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The PI's Perspective: Visiting Four Moons, in Just Four Years, for All Mankind

August 16, 2011

In June and July, members of the New Horizons science team, using the Hubble Space Telescope, discovered and confirmed that Pluto has a fourth moon! The new satellite, provisionally called P4, is fainter and therefore likely much smaller, than either Nix or Hydra or Charon – Pluto’s other three known moons. For comparison, while Charon is about as wide as the U.S. State of Colorado, Nix and Hydra are closer to the width of Vermont, and P4 is likely to be no wider across than Boulder County, Colorado.

New Horizons remains healthy and on course, now approximately 21 times as far from the Sun as the Earth is – well on its way, between the orbits of Uranus and Neptune.

On July 1, we completed our 2011 checkout of the spacecraft and its payload, which went very well. During that checkout, which spanned May and June, we conducted the first of two tests of our REX radio occultation experiment, using the moon to cut off a radio signal transmitted to New Horizons from Deep Space Network (DSN) antennas on Earth. This test involved many organizations, including the REX team, our mission operations team at the Johns Hopkins Applied Physics Laboratory, and the DSN itself. And it worked perfectly!

In June, we also accomplished some cruise science for our space plasma instruments – SWAP and PEPPSI – studying the charged-particle populations of the solar system. And over May and June we completed some much-needed spacecraft tracking; from every indication, we’re so close to a perfect course toward Pluto that will not need to conduct a course correction maneuver until at least 2013.

With this checkout behind us, we’ve returned our attention to planning the Pluto encounter. More specifically, the project team is working on the four-day command loads just before and just after the core nine-day load for Pluto closest approach. These “bookend” loads are the most critical portions of our Approach Phase 3 (AP3) and Departure Phase 1 (DP1) observations. Work is also well under way on the farther-out portions of AP3 and DP1. In addition, we’re analyzing and prioritizing responses to some 280 potential contingency scenarios for the 2015 encounter – just in case.

Pluto’s newest found moon (P4) orbits between Nix and Hydra, both of which orbit well beyond Charon. Could Pluto have additional moons? Perhaps, and the New Horizons team has proposed to the Hubble Space Telescope to look even harder – so that we can best plan our encounter observations, and ensure we don’t run into something we could have avoided.

New Horizons PI Alan Stern presented a mission overview talk last month at the U.S. Space and Rocket Center’s auditorium in Huntsville, Alabama.

And if all that isn’t keeping our little mission team busy enough, we’re also planning our first encounter rehearsal on New Horizons for summer 2012.

Designed as a stress test for the spacecraft, the “24-hour rehearsal” will include an intense one-day portion of the encounter near closest approach. We’ve rehearsed this portion of the timeline (and more) on our New Horizons ground simulator at APL in Maryland, and passed with flying colors. But there is no substitute for actually going through these paces on our spacecraft, verbatim. That kind of real-world test will prove the spacecraft is up to the task, and it’ll also let us check out some aspects of the timeline that we can only do in space. A good example: New Horizons will actually perform all the timelined attitude maneuvers and turns, which our ground simulator can only pretend to do.

The 24-hour rehearsal in 2012 is a precursor to the full, nine-day-long core encounter rehearsal that we will run on New Horizons during summer 2013.

What else is coming for New Horizons? We have our usual pair of “precession wakeups” from hibernation this November and in January 2012. In these annual activities we re-point our spacecraft and its communications antenna to account for Earth’s motion around the sun, and perform some spacecraft maintenance. Also in January, we will perform our second (and final) REX radio science lunar occultation test.

On tap in the coming months will be preparations for the new fault protection/autonomy and command and data handling software we’ll send up to the spacecraft next summer, as well as the planning for a jam-packed active checkout for 2012. The “C & DH” software change will feature a key bug fix, tracked down by project engineer Steve Williams of APL, which should reduce the probability of any computer resets during the 2015 encounter.

And also in the coming months, we’ll be kicking off our extensive space plasma hibernation cruise science observations with a test in October, and if all goes well, operational data collects beginning in early 2012.

While our spacecraft and operations teams are performing all those activities, our science team is leading a search for Kuiper Belt flyby targets, conducting studies of Pluto and its moons using ground-based telescopes, and planning a major scientific conference on the Pluto system for the summer of 2013.

That conference will allow the world’s astronomers and planetary scientists to review the state of knowledge about the Pluto system before our encounter and to begin detailed planning of ground-based and space-based campaigns to observe the planet and its moons in conjunction with the New Horizons flyby. The conference will also give researchers a chance to develop educated predictions about what New Horizons may find. We are discussing a similar kind of meeting for educators in 2014.

The New Horizons project expects to propose a stamp to the U.S. Postal Service to commemorate the historic flyby of Pluto and its moons that we will accomplish in 2015. But at least one country has already issued New Horizons stamps! Can you tell which country?

Finally, I’ll close by giving a big shout out of congratulations to NASA’s Dawn mission, which is now making the first reconnaissance of Vesta – the fourth-largest asteroid – which is about 500 kilometers across. Dawn’s exploration of Vesta is just beginning, but is already yielding spectacular results and showing us a much more complex world than many scientists imagined Vesta to be. You can read more about Dawn’s exploration of Vesta here.

From those of us looking forward to exploring a world almost 2,500 kilometers in diameter to those exploring fascinating Vesta, New Horizons salutes you. First-time exploration of new worlds simply rocks!

Well, that’s my update for now. Thanks again for following our journey across the deep ocean of space to a truly new frontier. I hope you’ll keep on exploring – just as we do!

- Alan Stern