Question Agena Target Vehicle (ATV) MFD

[4throck]

Hi,

I'm working on a LUA MFD that allows control of the Gemini Agena ATV.
It's on the right track and I can input the command codes and the ATV responds :thumbup:


But I have a question that perhaps someone can answer.

To control pitch and yaw you you input the codes:

410 Set Pitch/Yaw Mode to Minus Rotation (Down or to the Left)
411 Set Pitch/Yaw Mode to Plus Rotation (Up or to the Right)
441 Yaw Thrusters On
440 Yaw Thrusters Off
431 Pitch Thrusters On
430 Pitch Thrusters Off

Ok, but does exactly means Thrusters On? Is it a continuous trust until thruster off ? I'm not sure it makes sense. But if it was a single thruster "burst" them why the off command?

And because inputting commands takes a few seconds, I don't see how you could null the rotations.


Is rotation the key? Perhaps the Agena rotated at some fixed rate and the thrusters on/off in there to limit the rotation to pitch OR yaw. But I see no "rotation off command".


I'm confused by the actual implementation of this. There are more commands.
From my research the full list is this:

001 0000001 C-Band Beacon
010 0000010 S-Band Beacon On
011 0000011 Modulation Bus SelelctNormal
020 0000100 Modulation Bus SelelctReverse
021 0000101 Telemetry On
030 0000110 Telemetry Off
031 0000111 Stored Data Readout
041 0001001 Record Data
050 0001010 C and S-Band Beacons Off
060 0001100 Reset Timer Reset
061 0001101 Time Word Reset
070 0001110 L-BandBeaconOff
071 0001111 L-Band Beacon On
140 0011000 Approach Lights Of_
141 0011001 Approach Lights On_
151 0011011 Extend Boom Antenna
160 0011100 Antenna Transfer, _scent
161 0011101 Antenna Transfer, Orbit
200 0100000 Agena Status Display Off
201 0100001 Agena Status _sp_ On Bright i
211 0100011 Agena Status _sp_ On Dim
220 0100100 Adapter Unrigidize
221 0100101 Adapter Ridlgize
240 0101000 Stored Program Commands Disable
241 0101001 Stored Program Co_nds Enable
250 0101010 Acquisition Lights Off
251 0101011 Acquisition Lights On
260 0101100 Dipole Select
270 0101110 Spiral Select
271 0101111 Power Relay Reset
300 0110000 Horizon Sensor Off
301 0110001 Horizon Sensor On
310 0110010 Roll Horizon Sensor to Yaw, Inertial Reference Package On
311 0110011 Pitch Horizon Sensor to Yaw 3 Inertial Reference Package On
320 0110100 Horizon Sensor to Yaw Out of Phase
321 0110101 Horizon Sensor to Yaw in Phase
340 0111000 Velocity Meter Interrogate
341 0111001 Gyrocompass ing On
350 0111010 Geocentric Rate Off
351 0111011 Geocentric Pate On
360 0111100 Geocentric Rate Reverse
361 0111101 Geocentric Rate Normal
370 0111110 Attitude Control S "stem Pressure Low
371 0111111 Attitude Control S "stem Pressure High
400 1000000 Attitude Control S 'stem Off
4O1 1000001 Attitude Control S 'stem On
410 1000010 Pitch/Yaw Minus
411 1000011 Pitch/Yaw Plus
420 1000100 Pitch/Yaw Low Rate
421 1000101 Pitch/Yaw High Rate
430 1000110 Pitch Rate Off
431 1000111 Pitch Rate On
440 1001000 Yaw Off
441 1001001 Yaw On
450 1001010 Attitude Control System I_adband Narrow
451 1001011 Attitude Control S "stem Deadband Wide
460 1001100 Attitude Control S 'stemGain Low
470 1001110 Attitude Control S "stemGain High - Undocked
471 1001111 Attitude Control S "stem Gain High - Docked
500 1010000 Primary Propulsion System Cutoff
501 1010001 Primary Propulsion System Start
520 1010100 Velocity Meter Disable
521 1010101 Velocity Meter Enable
530 101O110 Velocity Meter Load 0
531 1010111 Velocity Meter Load l
540 1011000 Velocity Meter to Mode IV Off
541 1011001 Velocity Meter to Mode IV On
550 1011010 Secondary Propulsion System Thrust Cutoff
551 1011011 Secondary Propulsion System 16 Thrust
560 1011100 Secondary Propulsion System 200 Thrust
561 1011101 Secondary Propulsion System Ready
570 1011110 Hydraulics Gain - Undocked
571 1011111 Hydraulics Gain - Docked

There seem to be commands regarding geocentric rate and horizon pitch, but it's not clear for me how they might work. Perhaps the Agena had some sort of "Kill Rot" once the thruster off command was issued? Does someone know ?

 

[Saturn V]

IIRC, Mike Collins explained in "Carrying The Fire" that those keystrokes enabled the thrusters (similar to a circuit breaker), but did not actually fire them.

