Apollo 13 final mission broken in two ways, plus bonuses

[lapis urchin]

In the final mission, several terrible things happen, which has now cost me many hours to try to recover from, and I'm still unable to complete the mission.

1. Trying to maneuver to CM sep and LM sep was impossible from the CM. When trying to maneuver to 150 degrees in pitch, the ball would rotate wildly. At first I thought this was a ball issue, but then I looked outside and saw that the CM/LM was indeed spinning wildly, much more quickly than I would have expected, even from using 100% maneuvering power. I could eventually get past this with Backspace to kill rates, but it killed the immersion. This problem did not appear to exist when controlling from the LM, just the CM.

2. There's either a CM bug or a checklist landing bug. I've run the entire mission twice (because there are no reasonable save points available), and each time the drogues and main chutes fail to deploy entirely, and I crash land. I'm following the UI prompts and checklists to a T, and I'm unwilling to confirm this again since it will take so long. I have made dozens of successful CM landings prior to this.

Bonus 1) It's very difficult to tell what attitude to target for separation after the CM FDAI is powered up. Do we target LM attitude? CM attitude? You have to guess with context clues about who's talking.

Bonus 2) EMS auto roll is still unreliable (not specific to Apollo 13). I'll try to correct the roll manually, and I'll see the jets firing, but nothing happens. So then I have to switch to Free to get any control.

Apollo 13 final mission broken in two ways, plus bonuses

[ivory radish]

On 2. Pyros A and B were armed and Logic 1 and 2 were on and their governing cb's were closed including the associated heaters? Cold Pyros won't fire. It's probably a hole in the checklists between the CSM power down and CM power up checklists.

1. The CM/SEP attitude is 45 degrees yaw left or right; but in the case of an emergency, any attitude will do for SEP. Your chances of being hit by the SM are low, and I don't think collisions between spacecraft are modelled. That being said, I wouldn't sweat getting the CM into the right entry orientation; because as long as you are in a stable state with CMC Mode set to free, the aerodynamic forces should rotate the capsule to heatshield forward when the 0.05G light comes on. Then, you can engage CMC AUTO and let the computer fly your lift vector or hand fly it with the G meter. I have done this before on other scenarios to verify that the blunt body aerodynamics were properly modelled. They are.

The other thing is that when you get into the upper atmosphere before all the dynamic heating really starts to heat up the vehicle rotational control becomes much less sensitive to inputs.

The ball going nuts points to the IMU not being aligned properly. If that were the case, the white NO ATT light should be on. I would switch to the FDAI source to GDC, but those probably aren't properly aligned either. I don't know if the FDAI's could even be trusted, so I would probably be flying by hand to keep the horizon on the marks on the Commanders window.

[lapis urchin]

Pyros were armed, logics were on, but I don’t recall about the heaters. I also suspect it’s a checklist hole there.

Ya the aerodynamics definitely work for orienting the capsule once you hit .5G. I’m just referring to the LM and SM sep attitudes not being clear as to what ball you’re looking at in the UI prompts. It definitely doesn’t matter, but it would be nice for more clarity (a common theme across the game). With all my Apollo entries, I’ve never been able to see the computer successfully control my lift vector (even when following the video tutorial and the checklists outside of the Apollo 13 mission). At best, it will roll me to 45° and do nothing after that, resulting it atmo skip in lunar configurations. At worst, it will try to orient me prograde on entry. I’ve only been able to enter in free mode.

On the ball thing, it’s not just the ball going nuts. It’s the whole craft going nuts. I’m talking 90°+ per second. I thought it was the ball, but I confirmed it was actually the craft after looking out the window. I also saw jets firing during these freak outs, but there was no computer attitude control running on either computer. I’ve seen this in other missions too. Switching FDAI sources does nothing. I had no NO ATT light on. I did have a COMP light on once the CM DSKY powered up, and it never went away (both attempts on the mission).

For more details, I was in the CM trying to go from ball attitude 0,0,0 to 0,150,45 (which in retrospect I believe was actually intended for the LM ball). When I reached 150 pitch, the whole craft rolled 180° extremely quickly and then kept pitching in the same direction I was pitching. It’s almost like there’s some sort of physics engine coordinate system snafu happening. I can’t explain why jets started firing though. And it only happened when maneuvering from the CM. Doing the same maneuver from the LM worked fine (and remember they were still docked).

I remember feeling like it was almost an incredibly overpowered Dzhanibekov effect.

