1. The Firefly Satellite Mission Understanding Earth’s most Powerful Natural Particle Accelerator Union College Seminar, September 17, 2009

2. 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. CubeSat Scope 10 x 10 x 10 cm “1U” up to 10 x 10 x 34 cm “3U” 5-U and 6-U under development 1 kg per “U”. In practice this can be exceeded by at least 50%. 1-2 W per “U”, orbit-averaged 5-10 Mbits per day or more depending on ground station Secondary payload / ride of opportunity Altitude range 450 to 650 km based on orbit lifetime Except for orbit, the constraints are not so different from those on Explorer 1.

5. Quake-Sat ION-1 CanX-2GENESAT-1 Earth Science / IONOSPHERE University of Illinois, Urbana-Champaign NASA Ames 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 ION-1: http://cubesat.ece.uiuc.eduhttp://cubesat.ece.uiuc.edu 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 QuakeSat: http://www.quakefinder.com/services/quakesat-ssitehttp://www.quakefinder.com/services/quakesat-ssite Launch: April 28, 2008 Mission Duration: Still operational Formation Flying GPS radio occultation Greenhouse gas atmospheric Spectrometer CubeSats can fulfill a variety of missions! University of Toronto Stanford University Earth Science / ATMOSPHERE HELIOPHYSICS / UPPER ATMOSPHERE ASTROBIOLOGY / EXPLORATION

6. MIDEX SMEX Sounding Rockets BALLOONS NanoSats Flagship CubeSats provide low-cost… Focused science Constellation missions / multi-point measurements TRL improvement / technology validation Rapid response (think SN1987a) Student training / workforce experience Environmental monitoring (climate, space weather) MISSIONS PER YEAR MISSION LIFETIME COSTMASS 1-2 5 TO 20 YEARS $1B 1500 KG 1-2 3 TO 10 YEARS $200M 750 KG 1-2 1 TO 10 YEARS $100M 300 KG 20 5 MINUTES TO 2 MONTHS $3M TO $10M 10 KG TO 2000 KG 30+ 2 WEEKS TO 2 YEARS $100K TO $5M 1-5 KG

7. April 22, 2009

8. 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….

9. 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 Lightning

10. 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 radiation belts. POES measurements of radiation belt electrons

11. 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

12. 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.

13. RHESSI Updates Reuven Ramaty High Energy Solar Spectroscopic Imager Dramatic Expansion of database by RHESSI (Smith et al., Science, 2005) 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) 35 MeV electron bremsstrahlung spectrum atmospheric attenuation

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

15. Movie Break

16. 16 Red sprites occur from 50-90 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-to- air breakdown (or something else?). Lightning-related Phenomena

17. 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.

18. 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

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

20. 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?

21. 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

22. 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 horl distance designed to work day and night

23. Gamma Ray Detector Electrons < MeV interact in CaF2(Eu) Photons interact in BGO Electrons > 1 MeV interact in both 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. 200 cm 2 x 1 cm thick scintillator

24. 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.

26. 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

27. The Spacecraft VLF antenna (1.6 m tip to tip) Four-channel photometer Comm antennas GRD sensor (1 of 2) 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 and solar cell measurements for attitude determination Points within 30 degrees of nadir Attitude knowledge requirement 10 deg 1 µs accuracy to UTC 2 GB onboard storage

28. 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

29. 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.

30. 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

31. 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

32. 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!

34. RREA & RB D. RowlandDartmouth Physics Seminar April 14, 2009 Dwyer, GRL 2003