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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/OO6G34HFPYMMR2QWO2GVMOTUSZ2Y5UDN/?format=api",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/?format=api",
    "message_id": "[email protected]",
    "message_id_hash": "OO6G34HFPYMMR2QWO2GVMOTUSZ2Y5UDN",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/XNAPNJKTRVY75GB75V72JBZC7S5UJU7O/?format=api",
    "sender": {
        "address": "karn (a) philkarn.net",
        "mailman_id": null,
        "emails": null
    },
    "sender_name": "Phil Karn",
    "subject": "[amsat-bb] Re: Transponder",
    "date": "2011-08-06T19:29:09Z",
    "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/JHEDAW5SAHIPMHTIJ4AG5KKWFIIZ26YB/?format=api",
    "children": [],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "On 8/6/11 8:23 AM, George Henry wrote:\n\n> It doesn't appear that the satellite has any active or passive attitude control \n> system. \n\nCorrect.\n\n> I have heard that the spin should eventually settle around the same\n> axis as the antenna, but is there any reasonable hope that that would happen \n> during the satellite's operational lifetime?\n\nGood question. Theory says it will *eventually* happen, but how fast\ndepends on the mechanisms to dissipate mechanical energy in the\nspacecraft. Because the frame and the modules inside are so rigid, I\nthink the flexible 2m antenna will probably do most of the work.\n\nOne way to follow this is to measure the satellite's spin period very\naccurately over time. Assuming no external torque (e.g., atmospheric\ndrag, which will eventually become significant) then the spacecraft must\nconserve its original angular momentum. But as it dissipates excess\nenergy and converts to a spin around the preferred axis (i.e., shifts\nits angular momentum to the body axis with the greatest moment of\ninertia), the spin rate will decrease.\n\nE.g., if the moment of inertia around the axis of initial spin is, say,\n1, and the moment of inertia around the preferred (antenna) axis is 3,\nthen after it settles down the spin rate will be 1/3 of its original value.\n\nSo if we can follow the spin rate over time we can predict how long\nit'll take to reach a stable spin around the antenna axis. That does\nrequire knowledge of the moments and products of inertia, which I assume\nwere measured before launch.\n\n73, Phil\n",
    "attachments": []
}