A STRATOSPHERIC BALLOON FLIGHT PLATFORM AND ITS EMPLOYMENT IN GRAVITATIONAL WAVE COUNTERPART OBSERVATION EXPERIMENTS

The Cubesats Applied for MEasuring and LOcalising Transients (CAMELOT) initiative proposes to deploy a fleet of 3U nanosatellites in order to localise GRBs with all-sky coverage. The operation is based on measuring the time delay of the event trigger between satellites that are otherwise uniformly distributed around the Earth in low-Earth orbit (between 500 - 600 km of altitude). In this design, caesium-iodide crystals interact with soft gamma radiation by emitting optical photons. Utilization of this effect, each member of the fleet is equipped with four of such scintillators and the emitted photons are detected by multi-pixel photon counters (MPPCs). Precise timing is crucial for this concept, the timestamping of the events and the synchronisation is provided by GPS. In order to demonstrate the feasibility of the CAMELOT concept, a single-unit CubeSat, named "GRBAlpha" is currently being developed. GRBAlpha is equipped with a single block of scintillator but the other subsystems are all the same as it will be on the CAMELOT units. We describe this single-unit platform system, focusing on the model versions suitable for high-altitude stratospheric balloon flights. This model has a standardized layout (including pin-out configuration, signalling and bus communication) and compatible with significant proportion of CubeSat system vendors. This system of ours is also capable of hosting multiple payloads at the same time, optimizing the utilization of balloon experiments.

Atmospheric Neutron Monitoring through Optical Fiber-Based Sensing

The potential of fiber-based sensors to monitor the fluence of atmospheric neutrons is evaluated through accelerated tests at the TRIUMF Neutron Facility (TNF) (BC, Canada), offering a flux approximatively 109 higher than the reference spectrum observed under standard conditions in New York City, USA. The radiation-induced attenuation (RIA) at 1625 nm of a phosphorus-doped radiation sensitive optical fiber is shown to linearly increase with neutron fluence, allowing an in situ and easy monitoring of the neutron flux and fluence at this facility. Furthermore, our experiments show that the fiber response remains sensitive to the ionization processes, at least up to a fluence of 7.1 × 1011 n cm−², as its radiation sensitivity coefficient (~3.36 dB km−1 Gy−1) under neutron exposure remains very similar to the one measured under X-rays (~3.8 dB km−1 Gy−1) at the same wavelength. The presented results open the way to the development of a point-like or even a distributed dosimeter for natural or man-made neutron-rich environments. The feasibility to measure the dose caused by the neutron exposure during stratospheric balloon experiments, or during outer space missions, is presented as a case study of a potential future application.

Balloon-borne Cosmic Microwave Background experiments

Stratospheric balloon experiments play a unique role in current Cosmic Microwave Background (CMB) studies. CMB research has entered a precision phase, harvesting the detailed properties of its anisotropy, polarization and spectrum, at incredible precision levels. These measurements, however, require careful monitoring and subtraction of local backgrounds, produced by the earth atmosphere and the interstellar medium. High frequencies (larger than 180 GHz) are crucial for the measurements of interstellar dust contamination, but are degraded by atmospheric emission and its fluctuations, even in the best (cold and dry) sites on earth. For this reason, new balloon-borne missions, exploiting long-duration and ultra-long duration stratospheric flights, are being developed in several laboratories worldwide. These experiments have the double purpose of qualifying instrumentation and validating methods to be used on satellite missions, and produce CMB science at a relatively fast pace, synergically to ground-based CMB observatories.

Anisotropic pitch angle distribution of ~100 keV microburst electrons in the loss cone: measurements from STSAT-1

Electron microburst energy spectra in the range of 170 keV to 360 keV have been measured using two solid-state detectors onboard the low-altitude (680 km), polar-orbiting Korean STSAT-1 (Science and Technology SATellite-1). Applying a unique capability of the spacecraft attitude control system, microburst energy spectra have been accurately resolved into two components: perpendicular to and parallel to the geomagnetic field direction. The former measures trapped electrons and the latter those electrons with pitch angles in the loss cone and precipitating into atmosphere. It is found that the perpendicular component energy spectra are harder than the parallel component and the loss cone is not completely filled by the electrons in the energy range of 170 keV to 360 keV. These results have been modeled assuming a wave-particle cyclotron resonance mechanism, where higher energy electrons travelling within a magnetic flux tube interact with whistler mode waves at higher latitudes (lower altitudes). Our results suggest that because higher energy (relativistic) microbursts do not fill the loss cone completely, only a small portion of electrons is able to reach low altitude (~100 km) atmosphere. Thus assuming that low energy microbursts and relativistic microbursts are created by cyclotron resonance with chorus elements (but at different locations), the low energy portion of the microburst spectrum will dominate at low altitudes. This explains why relativistic microbursts have not been observed by balloon experiments, which typically float at altitudes of ~30 km and measure only X-ray flux produced by collisions between neutral atmospheric particles and precipitating electrons.

Precision CMB Measurements from Long Duration Stratospheric Balloons: Towards B-modes and Inflation

Observations of the Cosmic Microwave Background (CMB) have played a leading role in establishing an understanding of the structure and evolution of the Universe on the largest scales. This achievement has been enabled by a series of extremely successful experiments, coupled with the simplicity of the relationship between the cosmological theory and data. Antarctic experiments, including both balloon-borne telescopes and instruments at the South Pole, have played a key role in realizing the scientific potential of the CMB, from the characterization of the temperature anisotropies to the detection and study of the polarized component. Current and planned Antarctic long duration balloon experiments will extend this heritage of discovery to test theories of cosmic genesis through sensitive polarized surveys of the millimeter-wavelength sky. In this paper we will review the pivotal role that Antarctic balloon borne experiments have played in transforming our understanding of the Universe, and describe the scientific goals and technical approach of current and future missions.

THE ARGO-YBJ EXPERIMENT PROGRESSES AND FUTURE EXTENSION

Gamma ray source detection above 30 TeV is an encouraging approach for finding galactic cosmic ray origins. All sky survey for gamma ray sources using wide field of view detector is essential for population accumulation for various types of sources above 100 GeV. To target the goals, the ARGO-YBJ experiment has been established. Significant progresses have been made in the experiment. A large air shower detector array in an area of 1 km2 is proposed to boost the sensitivity. Hybrid detections with multi-techniques will allow a good discrimination between different types of primary particles, including photons and protons, thus enable an energy spectrum measurement for individual species. Fluorescence light detector array will extend the spectrum measurement to 100 PeV and higher where the second knee is located. An energy scale determined by balloon experiments at 10 TeV will be propagated to ultra high energy cosmic ray experiments.