[ivory radish]

Did you set the gimbal angles in the CM after you turned on AGS? I am going to bet if the NO ATT light is not on and a course alignment was not done that that's probably the source of the wild ride. I have had that happen when I missed doing a course alignment on the LM. The RCS went nuts when I switched to PGNS and got me into a three axis tumble. You probably need to work the LM course alignment PAD backwards and enter the gimbal angles for the CM based on the LM's gimbal angles. I think it is V06 N20E for both of them to show to the orientation of the spacecraft.

The 0, 150, 45 is the attitude for the CM. The LM should be something like 300, 30, -45. The LM is 180 out and clocked 60 degrees to the CM.

[lapis urchin]

I did set the gimbal angles. I completed the coarse alignment as per the transcript/checklist, so that’s another possible hole. But just to be super clear, this impossibly fast tumble happens when both spacecrafts are set to manual control anyway.

[ivory radish]

If AGS and LGS are truly out of the loop, then the problem is in the rotational and translation hand controller circuIts and possibly the CM RCS handover. I take It that this uncommanded tumble is not LM induced, but CM induced and appears after the CM RCS system is pressurized. I am thinking that if GDC and IMU outputs are garbage. the inertial references that the thrusters use to control rates are garbage.

[lapis urchin]

It’s not like the tumble just randomly starts though. It’s like there’s a magical attitude that, when you approach it, causes the jets to fire when they shouldn’t, and again, the rate of tumble is far greater than the jets can otherwise accomplish organically (fairly confidently). Yes it’s post CM RCS pressurization.

(Or rather, the rate of change of attitude leading into the tumble)

Even in free mode though?

[ivory radish]

Hmmm…I really question whether gimbal lock behavior is properly modelled. Does the tumble happen after the LM is jettisoned?

[lapis urchin]

You know, my first thought before Dzhanibekov effect was gimbal lock! Thats what the nav all movement looks like. But then I discounted that when I saw it was the craft actually moving. But maybe that’s actually it at a low level!

I don’t recall it happening after LM jettison, but I have seen this before while in the CM in other missions.

[ivory radish]

I am wondering whether the control laws for the manual thruster mode pass through the AGS. If that’s the case, it might be a DAP load issue. If your weights aren’t properly set, then the combined cg of the entire system is off. A small angle issue could explain why the thrusters start firing at a magical attitude. The guidance system logic might be written using the approximation sin(theta)=theta in radians.

[dim ruin]

Do you recall your ORDEAL settings here, like being on ORB RATE or INRTL? I know ORB RATE can cause this type of effect at some angles.

I will give the mission a go asap, to see if I can get it down successfully as a start

[dim ruin]

Meanwhile, if you want to get the completion and then return to it later when we figure out what the issue was, you can load into the mission, open the console and type:
s -mission -complete

[boreal island]

FYI Petri I ran this same mission a couple days ago. I can confirm the lack of chute deploys (I believe it was sequencer retros not re-armed after LM jettison)

However I did not observe any FDAI problems.

[boreal island]

so the CM AOH checklist for EARTH ENTRY -> EARTH LANDING includes a step SECS PYRO ARM (2) - ARM upon reaching 50k altitude.

However, the LUNAR ENTRY -> EARTH LANDING PHASE checklist does not include this step.

When arming the pyros on this mission, I got successful chute deploys.

that was the only change from mission checklists that I needed to execute

[dim ruin]

Thanks for the update!

[lapis urchin]

I thought to check that! ORDEAL was internal.

[shadow owl]

inertial 🙂

[boreal island]

guidance is internal, ORDEAL is inertial

[lapis urchin]

My iPhone REALLY doesn’t like letting me type inertial 🤦‍♂️

[low heart]

for this point:

1. Trying to maneuver to CM sep and LM sep was impossible from the CM.

I came across this issue as well.
I found the "attitude control - yaw" being in "mode cont" and ags/pngs also being set to "att hold" on the LM caused the issue.
This was causing the LM to fire thrusters which actively fights what the player is trying to manually maneuver the CM attitude to.

[low heart]

I found that the magical attitude is when the yaw dead band of the LM reaches its limit, that is when the yaw thrusters of the LM fire while you are in the CM trying to manually manoeuvre to sep attitude. If you push past the LM yaw dead band with the CM, that is when the LM AGS tries to compensate and creates a very confusing high rate of spin situation. In the LM, switching from mode cont to pulse for yaw fixed the issue for me.

[cinder thunder]

What attitude are you manuevering to? And unless I'm wrong, you should be using the LM to maneuver to sep attitude, not the CM. That should solve your LM att hold problem.

