Abstract: The atmospheric air drag in an ultra-low orbit (180-260 km) is one of the main factors that might shorten the life of a spacecraft in the orbit. A concept of the air-breathing helicon thruster (ABHT) onboard of a spacecraft for the ultra-low orbit long term maintenance is reviewed in this study. A contractive-shaped air inlet channel compacts well directly with an electrodeless helicon wave discharge tube. The inlet air blows onto the front window of the channel with an initial velocity of 7800 ms^-1 relative to the spacecraft, and the inlet air is compressed as the flow moving into the rear port of the contractive-shaped channel, and the flow velocity is decelerated, due to the collisions of the inlet particles with the channel wall. A pre-discharge sheath is set up in the rear port of the channel, with the upward leakage of the plasma generated in the discharge tube by helicon waves. The discharge rate of the pre-discharge sheath is assumed to be about 10%, and the electron temperature is about 10 eV, and the ion temperature, 0.2-0.3 eV. The existence of a pre-discharge sheath in the rear port of the channel makes the air density disturbance propagating downstream the channel with the velocity of the ion acoustic speed. The ion acoustic velocity in the pre-discharge sheath is larger than that of the gas flow velocity in the inlet channel, which is assumed to be 2000 ms^-1, and the inlet air will not be choked in the rear port of the contractive-shaped channel. The subsequent inlet gas molecules will not be reflected back from the channel to the atmosphere surround the spacecraft. Almost all molecules in the inlet go into the contractive-shaped channel, and then the tube, and are discharged and accelerated backward by the helicon plasma thruster at a larger directional velocity, a propulsion is thus generated enough to maintain the long-term operation of an ultra-low-orbit satellite.