The European Space Agency has finally discovered what went wrong during the descent of the Huygens probe it sent to Saturn’s moon Titan as part of the Cassini-Huygens mission launched in 1997. Both the Cassini and the Huygens missions were successful, but the latter didn’t perform without issue: the ESA says its probe started spinning the wrong direction during descent, a mystery that has now been solved.
Huygens was officially the first human-made probe to land on another celestial body located in the far reaches of our solar system. The probe was a success — it provided a large amount of information about the moon Titan during its nearly two and a half hour descent, including data about the moon’s winds, the quantities of gases in the atmosphere, and more.
The ESA notes, however, that Huygens had a bit of an unexpected issue as it landed — it was released with a counter-clockwise spin, which was meant to keep it stable while it slowly coasted toward the moon’s atmosphere from Cassini. This rate of spin slowed down quite a bit more than had been expected and, after a while, the probe started to spin clockwise.
As luck would have it, this clockwise spin took place at about the same rate that had been expected for the counter-clockwise spin, which means the probe remained fairly stable and though the timing of planned observations were now off, the difference wasn’t dramatic enough to have a significant impact on the data gathered.
Under an ESA contract, the University of Orléans in France conducted a two-year study to figure out what caused this unexpected spin change. The team found that the SEPS antenna and RA antenna on the probe introduced an ‘unexpected torque’ that was opposite that of the 36 angled vanes installed on the probe.
The vanes interacted in such a way that they unexpectedly amplified this torque, causing the probe to slow down until the negative torque took over, reversing the spin. Though this doesn’t help the now-defunct Huygens in any way, the findings will help influence future probe designs, helping experts avoid the same issue in the future.