From JPL NEO...
Near-Earth Object (NEO) Analysis of Transponder Tracking and Gravity Tractor Performance.
October 2008
A study, requested and funded by the B612 Foundation, was carried out by JPL scientists to determine the feasibility of using a gravity tractor concept for use in NEO impact mitigation and to build credibility for the concept. Using a hypothetical Earth impacting asteroid, simulations and analyses were carried out; this report presents the analysis results arising from an investigation into the:
* facility with which a spacecraft can be safely maintained in close proximity to an irregularly shaped, rotating asteroid (even a very simple control law allows proximity spacecraft operations).
* rapidity with which optical navigation and ground-based spacecraft radio tracking can be used to precisely determine the asteroid's current and future trajectories (only a few days/weeks of tracking are necessary).
* viability of using an impacting spacecraft to provide enough of a velocity change (deflection) to avert an Earth collision several years in the future (this is a viable primary deflection concept for the most common hazardous asteroids).
* density and sizes of so-called "keyholes" near the Earth. At an Earth close approach, a keyhole passage by an asteroid would ensure a subsequent Earth collision (a few % of deflected impactors may also require trajectory trimming to avoid a keyhole).
* utility of a gravity tractor in preventing the asteroid from entering one of these keyholes should the primary deflection attempt inadvertently push the NEO into it (a gravity tractor is a viable concept for trajectory trimming to avoid most keyholes).
This work, requested and funded by the B612 Foundation, was carried out by JPL scientists and engineers in the Guidance, Navigation and Control Section (343): D.K. Yeomans, S. Bhaskaran, S.B. Broshart, S.R. Chesley, P.W. Chodas, M.A. Jones, and T.H. Sweetser.
The complete report is available here (Word Document - 4.4 MB)
Link: JPL NEO News Article
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