Flying without guidance computers


Mar 30, 2021
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Intro - I figure I will play with watching what the orbits do until I can determine precise steps to take to visually confirm orientation with analogue tools (optics/FDAI and time and tracking changes to dV). To see if I can not just break free of Earth's gravity, but break free from the AGC entirely.

So I've been trying to learn to Astronaut without guidance computing, it's been quite a ride! But I've put together some basic tools so far.

Flying the CSM - Apollo

First is aligning to prograde/retrograde since the FDAI may wobble or become inaccurately aligned.

I wanted to show that it is doable here:
Fig 1-1

Fig 1-2

Fig 1-3

The Shaft of the Optics is set to 0deg so it's inline with the ship's long-axis, so as you can see, that's a pretty good alignment I believe, since the Guidance Computer only has the same thrusters to work with so I can't imagine it'd be any better in practice.

The procedure for this is:

If the star/target drifts left then:
Right-Thrust and Left-Roll.

Reverse if the target drifts right.

Let that maneuver play out long enough that the drift is nearly stopped.

How do you get close enough to this alignment for any of it to matter?

There's several methods and I'll detail them later but for now I've worked out two depending on if you're close to your orbit center or far from your orbit center.

Each method looks for the same indicator on the FDAI.

You're looking for a point on the FDAI where the spin axis really is. If you think about it, when the FDAI is aligned then the spin axis is at 90deg parallel on both hemispheres, the big red top/bottom. This wobbles, and depending by how much, well you can find it with a general assumption that it's near there.

Regardless, you can really find it by lining 90deg with your optics onto your target, the Moon or Earth (return) or some constellation that you know is opposite the target if you're really good with your star maps.

I actually think it would be amazing to make the FDAI 8-ball out of a flourescent material so when you have it aligned a new star map can be "imprinted" on it to see it glowing so you know what constellations to expect where at what angles relative to your IMU.

Anyway, but at a 90deg to your target, the Optics have to be set to compensate for the hull:

323deg on the Trunion or whatever it's called. The up/down axis.

I am pretty sure this is because the CSM has a sloped hull of about 67deg so to correct to 90 you have to offset it by 23deg. Anyway I've tested it, it's true.

Now that you have your CSM attitudinally adjusted so its long axis is 90deg perpendicular to your target, you just have to pitch or yaw toward that assumed roll point, it's pretty easy to recognize once you find it. Instead of the cross hairs moving over something, everything moves around them, and the roll is at its maximum speed.

At really high altitudes this is a challenge but guess the star will move perfectly horizontal so just zero in on the axis with the optics if you want that much precision (which is not necessary).

So now that you found your roll axis: depending on if you're near to the planet, you can roll to align the horizon. There are roll-indicator relationships when you are in prograde/retrograde that are interesting but I'll not discuss those here.

If you find your horizon, you just need to yaw with a slight-opposite roll to move smoothly across the plane. This is because your orbit is probably tight enough that the roll matters a few degrees or more depending on how fast you yaw.

It's really that simple.

[Add here for how to do this at high altitudes]

Every time you perform this maneuver you will correct nearly to prograde/retrograde.

Knowing these fundamentals you can also determine inside/outside burn directions.

The hard part comes next.

Where are you in the orbit? Periapsis or Apoapsis.

Now there's one sure fire way to do this, watch your pitch as you cross periapsis and you'll see the pitch nearly stands still. It's very obvious when looking at the moon through the optics or a star through a scope.

But, to be more useful, I think I'm going to have to start using the CLOCK more often.

Lastly - I need to figure out how to determine my dV's without a guidance computer. I'm sure it's going to come down to ratios/relationships based on the observed understandings of the orbit. For instance as you orbit the moon if you're in an ellipse then it gets bigger and smaller, this tells you an exact relationship between Periapsis and Apoapsis, so you will be able to determine the necessary ratios/relationships from there.

But baby-steps....

Lastly: an example that with blind-burns and general understanding of how my orbit evolves and an assumed understanding of the dV's based on the original dV given to get to the Moon, I was able to do the following:
Fig 2-1

Fig 2-2

I nearly circularized my orbit, I corrected based on the orbit map, but I know I can do this based on observation of the target (the Moon). So the next phase of testing will be to do this without the orbit map at all.

And then to duplicate it for a completely different mission parameter.

Knowing that your roll axis doesn't change for a given orbit if you determine that axis you can determine how circular your orbit is by pitching to retro/prograde and seeing how off it is from the true tangents at the Apses.


So other than predicting the dV, in general, I'm to the point where I can eyeball a "high" orbit.

A low orbit will be another thing entirely. But a high orbit which is safer and more stable is easier to eyeball.

Getting into that Orbit actually wasn't very hard, it's quite intuitive and was easier than circularizing it because all you have to do is monitor the arc of your orbit as you pass Periapsis and then corrective burn when the arc widens.

I'll diagram/explain it more later, I've been working on a lot of maneuvers not just the insertion. There's a lot to go over and only some of it I'm able to describe with relative accuracy.

[Note to self] - I'm going to have to start a mission keeping track of all my dV changes and mapping the time as well, so I can start to actually get better with this now that the basic maneuvers approximately get me oriented correctly using a drifting stable platform (the FDAI).
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