Alan Stern, New Horizons PI:
New Horizons has just completed a summer of intensive activities and entered hibernation on Aug. 20. The routine parts of the activities included thorough checkouts of all our backup systems (result: they work fine!) and of all our scientific instruments (they work fine too!). We also updated our onboard fault protection (a.k.a. “autonomy”) software, collected interplanetary cruise science data, and tracked the spacecraft for hundreds of hours to improve our trajectory knowledge. Added to this mix of routine summer wake-up activities for New Horizons were two major activities that had never been performed before.
Pluto and Charon: New Horizons LOng Range Reconnaissance Imager (LORRI) composite image showing the detection of Pluto’s largest moon, Charon, cleanly separated from Pluto itself. The frame on the left is an average of six different LORRI images, each taken with an exposure time of 0.1 second. The frame to the right is the same composite image but with Pluto and Charon circled; Pluto is the brighter object near the center and Charon is the fainter object near its 11 o’clock position. The circles also denote the predicted locations of the objects, showing that Charon is where the team expects it to be, relative to Pluto. No other Pluto system objects are seen in these images. When these images were taken on July 1 and July 3, 2013, the New Horizons spacecraft was still about 550 million miles (880 million kilometers) from Pluto. On July 14, 2015, the spacecraft is scheduled to pass just 7,750 miles (12,500 kilometers) above Pluto’s surface, where LORRI will be able to spot features about the size of a football field. (Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)
The first of these, conducted in early July, was planned imaging of Pluto and its largest satellite, Charon. As you can see from the image and caption above, we accomplished this using our LORRI long-focal length camera. Seeing these images, revealing our target as a true planetary binary, viscerally signaled to me that we’re nearing our destination and the end of the long, 3-billion-plus mile cruise we set out on back in January 2006.
The other unique activity was a complete flight rehearsal of the final week of flyby activities on approach to Pluto, along with the first data transmissions that will follow. This dry run, in which the actual flight sequence for closest encounter was loaded aboard New Horizons and executed exactly as it will be in July 2015, was a major test — and it succeeded brilliantly! We’d planned this test for more than six years and rehearsed it on our ground simulators dozens of times to work out the details and shake out the bugs. We’d even run a 22-hour segment of it on New Horizons in the summer of 2012 as a mini-test.
But actually executing the whole shebang this summer was our biggest effort yet, and New Horizons performed outstandingly! Although the final, excruciatingly detailed engineering reviews of the rehearsal won’t come until early September, the clear success revealed in quick-look data analysis proved to us that the close encounter sequence and spacecraft will perform as designed. And it also yielded a bonus — the measured fuel usage of the close encounter sequence was a little lower than our predictions, showing we’ll have a bit of bonus fuel in the tank after Pluto for the exploration of Kuiper Belt Objects.
The successful completion of this major milestone was, like the first image of Charon beside Pluto, a turning point that further signaled to us on the project that the end of our long cruise is nearing, and that the beginning of the actual encounter we built New Horizons for is palpably close. After all, encounter operations begin in just over 16 months, in January 2015!