Science JustificationRecall that New Horizons spacecraft is currently en-route to the TNO 2014 MU69.  CFHT played a critical role in acquiring the astrometric reference frame that was used for initial spacecraft targeting.  More recently the New Horizons trajectory planning has been switched to using the astrometric reference system provided by Gaia the space mission.   The CFHT MP based astrometry that Stephen Gwyn produced however was critical to the initial targeting and provided fantastic precision.   The current success of the New Horizons targeting is directly tied to that achievement.For the astrometric reference CFHT acquired exposures of all background fields agains which 2014 MU69 was and will be visible until the point of encounter (see Figure 1).  Those images of the approach field are now being used for navigation planning work and will be used as the spacecraft reference during optical navigation in the weeks and days prior to the closest approach with 2014 MU69.  Choosing a robustly detectable set of stars that are none-variable and whose positions can be well determined will be of critical importance to the navigation phase.To ensure the highest chance for success we would request to acquire a small mosaic of short MP images of the closest approach fields fields that CFHT imaged for us a few years.  We will use these images to check that none of the stars that we are planning for navigation are variables that might no-longer be visible in the field or that no new stars have brightened and would be blocking our view of encounter target.   These are small risks but, as with all space missions, we attempt to mitigate any risk we can.My request is for 10 minutes of exposure time to take a dither of 4x100s MP images of the 2014 MU69 approach field (18h30, -20d30) as seen from the spacecraft to ensure that none of the selected navigation stars is variable.  This imaging will also fill a small hole in the previous coverage that was previously missed.  We would like to schedule those observations as soon as possible.  Waiting until next summer would be problematic as the encounter would then only be a few months away and most of the careful planning should have been completed long before then.   The risk of stellar variability and the missing piece of sky coverage was only identified recently.   The missing sky coverage being the result of an increase in the scope of trajectories that are being investigated and our previous expectation was that variability would be identified by Gaia but the Gaia coverage along some of our paths is not complete.