Global distribution of TLEs and TGFs
• Horizontal distribution of sprites and their
  relation to lightning discharges
• Relationship between lightning, TLEs and TGFs

• SPRITE-SAT Science Instruments
• Imaging of TLEs, detection of Gamma-ray,
  observation of VLF waves
• CMOS Camera (LSI) 2 sets
• CCD Camera (WFC) 2 sets
• Gamma-ray detector (TGC) 1 set
• VLF antenna (VLF) 1 set

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4. SPRITE-SAT

• Specification
• Size 480480482 mm
• Mass 41 kg
• Power 17 W (max)
• Stabilization gravity gladient
• Orbit SSO (13-01 LT)
• Altitude 660 km
• Inclination 98 deg.
• Period 98 min.

Fig. Top view
Fig. Side view
Fig. SPRITE-SAT when in orbit
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4. SPRITE-SAT
Development Team

• CMOS, CCD Cameras
• H/W logic
• S/W development
• Optics development
• (Dept. of Geophysics, Tohoku Univ.)

Science Instruments (Dept. of Geophysics, Tohoku
Univ.)
SPRITE-SAT
Gamma-ray Detector (IASA/JAXA, UCSC)
Bus System (Dept. of Aerospace Engineering,
Tohoku Univ.)
VLF-ANT (Stanford Univ.)
H/W Development (AD. Co., Ltd.)
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5. SPRITE-SAT Bus System
MTM (Mechanical Test Model) of the satellite
Fig. MEM without shield panel.
Fig. MEM with shield panel.
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Making of flight model
In-house assembling with supports by small
companies
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6. Observation Modes
SPRITE MODE

• Nadir obs. using LSI-1,2 (FOV/35 deg)

imaging of lightning/sprite horizontal
distribution (29 fps)

• VLF is also operated

TGF MODE

• TGC, WFC(FOV/140 deg), VLF-ANT

• detection of TGFs and imaging of their
  parent lightning (30/60 fps)
• TGF and VLF timing with accuracy of 0.5 ms.

Fig. Obs. geometry
At SPRITE and TGF modes, event trigger scheme
will be used.
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TGF Obs. Mode
Sprite Obs. Mode
Using TGC and CCD camera with fish-eye lens, we
will identify the spatial relationship between
TGFs and lightning.
Using two CMOS cameras with band-pass
filters(740-830 nm, 762nm), we will identify the
horizontal distribution of sprite columns.
762nm
740-830 nm
FOV140 deg
FOV30 deg
Gamma-Ray
Sprite
Scattered Lightning Flashes
Cloud-to-Ground Discharge
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7. Science Instruments
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7. Imager (LSI-1, -2)
Lightning and Sprite Imager (LSI)
LSI-2 (for sprite detection)
762 nm
Most strong emission line of sprites severe
O2 absorption

• low alt. lightning emission ? absorption
• high alt. sprite emission (100?J) ? very weak
  absorption

LSI-1 (for lightning detection)
730-830 nm
Strong emission line of lightning

• gt90 lightning has energy of gt20?J

Fig. (top) Sprite emission spectrum calculated
by numerical simulation Milikh et al., 1997.
(bottom) Lightning emission derived from optical
observation Christian et al., 1996.
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LSI-1 2 - CMOS image sensors STAR250,
product of Cypress Semiconductor Co. are sued -
FOV 30
WFC - CCD image sensor ES2 by WATEC Co.,
Ltd. is used. - Equipped with fish eye lens. -
FOV 140.

• HSS.
• CCD image sensor ES2, by WATEC Co., Ltd.
  is used.- FOV 40

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7. Imager (LSI-1, -2, WFC)
29 frames/sec for LSI30 or 60 frames/sec for WFC
City light
dark image
x4 gain
LSB

Fig. sample dark image of CMOS camera

Differential of same pixel (Cn-Cn-1)
gt threshold ? (Cn-Cn-1 gt TP)
Lightning
Integration of (Cn-Cn-1) (FnFn (Cn-Cn-1))
Noise
calcuration of differencial
gt threshold ? (Fn-Fn-1gt TF)
trigger if the value exceed the threshold
Transient Emission(Lightning, TLEs)
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7.1 Verification of the trigger logic
GPS time counting system
Clock counting in FPGA
1PPS (Pulse Per Second)
Time data
PC
Imaging of display
CMOS(LSI)
dT 100 µsec
Lightning simulator
Time data
Camera parameters
Image header 16 Byte
Image data
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7.1 Verification of the trigger logic
Lightning flash with city light contamination
All the lightning events are triggered
Fig. Lightning emission with city light.
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comparison of LSI-1 (lightning) and LSI-2
(sprites) intensities
7.2 Sprite judgment logic by CPU
without sprite
Lightning
Lightning
Sprite
with sprite
Sprite
Lightning
Lightning
differential of two images is used in sprite
judgment
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8. VLF receiver

• BeCa boom for gravity gradient stabilization
  also works as VLF antenna.

