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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/WEXP6EWVKJWVR3HMWGK532PCHNWJGTOM/?format=api",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/?format=api",
    "message_id": "7C3470BC84FE47F8933DD47E5625DFBD@WA4SCA",
    "message_id_hash": "WEXP6EWVKJWVR3HMWGK532PCHNWJGTOM",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/DY2BXH2D2G2Q7YSMYTF6RY6F5VISAZZ2/?format=api",
    "sender": {
        "address": "APBIDDLE (a) UNITED.NET",
        "mailman_id": null,
        "emails": null
    },
    "sender_name": "Alan P. Biddle",
    "subject": "[amsat-bb] Re: AO-51 magnet reversal tonight",
    "date": "2009-12-03T23:17:00Z",
    "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/DY2BXH2D2G2Q7YSMYTF6RY6F5VISAZZ2/?format=api",
    "children": [],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "According to my prelaunch Echo manual, the S/C has black and silver kapton\ntape along the edges to impart spin.  The documentation mentions that the\nearlier microsats used painted antenna elements to achieve the same result.\n\nGiven enough time, the equilibrium rotation rate will be the result of a\nbalance of the torque from the tapes, and \"drag\" caused by the internal eddy\ncurrents.  I am not aware of any data for AO-51, but normally spacecraft\npassively stabilize in a matter of days, weeks, or rarely months.  Since the\nspin rate is falling slowly, it suggests, but does not prove, that the cause\nis a decrease in the applied torque from the kapton tapes.  \n\nKepton is widely used in S/C, but is subject to deterioration due to UV and\nparticularly atomic oxygen.  Going back to the Long Duration Exposure\nFacility and other tests in the 1980s, it was found that it and similar\n\"soft\" materials had significant changes in their optical and mechanical\nproperties.  Atomic oxygen levels have the usual exponential dependence on\naltitude, plus a factor of 10-1000 variation due to solar and magnetosphere\nconditions.  Effects on kapton by atomic oxygen were of considerable\ninterests to shuttle, ISS, and HST designers, though the reason was\nprimarily optical and contamination.  They of course have active pointing.\n\nIt would be interesting to know from the Olde Tymers whether similar changes\nwere found in much earlier LEO S/C, and how other LEO S/C using the same\nsystem as AO-51 have faired recently.\n\nAlan\nWA4SCA\n\n\n",
    "attachments": []
}