LM P52 orientation

[Cavalier]

So, the Apollo 11 schedule being what it is, and trying to keep track of the work that 3 very qualified test pilots/astronauts would be doing, I find myself behind, and running quickly up to the DOI TIG, still needing a P52. It seems to be a terribly time consuming process, as written, and I'm looking for ways to shave some of that time off. It leaves me asking a few questions. First, since the engineers went to a lot of trouble to facilitate the P57, and since that procedure only requires manipulation of the reticle, I wonder if that program can be used, or does it not actually align the IMU in all 3 axis? Second, I find myself wondering about the process of marking X and Y as a star crosses those axis on the AoT. What if the star could be centered in both axis. Could you not just mark both X and Y at that point? Finally, since I'm time constrained, I wonder if the requisite 4 or 5 marks on each axis are absolutely required, assuming that I am confident in the fidelity of the first or second pair of marks?

 

[indy91]

So, the Apollo 11 schedule being what it is, and trying to keep track of the work that 3 very qualified test pilots/astronauts would be doing, I find myself behind, and running quickly up to the DOI TIG, still needing a P52. It seems to be a terribly time consuming process, as written, and I'm looking for ways to shave some of that time off. It leaves me asking a few questions.

It takes some practice, but once you are familar with the LM activation procedure you won't get into time problems that much. It's always going to be challenging though, as you have to do work in two spacecraft.

First, since the engineers went to a lot of trouble to facilitate the P57, and since that procedure only requires manipulation of the reticle, I wonder if that program can be used, or does it not actually align the IMU in all 3 axis?

I don't think P57 can be used in orbit. They actually added a mode to P52 that uses the spirale/cursor alignment method to do a P52 while still docked to the CSM, but that method was not available until Apollo 15 so you can't use it.

Second, I find myself wondering about the process of marking X and Y as a star crosses those axis on the AoT. What if the star could be centered in both axis. Could you not just mark both X and Y at that point? Finally, since I'm time constrained, I wonder if the requisite 4 or 5 marks on each axis are absolutely required, assuming that I am confident in the fidelity of the first or second pair of marks?

Marks with the AOT are not very accurate. That's why they came up with the method to do up to 5 marks per star and calculate the average of them. You do get the best accuracy if you do 5 marks, alternating between X and Y, but the averaging method works with any of 3 to 5 marks. I think you would get a program alarm if you do fewer than 3 marks.

You can try to just center the star and mark with either X/Y. I think in reality it was difficult to get the attitude rate that low that you can really get the star exactly centered, so you would just do small attitude adjustments and wait for the star to cross one of the AOT line.

Marking X and Y at the same time is not recommended, I think it takes the LGC a few seconds to process a mark, so trying to do 2 marks at the same time can't be healthy. If you had the star centered for every mark you could just alternate between X and Y mark of course.

 

[Cavalier]

I dimly suspected those things, but I always like to ask the experts! I really think that if we were to dust off the plans, and built a new Apollo, there are folks here that, with trifling training on the physical equipment, could just fly a new moon landing.

And I don't feel all that bad about being behind at this point. Listening to the air-ground and flight director loops for Apollo 11, Aldrin and Armstrong started off about 30 minutes ahead of the flight plan, but were at least 10 minutes behind just prior to undocking. They obviously caught up though, and I wonder where they took up the slack. Maybe they were able to do some of the checkouts simultaneously.

So. An additional question: Are there any procedures that can not be done before uplinks from MCC? Aside, of course, from the aforementioned P52, which is option 3. If I know what I may be able to do early, I can get ahead of the power curve. As it is, I'll probably go through the entire power up a couple more times, just for luck, so if I have a feel for what needs to wait on the ground, I'll have a better shot of eventually getting to DOI.

 

[Cavalier]

Now, having proceeded through DOI, I'm having an even stranger problem. At this point, every maneuver though Yaw 0 causes me to go into gimbal lock. Somehow, I can't think that this is correct. I've tried this maneuver from Pitch 0 through Pitch 270 on starting at the same point on different saves. Weirdly, this is only true if I'm at Roll 90. I don't seem to have a good understanding of how gimbal lock works in the LM. I'm sure you're all tired of me by now (hope not ) but, any thoughts?

(just for reference, I'm at the point where I pitch down 195 to face the CSM. I can't do that without going into gimbal lock, but it seems that I can roll left or right 90, and yaw left or right 195. Since gimbal lock is a mechanical problem, it should be on a fixed spot on the FDAI, but I can pass through that spot at a different roll angle without trouble. I'm very confused.)

