On 16 May 2009, two days after launch, the GMSK-modulated High Data Rate downlink on ESA's Herschel spacecraft was successfully tested. For the first time in space, a High Data Rate modulation transmission from space used the GMSK modulation scheme. This modulation scheme has so far only been used on the ground by mobile telephone networks, but at a lower rate. The novelty of this modulation format is the spectral occupation bandwidth that allows a better spectrum sharing with other mission. The GMSK High Rate telemetry at 1.5 Mbit/s uses only about the same bandwidth as a Medium Bit Rate telemetry signal at 150 kbps. The plot shows the SPL and GMSK signals as received by ESA's 35m New Norcia Station. The satellite was transmitting with about 35 W RF power in X-Band via the Low Gain Antenna from a distance of about 280 000 km from Earth.
The successful operational use confirms the on-ground results obtained since 2001, when the GMSK implementation on the Herschel-Planck missions was announced at the ESA TT&C Workshop, and the compatibility between the on board transponders and ground segment nodes that have been developed and verified in the past years.