The Lunar Gravity Ranging System (LGRS) instruments on board the twin GRAIL spacecraft generate radio signals at Ka-band, X-band, and S-band. The time and frequency of each signal is referenced to its respective Ultra-Stable Oscillator (USO). The Ka-band and S-band signals are captured by the other spacecraft, and precise measurements of signal properties are recorded for later transmission to Earth. The X-band link is received by stations of the NASA Deep Space Network (DSN). Operations are continuous and simultaneous on both spacecraft except that the X-Band downlink to Earth is only used when a DSN station is available.
urn:nasa:pds:context:instrument:lgrs-a.grail-a
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