HERMES (High Energy Rapid Modular Ensemble of Satellites) Scientific Pathfinder (HERMES-SP) 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 such as Gamma-Ray Bursts (GRB) and the electromagnetic counterparts of Gravitational Wave Events (GWE). HERMES-SP main goal is to design and implement the first GRBs localisation experiment through a distributed space architecture realized by a 3 +3 CubeSat federation, each equipped with the novel detector to gain a wide deep space coverage and demonstrate capabilities in precisely localising the GRB event in space. HERMES-SP exploits synergies with an ongoing project funded by the Agenzia Spaziale Italiana (ASI). GRB localisation is gained by comparing time delays among the same event detection epochs occurred on - at least - 3 detectors spaced out on different satellites. Distribution in space and event detection are the fundamental ingredient to start building up the whole scientific experiment. HERMES-SP is aiming at demonstrating detection and localisation of high-energy transients feasibility with disruptive technologies and limited effort: simple payload on nano-satellites and a disruptive level of cost-effectiveness: 1-2 order of magnitude cost lower than that standard space projects (ESA class M mission, NASA Explorer mission), 1 order of magnitude lower lifecycle compared with 10-15 years for standard Space Science projects. The HERMES-SP represents also a step forward the HERMES Full Constellation (HERMES-FC), supposed to further increase the distributed detection points in space with several tents of detector-equipped CubeSats in LEO which timely and completely monitor the Universe listening for and chasing GWEs. It is, therefore preparatory for a proposal to European Entities (Commission, Space Agency), for the HERMES-FC implementation.