[low heart]

i found the exact moment where it asks you to set attitude control for Roll and Pitch from "mode cont" to "Pulse" and then skips over the Yaw switch which still has "mode cont" selected effectively leaving the LM AGS to attempt to maintain the LM Yaw value within the 5 degree/max deadband range due to LM AGS being set to "att hold". The next item it skips to in the script (not a running checklist) is "[1] ENG: BAL CPL: ON". This is just before SM seperation at the early stage of Apollo 13 mission 23 around 138h 07m 42s.

[low heart]

it is not until 2h50m later that this becomes a problem when you are asked to maneuver to the LM SEP attitude after doing a coarse align in the CM.
Screenshot from CM and LM provided showing the starting attitude (SM SEP) once the coarse align is done.

If "mode cont" is left on for yaw in the LM, you will never be able to achieve LM sep attitude due to LM resisting the attitude commands from the CM.

from the original post: "Bonus 1) It's very difficult to tell what attitude to target for separation after the CM FDAI is powered up. Do we target LM attitude? CM attitude? You have to guess with context clues about who's talking."

[shadow owl]

SM RCS is dead at that point, so you only can maneuver with the LM (at least historically)

[low heart]

SM has been jettisoned by this point

[shadow owl]

point remains then, you will not move the CM/LM stack with CM RCS

LM RCS is used until LM Jettison attitude

CM RCS is only hot fire checked, but not used for maneuvering the stack or attitude hold

and side note, Petri really needs to correct the altitude and velocity lights in the LM 😛

[low heart]

another observation, I am at 30mins from the RRT on the PAD and the objective screen says nothing due for another 10 mins which is 10 mins after I should be starting the EI-30 checklist. Another note is that the CM RCS thrusters are cold at this point and need 20 mins to heat up, can that pose a problem?

If you skip all the steps before p61, you do skip the cm rcs warm up

[shadow owl]

CM RCS was heated at EI-6h30m and hot fired at EI-4:30

[low heart]

but then they were cold by the time of RRT. Does that matter?

[shadow owl]

just saying how it actually was done

needed to use LM power to preheat the thrusters

[low heart]

can I assume 470R = Readout? I have not had to touch the DEDA before this mission so I wouldn't know.

[low heart]

here is a better screenshot
that first screenshot might have been me taking a screen clipping while HDR is on.
I dont think that is an issue with the sim.

[shadow owl]

Yeah R is "readout"

[shadow owl]

no I know thats what the lights are, they just shouldnt be on

only when the computer is expecting radar data and not getting it (ie P63)

[low heart]

Bonus 1) It's very difficult to tell what attitude to target for separation after the CM FDAI is powered up. Do we target LM attitude? CM attitude? You have to guess with context clues about who's talking.

Example: it is not clear if this should be done in the CM or LM.
I have to assume it is intended for the CM based on the word Odyssey. Not everyone automatically associates the name Odyssey with CM.

[low heart]

Bonus 1) It's very difficult to tell what attitude to target for separation after the CM FDAI is powered up. Do we target LM attitude? CM attitude? You have to guess with context clues about who's talking.

Example: the sim instructs me to "Maneuver towards the LM SEP attitude roll 130; pitch, 125; yaw, 012.4".
From the player perspective, I have only just finished the REFSMAT P52 Option 3 in the CM and then get told to maneuver. The logical assumption would be, I am in the CM, I assume you want me to maneuver the CM to LM SEP attitude as there is no clear instruction to move back into the LM and perform this maneuver.

[shadow owl]

I van only speak to what actually was done, not what reentry does

[low heart]

yeah no worries, just trying to raise awareness of this vagueness in an effort to help prevent others from wasting countless hours trying to complete the mission. Hopefully even get some of the wording changed in the reentry sim to make it easier for others.

The only clue is shown at 141h 02m mentioning that the LM has to be in the LM SEP attitude.
On the first couple of attempts when I was trying to get the CM into the requested attitude (which i now know to be incorrect), when I saw this message, I assumed this was a seperate attitude figure (specifically for the LM) that had been provided in a mission previous to mission 23.

[low heart]

Bonus 1) It's very difficult to tell what attitude to target for separation after the CM FDAI is powered up. Do we target LM attitude? CM attitude? You have to guess with context clues about who's talking.

Issue: The N46 and N47 DAP data load numbers are not specific about which vehicle you are meant to load them into.
I have to assume it is intended for the LM DAP as the LM should weigh more than the CM command module, right?
Not everyone might know that and might try to enter it into the CM DAP instead.
Even more confusing is that as soon as it provides those n46 and n47 values for the DAP, it then tells you to switch into the CM, which might incorrectly lead people to think you need to load the values into the CM DAP.