Apollo 11 manual landing

[Jairo]

Hi,

I read that Armstrong took the manual control, when he saw that the LM was going to a rocky place. But how much manual was that?

Was it complete control? Just attitude control with the computer managing the descent rate? Or was it choosing a new target with the grid at the window?

Thanks.

[PhantomWolf]

Manual control is basically fly by wire. Armstrong input the desired direction via a joystick and throttle and the computer determined how to fly acording to that.

[ka9q]

"Manual control" is better described as "semi-automatic" control. Instead of letting the computer land automatically, Armstrong put it into a mode where he could fly it essentially like a helicopter through the computer.

The LM flies by vastly different principles than a helicopter. It reacted to 16 binary inputs - the control valves for each of the RCS thrusters - plus the throttle and gimbal for the descent engine (three analog inputs). True "manual control" would have implied that Armstrong generated all these signals directly somehow, which he didn't. He pointed the stick in the direction he wanted to go and the computer figured out which RCS thrusters to fire and how to gimbal and throttle the main engine to get it there.

In the mode Armstrong used, I believe he'd tell the computer to maintain a certain rate of descent, increasing or decreasing it by toggling a switch much as you adjust the speed of an engaged cruise control. This too required some fairly complex calculations to account for the rapidly decreasing mass and shifting c.g. of the LM and the fact that the thrust vector wasn't always pointing down (as when Armstrong pitched over to speed past the boulder field).

[AstroSmurf]

There is a shareware lunar landing simulator for the PC out there - eaglelander3d.com/. It does a pretty good job of showing what landing was like. After a couple of practice runs, it was no big deal making a smooth landing, though I admit Armstrong spent less time faffing around than I did...

You can play with it for free, though you only get the last few minutes of the Apollo 11 landing.

[Obviousman]

After the P64 programme the LM would go into P65, which was a full auto landing. No-one ever used this, though, and after P64 crews would manually switch to P66, the semi-automatic programme.

From here: Apollo GNC Software (http://apollo.spaceborn.dk/guidance5.html)

Basically P66 can operate in four different ways:

* The computer controls both vertical speed as set by the crew and nulls the horizontal speed,
* The computer control only vertical speed as set by the crew, while the crew selects the attitude with the hand controls, to null the horizontal speed,
* The crew controls the throttle of the engine to control the descend rate, while the computer nulls the horizontal speed,
* The crew controls both the engine throttling and the attitude, and thereby lands the LM themselves. This is only practical for the two crewmembers at the same time.

P67 was full manual control.