GRBAlpha is a 1U CubeSat launched in March 2021 to a sun-synchronous LEO at an altitude of 550 km to perform an in-orbit demonstration of a novel gamma-ray burst detector developed for CubeSats. VZLUSAT-2 followed ten months later in a similar orbit carrying as a secondary payload a pair of identical detectors as used on the first mission. These instruments detecting gamma-rays in the range of 30-900 keV consist of a 56 cm2 5 mm thin CsI(Tl) scintillator read-out by a row of multi-pixel photon counters (MPPC or SiPM). The scientific motivation is to detect gamma-ray bursts and other HE transient events and serve as a pathfinder for a larger constellation of nanosatellites that could localize these events via triangulation.
At the beginning of July 2024, GRBAlpha detected 140 such transients, while VZLUSAT-2 had 83 positive detections, confirmed by larger GRB missions. Almost a hundred of them are identified as gamma-ray bursts, including extremely bright GRB 221009A and GRB 230307A, detected by both satellites. We were able to characterize the degradation of SiPMs in polar orbit and optimize the duty cycle of the detector system also by using SatNOGS radio network for downlink.
We present the detector performance and early science results from GRBAlpha, a 1U CubeSat mission, which is a technological pathfinder to a future constellation of nanosatellites monitoring gamma-ray bursts (GRBs). GRBAlpha was launched in March 2021 and operates on a 550 km altitude sun-synchronous orbit. The gamma-ray burst detector onboard GRBAlpha consists of a 75×75×5 mm CsI(Tl) scintillator, read out by a dual-channel multi-pixel photon counter (MPPC) setup. It is sensitive in the ∼30−900 keV range. The main goal of GRBAlpha is the in-orbit demonstration of the detector concept, verification of the detector’s lifetime, and measurement of the background level on low-Earth orbit, including regions inside the outer Van Allen radiation belt and in the South Atlantic anomaly. GRBAlpha has already detected five, both long and short, GRBs and two bursts were detected within a time-span of only 8 hours, proving that nanosatellites can be used for routine detection of gamma-ray transients. For one GRB, we were able to obtain a high resolution spectrum and compare it with measurements from the Swift satellite. We find that, due to the variable background, the time fraction of about 67% of the low-Earth polar orbit is suitable for gamma-ray burst detection. One year after launch, the detector
KEYWORDS: Sensors, Satellites, Computer aided design, Gamma radiation, Analog electronics, Solar cells, Control systems, Signal detection, Scintillators, Infrared sensors
Since transient events, such as gamma-ray bursts (GRBs), can be expected from any direction at any time, their detection and localization is difficult. For localizing transient events, we proposed the Cubesats applied for measuring and localising transients mission (CAMELOT), which will be a fleet of nanosatellites distributed evenly on low Earth orbits. As the first step, we designed a technical demonstration for the CAMELOT mission, named GRBAlpha. Even though this 1U satellite has a reduced size scintillator and different mechanical constraints, all the electronic subsystems and communication protocols are the same. GRBAlpha is operating in orbit since 2021 March 22 and it already detected numerous confirmed GRBs. For further details of the early results and ongoing operations see the related presentation at this conference. After this first success, we continue with the design of the 3U prototype of the CAMELOT satellite, which will host an eight times larger detector system integrated into two walls of the satellite. The main difference is the mechanical constraints of mounting the detector in its casing. While for GRBAlpha the reduced sized scintillator is located on the top (Z+) side of the satellite, for CAMELOT it is located on two of the sides. Since the CubeSat standard does not allow enough lateral extension on the sides, the casing has to be sunk into the satellite where it could interfere with the standard PC/104 stacking. Here, we present a solution on how to integrate the scintillator casing, the uniquely designed electronics and commercially available satellite subsystems.
