The space sector is facing significant upheavals, in particular in terms of cost reduction challenges, driven by the emergence of Low Earth Orbit constellations. Concerning solar power generation, it opens up perspectives for alternative solar photovoltaics technologies, instead of the highly performant & expensive III-V multi-junction devices. Crystalline silicon solar cells, which have fueled space developments, spark a renewed interest, thanks to their industrial maturity, high efficiencies on p-type substrates & costs of two to three orders of magnitude lower than those of III-V. In this context, we present here the results of electrons radiation hardness studies on p-type (Ga-doped) silicon heterojunction solar cells. Devices with thicknesses down to 60μm are manufactured and then characterized before and after 1MeV electrons irradiations. The best ultra-thin heterojunction cell shows an end-of-life (1.5x1014 e/cm2) externally certified efficiency of 15.1% under AM1.5G at room temperature; this translates into ~ 13.4% with AM0 spectrum. The benefits of thickness reduction with respect to radiation hardness are presented, and the cells improvement pathways discussed.