The key technologies associated with propellant on-orbit refilling was summarized whilst the system construction and the refilling procedures were introduced. Moreover

a suggesting research project was proposed for guiding the domestic researches. Several valuable conclusions were drawn as follows: (1) On-orbit gas-liquid separation technology is the basis of the propellant refilling. Membrane and vane tank can be used to separate the gas-liquid phases in a normal-temperature propellant tank

while screen channel liquid acquisition devices (LAD) may be the best choice for the cryogenic propellant tank. (2) Space thermal-insulation and boil-off control technologies must be applied in the on-orbit refilling operation of cryogenic propellant. (3) Venting approach can be used for normal-temperature propellant

and no-vent filling is suggested for the cryogenic propellant. Also

use of thermodynamic venting system (TVS) is beneficial to a larger refilling rate of cryogenic propellant. (4) A research scheme concerning the normal-temperature propellant first and then the cryogenic propellant is suggested in the domestic researches. Simultaneously

the present research platform and the latest research achievements should be referenced.