Date: 14 Jan 2014
LADEE caught zooming 9-km below LRO.
Imaging NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft with LROC required extremely precise timing, worked out by the LADEE, LROC, and LRO operations teams. LADEE is in an equatorial orbit (east-to-west) while LRO is in a polar orbit (south-to-north).
By happenstance the two spacecraft are occasionally very close - on 15 January the two came within 9 km of each other. Since LROC is a pushbroom imager, it builds up an image one line at a time, thus catching a target as small and fast as LADEE is tricky! Both spacecraft are orbiting the Moon with velocities near 1600 meters per second (3600 mph), so timing and pointing of LRO needs to be nearly perfect to capture LADEE in an LROC image.
LADEE passed directly beneath the LRO orbit plane a few seconds before LRO crossed the LADEE orbit plane, meaning a straight down LROC image would have just missed LADEE. Now is where the careful planning came into play. The LADEE and LRO teams worked out the solution: simply have LRO roll 34 degrees to the west so the LROC detector (one line) would be in the right place as LADEE passed beneath.
As planned at 8:10:51.693 PM EST on 14 January 2014 LADEE entered the NAC field of view for 1.35 milliseconds and a smeared image of the intrepid spacecraft was snapped. LADEE appears in four lines of the LROC NAC-R, and is distorted right-to-left.
Read the whole story: University of Arizona: Close Encounter!
Credit: NASA/GSFC/Arizona State University