states' security. Schweickart recognizes that choosing the manner and direction the asteroid should be "dragged" may be a difficult international decision, and one that should be made through the United Nations. An early NASA analysis of deflection alternatives in 2007, stated: "'Slow push' mitigation techniques are the most expensive, have the lowest level of technical readiness, and their ability to both travel to and divert a threatening NEO would be limited unless mission durations of many years to decades are possible." But a year later in 2008 the B612 Foundation released a technical evaluation of the gravity tractor concept, produced on contract to NASA. Their report confirmed that a transponder-equipped tractor "with a simple and robust spacecraft design" can provide the needed towing service for a 140-meters-diameter equivalent, Hayabusa-shaped asteroid or other NEO. Kinetic impact When the asteroid is still far from Earth, a means of deflecting the asteroid is to directly alter its momentum by colliding a spacecraft with the asteroid. The further away from the Earth, the smaller the required impact force becomes. Conversely, the closer a dangerous near-Earth Object (NEO) is to Earth at the time of its discovery, the greater the force that is required to make it deviate from its collision trajectory with the Earth. Closer to Earth, the impact of a massive spacecraft is a possible solution to a pending NEO impact. In 2005, in the wake of the successful U.S. mission that crashed its Deep Impact probe into Comet Tempel 1, China announced its plan for a more advanced version: the landing of a spacecraft probe on a small NEO in order to push it off course. In the 2000s the European Space Agency (ESA) began studying the design of a space mission named Don Quijote, which, if flown, would have been the first intentional asteroid deflection mission ever designed. ESA's Advanced Concepts Team also demonstrated theoretically that a deflection of 99942 Apophis could be achieved by sending a spacecraft weighing less than a tonne to impact against the asteroid. ESA had originally identified two NEOs as possible targets for its Quijote mission: and (10302) 1989 ML. Neither asteroid represents a threat to Earth. In a subsequent study, two different possibilities were selected: the Amor asteroid 2003 SM84 and 99942 Apophis; the latter is of particular significance to Earth as it will make a close approach in 2029 and 2036. In 2005, ESA