Re: Space Shuttle
I was a NASA contractor, responsible for reducing aerodynamic flight test data on the Space Shuttle Orbiter in the late 1980's and early 1990's. The Orbiter has (or had in the late 1980's) autoland capability. It was to be tested on one particular flight, I can't remember which one, but the test was cancelled within a few weeks of the flight.
The landing gear is not designed for the loads which would be encountered in high speed flight, much less the aerothermal environment of atmospheric entry. For weight savings, there is no inflight retraction mechanism. Thus, it is exceedingly important that the gear not be extended until _just_ before landing, and that when the landing gear switch is pushed that the gear comes down quickly and locks without fail. For that reason, the landing gear switch starts a quad-redundant fault-tolerant sequence which if all else fails will use pyrotechnics to blow off the gear doors and pressurise the gear extension hydraulics. This switch is one of the only switches in the cockpit which cannot be remotely commanded. Someone in the cockpit must flip the switch guard up and press the switch, even in an otherwise automatically controlled landing.
The Orbiter is very difficult to land. It has a very low L/D ratio and bleeds airspeed very fast. The joystick commands angular rates, not positions. This is the same way that it works onorbit (which is, after all, most of the mission), but is very alien to anyone who has flown a normal aircraft. (The simulators at Space Center Houston, the tourist area at Johnson Space Center, have a normal control system.)
When the nose gear is on the ground, the wing has a negative incidence angle and thus creates negative lift. Once the main gear is on the ground, the pilot must hold the nose high to bleed airspeed, then quickly and smoothly lower the nose before the elevons lose effectiveness. Lower the nose too early, and the nose gear can't take the lift force, lower it too late and you won't have enough command authority to lower it gently. Due to this problem, the drag chute is not deployed until the nose gear is safely on the ground.
On STS-3 (the third orbital flight), the astronaut in command got into a brief Pilot Induced Oscillation after he got the main gear on the ground, and nearly had a very bad day. At the time, we were still tuning control system gains, and it is extremely likely that the problem was not entirely his fault. But I don't think that he flew another mission.
The Orbiter is very difficult to land, and would greatly benefit from using an automatic landing system. But it would take big brass ones to sit with your hands in your lap and watch it land itself for the first time, knowing all the while that if things go bad that you can't add power and go around. Thus it will probably only be tested if the pilot and commander are incapacitated. (A mission or payload specialist could press the gear switch at the appropriate time.)