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Project Apollo - NASSP 6.4.3 released!
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Author Topic: Saturn rate change coding  (Read 1469 times)
eddievhfan1984
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« on: January 17, 2015, 08:09:02 AM »

I've just done the manual takeover of the SIVB in Apollo 7 again, and while the controls appear to be fine, I am a bit confused that the CMC control of the APS thrusters uses the rate settings in the DAP for the CSM, and not the settings for the LV (in the Launch checklist, there's a page for changing the rate settings of the DAP while in SIVB stack mode, which I followed). For example, based on the DAP settings in V48, the max maneuver rate is .2/sec, which the Saturn takeover mode uses. However, according to the preliminary flight plan, the maneuver rates should be .5 for roll, and .3 for all else. Can I get ahold of the erasable memory value in the AGC and use that to put the rate change in the LVDC, or can I not get at it?
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meik84
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« Reply #1 on: January 17, 2015, 12:39:14 PM »

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(in the Launch checklist, there's a page for changing the rate settings of the DAP while in SIVB stack mode, which I followed)
AFAIK Colossus 249's rates for SIVB takeover are 'hardwired' and not changeable. Artemis has changeable rates (at least GSOP says so). No idea about Comanche, we lack the GSOP for it.
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For example, based on the DAP settings in V48, the max maneuver rate is .2/sec, which the Saturn takeover mode uses. However, according to the preliminary flight plan, the maneuver rates should be .5 for roll, and .3 for all else.
Slowly, please. Confused You get 0.5 deg/s roll and 0.3 pitch/yaw in takeover mode or not? If not, I've to check my conversion factors in LVDC++...
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eddievhfan1984
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« Reply #2 on: January 18, 2015, 01:34:40 AM »

Yes, the preliminary flight plan says that the rotation rates for SIVB takeover should be .5/s for roll and .3/s for pitch and yaw. According to the checklist, this is an available setting in erasable memory, using V25N07. However, the max rotation rate I get from the DAP is about .2/s. Also, rate damping seems to be nonexistent from the autopilot...
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meik84
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« Reply #3 on: January 18, 2015, 09:05:43 PM »

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Yes, the preliminary flight plan says that the rotation rates for SIVB takeover should be .5/s for roll and .3/s for pitch and yaw.
You're right. I missed the fact that the FCC limits the attitude error signals to +/- 3.5 deg in roll and +/- 2.5 deg in pitch & yaw. Bangs Head 2 I set the conversion factors such that CMC's output would equal +/- 2.5 deg, which is wrong, of course. When I set it up that the output equals +/- 3.5 deg I get 0.5 deg/s roll and 0.3deg/s pitch & yaw.
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According to the checklist, this is an available setting in erasable memory, using V25N07.
The checklist obviously derives from AP 15's launch checklist. They flew with Artemis; we fly with Colossus. Colossus does not have that feature. The output is hardwired in the code (I've checked that) and not changeable.
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Also, rate damping seems to be nonexistent from the autopilot...
There is some sort of rate damping. When you move the stick, the CMC gives an output on its ICDU error counters. This is converted into a voltage, which is fed into the FCC as an attitude error signal. The FCC then fires the thrusters accordingly, which leads (due to preset biases in the FCC) to a rate of 0.3 deg/s (resp. 0.5 deg/s). When you return the stick into detent, the CMC zeroes its error counters and thus zeroes the error signal for the FCC. The FCC then damps the rate, but not to zero, due to the bias. Instead, it plainly reduces it to about 0.2 deg/s. This is perfectly right: when the LVDC would be active, it would monitor the attitude with its plattform and create an error signal to the FCC. The biases are there to prevent excessive APS firing and save fuel. But with the LVDC not active, we get this odd behaviour, which is perfectly normal. When you look at the AS-205 SIVB flight evaluation report, you'll see that the attitude error graph during SIVB takeover has little 'spikes': that's from the astronauts. They had to move the RHC in the opposite direction for a short time to overcome the bias and null the rate.
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eddievhfan1984
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« Reply #4 on: January 19, 2015, 03:20:55 AM »

So, do I make tweaks in the LVDC code, or should I look at the CMC data connectors?

Fair point about Colossus.

And I guess I was a little too used to the SCS' method of rate damping. haha
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