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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/XJXVYOF3N42VJTKHXQR5CSZUCUAOIVPE/",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/",
    "message_id": "[email protected]",
    "message_id_hash": "XJXVYOF3N42VJTKHXQR5CSZUCUAOIVPE",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/XJXVYOF3N42VJTKHXQR5CSZUCUAOIVPE/",
    "sender": {
        "address": "patrick (a) wirklich.priv.at",
        "mailman_id": null,
        "emails": null
    },
    "sender_name": "Patrick Strasser",
    "subject": "[amsat-bb] Re: Path to HEO",
    "date": "2013-05-02T06:20:44Z",
    "parent": null,
    "children": [],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "schrieb Ken Ernandes on 2013-04-30 09:49:\n> I note the disclaimer at the bottom, so I'll help with the incorrect assumptions.\n> \n> 1.  g = 9.81 m/sec only applies to one Earth radius (i.e., the Earth's surface).  Gravitational acceleration drops of as an inverse square of the radius.\n> 2.  GEO altitude is close to 36000 km, but GEO radius is approximately 42164 km (you must add the Earth's radius to altitude to get orbital radius)\n\nGotcha!\n\n> Gravity can be simplified by using a constant MU = 398600.4418 km^3/sec^2\n> \n> For any radius you can compute g by:\n> \n> g = MU / r^2\n> \n> But make sure you use radius and not altitude.  Mean Earth radius at mid-latitudes is approximately 6371 km and is 6378 at the equator.\n> \n> The speed (v) for an elliptical orbit can be computed from the current radius (r) and semi-major axis (a):\n> \n> v = sqrt(MU*(2/r - 1/a))\n> \n> This can be simplified for a circular orbit (r = a):\n> \n> v = sqrt(MU/a) \n\nThese are the formulas they did not tell us at school, thank you!\n\n> The more important thing is what Dan Schultz pointed out.  At 300 km altitude, atmospheric drag is a significant factor in a continuous drain of orbital energy.  This is less at 500 km and almost insignificant starting around 800 km.  The drop off is because drag is:\n> \n> 1. proportional to atmospheric density which drops off quickly with increased altitude.\n> 2. also proportional to the square of the speed relative to the atmosphere.\n> \n>  If you can get above 800 km without using up a lot of your fuel, you have a chance to make something workable.  \n\n>From the last few cubesat rides I reckon that going there instead of\nonly to 300 km is not that impossible.\n\nRegards\n\nPatrick\n-- \nEngineers motto: cheap, good, fast: choose any two\nPatrick Strasser <patrick at wirklich priv at>\n",
    "attachments": []
}