Space-based ultra-long wavelength radio astronomy — An overview of today´s initiatives

Space based ultra-long wavelength radio astronomy has recently gained interest. The need for large effective apertures spread over long ranges implies that advanced technologies are required, which is in reach at this moment. This together with the unexplored frequency band below 30 MHz makes these initiatives very interesting. Due to a combination of ionospheric scintillation below ~30MHz, its opaqueness below ~10MHz, and man-made radio frequency interference (RFI), earth-bound radio astronomy observations are either severely limited in sensitivity and spatial resolution or entirely impossible. In this paper we will present current initiatives to reach this new and unexplored low frequency band below 30 MHz.