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

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.

Quake-Sat ION-1

CanX-2 GENESAT-1

Earth Science / IONOSPHEREUniversity of Illinois, Urbana-Champaign

NASA Ames

Launch: June 20, 2003Mission Duration: 38 months

Deployable Search Coil / 3U

Looking for ELF/VLF precursors of Earthquakes

Most successful CubeSat so farQuakeSat-2 under development

Launch: July 26, 2006Mission Duration: Dnepr failure

762 nm Airglow imaging / 2U

Mesospheric structures / gravity waves / Spread-F

ION-2 under development

ION-1: http://cubesat.ece.uiuc.edu

Launch: December 16, 2006Mission 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-ssite

Launch: April 28, 2008Mission Duration: Still operational

Formation FlyingGPS radio occultationGreenhouse gas atmospheric Spectrometer

Cubesats can fulfill a variety of missions

University of Toronto

Stanford University

Earth Science / ATMOSPHERE

HELIOPHYSICS / UPPER ATMOSPHERE

ASTROBIOLOGY / EXPLORATION

April 22, 2009

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….

• 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

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

RHESSI UpdatesDramatic 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

Map of TGFs and Lightning

BATSE (green diamonds) & RHESSI (white crosses)

Line up well with the lightning map!

Movie Break

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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

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.

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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

Beams of electrons from TGFs?

Continuous source of energetic electrons for the Earth’s inner radiation belt?

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?• 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

InstrumentsGamma 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

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 cm2 x 1 cm thick scintillator

VLF Receiver

D. Rowland

• 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.

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

The Spacecraft

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

Student involvement - SienaJ. Williams, J. DeMatteo, R. Carrollworking with A. Weatherwax, J. Kujawski, M. McColgan, E. Breimer, R. Yoder

AWESOME VLF ReceiverGround-based VLF support.Already in progress.

GSEMATLAB Instrument Control Toolbox

Instrument modelingOptical photodiode collimator optimization

Data Processing and AnalysisMATLAB

LEGO Firefly MissionExperiment Expansion ModulesFFT, Filter bank, advanced triggering

Geographic Information SystemWorldwide lightning network

Quake-Sat ION-1

CanX-2 GENESAT-1

Earth Science / IONOSPHEREUniversity of Illinois, Urbana-Champaign

NASA Ames

Launch: June 20, 2003Mission Duration: 38 months

Deployable Search Coil / 3U

Looking for ELF/VLF precursors of Earthquakes

Most successful CubeSat so farQuakeSat-2 under development

Launch: July 26, 2006Mission Duration: Dnepr failure

762 nm Airglow imaging / 2U

Mesospheric structures / gravity waves / Spread-F

ION-2 under development

ION-1: http://cubesat.ece.uiuc.edu

Launch: December 16, 2006Mission 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-ssite

Launch: April 28, 2008Mission Duration: Still operational

Formation FlyingGPS radio occultationGreenhouse gas atmospheric Spectrometer

Cubesats can fulfill a variety of missions

University of Toronto

Stanford University

Earth Science / ATMOSPHERE

HELIOPHYSICS / UPPER ATMOSPHERE

ASTROBIOLOGY / EXPLORATION

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.

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

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• 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