This summer, an important milestone of the HEMERA EU infrastructure program has been achieved with the launch of several experiments on board high altitude balloons.
During August in Timmins, Canada, the Canadian Space Agency (CSA) and the Centre national d'études spatiales (CNES) have managed to launch in rapid sequence 4 balloons in the stratosphere, up to ceiling altitudes greater than 30km. Two of them have been flying the GRASS-2 (Gamma Ray Astronomy Small Sensor, built at IAPS) and CorMAG (Coronal Magnetograph, built at OATO) instruments. Furthermore in September, the BADG3R instrument (built at IASF-PA and OAS) was flown from the Kiruna (Sweden) balloon base, managed by the Swedish Space Science Corporation (SSC).

These instruments have been developed by INAF and ASI, with a specific funding program devoted to support Italian payloads of astrophysical interest programmed to fly with the HEMERA infrastructure. The two campaigns were fully successful. The teams have already started to analyse the data in order to fully exploit the scientific and technological potential of their measurements.

The GRASS-2 team with the CSA payload manager

GRASS-2 is an INAF project led by Dr. Lorenzo Natalucci. The instrument is a small, innovative gamma-ray detector aimed at measure the parameters of the cosmic and atmospheric background in the stratosphere. It was launched from Timmins on August 12 and the instrument has been taking data for 11.5 hours (~3h at the floating altitude of 32.5 km). It consists of an array of 64 small (6mm size) square scintillation detectors coupled to a 64 pixel Silicon Photomultiplier (SiPM)  to convert light into electrical signal. Compared to its first version, launched in 2021, this detector has spatial resolution and imaging capability through the use of a coded mask. This approach has already been proved useful in satellite missions like e.g. INTEGRAL and Swift. In the future, this technology will allow to develop more compact and lighter imaging spectrometers than already available. This will allow, in particular, to detect and position rapidly variable celestial sources, such as gamma-ray bursts, gravitational wave and neutrinos counterparts.

The gondola with CorMAG onboard and the INAF team

CorMag is an INAF project led by Dr. Silvano Fineschi. It was launched on August 17 aboard the gondola of a stratospheric balloon from the CNES base in Timmins, Ontario, Canada. The flight lasted a total of 8 hours, of which 6 at the observation altitude of 36 km.

CorMag is an experiment for the study of the magnetic field of the solar corona; the tenuous external atmosphere of the Sun composed of plasma at extremely high temperatures of several million degrees. By creating an "artificial eclipse" with a special occulter inside its telescope, CorMag observes the visible light diffused and polarized by the iron atoms strongly ionized by the high coronal temperatures. These observations provide unique information on the magnetic field of the corona of which it is considered the "engine", being responsible for its high temperatures, the acceleration of the solar wind, and solar storms.

As part of the CorMag project, Inaf has also developed a system - unique of its kind - which allows the telescope to point and track the Sun - regardless of the oscillations of the gondola during flight - with an accuracy of 10 arc seconds.  The preliminary analysis of the performance of the telescope and of the pointing and tracking system has shown the potential of the CorMag experiment, and its recovery in good condition after landing, makes it possible to reuse it in further future stratospheric flights.

BADG3R mounted in flight configuration on its steel structure. In the foreground the battery pack, on the left side the detector module connected with 24 coaxial signal cables and 4 power connectors to the OBDH system that can be seen on the bottom

The BADG3R experiment is an INAF project led by Dr. Stefano Del Sordo. It is born from a collaboration between two INAF institute (IASF and OAS), IMM/CNR of Parma and the DIFC of the University of Palermo. The payload has been successfully launched the 7^th of September 2022 from the SSC/Esrange facility in Kiruna (Sweden). The duration of the flight, at the floating altitude of 34 km, was about 5 hours.

The BADG3R payload is a hard X/soft gamma detector (10 – 1000 keV) based on an innovative CZT spectrometer with 3D spatial resolution. This sensor, based on a CZT crystal of 20x20x6 mm³ , implements a drift strip configuration for the anodes coupled with a segmented cathode mounted orthogonally with respect to the anodes strips. This configuration allow a sub-millimeter spatial resolution and then a high segmentation of the sensitive volume ,using a limited number of electronic channels and also a fine spectroscopy (1% @  511 keV) The possibility to fully exploits this feature is guaranteed by the use of a complete digital reading system of the signals.

The BADG3R experiment was designed for two main goals, a technological one and a scientific one. The first is to validate, in a pseudo-spatial environment, the sophisticated technological solutions developed in the realization of the CZT sensor. The second goal is to evaluate and confirm the performance, already obtained on ground, in a charged particles rich environment of its nature quite hostile to this type of detectors. In particular we wish to evaluate the real advantages of the digital approach, through an off-line analysis, to reconstruct the background spectrum and eventually to discriminate between charged particles and photons exploiting the good performance in spatial and energy resolution of this sensor.