  A strong indication is presented that the space-based gravitational antennas,
in particular the LISA concept introduced in 2017 in response to the ESA call
for L3 mission concepts, are going to be sensitive to a strong background
signal interfering with the prospected signal of gravitational waves. The false
signal is due to variations in the electron number density of the solar wind,
causing variations in the refractive index of plasma flowing through
interplanetary space. As countermeasures, two solutions are proposed. The first
solution is to deploy enough solar wind detectors to the LISA mission to allow
for reliable knowledge of the solar wind background. The second solution is to
equip the LISA interferometer with a second laser beam with a distinct
wavelength to allow cancelling of the background solar wind signal from the
interferometric data.