 

[4throck]

:thumbup: OK, that's a start, but still unclear...

How can you effectively remotely control a spacecraft using a system of two 8 digit dials and a binary switch? It's beyond me! :lol:

 

[Urwumpe]

How can you effectively remotely control a spacecraft using a system of two 8 digit dials and a binary switch? It's beyond me! :lol:

Maybe you don't do that just like that - I think the communication sequence was a bit more capable.

Will look for the reference... somewhere on my tablet.

 

[4throck]

Thanks is advance.:tiphat:

I'm trying to follow the old Gemini addon that had the control feature using that small set of codes. In reality we don't need much more beyond being able to ignite the Agena's engine, because once docked the Gemini spacecraft will provide orientation.

But it would be nice to have something that approximates reality better. I've tracked down the complete command list that I posted above, but the text is not clear as to the actual operation.
My source is http://www.ibiblio.org/apollo/Documents/GeminiManualVol2Sec2.pdf
around page 8-274. There's even a diagram with the 2 dials and the switch.


It's just like using emulators for obsolete home computer systems. You need to know that the Basic command LOAD "" makes the ZX Spectrum load from tape. Obvious if you learned that from the original manual, obscure and cryptic if you know little of the system. :lol:

 

[Urwumpe]

Yes - I use the same reference actually There are quite many gemini documents, that don't appear on the html page.

But some sequences look like you can also specify parameters to the commands.

 

[meson800]

From your source,

For example; Target Docking Adapter Acquisition Lights On command number is
251. To transmit this message the Gemini pilot adjusts the encoder controller
to the following positions: the outer octal dial is turned to 2, the inner
octal dial is turned to 5, and the binary switch (XMIT_ is positioned to 1 and
held until the message cycle described in this sectionlis completed.)

Seems like you would just input the hundred's place on the outer dial, the ten's place on the inner dial, then use the switch to enter the last digit. :shrug:

Is that what you are looking for?

 

[4throck]

Yes, I have it set up so that you can input the code, no problem. The two dials go from 0 to 7, and using the MFD buttons you can choose the current dial and increase / decrease the number. Conceptually it's close to the real thing.

So you input 501 and the engine goes full throttle, you input 500 and it stops. I already got that working and it's fine.
This is enough for a docked situation where you raise your orbit using the Agena while sitting in the Gemini.:thumbup:


But for docking, the astronauts could adjust the Agena's attitude. That is the unclear part. Indeed, there seems to be some rate/speed parameters that can be inputed.

For now I'm only interested in attitude control, nothing else.
I accept suggestions, having in mind that the closer to Orbiter's default autopilots or keypresses, the better.

 

[Urwumpe]

The command encoder was possibly just one way to interact with the agena, since there are also commands to program DV counters of the agena.

 

[4throck]

Got some more data. This is a nice document with the actual command sequences for several situations:

http://www.ibiblio.org/apollo/Documents/agena_commands.pdf


I've proceed as simply as possible. There are 4 control jets on the back of the Agena, belonging to 2 different systems. I'm treating them all the same, and configured RCS accordingly. If I understood the docs correctly, the commands activate a single "pulse" of the RCS system

So when you input "410 Set Pitch/Yaw Mode to Minus Rotation" you get your 4 thrusters to do:

10
11

Plus rotation mode will get you:

11
01

Now the fun part! If you input pitch off, then the last two commands will give these thrusters:

10
10

and

01
01

So with some thinking ahead you can rotate just in Yaw and Pitch. Those thruster combinations make some sense at least.



It works, although the process of inputting the codes is slow. For now (and it helps debugging the logic implementation) my code is simply activating the thrusters until they are shut off. Also, I have the RCS jets quite visible (not realistic), but I can show you the MFD working!

 

[4throck]

Here's a functional release:

[ame="http://www.orbithangar.com/searchid.php?ID=6381"]http://www.orbithangar.com/searchid.php?ID=6381[/ame]

I'm using a fixed rotation rate to limit the pitch/yaw thrusters. After a point, they shutdown.
I've also interpreted the mention to Geocentric rate as the default Orbiter prograde / retrograde autopilots.

Code is simple and effective, i'm not worrying about optimization or fancy GUI, just getting it to work is enough for now.
There are some bugs, like one of the dials going up to 8, that are simple IF logic stuff. But since they don't cause any crashes, I didn't waste any time fixing them. Feel free to fix them or improve the MFD, I don't mind at all.

 

[estar]

If you look on here you will find all the documents I have on the Agena commands.

http://www.ibiblio.org/mscorbit/document.php

I believe what the Agena is that it has a reference platform setup that allow it to perform reference motions similar to Orbiter's ability to orient a spacecraft prograde, retrograde, etc relative to the path of the orbit.

Most of the command are in essence preparatory steps to turn on the right hardware and electronics.