Operating the Apollo LM DSKY

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With this javascript DSKY you can get a bit of a feeling what it was like to work with the DSKY. The astronauts used this device to communicate with the guidance computer. The crew could ask and pass information to the computer and vice versa. It was sometimes even called 'the third crew member'!

This simulator knows only part of the real DSKY, but there are sufficient features to actually perform an orbit change with the descent engine!

A look around on the panel shows you:

some status lights,

a flashing ligt (COMPACTY) which indicates computer activity,

a PROG indicator with a number, which is the identifier of the program that is running now,

a VERB and NOUN with numbers that are dimmed, read about those below

three rows with numbers, these are called REGISTERS and can display usefull info

and a keyboard with numerical and function keys.

The basic way of communicating with the computer was via VERB and NOUN codes. The verb codes were a kind of action requests, while the nouns indicated what that action should be taken upon. Verb 05 means display, and Noun 65 means LGC time. So if you now would press

VERB 05 NOUN 65 ENTER

you will get the time of the computer. Try it for yourself. If you make a mistake, just press the VERB or NOUN key again, and try again.

If you keyed the codes correctly, you will now see three numbers in the display below the verb and noun code. These three displays are the REGISTERS, the first one is REGISTER 1, then 2 and finally 3. When displaying noun 65, you see the elapsed time since launch in hours (register 1), minutes (R2) and hundredths of seconds (3).

Another way of displaying things is to monitor them. If you monitor something, you will have a periodic update of it. Monitor can be done with verb 15. Try it out! Key in:

VERB 15 ENTER

Notice that you don't need to enter the noun, since that is still there! Otherwise, key NOUN 65 before the ENTER, but after the VERB 15.

If correct, you now see that the time is being updated regularly.

Performing a program change

To begin the maneuver, we have to change the program to P40. We do that by:

VERB 37 ENTER

Note that the VERB number now starts flashing. This is to indicate that the computer needs more information. Therefore give it the program number 40:

40 ENTER

The flashing should stop now, and you should see that PROG has changed to 40. Ok, we are beginning the procedure now. First the computer will ask you to authorise the change in velocity that it has computed before in P34 (the program you just came from). In a second you will see that the three registers contain numbers, which are the velocity changes in feet/sec on each axis. You'll have to authorise this and we can do that by keying:

VERB 33 ENTER

which means 'Proceed without data'. You basically tell the computer here to go on with what it has. You could also have terminated the program completely (VERB 34) or entered new values

The next thing the program does is to give you the gimbal angles that the stable platform will see at the end of the burn. Authorise here again with VERB 33 ENTER.

Now the program will start monitoring NOUN 40. This gives you the time until the ignition in minutes and seconds in R1, the desired delta v in tenths of feet per second in R2 and the achieved delta v in R3, which is ofcourse 0 as the engine is not running yet! The next action will be at T - 30 seconds. If we are now closer than 45 seconds (maybe you were too slow!), you will see an ALARM that you have to clear . Otherwise, the count down starts and you can see time ticking away.

At T-30 seconds, the computer starts the ullage burn with the RCS to settle the propellants in the tanks. You can see that in register 3 that slowly starts counting: the LM is changing its velocity.

At T-5 seconds, the computer asks you with VERB 50 and NOUN XX to enable the engine: you reply with ENTER. Be ready for this one, as you don't have much time!

At T=0 seconds, the computer starts the engine and you see that R3 now starts to count much faster. The R1 register now displays estimated time to engine shut down. When that happens, the computer shows you the error in delta v which you have to confirm with VERB 33 ENTER. Then it shows you the new apogee and perigee height plus the time till perigee. That you also confirm with VERB 33 ENTER. Finally the computer flashes V50N07, which is a request to change the program to something else. You can change to the idle program 0 with VERB 37 ENTER 00 ENTER.

That is it! You have now used the DSKY to change the orbit of the LM!