Alex said:

"Huygens' angle of attack, however, can be adjusted plus or minus a degree or two at release, which could affect its landing site."

This comment shows a common terminology error (people make this mistake all the time). "Angle-of-attack" for an axisymmetric vehicle is the angle from the vehicle's axis-of-symmetry to the free stream velocity vector. Huygen will undergo "ballistic entry" into Titan's atmosphere (a non-lifting entry at zero angle-of-attack). The quantity that Alex was actually referring to is called "entry angle", "velocity angle" or simply "gamma". There are always two forms of gamma. One is in the inertial frame and the other is in the atmosphere relative frame. The value of gamma is meaningless unless it is referenced to a specific altitude. This leads to one of my pet hates: People can actually get papers published in archive journals where they specify an entry angle but do not specify the reference frame or altitude (the number is meaningless). Without a valid entry angle, it is impossible to reproduce the trajectory, so the paper's results are impossible to verify (this really reflects badly on the journal editor).

The entry angle for Huygen at Titan is based upon the whims of Cassini's final velocity vector when Huygen was ejected and the celestial mechanics of Titan. However it is my understanding the timing sequence for Huygen's EDL (Entry, Descent and Landing) is hard wired and not reprogrammable. In essence Huygen's EDL sequencer is like a washing machine controller and not a true autopilot (computer). Because the sequencer is hard wired, a specific entry angle and error range are assumed. Obviously Huygen could come in with different enty angles, but the various subsystems would get turned on-and-off at wrong times.

This revelation about Huygen's EDL sequencer left me dumb founded when I first heard it.

Gary