Abstract: The invention proposes a memory relay system for observation spacecraft, for example observation satellites or interplanetary probes. The object of the invention is to alleviate the absence or possible failure of onboard memory of these craft. The system of the invention provides a substitute solution which returns full functionality to an observation system capable of acquiring and transmitting observation data but not of storing it. In accordance with the invention, an artificial satellite or craft comprising at least one transponder and at least one writable memory is disposed near an observation satellite or a probe. The transponder is capable of receiving signals transmitted by the observation satellite or probe and then transmitting the signals to the Earth or to another destination. The memory of this artificial satellite or craft stores the information received until it is retrieved and retransmitted to the receiving station, a station on the ground, for example.