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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/QOZ5H2EINGKURZ4GFXLMWPTOBHCSQUJ3/",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/",
    "message_id": "CAJCSnObgzsj2ihuiahh-KpmhDYgon23tPLRJ3ENFq4O+oZO7Yg@mail.gmail.com",
    "message_id_hash": "QOZ5H2EINGKURZ4GFXLMWPTOBHCSQUJ3",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/QOZ5H2EINGKURZ4GFXLMWPTOBHCSQUJ3/",
    "sender": {
        "address": "scott23192 (a) gmail.com",
        "mailman_id": "120e10e05ba14969a11da0a96d21e355",
        "emails": "https://mailman.amsat.org/hyperkitty/api/sender/120e10e05ba14969a11da0a96d21e355/emails/"
    },
    "sender_name": "Scott",
    "subject": "[amsat-bb] Correction: Chandrayaan-2 not using \"Earth Gravity\tAssist\"",
    "date": "2019-07-29T21:05:52Z",
    "parent": null,
    "children": [],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "Hello!\n\nOne of the things I enjoy most about the hobby is learning new things.  If\nthat comes at the expense of correcting something I said or did\nincorrectly, that's fine.\n\nI recently posted on Twitter about how fortunate I had been to be in the\nright place at the right time to record an entire 2-hour fly-by of the\nISRO Chandrayaan-2 spacecraft which is working towards a moon landing in a\nfew weeks.\n\nhttps://twitter.com/scott23192/status/1155528793831944193\n\n... in that post, I referred to the situation as an Earth\n\"gravity-assist\".  That was not the correct term for the flight\nof Chandrayaan-2 and if you'd like to hear what the difference is, please\nread on.\n\nEdgar, DF2MZ, was kind enough to fill me in on the distinction.  To\naccomplish a gravity-assist, an object (Chandrayaan-2 in this example)\nneeds to fly by another object (Earth in this case) in a path ideally\ndescribed as \"hyperbolic\".   Put simply, it's a one-time fly-by as opposed\nto a recurring orbit.  You can read about the theory of this type of\nalignment here:\n\nhttps://en.wikipedia.org/wiki/Gravity_assist\n\nThis is not the case with Chandrayaan-2, which is why the ISRO is using a\nschedule of rocket firings to boost its orbit farther and farther from\nEarth.  When an object like Chandrayaan-2 is in a recurring orbit (often\ndescribed as \"elliptical\"), it's more-or-less going to stay there unless\noutside forces change that.  I guess the most common forces would be\ngravity or rocket firings.\n\nFor an amazing, mathematically correct animation of Chandrayaan-2's journey\n(complete w/ on-schedule rocket firings), check out:\n\nhttp://sankara.net/chandrayaan2.html\n\n(the last \"big loop\" that eventually makes the lunar capture possible will\nblow your mind)\n\nSo that's the difference between the two circumstances and I wanted to set\nthe record straight.  I greatly enjoyed being able to record the\nspacecraft's S-Band downlink throughout the entire pass but didn't want to\nleave an incorrect description of the pass hanging out there.  In the end\nit was a nice bonus to learn something new about the nature of orbits since\nthey play such a major role in our hobby.\n\nThanks,\n\n-Scott,  K4KDR\n",
    "attachments": []
}