SmallSat Missions @ Goddard
Firefly

Figure 1: Dr. Doug Rowland
Figure 1: Dr. Doug Rowland

Firefly was GSFC's first CubeSat. It was a 3U CubeSat mission led by GSFC principal investigator Dr. Doug Rowland in a collaborative effort funded by the National Science Foundation that included partnerships with the Universities Space Research Association, Siena College, University of Maryland Eastern Shore, and Hawk Institute for Space Sciences. The overall objective of the mission was to study the relationship between lightning and Terrestrial Gamma-ray Flashes (TGFs), which are sudden (transient) energetic bursts in the upper atmosphere. TGFs are suspected to be produced by beams of energetic electrons, which are accelerated in the intense electric fields generated by large thunderstorm systems. These electron beams are more powerful than any produced in near-Earth space, and understanding their acceleration mechanisms would shed light on a physical process that may occur on other planets, or in astrophysical environments, as well as in the sun’s corona. Firefly looked to study which types of lightning produced these electron beams and associated TGFs as well as the occurrence rate of the TGFs that are weaker than any previously studied.

In order to meet the mission science objectives, the spacecraft had an instrument suite to measure gamma rays, electrons, and lightning signatures. The following table summarizes each instrument and their associated capabilities.

Instrument Physical Description Measurements & Ranges Science Products
Gamma Ray Detector (GRD)

Measures the energy and arrival time of X-ray and gamma-ray photons as well as the energetic electron flux. 		64 cm² x 1 cm thick scintillator crystal arranged in a phoswich configuration with a 4 mm thick layer of PVT plastic scintillator
  • Photons – 100 keV to 10 MeV
  • Electrons – 100 keV to 2 MeV
  • Count rates up to 100,000/s
  • Gamma ray energy and time of arrival
  • Energetic electron energy time of arrival
  • Background spectra
Optical Lightning Detector (OLD)

Detects the arrival time of the optical signal associated with lightning. 		Four overlapping Hamamatsu silicon PIN diodes
  • 98% of all lightning optical power
  • Sample rate of 100 ksamples/s at 16-bit
 Optical power waveform with some localization
Very Low Frequency (VLF) Receiver

Measures single-axis electric field signatures. 		3 m monopole BeCu antenna
  • ±20 mV/m
  • Sample rate of 40 ksamples/s at 16-bit
 ELF/VLF electric field waveforms

The instruments were packed within the 3U volume as shown in the following illustrations.

Figure 2: Firefly Exterior Illustration
Figure 2: Firefly Exterior Illustration
Figure 3: Firefly Interior Illustration
Figure 3: Firefly Interior Illustration

The spacecraft was comprised of COTS components from vendors such as Pumpkin (structure and processor), Clyde Space (EPS, batteries, and solar panels), and AstroDev (radio). It utilized a passive attitude control system that was controlled via the 3 m gravity gradient boom with a 30 g tip which provided pointing within 20° of nadir. The solar cells were body mounted and located on all four faces of the body. The spacecraft’s specifications are summarized in the following table:

Spacecraft Mass 4 kg
Spacecraft Power 3 W orbit average
Spacecraft Stabilization
  • Deployable 3 m gravity gradient boom and magnetorquers for attitude control
  • 3-axis attitude magnetometer and solar cell measurements for attitude determination
  • Attitude knowledge requirement < 10°
GPS Receiver Accurate time to UTC (1 µs accuracy to UTC)
RF Communication
  • UHF @ 425 MHz with a downlink of 19.2 kbit/s
  • 2 GB of onboard storage capacity
  • Daily data volume of 10-20 MB

Firefly was manifested on ORS-3 (Operationally Responsive Space-3) as a secondary payload as part of the ELaNa-4 campaign. Prior to launch to the spacecraft underwent dimension verification for P-POD fitment, mass properties measurements, and vibration testing at NASA Wallops Flight Facility. The following are images associated with that process.

Figure 4: Firefly pre-inspection
Figure 4: Firefly pre-inspection
Figure 5: Firefly vibration testing
Figure 5: Firefly vibration testing
Figure 6: Firefly mass properties measurement
Figure 6: Firefly mass properties measurement

On November 20, 2013, Firefly was launched to orbit by ORS-3's Minotaur-1 launch vehicle out of the Mid-Atlantic Regional Spaceport (MARS) on Wallops Island, VA. The desired mission operations duration was one year with a minimum success of three months. First contact was made with Firefly on January 7, 2014 and telemetry indicated that the spacecraft was healthy. However, instrument data was never received from the spacecraft for the duration of the mission. It is suspected that issues occurred with the interface circuitry between the instrument and spacecraft bus. Firefly de-orbited on November 2, 2017. Despite not achieving the desired science returns, Firefly paved the way for future CubeSat missions at GSFC by providing valuable experience in the integration, testing, launch, and communication with these systems.