1. The Firefly Satellite Mission Understanding Earth’s most Powerful Natural Particle Accelerator

2. The Firefly Team
April 22, 2009

3. 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.

4. Cubesats can fulfill a variety of missions
Quake-Sat
ION-1
Earth Science / IONOSPHERE
HELIOPHYSICS / UPPER ATMOSPHERE
Stanford University
University of Illinois, Urbana-Champaign
Launch: June 20, 2003
Mission Duration: 38 months
Deployable Search Coil / 3U
Looking for ELF/VLF precursors of Earthquakes
Most successful CubeSat so far
QuakeSat-2 under development
Launch: July 26, 2006
Mission Duration: Dnepr failure
762 nm Airglow imaging / 2U
Mesospheric structures / gravity waves / Spread-F
ION-2 under development
CanX-2
GENESAT-1
Earth Science / ATMOSPHERE
ASTROBIOLOGY / EXPLORATION
University of Toronto
NASA Ames
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
Launch: April 28, 2008
Mission Duration: Still operational
Formation Flying
GPS radio occultation
Greenhouse gas atmospheric Spectrometer
QuakeSat:
ION-1:

5. April 22, 2009

6. 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….

7. Lightning
Until recently, lightning was thought to be an entirely conventional discharge.
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

8. 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

9. 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 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

10. 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 km altitude
Approximately 15/month detected
RHESSI has 20 MeV stopping power
976 events detected to date (7 years)

11. Map of TGFs and Lightning
BATSE (green diamonds) & RHESSI (white crosses)
Line up well with the lightning map!

12. Movie Break

13. Lightning-related Phenomena
Red sprites occur from km, 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-to-air breakdown (or something else?).

14. 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.

15. 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

16. Beams of electrons from TGFs?
Continuous source of energetic electrons for the Earth’s inner radiation belt?

17. 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?

18. What do we need?
Single platform that measures gamma rays, electrons, and lightning signatures
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
1 MHz or (preferably) better
Over flights of ground-based receivers for lightning characterization

19. Instruments Gamma Ray Detector (GRD) VLF wave receiver (VLF)
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 horl distance
designed to work day and night

20. Gamma Ray Detector Electrons < MeV interact in CaF2(Eu)
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

21. VLF Receiver
Measure electric field signatures in the range of 100 Hz to 1 MHz
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.
D. Rowland

22. Optical Photodiodes FOV Calculations
Minimum and maximum field of view were 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

23. The Spacecraft Mass: 4.5 kg Power: 3 W orbit-averaged Comm: 425 MHz
VLF antenna
(1.6 m tip to tip)
Four-channel photometer
Comm antennas
GRD sensor
(1 of 2)
Mass: 4.5 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 and solar cell measurements for attitude determination
points within 30 degrees of nadir
attitude knowledge requirement 10 degrees
1 µs accuracy to UTC
2 GB onboard storage

24. Student involvement - Siena J. Williams, J. DeMatteo, R
Student involvement - Siena J. Williams, J. DeMatteo, R. Carroll working with A. Weatherwax, J. Kujawski, M. McColgan, E. Breimer, R. Yoder
AWESOME VLF Receiver
Ground-based VLF support.
Already in progress.
GSE
MATLAB Instrument Control Toolbox
Instrument modeling
Optical photodiode collimator optimization
Data Processing and Analysis
MATLAB
LEGO Firefly Mission
Experiment Expansion Modules
FFT, Filter bank, advanced triggering
Geographic Information System
Worldwide lightning network

25. Cubesats can fulfill a variety of missions
Quake-Sat
ION-1
Earth Science / IONOSPHERE
HELIOPHYSICS / UPPER ATMOSPHERE
Stanford University
University of Illinois, Urbana-Champaign
Launch: June 20, 2003
Mission Duration: 38 months
Deployable Search Coil / 3U
Looking for ELF/VLF precursors of Earthquakes
Most successful CubeSat so far
QuakeSat-2 under development
Launch: July 26, 2006
Mission Duration: Dnepr failure
762 nm Airglow imaging / 2U
Mesospheric structures / gravity waves / Spread-F
ION-2 under development
CanX-2
GENESAT-1
Earth Science / ATMOSPHERE
ASTROBIOLOGY / EXPLORATION
University of Toronto
NASA Ames
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
Launch: April 28, 2008
Mission Duration: Still operational
Formation Flying
GPS radio occultation
Greenhouse gas atmospheric Spectrometer
QuakeSat:
ION-1:

26. 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.

27. 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 only 8x5, during business hours
Ramp down HV in South Atlantic Anomaly

28. 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

29. Status 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!

30. April 22, 2009