This July, over 100 U.S. planetary scientists jointly petitioned NASA to find new opportunities to explore the outer solar system at moderate cost.

New Horizons I (pluto.jhuapl.edu) is the inaugural mission in NASA�s New Frontiers program�a series of mid-sized planetary exploration projects. This mission was competitively selected by NASA in 2001 after an intensive, peer review competition between industry-university teams.

The mission is on track toward a planned launch in January, 2006�just over 15 months hence; the mission is scheduled to reach Pluto-Charon in the summer of 2015. With New Horizons, the United States will complete mankind�s first reconnaissance of the planets�a historic and inspirational contribution of our nation and our time.

The objective of New Horizons (NH) is to make the first reconnaissance of the solar system�s farthest planet, Pluto, its comparably-sized satellite Charon, and to then flyby one or more Kuiper Belt Objects (KBOs) farther from the Sun.

The exploration of the Kuiper Belt and Pluto-Charon was ranked as the #1 new start priority for planetary exploration by the National Research Council�s recently completed Decadal Survey for Planetary Science.

The New Horizons spacecraft carries a suite of seven advanced, miniaturized instruments to obtain detailed imagery, spectroscopy, temperature maps, gravitational data, and in situ composition and density sampling of the exotic, icy Pluto-Charon binary and a modest-sized (~50 km diameter) KBO.

In doing so, the mission will reveal fundamental new insights into the nature of the outer solar system, the formation history of the planets, the workings of binary worlds, and the ancient repository of water and organic building blocks called the Kuiper Belt.

Beyond its scientific ambitions, New Horizons is also breaking ground in lowering the cost of exploration of the distant, outer solar system�for it is being built and launched for what are literally dimes on the dollar compared to deep outer solar system missions like Voyager, Galileo, and Cassini.

The concept of flying a second New Horizons mission was born in 2002. Over the past two years, this has been studied by the mission team, debated in the scientific community, and discussed in the space press. The objectives of New Horizons II are straightforward:

Provide backup to the science NASA is investing in with New Horizons I; Broaden and deepen the science that can be accomplished by a single mission to this region of the solar system beyond the giant planets; And do so at significantly less cost than New Horizons I.

The first objective of New Horizons II is to provide important backup to the high priority science that New Horizons 1 was selected to collect.

We on the mission team for New Horizons are acutely aware that our tiny, relatively low cost spacecraft must travel over 9 years to cover the mind-boggling 5 billion kilometers between Earth and Pluto-Charon, and even farther to reach KBOs.

This journey is both farther and longer than any spacecraft ever has had to undertake to reach its primary target, and the risks inherent in sending a lone spacecraft on such a long journey have long been known.

NASA has protected against such risks in the past by building and flying a second spacecraft to ensure that a high priority mission has the best possible change to accomplish its objectives.

A two spacecraft strategy saved NASA�s first flyby missions to Mars and Venus, and NASA�s first Mars orbiter mission too.

The damaging impact of the Genesis mission onto the Utah desert just last month reiterated to many the need for backup spacecraft on high-profile and high-priority space exploration missions.

New Horizons II�s highest priority is to provide a prudent backup to the top-ranked science that NASA is investing in with New Horizons I.

Of course, sometimes when NASA flew two spacecraft on long and distant journeys, both spacecraft reached their targets successfully, as did both Voyagers, both Vikings, and this year�s stunning MER Mars rovers.

In each of those cases, a dramatic one-two punch was achieved for both exploration and science. Thus, if New Horizons I and II both succeed, then NASA and the United States will have achieved a far greater science return at a lower average cost per mission and mission target than one spacecraft alone could accomplish.

The most exciting candidate trajectory we have identified so far for New Horizons II takes it to the Kuiper Belt via a fast trajectory that involves both Jupiter and Uranus flybys on the way.

This exciting trajectory initiates its KBO flybys with a mammoth (400-to-500 km sized) Kuiper Belt binary called 1999 TC36. "TC36" is almost 10 times bigger than any KBO NH I can possibly reach after Pluto-Charon; even TC36�s satellite is more than twice as large as any KBOs NH I can target! After TC36, NH II would go on to explore one or two additional, smaller KBOs.

This trajectory would flyby a total of three or four KBOs, far more than the zero to one KBOs that can be reconnoitered by New Horizons I alone, owing to the well known power supply fueling problems New Horizons I has been saddled with.

The Senate specifically recognized this point and noted that New Horizons II is needed to satisfy the key goal of the Planetary Decadal Survey with regard to Kuiper Belt exploration�to sample the diversity of bodies in the Belt (e.g., big and small, with and without satellites, etc.).

New Horizons II�s Uranus 2014 flyby follow up to Voyager�s Uranus system explorations 30 years previously will be a stunning exploration accomplishment its own right�and again something only the United States can do.

Beyond bringing far more sophisticated remote sensing instruments and a dust detector to the Uranian system, New Horizons II can arrive near the time of Uranus�s equinox, a geometry that allows all of the Uranian system to be explored�something Voyager�s solstice arrival geometry of 1986 was denied.

The Uranian equinox opportunity that NH II can achieve in 2014 will not reoccur until almost 2050. It is no exaggeration to say that the timing of the NH II Uranus-KBO exploration combination is literally once in a lifetime.

Preliminary studies have shown that a second New Horizons mission can be built and launched for significantly less than New Horizons I�but only if the second craft is identical to the first, and only if it can be built on the heels of the first.

Otherwise, mundane but real issues including electronic parts availability, launch vehicle evolution, and inflation will defeat the anticipated savings.

The New Horizons II study funds called for by the U.S. Senate will allow the potential implementation of this mission to be evaluated technically and programmatically, in order to determine exactly how much savings can be achieved by leveraging on the investment already made in New Horizons I.

If the savings are substantial, and if the scientific and risk reduction benefits of New Horizons II justify the costs, mission development could be underway by 2006.

NASA Administrator O�Keefe likes to say that NASA�s job is to "Inspire, Innovate, and Discover," and he is right! By breaking down cost barriers and going where no one has gone before, New Horizons II offers to further the Agency�s exploration mission, inspire the public, and achieve breakthrough discoveries in an innovative, cost saving way.

Alan Stern is the Principal Investigator of NASA�s New Horizons mission, and a planetary scientist. He is an Executive Director of the Space Science and Engineering Division of the Southwest Research Institute; he lives and works in Boulder, Colorado. Related Links
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