  In radio astronomy, the Ultra-Long Wavelengths (ULW) regime of longer than 10
m (frequencies below 30 MHz), remains the last virtually unexplored window of
the celestial electromagnetic spectrum. The strength of the science case for
extending radio astronomy into the ULW window is growing. However, the
opaqueness of the Earth's ionosphere makes ULW observations by ground-based
facilities practically impossible. Furthermore, the ULW spectrum is full of
anthropogenic radio frequency interference (RFI). The only radical solution for
both problems is in placing an ULW astronomy facility in space. We present a
concept of a key element of a space-borne ULW array facility, an antenna that
addresses radio astronomical specifications. A tripole-type antenna and
amplifier are analysed as a solution for ULW implementation. A receiver system
with a low power dissipation is discussed as well. The active antenna is
optimized to operate at the noise level defined by the celestial emission in
the frequency band 1 - 30 MHz. Field experiments with a prototype tripole
antenna enabled estimates of the system noise temperature. They indicated that
the proposed concept meets the requirements of a space-borne ULW array
facility.
