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    Re: Hybrid artificial horizon
    From: Paul Dolkas
    Date: 2020 Jul 29, 03:24 +0000

    The alloy he’s talking about is called Gallinstan (or something like that) and it’s what is in “mercury” thermometers these days. Gallium, Indium & Tin.  Fairly expensive though – I looked into it as part of a class project I had a few years back to design a sextant for use on the moon/Mars. I was going to use Gallinstan  to form an internal artificial horizon. (Ultimately I decided to use an electronic inclinometer, but that’s another story…)

     

    Paul Dolkas

    650 464 5106

     

    From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of Robin Stuart
    Sent: Tuesday, July 28, 2020 9:00 AM
    To: Paul Dolkas <paul{at}dolkas.net>
    Subject: [NavList] Re: Hybrid artificial horizon

     

    With the discussion of mercury artificial horizons (AH), I wondered whether gallium had been considered as a substitute. It has low toxicity and melts at 30°C. At under half the density of mercury, you need to purchase less than half the weight to get the same volume for the AH.
    Searching Navlist shows that a gallium alloy was suggested for this purpose by George Huxtable in 2002. http://fer3.com/arc/m2.aspx/Liquid-metals-for-artificial-horizons-Huxtable-apr-2002-w6154. There is also research on the web on gallium for spinning parabolic mirrors http://adsabs.harvard.edu/full/1997PASP..109..319B


    Although gallium will solidify nominally at 30°C it apparently has a tendency to supercool and remain liquid below that temperature. The eutectic alloy George mentions has a melting point of -19°C. Even if the gallium were to solidify, I wonder whether it would retain its level and surface reflectivity.


    Another and perhaps the most important consideration is that having chunk of metal that melts with the heat of your hand sounds like a lot of fun!


    Robin Stuart

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