8Ball - Dead Reckoning blind and nailing it. (or how to fly with misaligned gimbal that can't be fixed)

IDNeon

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TL;DR is at the end after a break like this :: ------------- :: SPOILER || ALL of this is BRILLIANT. I'm not brilliant, the fact this even exists in the natural world to be discovered is brilliant. How orbits work with the 8ball instrument is amazing.

Disclaimer: I haven't evaluated yet whether or not I tricked my gimbal into being misaligned and did not fix it with a computer/tools meant to align the inertia to a reference that makes sense. That said, well, now learn to fly without all that fancy computer stuff.

STORY: I had a load of fun and wanted to share, also don't want to get laughed at if someone thinks there's an obvious "better way", that was not the point. The point for me was to become much better with the 8Ball and EVERYTHING it can tell you.

Also expect edits or additions, it's late and I wanted to write everything down before bed, I been at this like 12 hours straight. But do remember, never flew a space sim before 2days ago.

I chose Apollo space flight sim, I've flown nothing else. Long story short, did a lot of practice figuring out the systems and basics, but last 12 hours or so I just got full OCD and challenged myself to figure out how to orient myself without any other guidance and I think I worked a system out.

The tool chosen was the 8Ball and for whatever reason (maybe a glitch or maybe I don't understand orbital mechanics and burns at all), my 8Ball was no longer conveniently 0/0/0 for prograde or 0/0/180 for retrograde. I figure there's a way to align/program the guidance to make it convenient with relation to your inertia but, whatever, wasn't my primary focus for the day.

Instead I wanted to dead reckon back to prograde and retrograde, no visual queues or anything. Now, naturally, I don't know anything so at first I did use 3rd person camera and look out the window to keep on track of discovering a system that works. But once I understood how it works that all went -well- out the window. Last bit of detail, this was after entering a lunar orbit for my first time and learning how to adjust it to something resembling circular.

Just how accurate was my dead reckoning? Well I got to the point where I no longer had to adjust my attitude during time elapses, meaning I was aligned to prograde\retrograde attitude (except for the pitch which naturally changes) for some 100+hours (time elapsed) in an orbit. This gave me a lot of time to study the pendulum/clock pattern that develops in the 8Ball.

Now:
The first trick was figuring out how to get the right attitude from an 8ball.

Let's say you just parked in orbit, it's semi-circular. You have NO visual queues. If you watch your 8Ball for a very long time ... or you time elapse so that it spins quickly, it appears random at first, wobbling every which way.

In Apollo the 8Ball has another indicator around it for roll, this seems to swing wildly or go in circles.

I mean, this happens if you're like me, and decide to throw yourself into orbit without the computer because well "F***- it we're going live."

Regardless how you ended up here, now what?

If you watched an orbit, you'll notice that the 8Ball is actually spinning around an axis, makes sense, because so are you. Three to be precise, and in a properly trimmed orbit, the ship spins in only one axis. The one we are interested in happens to make you barrel roll through your entire orbit. Not precisely (and I chock this up to an imprecise orbit). Mine happened to fluctuate around 30degrees and 20degrees in orbital position (using that 360deg positioning system) for every 360degree roll.

I believe it would be as simple as marking a small curve on your 8Ball and then triangulating it, navigating to the point it defines. Or if you don't care about pretending being on a schedule, you can just navigate to it with adjustments as you fast-forward through your orbit.

Once you are aligned to that axis and your barrel roll is good you can fine tune the mark. If you're good at navigation then you should be able to nail the center of a circle in just 2/3rds of an arc (2/3rds of a roll).

So I'd say you can do this procedure in 20minutes or less real time.

[SKIP A STEP]
Here is a little cheating, because it is easy to just look out your window and roll until you see the horizon outside. But I'm certain that a pattern exists and from this pattern you can actually predict when to YAW. So that prediction is the step skipped, I haven't worked out that predictor yet.

Once you have a reference (when to YAW), it's a technical procedure that I worked out painstakingly...so here's a good time to answer WHAT IF YOU MESS UP?

No big, you remembered where that axis is right? Just attitude back to it, it's always the same anywhere in the orbit. Once there, start this step again.

It turns out you have to ROLL opposite the prograde. At least I'm sure it is there to compensate the roll of the orbit, I don't want to sound confident in the reasons, it just is FACT. You need to YAW 90deg....Basically you can't deviate in this maneuver, you HAVE TO LAND on your mark in a "straight" line across the 8Ball (which is curved). So I don't know if the ROLL is counteracting some funky Non-Euclidean Geometry or simply my orbit was fast enough that I had to actively counter the roll. If you don't complete the YAW in a straight line on a curved ball you're going to be off and make your life a lot harder.

So let's talk about the pendulum, as I call it.

Now that you've entered a prograde/retrograde alignment you are going to notice you still "ROLL". I am not sure if this varies in ANY way depending on factors, but I would imagine if you turned left it swings across the right 90deg horizontal, and if you turn right it will swing across the left 90deg horizontal.