• Analog circuit for the VLF receiver provided by
  Stanford Univ.

Fig. SPRITE-SAT with extended boom

• Specification
• freq. range lt25 kHz
• sampling freq. 100 kHz

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SPRITE-SAT will provide important practical
information to following missions, such as,
TARANIS, ASIM and GLIMS/ISS
- Brightness and spectrum of lightning flashes
/sprites measured with nadir looking cameras -
Detection frequency of sprite /TGF events using
same time of instruments - will contribute to
improve the triggering method/criteria
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10. Summary

• SPRITE-SAT equipped with 3 cameras, VLF receiver
  and TGF detector, will be launched in January
  2009.
• Manufacturing of flight model of BUS and SI is
  almost completed. Now final assembling of
  satellite. The delivery to JAXA will be in
  November.
• SPRITE-SAT must be a good precursor mission for
  TARANIS, ASIM and GLIMS, providing important
  practical information.
• Collaborative proposal with ground-based / space
  observations are very welcome.

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Abstract
SPRITE-SAT is now being developed in-house by
the Tohoku University team, which will be
launched in summer, 2008. The total weight of the
satellite would be less than 50 kg, including 4-5
kg science mission payload. There are two
scientific objectives in this micro-satellite
mission (1) to identify the generation
mechanisms of sprites by investigating their
horizontal structures, (2) to identify the
generation mechanisms of TGFs by investigating
their source location and relationship to
lightning discharges. Lightning and Sprite
Imager-1 and -2 (LSI-1 and 2) are CMOS cameras
with 512 x 512 pixels and the pixel size of 25
?m, which pointed at nadir to take images of the
horizontal structures of lightning and sprites.
In order to detect lightning emissions, we equip
LSI-1 with a broadband filter between 740 and 830
nm. We also equip LSI-2 with a rather narrow
band-pass filter centered at 762 nm. The optics
and the detector array altogether yield an
effective field of view (FOV) of 35 deg, giving
the pixel resolution of less than 660 m from the
altitude of 660 km. Wide Field CCD imager (WFC)
is a CCD camera with 659 x 494 pixels and the
pixel size of 7.4 um, which takes images of
lightning discharges inducing TGFs. WFC is also
pointed at nadir and is equipped fish-eye lens
(FOV is larger than180 deg). The outputs of all
cameras are digitized by 10 bit A/D conversion.
One instrumental case contains LSIs and WFC and
the total weights is 630 g. In order to
detect TGFs, terrestrial gamma-ray counter (TGC)
which consists of CsI scintillator is installed
at the satellite. TGC can detect gamma-rays in
the energy range from 30keV to a few MeV. This
satellite also equips a VLF antenna which
receives VLF radiations from lightning
discharges. At the presentation, we will show the
specifications of the instruments and the status
of the satellite development more in detail.
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7. Imager (LSI-1, -2, WFC)
LSI-1?2

• CMOS?512x512 pix440x440pix
• 1/38 s, 10bit output
• FOV24.8 x 24.8 degSpatial Res. lt660
  mDetection Rate 1.23 /day
• 20µJ 3LSB (SN12)

WFC

• CCD?659x494 pix
• 1/60 s, 10bit output
• FOV gt 140 deg
• 20µJ 230LSB (SN81)

LSI-1
LSI-2
WFC
Power1.94 W
Mass630 g
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7.1 Verification of the trigger logic
Lightning emission without city lights
All the lightning events are triggered
10km
10km
Possible to detect lt3 LSB emission
Possible to detect gt90 lightning events
Fig. Typical lightning image
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7. Imager (LSI-1, -2, WFC)
SHU
Temporal data save memory
data compression
SRAM (8M)
SRAM (8M)
2nd trigger (TLEs detection)
Satellite BUS
CMD
DSP(TMS320VC5510)
FPGA (Virtex-2)
data
Science Instruments
Control of SI
ROM
1st trigger (lightning detection)
ROM
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7. Imager (LSI-1, -2, WFC)
Specification
LSI-1, 2
WFC (Wide Field CCD Camera)