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    Re: Sextant practice on the space station
    From: Frank Reed
    Date: 2020 Jul 18, 23:13 -0700

    Sean, you wrote:
    "They couldn't just give them a program which would tell them the apparent angular distance between any two celestial bodies? Or at least an almanac, calculator and a set of instructions?"

    Right?! But that's not the space station way... 

    In one of the photos showing an astronaut taking sights, there is a carefully choreographed printed schedule (see link below) listing the star pairs that are to be used, in order, and displaying the correct angular distance. It's this last bit that kills any science in these experiments. If the list tells you you're supposed to get 12°14.5' then there will be a tendency to seek out successful sights. Anyone who has done experimental work of any kind has experienced this at some point. It's not because observers are dishonest or ineffective. It's because observers are human. For sextant sights, a sight with an unusually large error (maybe anything greater then 2') will be ignored and left unrecorded, skewing the statistics. And sights within a couple of tenths will be "nudged" a tenth here and there in the right direction. Doesn't this seem like a typical case where the observational results would benefit from double-blinding?

    Also, the article's claim that the astronauts were surprised by the speed at which they lost track of a given star pair sounds peculiar to me. Obviously the simulator on Earth would display the real motions. The simulators have extremely high fidelity and display the earth and the stars almost exactly as the astronauts would see them including all motions. This is trivial.

    As I have noted before, I am skeptical of this whole thing. Are we really imagining astronauts in five or seven years, on their way to the Moon, using a handheld Astra IIIB sextant?! Why?? And, even if an emergency arose, how?? It's one thing to practice with a sextant in that spectacular glass viewing room on the ISS know as the "Cupola". But no crew-carrying (manned) spacecraft on anyone's "drawing board" has windows like that (except the SpaceX Starship, which exists in Elon Musk's separate universe). 

    These sextant games are space station "make-work". They have almost zero practical value, even as a backup in an extreme situation. The proper backup to a $10-million space navigation supercomputer and its suite of sensors is a handheld supercomputer with the best digital camera system ever made (it's called an iPhone 11 Pro and it'll only set you back $1500 at worst). 

    By the way, here's the NASA press release quoted in the article I linked previously. In addition to the text, it includes a few photos, among them the photo that the shows the over-choreographed work schedule:
    https://www.nasa.gov/mission_pages/station/research/news/sextant-investigation-astronauts-add-expertise-refine-space-station-science-in-orbit/

    Frank Reed

       
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