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Calm Before Close Approach
February 15, 2007

If you look at our "Where Is New Horizons?" page, which displays the spacecraft's trajectory status, you'll see we're right on Jupiter's doorstep. And it's true. Jupiter already appears one-third of a degree across — just a little smaller than the full Moon as seen from Earth — and growing every day. By early next week, Jupiter will be almost two-thirds of a degree across. And by closest approach, just over 2 weeks from now, Jupiter will loom 3.6° across — about the size of a golf ball held at arm's length. That may not sound like much, but it beats the size of anything we have or will pass on the way to Pluto, except Earth itself in the first 2 hours of the flight. (FYI: We passed the Moon at a range of about 184,000 kilometers [114,000 miles], making its maximum size some 9 hours after launch just a tad under 1.1° across.)

Well, enough trivia. What's on tap for New Horizons? This is the third week in our lull before the ramp up to closest approach begins February 24. To illustrate this lull compared with the approaching storm, we currently are performing two or three observation sequences per day, most of which measure charged particles and the solar wind with the PEPSSI and SWAP instruments. Between February 24 and March 4, however, we'll conduct 10 to 20 observation sequences per day, with all six encounter instruments participating. So, over the next week on the approach to Jupiter, our bread-and-butter observations will be of energetic particles and the solar wind, with only a single Alice ultraviolet spectrometer calibration (using Europa) to spice up the schedule.

Of course, that doesn't mean we aren't busy. We're planning a full science-team meeting for closest approach; and we're completing the review process of the closest-approach command loads after running them on NHOPS — our spacecraft simulator. We're also putting in place our entire March through June operations plan, which will include observations of Jupiter's magnetotail, a trajectory course correction, a practice run at spacecraft hibernation, and various other spacecraft and instrument tests to complete the final bits of commissioning before we enter hibernation this summer. I'll be back with more news next week.

- Alan Stern

During the Jupiter encounter, you'll also be able to read Alan Stern's blog on Astronomy magazine; check out for details.

Postscript: I am in awe of the Jupiter encounter we are so smoothly executing half a billion miles away. A great many people didn't think we could pull off an exciting encounter with hundreds upon hundreds of observations, but now we are in the thick of it. And it's due to the team's hard work, dedication, and virtuoso performances.

And just think, today is the last day we could possibly have launched to Pluto on the Atlas 5. It would have been good to fly even at this late date, but it would have been a 13-plus-year slog with no Jupiter encounter along the way.

We've come so far from those days when New Horizons was only a design, and then only under construction, or in thermal vacuum testing, or down at the Cape awaiting an RTG and a launch vehicle that could be certified to fly. Now, the curtain rises on our close approach to Planet 5: Zeus awaits our arrival in less than two weeks. It's really happening. Enjoy the ride!

- A.S.