The synodic period with respect to Earth Psyn ¼ jP1 Earth P1 asteroidj1 is thus long. The four year PS1 survey has a low efficiency for detecting objects with long synodic periods and the solution is to survey over a longer time period or to survey the sky at smaller solar elongations. The suite of next generation surveys (e.g. Pan-STARRS, LSSTC) will survey the sky for about a decade and will increase the completion statistics at all impactor sizes. Surveying closer to the Sun is realistic only from future space-based platforms (e.g. Tedesco et al., 2000; Jedicke et al., 2003; Hildebrand et al., 2007; Mottola et al., 2008).