HERMES (High Energy Rapid Modular Ensemble of Satellites) is a mission concept based on a constellation of nano-satellites in low Earth orbit (LEO), hosting new miniaturized detectors to probe the X-ray temporal emission of bright high-energy transients.

HERMES is placed in the segment of space astrophysics with distributed space architecture that exploits the creation of fleets of small satellites, low cost and easy to build, that work together.
The project involves the launch, by 2025, of 6 nano-satellites of the 3U class, i.e. with dimensions 10x10x30 cm and weighing 6 kg each, which constitute a demonstrator (pathfinder) of the mission.

Logo for HERMES (High Energy Rapid Modular Ensemble of Satellites)

11 partners from 5 European countries joined forces to design, build and fly the HERMES fleet under the scientific coordination of Dr. Fabrizio Fiore. HERMES has received funding from the European Union’s Horizon 2020 research and innovation programme for the construction of three of the six satellites and from the Italian Space Agency (ASI) for the remaining three.

Possible in-orbit configuration of 3 3U nano-satellites of the HERMES Pathfinder project - Credit: HERMES.

HERMES was designed to scan the sky for gamma-ray bursts, which are created when stars die or collide and briefly emit more energy than an entire galaxy. These observations can only be made by space telescopes and are critical to advancing our understanding of extreme physics and also have the potential to uncover traces of quantum gravity.
The principle of the mission is to combine the signal delay detected by at least three of the six satellites, separated by thousands of kilometers, to triangulate the position of the transient gamma source in the sky.

6 HERMES modules (from top right and bottom row) and the module mounted on board the SpIRIT mission (top left) - HERMES credits.

A first test of the detector that will be positioned on board HERMES was conducted by mounting it on board the Australian Space Agency’s nanosatellite SpIRIT (Space Industry Responsive Intelligent Thermal) successfully launched from the Vandenberg base in California, United States, using a Falcon 9 launcher from the American company SpaceX.
The take-off took place when it was 7.43pm in Italy on December 1, 2023. The nanosatellite is now in a polar orbit 513 km above the Earth.

Our observatory participates in the HERMES project regarding the scientific exploitation of data.
Recently OAB researchers led scientific work in which they estimate that HERMES will be able to detect approximately 200 long and 20 short Gamma Ray Bursts per year.
The latter are very interesting for multi-messenger astrophysics as they are electromagnetic counterparts of gravitational waves detectable with current terrestrial interferometers.
The former will instead provide a uniform census of the population of long GRBs, allowing us to estimate how the energy released in the few seconds of duration of these cosmic explosions is produced.

Lara Nava - lara.nava AT inaf.it
Giancarlo Ghirlanda - giancarlo.ghirlanda AT inaf.it