In February 2007, the fourth and last satellite of the BeiDou-1 system, BeiDou-1D (sometimes called BeiDou-2A, serving as a backup satellite), was sent up into space. It was reported that the satellite had suffered from a control system malfunction but was then fully restored.
బీడ్యూ-1డీ ఉపగ్రహం ఉద్దేశం ఏమిటి?
serving as a backup satellite