Space Test Program-Houston 4-FireStation (STP-H4-FireStation ) - 07.29.14
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Space Test Program-Houston 4-FireStation (STP-H4-FireStation) investigates how Earth’s upper atmosphere generates very brief, very intense flashes of gamma radiation. Since their discovery in 1994, the flashes have been linked to lightning, but researchers are not sure which types of lightning generate these gamma-ray flashes or how they form. STP-H4-FireStation measures the optical light and radio waves from lightning while also measuring the gamma ray and energetic radiation it produces. Results from the investigation will help researchers better understand the physics of lightning.
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Goddard Space Flight Center, Greenbelt, MD, United States
Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)
National Laboratory - Department of Defense (NL-DoD)
ISS Expedition Duration
March 2013 - March 2015
Previous ISS Missions
The instrumentation for STP-H4-FireStation was previously developed for the NSF Firefly CubeSat. Similar missions that have studied energetic radiation from lightning include CGRO, RHESSI, and Fermi as well as near-term and current ISS experiments GLIMS and ASIM.
Space Test Program-Houston 4-FireStation (STP-H4-FireStation) is critical to understand the discharge mechanism that allows lightning to occur. Runaway Relativistic Electron Avalanche models that are thought to generate gamma ray flashes observed from space may be intimately linked to the mechanisms that cause lightning in the first place.
Similar processes are expected to occur on other planets. In particular, the processes that take place in the Earth’s stratosphere may also take place close to the Martian surface, which is nearly in the same pressure regime. These processes might occur in planetary dust storms or dust devils, and can produce chemical reactions on the Martian surface.
The lightning-generated radiation may serve as a “seed population” for the inner Van Allen radiation belts.
STP-H4-FireStation spends one year on orbit making nearly continuous observations of lightning and energetic radiation. The resulting dataset provides tests for existing models of gamma ray flash generation, and deepen our understanding.
STP-H4-FireStation is also used to “exercise” the SpaceCube system, and demonstrate its capability to interface with and control a complex scientific instrument with high data throughput.
Space Test Program-Houston 4-FireStation (STP-H4-FireStation) consists of two components – a gamma ray / photometer system, that measures the optical flashes from lightning, the gamma ray emissions, and the secondary energetic electrons, and a radio receiver system that measures the electric and magnetic field signatures of lightning. The gamma ray / electron detector is a single scintillator “phoswich” (a phosphor sandwich detector) configuration, using GYSO:Ce (scintillator crystal) and PVT (plastic) scintillator, allowing the discrimination between electrons and gamma rays via the decay time of the signal, and using pulse height analysis to determine the energy of the incoming radiation. The optical system consists of nine fast photodiodes (sampled at 100 kHz) with different look directions in order to identify lightning, trigger the wave receiver burst memory, and provide a rough localization of lightning flashes within several viewing sectors.
The radio receiver consists of a dipole electric field antenna in a “rabbit-ears” configuration, 24 in long, and a “search coil” magnetic loop antenna wrapped around a ferrite core. The electric dipole covers the frequency range 100 Hz to 30 MHz, and the magnetic loop antenna runs from 20 Hz to 10 kHz.
The gamma ray detector can timetag individual events with sub-microsecond accuracy and can handle average count rates of about 100K counts per second, with 2 μs dead time.
STP-H4-FireStation takes continuous measurements of the electron and gamma ray spectra, as well as the count rate every millisecond and the light levels in the photodiodes at 1 kHz rate. When the count rate rises above a threshold, the high rate photometer digitization data is stored and sent to the ground, as well as the radio receiver data, to provide a tens of millisecond-long “snapshot” of the optical and radio signatures that produced a given gamma ray or electron enhancement.
Understanding electrical discharge processes can provide insight into similar processes on other planets. On Mars, which has a slightly lower atmospheric pressure than Earth, similar discharges may occur in dust storms and might produce chemical reactions on the surface. Understanding electron acceleration and transport also holds promise for heliophysics, the study of the sun and solar radiation.
Results from the STP-H4-FireStation investigation will provide new information about Earth and how it works. By understanding how lightning generates high-energy radiation, scientists can learn more about the physics of this common yet mysterious process.
Minimum success will be achieved after 3 months of observations, which should allow enough observations of lightning-generated gamma radiation and associated lightning signatures.
STP-H4-FireStation operates in a continuous-viewing mode throughout the 1-year on-orbit.