Asteroid 1950DA is the most dangerous NEO, and is due to make a very close pass in seven centuries from now in 2880 (currently has a 1 in 300 chance of collision). This object is large and fast, and would be a continental level killer if it collides.<br /><br />We have 57 years worth of orbital information on this object currently, and so we know its future orbit, <i>considering that which we understand</i> quite well, and based upon the factors which we understand well, the chance of collision is uncomfortably high. What we don't understand very well for future trajectory predictions are several very small but important effects, such as the impact of solar radiation, solar wind, thermal re-radiation (Yarkovsky effect), mass distribution of the object, rate of rotation and how this impacts thermal re-radiation, etc. These very minor effects can cause significant orbital pertubations, especially 7 centuries into the future. So the chance of collision in the future is probably less than 1 in 300, but it could be more.<br /><br />If there is any asteroid which will require a future visit and mission, this is it. On the upside, we have 769 years to plan for this, if needed. But if a diversion of the object were necessary, it would be much , much easier to do sooner than later in terms of energy required.<br /><br />If we did send a mission to an LEO, I prpose we land a radar beacon, laser reflectors and instruments to monitor solar wind, radiation, temperature on the surface of 1950DA. Such instruments and beacons would allow us to track its orbit far more precisely. And even more important, by tracking its actual orbit versus its projected orbit, and with strong knowledge of irradiation and solar wind effects, we can then understand and model these minor trajectory perturbations and their impact on the object's future motion. This will allow a much better calculation into the future of 1950DA and a much better assessment of whether there actually is a risk. <b></b> <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>