Editing Cassini–Huygens (section)

== ''Huygens'' probe ==
{{Main|Huygens (spacecraft)}}
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| image1 = Huygens surface color.jpg
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| caption1 = ''Huygens'' view of Titan's surface
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| caption2 = Same image with different data processing
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The ''Huygens'' probe, supplied by the [[European Space Agency]] (ESA) and named after the 17th&nbsp;century Dutch astronomer who first discovered Titan, [[Christiaan Huygens]], scrutinized the clouds, atmosphere, and surface of Saturn's moon Titan in its descent on January 15, 2005. It was designed to enter and brake in Titan's atmosphere and parachute a fully instrumented robotic laboratory down to the surface.<ref name=huygens.landing/>

The probe system consisted of the probe itself which descended to Titan, and the probe support equipment (PSE) which remained attached to the orbiting spacecraft. The PSE includes electronics that track the probe, recover the data gathered during its descent, and process and deliver the data to the orbiter that transmits it to Earth. The core control computer CPU was a redundant [[MIL-STD-1750A]] control system.

The data were transmitted by a radio link between ''Huygens'' and ''Cassini'' provided by Probe Data Relay Subsystem (PDRS). As the probe's mission could not be telecommanded from Earth because of the great distance, it was automatically managed by the Command Data Management Subsystem (CDMS). The PDRS and CDMS were provided by the [[Italian Space Agency]] (ASI).

After ''Cassini''{{'s}} launch, it was discovered that data sent from the ''Huygens'' probe to ''Cassini'' orbiter (and then re-transmitted to Earth) would be largely unreadable. The cause was that the [[Bandwidth (signal processing)|bandwidth]] of signal processing electronics was too narrow and the anticipated [[Doppler shift]] between the lander and the mother craft would put the signals out of the system's range. Thus, ''Cassini''{{'s}} receiver would be unable to receive the data from ''Huygens'' during its descent to Titan.<ref name=bbc1/>

A work-around was found to recover the mission. The trajectory of ''Cassini'' was altered to reduce the line of sight velocity and therefore the doppler shift.{{r|bbc1|tsr1}} ''Cassini'''s subsequent trajectory was identical to the previously planned one, although the change replaced two orbits prior to the ''Huygens'' mission with three, shorter orbits.
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