In recent years, the number of CubeSats (U-class spacecrafts) launched into space has increased exponentially marking the dawn of the nanosatellite technology. In general, these satellites have a much smaller mass budget compared to conventional scientific satellites, which limits shielding of scientific instruments against direct and indirect radiation in space. We present a simulation framework to quantify the signal in large field-of-view gamma-ray scintillation detectors of satellites induced by x-ray/gamma-ray transients, by taking into account the response of the detector. Furthermore, we quantify the signal induced by x-ray and particle background sources at a Low-Earth Orbit outside South Atlantic Anomaly and polar regions. Finally, we calculate the signal-to-noise ratio (SNR) taking into account different energy threshold levels. Our simulation can be used to optimize material composition and predict detectability of various astrophysical sources by CubeSats. We apply the developed simulation to a satellite belonging to a planned CAMELOT CubeSat constellation. This project mainly aims to detect short and long gamma-ray bursts (GRBs) and as a secondary science objective, to detect soft gamma-ray repeaters (SGRs) and terrestrial gamma-ray flashes (TGFs). The simulation includes a detailed computer-aided design model of the satellite to take into account the interaction of particles with the material of the satellite as accurately as possible. Results of our simulations predict that CubeSats can complement the large space observatories in high-energy astrophysics for observations of GRBs, SGRs, and TGFs. For the detectors planned to be on board the CAMELOT CubeSats, the simulations show that detections with SNR of at least 9 for median GRB and SGR fluxes are achievable.
The timing-based localization, which utilize the triangulation principle with the different arrival time of gammaray photons, with a fleet of Cubesats is a unique and powerful solution for the future all-sky gamma-ray observation, which is a key for identification of the electromagnetic counterpart of the gravitational wave sources. The Cubesats Applied for MEasuring and Localising Transients (CAMELOT) mission is now being promoted by the Hungarian and Japanese collaboration with a basic concept of the nine Cubesats constellations in low earth orbit. The simulation framework for estimation of the localization capability has been developed including orbital parameters, an algorithm to estimate the expected observed profile of gamma-ray photons, finding the peak of the cross-correlation function, and a statistical method to find a best-fit position and its uncertainty. It is revealed that a degree-scale localization uncertainty can be achieved by the CAMELOT mission concept for bright short gamma-ray bursts, which could be covered by future large field of view ground-based telescopes. The new approach utilizing machine-learning approach is also investigated to make the procedure automated for the future large scale constellations. The trained neural network with 106 simulated light curves generated by the artificial short burst templates successfully predicts the time-delay of the real light curve and achieves a comparable performance to the cross-correlation algorithm with full automated procedures.
Due to the advancement of nano-satellite technology, CubeSats and fleets of CubeSats can form an alternative to high-cost large-size satellite missions with the advantage of extended spatial coverage. One of these initiatives is the Cubesats Applied for MEasuring and LOcalising Transients (CAMELOT) mission concept, aimed at detecting and localizing gamma-ray bursts with an efficiency and accuracy comparable to large gamma-ray space observatories. While precise attitude control is not necessary for such a mission, attitude determination is an important issue in the interpretation of gamma-scintillator detector data as well as for telemetry. The employment of star trackers is not always a viable option for such small satellites, hence another alternative is necessary. In this correspondence we present a new method, utilizing thermal imaging sensors to provide simultaneous measurement of the attitude of the Sun and the horizon by employing a homogeneous array of such detectors and show that with the proposed setup the location of an infrared point source can be determined with an accuracy of 400. We also introduce our ongoing work on a simulation model aimed at testing the applicability of our attitude determination algorithm. The first part of the simulation determines the orbit and rotation of a satellite with arbitrary initial conditions while its second part will do the attitude determination based on a multiplicative extended Kalman filter..
GRBAlpha is a 1U CubeSat mission with an expected launch date in the first half of 2021. It carries a 75 × 75 × 5 mm CsI(Tl) scintillator, read out by a dual-channel multi-pixel photon counter (MPPC) setup, to detect gamma-ray bursts (GRBs). The GRB detector is an in-orbit demonstration for the detector system on the Cubesats Applied for MEasuring and LOcalising Transients (CAMELOT) mission. While GRBAlpha provides 1/8th of the expected effective area of CAMELOT, the comparison of the observed light curves with other existing GRB monitoring satellites will allow us to validate the core idea of CAMELOT, i.e. the feasibility of timing-based localization
We propose a fleet of nanosatellites to perform an all-sky monitoring and timing based localisation of gamma-ray transients. The fleet of at least nine 3U cubesats shall be equipped with large and thin CsI(Tl) scintillator based soft gamma-ray detectors read out by multi-pixel photon counters. For bright short gamma-ray bursts (GRBs), by cross-correlating their light curves, the fleet shall be able to determine the time difference of the arriving GRB signal between the satellites and thus determine the source position with an accuracy of ∼ 100 . This requirement demands precise time synchronization and accurate time stamping of the detected gamma-ray photons, which will be achieved by using on-board GPS receivers. Rapid follow up observations at other wavelengths require the capability for fast, nearly simultaneous downlink of data using a global inter-satellite communication network. In terms of all-sky coverage, the proposed fleet will outperform all GRB monitoring missions.
