Transcript Slide 1

The Firefly Satellite Mission
Understanding Earth’s most Powerful
Natural Particle Accelerator
The Firefly Team
April 22, 2009
What is Firefly?
• Firefly is a nanosatellite (4.5 kg, 10x10x34 cm), funded by the
National Science Foundation, to study the phenomenon
known as Terrestrial Gamma ray Flashes (TGFs).
• NSF is developing a series of CubeSat missions to study the
Earth’s upper atmosphere and space weather.
– The plan is to launch two missions per year - $1M per mission!
• Firefly is the second funded mission.
– The first, called the Radio Aurora Explorer (RAX), led by Jamie Cutler
(Michigan) and Hasan Bahcivan (SRI) will launch Feb 2010 and study
ionospheric density structures associated with the aurora.
Very Early Investigations
Since we are still
struggling to understand
how lightning works 250
years after Franklin’s kite
experiment, perhaps we
are missing something
important….
Lightning
• Until recently, lightning was thought to be an
conventional discharge.
entirely
• Lightning is really an exotic kind of discharge that involves
runaway electrons, which are accelerated to nearly the speed
of light and produce large numbers of x-rays (gamma rays) .
• Since the standard models of lightning do not include
runaway electrons, nor do they predict x-ray and gamma-ray
emission, clearly we need to revisit these models.
• X-rays (gamma rays) give us a new tool for studying lightning
What are TGFs?
• TGFs are brief (1 ms long) intense (flux higher than a solar
flare, spectrum harder than cosmic gamma ray bursts) bursts
of gamma rays coming from the Earth’s atmosphere.
• TGFs may be the result of energetic electrons, accelerated
by intense thunderstorm electric fields, from thermal
energies to tens of MeV in less than one millisecond.
• Secondary electrons produced by TGFs can escape the
atmosphere, and may provide a weak but continuous source
of energetic electrons for the Earth’s inner radiation belt.
POES measurements of
radiation belt electrons
Terrestrial Gamma-ray Flashes
• Bright flashes of gamma-rays first
observed by BATSE (CGRO)
while it was searching for GRBs
• Much shorter then cosmic
Gamma-Ray Bursts
– ~1 ms vs. 1-100 s
• Much harder spectrum than
cosmic GRB’s
– break at 30 MeV vs. 250 keV
– power law slope -1 vs. -2
• Approximately 1/month detected
• Appeared to be coming from nadir
(the Earth), and observed when
CGRO flew over thunderstorms
G. J. Fishman et al., Science, 1994
Movie Break
Firefly Science
Objectives
• Are TGFs produced only in association with lightning?
• What kinds of lightning do and do not produce TGFs (polarity, peak
current, stroke geometry, charge transferred, presence / absence of sprites
and other Transient Luminous Events)?
• What are the fluxes of energetic electrons (100 keV to 10 MeV)
accelerated over lightning?
• What is the relative timing of the optical, VLF, electron, and gamma-ray
signatures associated with TGFs and what does this imply about the
acceleration mechanism?
• What are the spatial extents of the gamma-ray and electron emissions?
• What is the occurrence frequency of very weak TGFs?
What do we need?
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Single platform that measures gamma rays, electrons, and
lightning signatures
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provides accurate relative timing
discriminates electron from gamma ray counts
uses VLF and optical signatures to discriminate weak TGFs from statistical
fluctuations
Accurate relative timing (1 µs)
Accurate absolute timing to UTC (better than 1 ms)
Fast detector
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1 MHz or (preferably) better
Over flights of ground-based receivers for lightning
characterization
Instruments
Gamma Ray Detector (GRD)
• Bismuth Germanate
• photons from 20 keV to 20 MeV
• count rates up to 1 MHz
• electrons from 100 keV to 10 MeV
• count rates up to 300 kHz
• snapshots, spectra, and count rate histograms
VLF wave receiver (VLF)
• single-axis electric fields 100 Hz to 20 kHz
Optical photodiode (OPD)
• provides localization of lightning
• detect lightning within about 400 km
• designed to work day and night
Gamma Ray Detector
200 cm2 x 1 cm thick scintillator
BGO and CaF2(Eu) have different light decay times (300 ns, 900 ns). By
integrating the resulting charge signal with two different shaping
amplifiers, the nature of the incoming radiation can be determined, and
the energy can be measured by standard pulse-height analysis.
• Electrons < MeV interact in CaF2(Eu)
• Photons interact in BGO
• Electrons > 1 MeV interact in both
VLF Receiver
• Measure electric field signatures in the range of 100 Hz to 1 MHz
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User selectable anti-aliasing filter of 30 kHz, 180 kHz, and 1080 kHz.
1.0 m tip-to-tip electric dipole antenna
Dual, multiplexed 6 MHz ADCs for all science instruments
We gratefully acknowledge collaboration with Stanford University.
• Time-tag VLF events for ground-based VLF correlation
– Primary goal is 1ms timing accuracy to UTC.
– Secondary goal is 1us timing accuracy to UTC.
