Advanced Question Is it possible to do earth-to-earth astronomical navigation using an sextant in orbiter?

[hidromagnetismo]

Is it possible to do earth-to-earth astronomical navigation using an orbiter sextant?

I don't mean using the sextant of the NASSP project, but rather flying a Cessna 172 without using a VOR, just using the stars to know the location.

Is Orbiter 2016 realistic with the nautical almanacs?

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Translated from Spanish by deepl

 

[Urwumpe]

Is it possible to do earth-to-earth astronomical navigation using an orbiter sextant?

I don't mean using the sextant of the NASSP project, but rather flying a Cessna 172 without using a VOR, just using the stars to know the location.

Is Orbiter 2016 realistic with the nautical almanacs?

No idea, never checked it against one. The star data should be accurate, but the shape of Earth isn't, so there could be some errors when converting geocentric latitude to geographic latitude.

Also, for using a sextant, you would need to write an add-on for it, or at least be able to pick the local horizon angle of a star from a MFD.

 

[hidromagnetismo]

So, even if there are non-spherical perturbations, the geometrical mesh of the earth in orbiter is a sphere?

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Translated from Spanish by deepl

 

[n72.75]

So, even if there are non-spherical perturbations, the geometrical mesh of the earth in orbiter is a sphere?

That's correct. I would love to find a way to make that not be the case, though.

 

[Thunder Chicken]

In addition to the comments made by Urwumpe, to my knowledge there is no modeling for atmospheric refraction which can affect actual sightings for stars within about 15 degrees of the horizon, so care would need to be taken to NOT perform any refraction corrections for sightings in Orbiter.

Sounds like a cool add-on idea. This is how military aircraft and airliners flying trans-oceanic routes had to navigate until not so long ago. 747s and even the Concorde had sextant windows (and navigators) and I am personally aware of sextants being used on KC-135 tankers for mid-ocean rendezvous until the mid-1990s.

 

[Urwumpe]

In addition to the comments made by Urwumpe, to my knowledge there is no modeling for atmospheric refraction which can affect actual sightings for stars within about 15 degrees of the horizon, so care would need to be taken to NOT perform any refraction corrections for sightings in Orbiter.

Sounds like a cool add-on idea. This is how military aircraft and airliners flying trans-oceanic routes had to navigate until not so long ago. 747s and even the Concorde had sextant windows (and navigators) and I am personally aware of sextants being used on KC-135 tankers for mid-ocean rendezvous until the mid-1990s.

The question is just how to do it. Does somebody have a good mesh of an old ship of the line?

(My personal preference would be the HMS Trafalgar... the peak of british tall ship building at that period of time)

 

[Thunder Chicken]

The question is just how to do it. Does somebody have a good mesh of an old ship of the line?

(My personal preference would be the HMS Trafalgar... the peak of british tall ship building at that period of time)

I don't know about ships of the line, but to implement celestial navigation in Orbiter maybe a simple Camera MFD install and some reticle protractor VC to measure the angle would do as a proof of concept? Couldn't do local noon sightings or anything like that, but you could shoot some stars with it and get a fix.

 

[Urwumpe]

I don't know about ships of the line, but to implement celestial navigation in Orbiter maybe a simple Camera MFD install and some reticle protractor VC to measure the angle would do as a proof of concept? Couldn't do local noon sightings or anything like that, but you could shoot some stars with it and get a fix.

Actually it was a joke. The surface winds in Orbiter would be deadly for such ships. ?

I think the minimum use case could even be done with the HUD. Sighting local landmarks might still be harder that way, but maybe a button to flip the perspective while saving the mark of a sighting could do it.

 

[hidromagnetismo]

1. sextant (texture with scales)
2. slide rule (sine, cosine, tangent, multiplication and division)
3. mechanical calculator (for addition and subtraction)
4. various synchronized mechanical needle clocks
5. aeronautical / nautical scale

I think that would be all it takes to have a real backup!

Such a working add-on would put orbiter in a category far superior to other simulators.


Translated from Spanish

 

[Thunder Chicken]

I think the minimum use case could even be done with the HUD. Sighting local landmarks might still be harder that way, but maybe a button to flip the perspective while saving the mark of a sighting could do it.

Using the HUD simply by pitching up and reading the angle relative to the local horizon would work if you have a high performance aircraft, but would be somewhat limited for a C172. Might work it into some minimum controllable airspeed / power-on stall practice. Zoom climb, get fix, stall, recover.

 

[malcontent]

I love that a sim for space flight could, in theory, model a ship with a sextant.

 

[Urwumpe]

Using the HUD simply by pitching up and reading the angle relative to the local horizon would work if you have a high performance aircraft, but would be somewhat limited for a C172. Might work it into some minimum controllable airspeed / power-on stall practice. Zoom climb, get fix, stall, recover.

Or you pick a star with a low angle to the horizon....

 

[Thunder Chicken]

Or you pick a star with a low angle to the horizon....

Not necessarily...

Would need to be rather quick with your sighting though.

 

[Arvil]

; === Physical Parameters ===
Mass = 5.973698968e+24
;Size = 6.378165e6 ; equatorial radius
Size = 6.37101e6 ; mean radius
JCoeff = 1082.6269e-6 -2.51e-6 -1.60e-6 -0.15e-6
; harmonic coefficients for shape description

Blimey! With the above from the Earth.cfg file, I had assumed the Earth was modeled with the flattening factor, never actually landed at the equator and poles to check the radii. How 'bout dat.

 

[Arvil]

1. sextant (texture with scales)
2. slide rule (sine, cosine, tangent, multiplication and division)
3. mechanical calculator (for addition and subtraction)
4. various synchronized mechanical needle clocks
5. aeronautical / nautical scale

Or in the day of the tall ships, no slide rule, spherical trig was done on your slate and chalk with a book containing trig and logarithm tables, nautical almanac for Sun's declination. Not sure the slide rule has the resolution (I still have my Pickett).
I can do addition and subtraction on my 9-digit bead abacus, but, multiplication and division can be done on it, but, I never learned that.

Maybe not too bad on a Cessna, but, in orbit, 'nooning' would have to be really quick, then to do the math manually, it would take several orbits to calculate where you were several orbits ago.

 

[Urwumpe]

Well, for practicing it, we should have something slower. Could we extend the Ommu concept to allow tools? In that case, we would just need to implement a number of navigation tools, that any astronaut during EVA could use.

GitHub - amaudsley/oMMU

Contribute to amaudsley/oMMU development by creating an account on GitHub.

github.com

 

[n72.75]

Plenty of other bodies in Orbiter are non-spherical (vestas, phobos, etc). Maybe you'd just need to make the atmosphere relative to a mean ellipsoid surface and work whatever magic needs to happen on the rendering end of things to make the limb look right at large distances.

You could also do atmospheric refraction all on the rendering side of things.

 

[Thunder Chicken]

Maybe not too bad on a Cessna, but, in orbit, 'nooning' would have to be really quick, then to do the math manually, it would take several orbits to calculate where you were several orbits ago.

This reminded me of this classic:

 

[jedidia]

This reminded me of this classic:

Ah, putting algorithms into words... always a fun pastime!
This particular one kinda keeps reminding me of Granny Weatherwax. She always knows where she is. Occasionally she might lose track of where everything else is at, but she always knows that she is right here! ?

 

[Krishnan]

If I recall from my Orbiter Hangar Dumpster Diving and Downloading all the MFDs, I found a particular Sextant MFD. I'll try to find it.