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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/66W7QSOIN3SIGUFRFJ2YLICIAO4UCF2Y/?format=api",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/?format=api",
    "message_id": "[email protected]",
    "message_id_hash": "66W7QSOIN3SIGUFRFJ2YLICIAO4UCF2Y",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/FEXPG4RQD7ZO6OKCJGXPWK2R5QC6BZSW/?format=api",
    "sender": {
        "address": "karn (a) philkarn.net",
        "mailman_id": null,
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    },
    "sender_name": "Phil Karn",
    "subject": "[amsat-bb] Re: ARISSat-1 battery eclipse voltage decreasing",
    "date": "2011-08-13T23:02:03Z",
    "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/FEXPG4RQD7ZO6OKCJGXPWK2R5QC6BZSW/?format=api",
    "children": [
        "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/4NSUMODGP55HMBJSVGDNBSCQQKTBLKPB/?format=api"
    ],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "On 8/11/11 8:46 PM, Gould Smith wrote:\n\n> Kenneth Ransom, N5VHO has plotted the battery min/max for the last 8 days. We see that the battery voltage is decreasing at a faster rate than expected.  Kenneth's graph can be found on the arissat1.org site under FAQ  \n> http://www.arissat1.org/v3/index.php?option=com_content&view=section&layout=blog&id=13&Itemid=134\n\nDisclaimer: what follows is entirely my own personal opinion, not\nnecessarily that of the ARISSat-1 team or anyone else. I might be\nmissing information that would affect my analysis.\n\nKen's plot is extremely valuable. It strongly suggests battery failure,\nnot a negative power budget as Tony, AA2TX suggests. Note the sharp and\nconsistent *increase* in daylight battery voltage that occurred late on\nAug 11, roughly coincident with sharp *decreases* of voltage during\neclipse and reports of computer resets and extended low power operation.\nThis is inconsistent with a negative orbit-average power budget. If that\nwere the case, the battery would never reach full charge and the voltage\nwould never rise so high.\n\nThis plot suggests that one or more cells in the battery have lost\nsignificant capacity. The cell with the lessened capacity reaches full\ncharge very quickly and then goes into overcharge, allowing the overall\nvoltage of the string to rise. Then of course the voltage falls very\nquickly in eclipse as the impaired cell(s) rapidly discharge.\n\nAs Luc Leblanc points out, silver-zinc (Ag/Zn) batteries have long been\nthe battery of choice in the aerospace industry where their high energy\ndensity (almost comparable to li-ion), long shelf life and reliability\noutweighs the obviously high cost.\n\nThe Apollo/Saturn program apparently used Ag/Zn batteries exclusively,\npowering everything from the guidance system in the Saturn V to the\nlunar module to the portable life support systems the astronauts used on\nthe lunar surface.\n\nBut these features are associated with Ag/Zn as a *primary* battery, one\nthat is never recharged. Only the three entry batteries in the command\nmodule were ever recharged, and then only a few times during a mission\nafter moderate discharges. Those Ag/Zn batteries had rated cycle lives\nmeasured in the single digits; Luc's figures show only modest\nimprovements since then.\n\nAnother unusual feature of Ag/Zn batteries is a two-stage discharge\nprocess. When the battery is fully charged, the positive plate contains\nAgO, silver oxide with the silver in the +2 valence. As the battery\ndischarges, the silver is first reduced to Ag2O, with silver in the +1\nvalence, and then eventually to metallic silver, Ag, with valence 0.\n\nThis two-stage conversion of silver means that fairly high voltages are\nneeded to fully charge the battery. During the Apollo 7 mission, the\nshakedown flight of the Apollo command module in 1968, the entry\nbatteries could not be fully recharged because the battery charger could\nnot lift the battery terminal voltage high enough through the line\nresistance. Over 39V is needed to fully charge a nominal 28V battery.\nAccording to Ken's graph the voltage has never been this high, and we\ndon't know its initial state of charge. This suggests another possible\nfailure mechanism besides exceeding the battery's cycle life: despite a\npositive power budget, the battery was never fully recharged, and\noverdischarge of one or more cells caused cell reversal and damage.\n\n-Phil\n",
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}