The European Space Agency (ESA) and NASA have reworked the mission of the NASA Cassini Saturn orbiter spacecraft and ESA's Huygens probe to ensure that the Cassini mother ship can collect data from the lander. The redesign means, however, that Huygens' landing on the Saturn moon Titan will be delayed from November 2005 to February 2006.

The mission rethink was required after an error in the design of the Huygens' communications equipment, discovered after its launch, meant that the Doppler effect - the change in the apparent frequency and the wavelength of waves due to motion between the two craft - would change the frequency of the craft's communications with Cassini during the descent and landing. Left uncorrected, the science data from Huygens would have been lost.

Cassini was to have been travelling at 19,200km/h towards a 1,210km (750 miles) fly-past of Titan as Huygens lands.

Engineers have designed a Huygens landing phase and Cassini fly-by that will reduce the relative speeds of the spacecraft. This means Cassini will fly pass Titan at a greater distance of 68,800km.

Source: Flight International