 

[meik84]

The gimbal arrangement (or better: axis arrangement) in the LM is different from the CSM. In the CSM the middle gimbal (which is the one critical for gimbal lock) corresponds to the yaw axis, in the LM it corresponds to the roll axis. That's why the red 'danger' zone on the LM FDAIs is not on the ball, but on the outer roll ring. By rolling to 90° (or trying to do that) in that axis you brought the middle gimbal angle to more then 85°, and that's where the LGCs safety catch comes in and puts the IMU in coarse align. Preventing that is easy: don't roll to the red areas on the FDAI, preferrably by yawing. Yes, that's the direct opposite to the CSM where you'd avoid yawing to much and roll instead, but that's how it is. In the "Spider" episode of "From the earth to the moon" an engineer puts it like that: "But that'll require the astronauts to fly the LM with a 90° change in axes." Answer from Tom Kelly: "Astronauts are smart. They'll figure it out." And so must we...

 

[Cavalier]

Ok, that makes sense. It's much harder to figure the LM out because documentation on it is so thin. I have 2 versions of the LM familiarization, and they primarily talk about where to find controls (self-evident basics) or engineering and placement (not relevant for the sim). This isn't surprising, I suppose, and undoubtedly more useful documentation still exists, but I haven't got it yet. I look forward to when some more sim-related documentation comes along (I know, when y'all have a spare moment :lol. In the mean time, I hope my obtuse questions don't annoy. Thanks!

I think I'll just quote the estimable Mike Collins, "How about sending me a fourth gimbal for Christmas."

 

[meik84]

It's not that bad. Both volumes of the LM AOH are available. The only flaw of both is that they aren't bookmarked, so browsing them is not very comfortable. The quality is also not the best, but I've seen worse. The systems handbooks are the worst in that respect with their large foldouts being chunked in small pieces. Try to trace a circuit which runs from the upper left corner to the lower right corner over 5 to 6 pages without confusing one line with the other. :rant:

 

[Cavalier]

Try to trace a circuit which runs from the upper left corner to the lower right corner over 5 to 6 pages without confusing one line with the other. :rant:

Lord save me!!! :lol:

I'm phenomenally glad that I don't need to do that, and just as grateful that there are people that are willing and able to do that for the rest of us. Without you folks, I would never have been able to, at least virtually, chase a dream that I've had since I was a child and the Apollo program was still a real thing. My hats off to you guys (and/or gals)! :tiphat:

---------- Post added 10-03-19 at 05:39 AM ---------- Previous post was 10-02-19 at 08:00 PM ----------

So now, (no pressure folks), I say Multipayer!!! Bruahahaha!

What does the community think about taking a look at the posibility of at least a full crew, with a possible extension of Flight control (a room of very smart mostly sober folks to send messages...
All that would add an order of magnitude to the simulation. Think of this as a joke, unlesss... someone thinks it can work...

There, My crazy/not crazy flip/flop for the evening.

 

[meik84]

Isn't there some sort of MCC project already? AFAIK the sim already puts out telemetry and can receive uplinks via TCP. Currently we only use it for uplinks to the AGCs from the MFDs, but from my limited understanding of network technology it should be possible to go beyond the localhost. Don't know how to do that, though...
More then one crew member...huh. That'd require multiplayer support from orbiter itself and should be something for Dr. Schweiger, not us.

 

[indy91]

Isn't there some sort of MCC project already? AFAIK the sim already puts out telemetry and can receive uplinks via TCP. Currently we only use it for uplinks to the AGCs from the MFDs, but from my limited understanding of network technology it should be possible to go beyond the localhost. Don't know how to do that, though...

We indeed have a telemetry client for the CSM. A while ago I updated the files a bit (https://github.com/indy91/telemetryClient), although I never managed to update it to a current Visual Studio version, so it only builds in Visual Studio 2010. The GroundStation.exe file in that repo should work fine though. High bitrate telemetry is buggy for some reason, haven't figured out why. And the LM also theoretically sends out a lot of telemetry already, but nobody has created a telemetry client for it yet.

 

[Thymo]

We'd probably be better of starting something from scratch.
I'm pretty sure that old thing is .NET, not a lot of us can code in that.

 

[Cavalier]

If I remember correctly, .NET is not a big jump from C++, so if you can do one, you just need to learn the interconnection protocol, and BAMB! Niels' yur parder! Well, maybe not quite that easy. I wholeheartedly support any (even clunky tries at getting 3 folks from all over on some headphones and mikes stuffed into one spacecraft. Judging by the posts and replies I see hear around, I'll feel the most ignorant member, but I could keep the CSM warm, and the dishes all washed up.