The control and feedback systems of autonomous meter-classed telescopes is different from one to another, however these systems all have the same purpose. We intended to design a multi-functional and modular electronics that is capable of controlling the mechanics, give feedback of the position of the telescope and/or the dome and communicate with each other and a higher level overseer. We are going to use these electronics in the "Fly’s Eye," the ”Transient Astrophysical Object” project for other telescopes. We will show that our concept is a cheap, reliable, effective way to get a control small-size astronomical observatories.
In order to provide a continuous, multi-color time-domain surveying of the brightest regime of the naked-eye optical sky, we designed the Mosaic Array of Numerous Ultrasmall Lens (MANUL). This device is a palm-sized “astronomical observatory,” featuring optics, filters and all necessary electronics (including a TCP/IP-based downlink), all are mounted on 2-inch printed circuit boards. Based on these units, a modular and mosaic arrangement of CMOS imaging sensors with an effective resolution of 1’/pixel can be built. Here we introduce the main design concepts, the early prototyping and the results of the preliminary photometric quality analysis of this initiative.
The Fly's Eye camera system is a multiple-passband full-sky surveying instrument employing 19 wide-field cameras in a mosaic arrangement on a spherical frame. The cameras equipped with fast focal ratio lenses and Sloan filters. The cameras are supported by single mount while the sidereal tracking, i.e. the compensation for the apparent celestial rotation is performed by a hexapod mount. As discussed in our earlier design-related publications, this tracking is unavoidable when considering 0:3 gigapixel imaging, a field-of-view diameter of 120° and exposure times around a few minutes. With this camera system we intend to perform time-domain astronomy and observe several kind of astronomical phenomena based on variability.
The Fly's Eye Project is a high resolution, high coverage time-domain survey in multiple optical passbands: our goal is to
cover the entire visible sky above the 30° horizontal altitude with a cadence of ~3 min. Imaging is going to be
performed by 19 wide-field cameras mounted on a hexapod platform resembling a fly’s eye. Using a hexapod developed
and built by our team allows us to create a highly fault-tolerant instrument that uses the sky as a reference to define its
own tracking motion. The virtual axis of the platform is automatically aligned with the Earth’s rotational axis; therefore
the same mechanics can be used independently from the geographical location of the device. Its enclosure makes it
capable of autonomous observing and withstanding harsh environmental conditions. We briefly introduce the electrical,
mechanical and optical design concepts of the instrument and summarize our early results, focusing on sidereal tracking.
Due to the hexapod design and hence the construction is independent from the actual location, it is considerably easier to
build, install and operate a network of such devices around the world.
In order to attain precise, accurate and stateless positioning of telescope mounts we apply microelectromechanical
accelerometer systems (also known as MEMS accelerometers). In common practice, feedback from the mount
position is provided by electronic, optical or magneto-mechanical systems or via real-time astrometric solution
based on the acquired images. Hence, MEMS-based systems are completely independent from these mechanisms.
Our goal is to investigate the advantages and challenges of applying such devices and to reach the sub-arcminute
range { that is well smaller than the field-of-view of conventional imaging telescope systems. We present how
this sub-arcminute accuracy can be achieved with very cheap MEMS sensors. Basically, these sensors yield raw
output within an accuracy of a few degrees. We show what kind of calibration procedures could exploit spherical
and cylindrical constraints between accelerometer output channels in order to achieve the previously mentioned
accuracy level. We also demonstrate how can our implementation be inserted in a telescope control system.
Although this attainable precision is less than both the resolution of telescope mount drive mechanics and the
accuracy of astrometric solutions, the independent nature of attitude determination could significantly increase
the reliability of autonomous or remotely operated astronomical observations.
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