Optical Photodiodes
• FOV Calculations
•Minimum and maximum field of view were
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calculated based on the geometry of the
photo detector and collimator
The square photodetector was modeled as
two circles: inscribed (min) & circumscribed
(max)
Equations developed using geometric
models and implemented in Matlab
The Spacecraft
• Mass: 4.0 kg
• Power: 3 W orbit-averaged
• Comm: 425 MHz
• 19.2 kbps downlink
• GPS for accurate timing to UTC
• Gravity gradient boom and
magnetotorquers for attitude control
• 3-axis attitude magnetometer
• Points within 30 degrees of nadir
• 1 µs accuracy to UTC
• 2 GB onboard storage
Four-channel
photometer
GRD sensor
(1 of 2)
VLF
antenna
(1.6 m tip to
tip)
Comm
antennas
Student Involvement at Siena
Experiment Expansion Modules
FFT, Filter bank, advanced triggering
AWESOME VLF Receiver
Ground-based VLF support.
GSE
MATLAB Instrument Control Toolbox
Instrument modeling
Optical photodiode collimator optimization
Data Processing and Analysis
LEGO Firefly Mission
Geographic Information System
Worldwide lightning network
Operations Concept
• Prime data are 100 ms “snapshots” triggered by increase in
gamma ray counts, electron counts, VLF signal, or optical
signal
• Trigger levels adjustable from ground
• Expect ~50 snapshots per day
• Expect 1-5 weak TGFs / day, 1 strong TGF every 2-3 days
• Duty cycle of about 50% to save power (on during eclipse)
• Ground contacts
• Ramp down HV in South Atlantic Anomaly
Schedule
• Project start: Sept 18, 2008
• Mission Requirements Review: Jan 12, 2009
• Design Review: June, 2009
• Experiment Integration: January 2010
• Spacecraft level environmental testing:
– Feb / March 2010
• PPOD environmental testing: April 2010
• Launch: August 2010
Status
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Successful Mission Requirements Review in Jan 2009
Prototyping instruments
Flight software and mechanical design underway
Procurements for commercial subsystems underway
Attitude Control System design underway
August 2010 launch!
April 22, 2009
Cubesats can fulfill a variety of missions
Quake-Sat
Stanford University
Earth Science / IONOSPHERE
Launch: June 20, 2003
Mission Duration: 38 months
ION-1
HELIOPHYSICS / UPPER ATMOSPHERE
University of Illinois,
Urbana-Champaign
Deployable Search Coil / 3U
762 nm Airglow imaging / 2U
Looking for ELF/VLF precursors
of Earthquakes
Mesospheric structures /
gravity waves / Spread-F
Most successful CubeSat so far
QuakeSat-2 under development
CanX-2
Earth Science / ATMOSPHERE
University of Toronto
Launch: July 26, 2006
Mission Duration: Dnepr
failure
ION-2 under development
GENESAT-1
NASA Ames
Launch: April 28, 2008
Mission Duration: Still
operational
Formation Flying
GPS radio occultation
Greenhouse gas
atmospheric Spectrometer
QuakeSat: http://www.quakefinder.com/services/quakesat-ssite
ASTROBIOLOGY / EXPLORATION
Launch: December 16, 2006
Mission Duration: ~ 1 year
Supports E. Coli growth in
space and performs genetic
assays to study changes due
to space environment / 3U
Pharmasat under development
ION-1: http://cubesat.ece.uiuc.edu
RHESSI Updates
Dramatic Expansion of database by
RHESSI (Smith et al., Science, 2005)
35 MeV electron
bremsstrahlung spectrum
atmospheric attenuation
• Evidence for 35 MeV electron source at 15-20 km altitude
• Approximately 15/month detected
• RHESSI has 20 MeV stopping power
• 976 events detected to date (7 years)
Map of TGFs and Lightning
BATSE (green diamonds) & RHESSI (white crosses)
Line up well with the lightning map!
Some TGF Basics
• Gamma rays produced as bremsstrahlung from
energetic electron acceleration.
• Energetic electrons may be accelerated deep in
stratosphere, or in mesosphere
• Most of the gamma rays and electrons are
absorbed by the atmosphere.
• Secondary electron production via Compton
scattering or pair production gives rise to
energetic electron population that can escape.
A Brief History of Runaway Electrons
• C.T.R. Wilson (1925) first proposes
the idea that runaway electrons can
be produced in a thunderstorm
• Gurevich et al. (1992) predicts
relativistic runaway electron
avalanches with a seed population
of relativistic electrons from cosmic
ray showers.
• J.R. Dwyer (2003) introduces
Relativistic Breakdown that
includes the feedback due to
positrons and gamma rays and
generates a self-sustaining
breakdown of the electric field from
a single MeV electron.
Dwyer, GRL 2003
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Beams of electrons from TGFs?
Continuous source of energetic electrons for the
Earth’s inner radiation belt?
Lightning-related Phenomena
Red sprites occur from 5090 km, 0-100 ms after
lightning. Large charge
moment change in a CG+
flash.
Elves are prompt expanding
rings at the edge of the
ionosphere driven by the
EMP of a return stroke.
Blue jets occur near cloud
tops and may be a cloud-toair breakdown (or
something else?).
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CubeSat Concerns
• Problem areas:
– Comm, power, ACS, radiation effects
• As of last year’s CDW, all data downloaded from
all CubeSats would have fit on a single CD
– ~550 MB
• QuakeSat was responsible for 450 MB by itself.
• Many CubeSats never make ground contact.