If you are ACCURATE, it will swing approximately 80 degrees, 40deg above and 40deg below that horizontal. I'm honestly am not exactly sure if this would be accurate to real life. I am not sure yet the exact pattern because half the time is spent in pitch dark of the moon. But:

[HOPE TO ADD PATTERN HERE]

There are 6 pendulum swings per orbit, and there is either a perpendicular (LM or SCS booster to center of mass of orbit) or a prograde (or retrograde) or an oblique angle (LM or SCS pointing toward horizon) at the end of each pendulum swing.

This is because there is also one of those options at the halfway point of each pendulum swing.

So imagine a ticking clock, instead of tick-tock it's tick-tack-tick-tock.
Prograde-Oblique-Perpendicular-Oblique-Retrograde-Oblique...

In a clock-cycle of 6 pendulum swings per orbit.

Remember this is your ROLL indicator.

Now armed with this information you should NOT need any more information to predict and correct to retrograde or prograde at any state of the orbit as long as you keep track of the number of "ticks" the clock has made.

[IMPORTANT]

Now that you understand all the pieces, let me tell you how F-ING brilliant this is.

The Pendulum "clock" that is your ROLL indicator is actually a NOW A PITCH INDICATOR.

So, your 8Ball is "going crazy", not really, it's just gliding across a globe in a line that isn't straight up and down on your coordinate system, but NONE of that matters.

Your new coordinate system, and all you care about, is your ROLL indicator.

And it swings 180degrees in pitch, even though it only swings about 80degrees on the actual indicator itself. If you fine tune the use of it with your Pitch thrusters, you'll see it complete the full 45 degree swing but that is splitting hairs.

So, thank you for reading my story of how I got here, if you didn't want to read it all:



::::::::::::::::::::::::::::::::::::::::--------------------------------------------------------------------------------------------------------------------------------------------::::::::::::::::::::::::::::::::::::::::

To Dead Reckon nearly precisely with your 8Ball and nothing else:

NOTE: If you can follow these steps and orient to prograde/retrograde alignment and enable your roll indicator to function as a pitch indicator; then your 8Ball now serves as a proper navigation tool without the aid of any other device. You can now manage your precise location over the orbited target and alter it based on whatever you use to plan your burn. If you know your attitude for the burn...you can now align to it off your new "stable platform" without further guidance.

1) When in orbit triangulate the center of the circle on the 8Ball by watching a curve and deducing it, or watching the whole 8Ball spin.
2) Zero in on the center and watch that your [ROLL INDICATOR] turns completely around the bevel. Should take one orbit to nail down.
3) Watch for horizon of Planet out window (still working out predicting its location with only the 8ball).
4) [YAW] 90deg whichever direction you feel (prograde/retrograde) AND Roll opposite of the orbit-induced roll to compensate and land on your mark precisely without correction.
5) Observe that your [ROLL INDICATOR] now swings back and forth like a pendulum as you proceed through your orbit.
5a) This proper swing also indicates you [YAW'd] a correct amount. If your YAW was off then your roll would not fit precisely within the proper swing (~80deg on the dial)
6) Know that your start of the swing represents your [RETROGRADE / PROGRADE] so consider this pendulum a clock. Start a timer if you have to.
7) Know that [HALF] of the swing = 90deg. [ONE] swing = 180deg.
8) This is why at the top and bottom and halfway point you alternate between prograde, retrograde and perpendicular.
9) To get to [RETROGRADE / PROGRADE] just pitch up/down (whichever) until your [ROLL INDICATOR] is at the appropriate position based on how many swings you have had.
10) Precise attitude adjustments more than just landing back on prograde/retrograde will be worked on for future update.

:::::EXAMPLE:::::

(Will devise an example as I walk through my own instructions later after some rest)
 
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IDNeon

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Eventually I'm going to substantially overhaul this thread.

This post is for MYSELF to put notes on what to test and post results through edits.

[FIRST] - need to determine how to correct 8ball so that YAW-0 PITCH-0 == prograde when it actually does.

I expect without automatic pitch corrections you can't keep this orientation naturally so the PITCH should rotate 360deg through the entire orbit.

I want to better determine the correct way to do this...if that is at ALL possible.
 

N_Molson

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Do know a bit about vectors, and what the "Gimbal Lock problem" is ?
 

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Do know a bit about vectors, and what the "Gimbal Lock problem" is ?
Look, a sailor didn't understand how the wind works to sail the wind, they just listened to all the feedbacks, trim of the sails, heel of the ship, angle of attack, etc.

But my understanding of the guidance system is you correct it programmatically from star readings in P51 and P52.

Does that correction physically change the motion of the IMU?

Apollo 11 had gimbal lock, correct? So if they were doing everything correctly, what is the real risk to a physical gimbal lock and it doesn't appear running IMU realignment prevents it? Or did they fail to do it correctly?
 

N_Molson

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See there :

https://en.wikipedia.org/wiki/Gimbal_lock#On_Apollo_11

Astronauts are not like sailors they drafted from the streets and taverns in the 17th century, they are highly trained specialists. Most have a PhD related to space engineering or something very mission-specific like biology, medicine or geology.

