Physics, abstract
physics/0608155

From: Russell Schweickart [view email]

Date: Tue, 15 Aug 2006 20:08:11 GMT (676kb)

Threat Characterization: Trajectory Dynamics

Authors: Russell Schweickart (B612 Foundation), Clark Chapman, Dan Durda, Bill Bottke, David Nesvorny (Southwest Research Institute), Piet Hut (Institute for Advanced Studies)

Comments: Submitted to NASA Workshop on Near-Earth Objects, Vail, Colorado, June 2006

Subj-class: Space Physics

Given a primary interest in "mitigation of the potential hazard" of near-Earth objects impacting the Earth, the subject of characterization takes on an aspect not normally present when considering asteroids as abstract bodies. Many deflection concepts are interested in the classic geophysical characteristics of asteroids when considering the physical challenge of modifying their orbits in order to cause them to subsequently miss an impact with Earth. Yet for all deflection concepts there are characteristics of the threat which overwhelm these traditional factors. For example, a close gravitational encounter with Earth some years or decades prior to impact can reduce the velocity change necessary for deflection by several orders of magnitude if the deflection precedes the close encounter (or encounters). Conversely this "benefit" comes at a "price"; a corresponding increase in the accuracy of tracking required to determine the probability of impact. Societal issues, both national and international, also characterize the NEO deflection process and these may strongly contend with the purely technical issues normally considered. Therefore critical factors not normally considered must be brought into play as one characterizes the threat of NEO impacts.

http://arxiv.org/abs/physics/0608155

Physics, abstract
physics/0608156

From: Russell Schweickart [view email]

Date: Tue, 15 Aug 2006 20:08:48 GMT (194kb)

Threat Mitigation: The Asteroid Tugboat

Authors: Russell Schweickart (B612 Foundation), Clark Chapman, Dan Durda, (Southwest Research Institute), Piet Hut (Institute for Advanced Studies)

Comments: Submitted to NASA Workshop on Near-Earth Objects, Vail, Colorado, June 2006

Subj-class: Space Physics

The Asteroid Tugboat (AT) is a fully controlled asteroid deflection concept using a robotic spacecraft powered by a high efficiency, electric propulsion system (ion or plasma) which docks with and attaches to the asteroid, conducts preliminary operations, and then thrusts continuously parallel to the asteroid velocity vector until the desired velocity change is achieved. Based on early warning, provided by ground tracking and orbit prediction, it would be deployed a decade or more prior to a potential impact. On completion of the initial rendezvous with the near-Earth object (NEO) the AT would first reduce the uncertainty in the orbit of the asteroid via Earth tracking of its radio transponder while it is station keeping with the asteroid. If on analysis of tracking data a deflection is required the AT would execute a reconnaissance phase collecting and processing information about the physical characteristics of the asteroid to support subsequent operations. The AT would then dock at the appropriate pole (i.e. on the spin axis), attach to the asteroid surface, and initiate a NEO reorientation maneuver. Following completion of the NEO reorientation the AT would initiate the deflection phase by thrusting continuously parallel to the asteroid velocity vector until the resultant target orbit is achieved. The orbit of the asteroid is continuously monitored throughout the deflection process and the end state is known in real time. If one assumes a nuclear-electric propulsion (NEP) system similar to that formerly under development in the recently canceled Prometheus Program, the AT would be capable of deflecting threatening NEOs up to 800 meters in diameter or more.

http://arxiv.org/abs/physics/0608156

Physics, abstract
physics/0608157

From: Russell Schweickart [view email]

Date: Tue, 15 Aug 2006 20:09:23 GMT (213kb)

Threat Mitigation: The Gravity Tractor

Authors: Russell Schweickart (B612 Foundation), Clark Chapman, Dan Durda, (Southwest Research Institute), Piet Hut (Institute for Advanced Studies)

Comments: Submitted to NASA Workshop on Near-Earth Objects, Vail, Colorado, June 2006

Subj-class: Space Physics

The Gravity Tractor (GT) is a fully controlled asteroid deflection concept using the mutual gravity between a robotic spacecraft and an asteroid to slowly accelerate the asteroid in the direction of the "hovering" spacecraft. Based on early warning, provided by ground tracking and orbit prediction, it would be deployed a decade or more prior to a potential impact. Ion engines would be utilized for both the rendezvous with the asteroid and the towing phase. Since the GT does not dock with or otherwise physically contact the asteroid during the deflection process there is no requirement for knowledge of the asteroid's shape, composition, rotation state or other "conventional" characteristics. The GT would first reduce the uncertainty in the orbit of the asteroid via Earth tracking of its radio transponder while station keeping with the asteroid. If, after analysis of the more precise asteroid orbit a deflection is indeed indicated, the GT would "hover" above the surface of the asteroid in the direction of the required acceleration vector for a duration adequate to achieve the desired velocity change. The orbit of the asteroid is continuously monitored throughout the deflection process and the end state is known in real time. The performance envelope for the GT includes most NEOs which experience close gravitational encounters prior to impact and those below 150-200 meters in diameter on a direct Earth impact trajectory.

http://arxiv.org/abs/physics/0608157