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doi.org
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Threat Mitigation: The Gravity Tractor (2006) Schweickart, Russell; Chapman, Clark; Durda, Dan; Hut, Piet, Submitted to NASA Workshop on Near-Earth Objects, Vail, Colorado, June 2006 [arXiv:physics/0608157.pdf], available at [1]نسخة محفوظة 31 يناير 2017 على موقع واي باك مشين.