Apollo IMU was designed with a flaw because it allowed to save some precious kilograms. The issue was fixed in the Space Shuttle.

What is mechanically happening to the IMU when you http://nassp.sourceforge.net/wiki/IMU_Realign_checklist_(Virtual_AGC) follow this realignment?

What is going into NASSP code ? Only NASSP devs can answer. Most of the code is available on the site AFAIK, so you can even check yourself.
 

IDNeon

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See there :

https://en.wikipedia.org/wiki/Gimbal_lock#On_Apollo_11

Astronauts are not like sailors they drafted from the streets and taverns in the 17th century, they are highly trained specialists. Most have a PhD related to space engineering or something very mission-specific like biology, medicine or geology.

Apollo IMU was designed with a flaw because it allowed to save some precious kilograms. The issue was fixed in the Space Shuttle.



What is going into NASSP code ? Only NASSP devs can answer. Most of the code is available on the site AFAIK, so you can even check yourself.
You belittle sailing,
- I suggest you watch that. One of the most epic battles ever fought was in near tropical storm force winds between a 100-gun ship of the line and two frigates.

They were somehow able to keep on each other for nearly 12 hours in raging seas, still hitting each other with shot, despite the storm and night, with a strong heave-to caused by the rudder effect of amount of sail ON WHICH MASTS the sail was applied...all changing with the changing winds AND the lost of masts which changed steerage.

They were able to maneuver each other and navigate against relative targets, without preplanning, all hands following EXACT orders.

The Indefatigable actually CROSSED THE WIND two times in the battle. A manuever that requires most of the entire compliment of crew to accomplish, great skill and coordination for a square rigger, and if you FAIL you get LOCKED IN THE IRONS and unable to steer, and begin to back into the waves which will tear off a rudder and swamp your boat.

This is how most treasure galleons sank.

They had to do this IN REAL TIME without a bunch of telemetry from the ground .... They also didn't have any visual frame of reference except each other and their cannon fire at night and the distant lanterns. The moon was absent until very early in the morning.

They did this by PAYING ATTENTION.

So an Astronaut can do something more too, or are you saying Humans are forever stuck to requiring 10,000 man hours of training/preparation for every planned burn and thrust in flight?


------------------------------------------------------------------------------------

Expound upon the issue. Are you referring to Gimbal Lock which is solved by a fourth Gimbal?
 

N_Molson

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I did quite a lot of sailing in my young days actually.

17th century officers often came from aristocracy and studied in military academies, yes. Sailors were not, casualties were high during those battles and cannon fodder was needed. It was not uncommon to have children/teenagers on board, that were the "trainees". Sailors that survived battles gained experience and if they were lucky enough to have a good commander they learned all the tricks and became some kind of an elite crew, more likely to survive battles than others.
 

IDNeon

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I did quite a lot of sailing in my young days actually.

17th century officers often came from aristocracy and studied in military academies, yes. Sailors were not, casualties were high during those battles and cannon fodder was needed. It was not uncommon to have children/teenagers on board, that were the "trainees". Sailors that survived battles gained experience and if they were lucky enough to have a good commander they learned all the tricks and became some kind of an elite crew, more likely to survive battles than others.
Yeah man, my point is everything requires paying attention to the feed back mechanism you have available, and the better you do the more successful.

I don't think you're seeing the value of what I worked out with the 8ball, the question I have for you which you haven't really adequately explained is does this maneuver cause you to get into Gimbal Lock? And if it did what would be THAT remediation? I don't think this maneuver increases the risks any. You're still just "misaligned" to a fixed reference which is your original 0/0 (prograde) orientation?

Scenario: No AGC, No Telemetry. This makes Optical IMU realignment useless.

You can STILL orient to Prograde/Retrograde. Which means you have a VERY REAL chance of making it back and not being lost in space.

Why not play with the method and see what you think of it?
 

N_Molson

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Why not play with the method and see what you think of it?

Man if everyone comes with his own "method" and tells you "what don't you try it in such configuration"... I mean, there's only 24 hours in a day... sadly...
 

IDNeon

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Man if everyone comes with his own "method" and tells you "what don't you try it in such configuration"... I mean, there's only 24 hours in a day... sadly...
The method I proscribed is worth looking into.

I just followed this and realigned the IMU - http://nassp.sourceforge.net/wiki/IMU_Realign_checklist_(Virtual_AGC)

And well, it doesn't allow me to navigate to prograde 0/0/0 or retrograde 0/0/180. There is a drift in the 8ball that is "ineligible". That is to say now the visual guidance is impossible to read (It is impossible to infer prograde or retrograde from the 8Ball) and I have to rely upon telemetry and flight proscription.

I do NOT think I did the IMU realign incorrectly, but I'll try it a few more times to see if the error is human or if I simply misunderstood the goal of the IMU - Realign which is DIFFERENT from my goal.

My goal is it KNOW prograde/retrograde at all times of the orbit and not have to calculate it or request its attitude from some other source.

My Method made it possible to know prograde/retrograde at a GLANCE.
 
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