Some things never go out of style (or usefulness)

[Loren Beach]

https://www.nasa.gov/mission_pages/station/research/experiments/explorer/Investigation.html?#id=7646

That link was from this morning's e-magazine article from BoatUS.
https://www.boatus.com/expert-advic...ant-in-space?utm_source=bmag&utm_medium=email

 

[toddster]

I seem to recall that Apollo capsules had sextant reticules built-in to the windows, or some such arrangement. And Apollo 13 (at least) used them as the primary means to navigate home.

 

[Kevin A Wright]

KISS never goes out of style. And would be a whole lot easier to use in space than when on the deck of a ship in heavy seas. Also no cloud cover to worry about.

Also would imagine it is incredibly accurate. Triangulation becomes more accurate the longer the 'legs' of the triangle. With the nearest stars 4 light years away that's not a bad base for your calculations.

Kevin Wright
E35 Hydro Therapy

 

[bgary]

What I've never understood is... how, exactly, did they line up the stadia in the window?

With a sextant, your eye position is fixed relative to the mirrors. In a space capsule, (presumably) you're looking out at stars through a window that has lines/marking etched on it. Would't accuracy be highly dependent on holding your head in exactly the right place? Or something?

B

 

[tenders]

Interesting question with the window stadia. Maybe, with the angles are fixed on the window, they would line up the objects by moving around in the capsule and then measure the distance from eye to window. Or, from a known vantage point, they’d wait until whatever they were looking at lined up in the stadia and then knew exactly when they were located at a predetermined situation (or if they were ahead of or behind that point).

When I used a stadimeter in the Navy during multi-ship underway replenishments and fleet maneuvers, where a certain distance from another ship was desirable, we rarely read the angle off the stadimeter to determine distance. Radar is usually good enough for that. We usually SET the stadimeter to the angle corresponding to, say, 1000 yards, and looked through the stadimeter to determine whether we were too close or too far from the reference point.

Haven’t thought about having done that in a long time! Big adventure conning a ship at 12-18 knots from 1000 yards behind an oiler to 150 feet beside that oiler, and holding it for half an hour. Definitely a team sport.

 

[toddster]

edit: found a photo of it - looks like this doesn't involve the window at all http://www.astronomy.com/news/2018/06/the-story-of-the-apollo-sextant

If I ever knew the details, I've forgotten, but I'm under the impression that there is a fixed mount somewhere. The process is depicted in a scene in the movie "Apollo 13" but I have no idea if it is shown accurately. If I understand correctly, the window is incorporated because they had to not only know their position, but also the alignment of the spacecraft axis, if they were to make manual course corrections with no computer or gyros.

 

[paul culver]

What I've never understood is... how, exactly, did they line up the stadia in the window?

With a sextant, your eye position is fixed relative to the mirrors. In a space capsule, (presumably) you're looking out at stars through a window that has lines/marking etched on it. Would't accuracy be highly dependent on holding your head in exactly the right place? Or something?

B

As an obscure aside, Boeing aircraft have a visual device mounted up by the magnetic compass that the pilots use to adjust their seat positioning before landing. Apparently it is important to standardize the eye position to get the right perspective on the rapidly approaching runway.

Paul

 

[Tin Kicker]

Gemini XII was the first US spacecraft to use a sextant and here is the test report from about 51 years ago. They had a fixed mount but did not look like a sextant you would recognize, unless you had seen the ones made for WW2 airplanes.
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19690005000.pdf

Apollo's was a very different design which was also built in. You can see it in DC at the Air & Space museum which is a short walk from my office.

Paul Culver -
Most transport airplanes have what is called an eye locator and it's not just for runway perspective, as most of the cockpit instrumentation ergonomics focus on that point. In the new airplanes with heads up displays, eye location is critical.

 

[Kevin A Wright]

As an obscure aside, Boeing aircraft have a visual device mounted up by the magnetic compass that the pilots use to adjust their seat positioning before landing. Apparently it is important to standardize the eye position to get the right perspective on the rapidly approaching runway.

Paul

You know this is important on our boats when 'landing' as well. When I first switched from an E27 to an E35 sometimes I forgot I was on a different boat when coming in to dock. The deck and layout were so similar I had to retrain my visual cues to figure out where I was. Evidently I was unconsciously using the sight line from my eye to the edge of the port gunnel amidships to estimate my distance from the dock. With the higher deck and wider angle to amidships on the E35 I kept bringing her in about 2 feet away from the slip while thinking I was about to scrape the dock.

Took a while to reprogram my neurons after 20+ years of the E27 but 5 years in I think I've done it.

Kevin Wright
E35 Hydro Therapy

 

[paul culver]

You know this is important on our boats when 'landing' as well. When I first switched from an E27 to an E35 sometimes I forgot I was on a different boat when coming in to dock. The deck and layout were so similar I had to retrain my visual cues to figure out where I was. Evidently I was unconsciously using the sight line from my eye to the edge of the port gunnel amidships to estimate my distance from the dock. With the higher deck and wider angle to amidships on the E35 I kept bringing her in about 2 feet away from the slip while thinking I was about to scrape the dock.

Took a while to reprogram my neurons after 20+ years of the E27 but 5 years in I think I've done it.

Kevin Wright
E35 Hydro Therapy

Reminds me of when I was being taught how to dock sideways to a dock. The instructor had us approach head-on until we saw the dock disappear under the bow, then turn hard right and reverse the engine. Noting that I was taller than the instructor I decided to flex my knees to bring my eye level down to his, just to be sure. It worked!