...they actually forgot to account for Doppler shift when deploying the Huygens probe to Titan: as planned, the 5.5km/s velocity change as Huygens reentered Tit

...they actually forgot to account for Doppler shift when deploying the Huygens probe to Titan: as planned, the 5.5km/s velocity change as Huygens reentered Titan would have caused Cassini's receiver to lose lock on the signal (due to a timing change, rather than a frequency shift, IIRC). As Huygens had no storage and ran on batteries this would cause a total loss of mission. The problem was discovered after launch, and corrected for --- not by reprogramming the receiver, but by changing Cassini's flight profile to reduce the Doppler shift: http://www.thespacereview.com/article/306/1 http://www.thespacereview.com/article/306/1