Great Timing

The LRO gets a picture of LADEE passing below. Click for larger. Image Credit: NASA/Goddard/Arizona State University

Precision tracking is a better title, two spacecraft around the moon and on crossing orbits cross paths. One spacecraft (LRO) was about 9 km / 5.6 miles above the other (LADEE) and they manage a picture of the lower craft.

For me the fun thing these are two different missions with different teams and they had enough interaction to know this was coming, really this is good.

You can get somewhat of a better look by clicking here, I zoomed in on the LADEE and you can see the limitation in the way the LRO camera (LROC) takes a picture. Well limitation to catching another spacecraft passes by, as a lunar imager it is amazing.

Here is a link to an unannotated version of the image above.

LADEE is in an equatorial orbit (east-­to-­west) while LRO is in a polar orbit (south-­to-­north). The two spacecraft are occasionally very close and on Jan. 15, 2014, the two came within 5.6 miles (9 km) of each other. As LROC is a push-broom imager, it builds up an image one line at a time, so catching a target as small and fast as LADEE is tricky. Both spacecraft are orbiting the moon with velocities near 3,600 mph (1,600 meters per second), so timing and pointing of LRO must 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. 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 8:11 p.m. EST on Jan. 14, 2014, LADEE entered LRO’s Narrow Angle Camera (NAC) field of view for 1.35 milliseconds and a smeared image of LADEE was snapped. LADEE appears in four lines of the LROC image, and is distorted right­to­left. What can be seen in the LADEE pixels in the NAC image?

Here’s the press release

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