  Our understanding of the universe relies mostly on electromagnetism. As
photons are the messengers, fundamental physics is concerned in testing their
properties. Photon mass upper limits have been earlier set through pulsar
observations, but new investigations are offered by the excess of dispersion
measure (DM) sometimes observed with pulsar and magnetar data at low
frequencies, or with the fast radio bursts (FRBs), of yet unknown origin.
Arguments for the excess of DM do not reach a consensus, but are not mutually
exclusive. Thus, we remind that for massive electromagnetism, dispersion goes
as the inverse of the frequency squared. Thereby, new avenues are offered also
by the recently operating ground observatories in 10-80 MHz domain and by the
proposed Orbiting Low Frequency Antennas for Radio astronomy (OLFAR). The
latter acts as a large aperture dish by employing a swarm of nano-satellites
observing the sky for the first time in the 0.1 - 15 MHz spectrum. The swarm
must be deployed sufficiently away from the ionosphere to avoid distortions
especially during the solar maxima, terrestrial interference and offer stable
conditions for calibration during observations.