In an aside, YAAAAAAHHHHHOOOOOOOOaaaaahhhhhh! or, Huston, the Eagle has landed on all twos with minimal structural damage... And we'd talk about the scenery, but, well, we're just having so much fun in this minuscule bouncy castle! Bounce! Bounce! Master Alarm off - Bounce!

Just a couple actual serious questions: I think I went through all the steps from powerup to landing, and I still show an Ascent Pressure light in C/W. It's been on from the start. Did I miss an obvious step? Also, when you reach Luna Firma, I have the controller in ROT. Do I need to switch it to Trans in order to knock it out of detent? On my first landing, the forward 2 quads kept firing -X (vector of thrust is still X on the LM) until I was afraid that I'd be buried in the ground. I didn't think to switch to translate in time, and just turned pngcs off to stop the firing. I also started at about 8.9 Nm, which felt a little low, and the pitchover didn't leave me as much time as I would have liked to pick my nice picknik spot, but, whay-hay! We are in walk away condition, so the landing must have been good.

 

[indy91]

In an aside, YAAAAAAHHHHHOOOOOOOOaaaaahhhhhh! or, Huston, the Eagle has landed on all twos with minimal structural damage... And we'd talk about the scenery, but, well, we're just having so much fun in this minuscule bouncy castle! Bounce! Bounce! Master Alarm off - Bounce!

Congrats for a successful landing!

Just a couple actual serious questions: I think I went through all the steps from powerup to landing, and I still show an Ascent Pressure light in C/W. It's been on from the start. Did I miss an obvious step?

That is normal, the light will be on the entire time, until the ascent system is pressurized. As this is a rather annoying condition they finally changed the behavior of the light for Apollo 14 and later, so that it only shows offnominal pressure in the helium tanks, not the propellant tanks itself. We simulate this as well, so you wouldn't get the light on Apollo 14 and later.

Also, when you reach Luna Firma, I have the controller in ROT. Do I need to switch it to Trans in order to knock it out of detent? On my first landing, the forward 2 quads kept firing -X (vector of thrust is still X on the LM) until I was afraid that I'd be buried in the ground. I didn't think to switch to translate in time, and just turned pngcs off to stop the firing.

Out-of-detent only really applies to the ACA (rotational control). The ACA had a detent to keep it in the centered position and you needed a little bit of force to get it out-of-detent. There is a fairly small area where you have the ACA out-of-detent, but aren't commanding an attitude rate yet. So deflecting the ACA just a little bit from the center. Out-of-detent causes the DAP to reset the attitude it is trying to hold and that is what stops the firing of the thrusters, as the attitude while landed is now what it will try to hold. In my experience doing this procedure is impossible with a keyboard, and not easy to get working even with a joystick. Not really sure why, maybe because most joysticks don't really have this detent. So I also often just switch off PGNS control until I'm out of P66. With later LM software versions you just needed to press PRO in P66 to re-center the attitude for attitude hold. Works much better in NASSP.

I also started at about 8.9 Nm, which felt a little low,

8.9NM altitude above the landing site at PDI sounds about right. The target altitude is actually 50,000 feet (8.23 NM), so 8.9 is even a little high. But it is the normal number we are getting with the "old" DOI targeting, which the MCC is still using. The newer targeting (part of the Lunar Descent Planning Processor, already implemented in the RTCC MFD) gets it much closer to 50k feet.

and the pitchover didn't leave me as much time as I would have liked to pick my nice picknik spot, but, whay-hay! We are in walk away condition, so the landing must have been good.

The Apollo 11 pitchover is not as significant as for later missions, I have noticed that as well. Early in P64 you can barely even see the surface yet. But I think this is normal.

 

[meik84]

In my experience doing this procedure is impossible with a keyboard, and not easy to get working even with a joystick.

I'd try a short tab on any of the numpad keys. Works for me in most cases. Maneuvering with keyboard controls isn't very nice anyway; you hold the key to long and direct RCS kicks in, messing up the automatic rate control. Ignoring the checklist and switching of direct RCS is the only way there.

Early in P64 you can barely even see the surface yet.

Well, the main goal of Apollo 11 was to land at some spot, not a precision landing. Armstrong took that seriously and had no intentions to use the LPD, so it's possible that this constraint was never introduced in trajectory planing.
The early stages of planing went even further and didn't include an EVA, so it would've been land, stay some minutes/hours, lift off (maybe as demonstration of an emergency lift off). Some sources state that Neil was a strong advocate of that idea. Don't know if it's true, but it would've fit him.