# Grammar in space? (noun and verb in movie Apollo 13) **URL:** \ **Category:** Factual Questions\ **Created:** [June 8, 2010, 1:21pm UTC](https://boards.straightdope.com/t/grammar-in-space-noun-and-verb-in-movie-apollo-13/542418 "2010-06-08T13:21:34Z")\ **Posts on this page:** 3\ **Page:** 2
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [June 11, 2010, 3:26am UTC](https://boards.straightdope.com/t/grammar-in-space-noun-and-verb-in-movie-apollo-13/542418/21 "2010-06-11T03:26:51Z")
> [@Leaffan](#): > > Well, that certainly clears it up nicely. 😕 Sorry, I was addressing the statement that “It’s not like they had optical sensors monitoring the position of the Sun, Moon, and Earth,”; while the Apollo system didn’t, later ballistic missile systems and interplanetary probes do, in fact, use optical stellar measurements for alignment. How they do this is fairly simple in concept, and essentially identical to how sailors navigated before LORAN and GPS. That is to say, they took a reference on some “fixed” celestial light source (like the Sun at local noon or a co-axial star like Polaris) and measured the angle from the horizon, then referred a reference table to find the latitude. Similarly, astronauts will take two or more sets of sightings between fixed points and triangulate (or look in a cross-referenced table) to determine their position and orientation. Velocity is determined by measuring the difference in position between sightings. For a vessel in a conic section orbit, you have to take multiple sightings in order to figure out the shape of the orbit and location within it. Once you have position and velocity, you just punch that into the navigation computer, and it figures out the impulse curves (i.e. when and in what direction to apply thrust) for a desired (usually pre-programmed) final velocity and position; in the targets world this desired objective is called a “pierce point”; in orbital mechanics, this is usually called a trans-whatever injection orbit or final orbit. Although in theory this can be done manually on a manned vessel (as with the multiple correction burns during the Apollo XIII abort) in normal operations the engine firing is performed by an automatic system for both precision and because it is very easy to become disoriented during such maneuvers. The Earth’s magnetic field is never used as a reference for rockets and missiles because it is just too inconsistent to be useful. Even aircraft pilots frequently have problem when flying over mountains or areas with large iron deposits. Some early work was done with cruise missiles to try to use magnetic guidance but it proved to be too unreliable, and most systems used inertial measurement prior to the development of terrain contour matching (TERCOM) systems. Stranger ---
**Author:** ![whatami](https://avatars.discourse-cdn.com/v4/letter/w/85f322/32.png) [@whatami](https://boards.straightdope.com/u/whatami)\ **Post date:** [June 11, 2010, 4:56am UTC](https://boards.straightdope.com/t/grammar-in-space-noun-and-verb-in-movie-apollo-13/542418/22 "2010-06-11T04:56:35Z")
> [@JoeH2O](#): > > Sure, back in the early days, ICs were in their infancy and weren’t proven in a space environment, so they went back to weaving the memory. > > They would write programs and these would print out in binary on huge sheathes of that printer paper with the alternate folding and the perforated edges and this would be take off the Little Old Ladies. There were many of them, and they painstakingly wove the programs into rope. > > Every half foot or so there was a metal ring on a core of cable, and alongside that core would run a second cable. For a binary 1 they would pass the cable through the metal ring, for a 0 they would pass it over the outside, skipping it out. In this way a long “rope” would have a program that started at one end, and was written linearly along its length. The official name was Core Rope Memory. I see that it had a considerable advantage in memory density compared to magnetic memory of the period. > > [Core rope memory - Wikipedia](http://en.wikipedia.org/wiki/Core_rope_memory) When you started the second paragraph, I really thought you were making shit up. Thanks for the info, I’ve been keeping up and reading answers on my phone and I only have edge service here. It’s been…slow. ---
**Author:** ![Leaffan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leaffan/32/299_2.png) [@Leaffan](https://boards.straightdope.com/u/Leaffan)\ **Post date:** [June 11, 2010, 7:43pm UTC](https://boards.straightdope.com/t/grammar-in-space-noun-and-verb-in-movie-apollo-13/542418/23 "2010-06-11T19:43:29Z")
> [@Stranger\_On\_A\_Train](#): > > Sorry, I was addressing the statement that “It’s not like they had optical sensors monitoring the position of the Sun, Moon, and Earth,”; while the Apollo system didn’t, later ballistic missile systems and interplanetary probes do, in fact, use optical stellar measurements for alignment. How they do this is fairly simple in concept, and essentially identical to how sailors navigated before LORAN and GPS. That is to say, they took a reference on some “fixed” celestial light source (like the Sun at local noon or a co-axial star like Polaris) and measured the angle from the horizon, then referred a reference table to find the latitude. Similarly, astronauts will take two or more sets of sightings between fixed points and triangulate (or look in a cross-referenced table) to determine their position and orientation. Velocity is determined by measuring the difference in position between sightings. For a vessel in a conic section orbit, you have to take multiple sightings in order to figure out the shape of the orbit and location within it. > > Once you have position and velocity, you just punch that into the navigation computer, and it figures out the impulse curves (i.e. when and in what direction to apply thrust) for a desired (usually pre-programmed) final velocity and position; in the targets world this desired objective is called a “pierce point”; in orbital mechanics, this is usually called a trans-whatever injection orbit or final orbit. Although in theory this can be done manually on a manned vessel (as with the multiple correction burns during the Apollo XIII abort) in normal operations the engine firing is performed by an automatic system for both precision and because it is very easy to become disoriented during such maneuvers. > > The Earth’s magnetic field is never used as a reference for rockets and missiles because it is just too inconsistent to be useful. Even aircraft pilots frequently have problem when flying over mountains or areas with large iron deposits. Some early work was done with cruise missiles to try to use magnetic guidance but it proved to be too unreliable, and most systems used inertial measurement prior to the development of terrain contour matching (TERCOM) systems. > > Stranger Thanks. That’s amazing stuff, really. 🙂 [Previous page](https://boards.straightdope.com/t/grammar-in-space-noun-and-verb-in-movie-apollo-13/542418.md?page=1)