Nine years ago this week, one of the longest and most historic missions ever in the annals of planetary exploration began, with the launch of NASA’s New Horizons spacecraft towards one of the last unexplored destinations in the Solar System that haven’t been witnessed still by human eyes. Today, more than 5 billion kilometers away from home, the small piano-sized robotic spacecraft has finally began its much-anticipated long-range reconnaissance of Pluto, while approaching ever closer to the mysterious dwarf planet, marking the official start of humanity’s first close-up study of one of the largest planetary bodies in the expansive Kuiper Belt that dominates the outer Solar System.
The New Horizons mission represents the culmination of decades worth of efforts by NASA and the planetary science community to explore this completely unknown part of the Sun’s planetary family. Going back to the days of the space agency’s Voyager Grand Tour of the 1970s and ’80s, scientists and engineers had briefly considered at the time sending Voyager 1 toward Pluto following its encounter with Saturn in 1980. Yet, doing so would mean putting the spacecraft toward a trajectory that would prohibit a close examination of Titan, and Saturn’s largest and more intriguing moon was eventually chosen instead, as it represented a more interesting scientific target. As Pluto was approaching perihelion in 1989, many proposals calling for a dedicated mission to the distant dwarf planet were sent to NASA, with none of them ever advancing beyond the mission concept phase. One of them, the Pluto Kuiper Express, held much potential of being realised in the 1990s, but the space agency eventually cancelled the mission in 2000, reacting to a series of cost overruns and budget cuts imposed by the White House at the time. An intense lobbying campaign on Congress that was coordinated by the planetary science community, led to a re-authorisation by the Senate which allowed NASA to continue with a Pluto-dedicated mission. It was out of this campaigning effort that New Horizons arose, as the first of a New Frontiers-class of missions, with a cost of $650 million throughout its operational cycle.
Launched on 19 January 2006 from Cape Canaveral on board a United Launch Alliance Atlas V 551 rocket, New Horizons was placed into a direct Sun-escape trajectory toward Pluto, while setting a new record as the fastest man-made object to ever leave our planet, with an Earth-relative speed of 58,536 km/h. Indicative of the spacecraft’s breakneck velocity was the fact that it sped past the Moon’s orbit in just under nine hours and reached Jupiter in just over a year later in February 2007, for a scheduled crucial gravity assist which put it in its final course toward its rendezvous with Pluto. Ever since the Jupiter flyby, New Horizons has spent most of its time since in hibernation while quietly passing the orbit of Saturn in June 2008, Uranus in March 2011, and Neptune in August 2014, exactly 25 years to the day after another one of humanity’s robotic emissaries to the stars, Voyager 2, had flown by Neptune during the culmination of its planetary Grand Tour of the outer Solar System.
As reported in a past AmericaSpace article, New Horizons was finally awakened from its electronic hibernation for the last time on Dec. 6, 2014, following its long, silent cruise through interplanetary space, in order to allow the mission’s science and engineering teams to prepare the spacecraft for its upcoming rendezvous with Pluto. Since that final wake-up call, New Horizons underwent a rigorous and comprehensive health-check, so that ground controllers could ensure that all of the spacecraft’s science instruments and mechanical subsystems were operating normally, while they uploaded to its onboard computers the entire suite of command sequences that it will carry out during the following months throughout its approach, encounter and departure from the Pluto system. These critical pre-encounter preparations were successfully completed on Jan. 15, marking the official start of the mission’s long-range reconnaissance of Pluto and its menagerie of five known moons, while the spacecraft was approximately 225 million kilometers away, or 1.5 times the Earth-Sun distance. “We’ve completed the longest journey any craft has flown from Earth to reach its primary target, and we are ready to begin exploring!” said Dr. Alan Stern, Principal Investigator for New Horizons at the Southwest Research Institute in Boulder, Colo.
New Horizon’s approach towards Pluto has been divided by the mission’s science team into several smaller phases. The first one, called Approach Phase 1, which lasts from Jan. 15 to Apr. 4, will be partly devoted to science measurements of the background interplanetary dust environment in the vicinity of the Pluto system and the high-energy particle population coming from the Sun. More importantly, New Horizons will undertake during that time, an optical navigation campaign in order for ground controllers to determine Pluto’s exact position against the fixed background stars. This will help them to maintain the spacecraft’s proper course towards Pluto and allow for the correction of any deviations in its pre-programmed trajectory. The optical navigation campaign is one of the most critical parts of New Horizons’ approach phase operations, without which the spacecraft would face the risk of veering off course and lose Pluto by thousands of kilometers, during its scheduled close passage of the dwarf planet in July. “We need to refine our knowledge of where Pluto will be when New Horizons flies past it,” says Mark Holdridge, Encounter Mission Manager for New Horizons, at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. “The flyby timing also has to be exact, because the computer commands that will orient the spacecraft and point the science instruments are based on precisely knowing the time we pass Pluto – which these images will help us determine.”
Despite its great scientific and navigational importance of Approach Phase 1, New Horizons will not be returning any detailed images of Pluto during that time. At the spacecraft’s current location, the small dwarf planet occupies no more than a couple of pixels of the cameras onboard New Horizons, making any surface details hardly discernible at all. Scientists and the public alike will have to wait for the start of Approach Phase 2 on Apr. 4, to have their first detailed views of Pluto’s topography. By that time, New Horizons will be half its current distance away from the distant planet, and the images it will be returning will only be getting better with each passing day, eventually surpassing those returned from the Hubble Space Telescope by mid-May. These images will allow scientists to clearly discern the color variations on Pluto’s surface, helping to shed more light to its chemical composition, and even possibly detect any hidden moons and rings that might be circling the planet as well. By Approach Phase 3 which will begin on Jun. 23, when New Horizons will be approximately 20 million kilometers away from Pluto, it will be returning images of such clarity, that will allow scientists to study the atmospheric structures of Pluto and Charon and create the first ever detailed global maps of their surfaces. The imaging resolution will continue to increase steadily with each passing day, until the time of closest approach on July 14, when New Horizons will be able to take images of Pluto’s surface with a resolution of 0.1 km per pixel. “At closest approach to Pluto – about 10,000 km up – the onboard Long-Range Reconnaissance Imager can resolve details almost as well as a spy camera,” says Stern. “The view will be incredible. If we flew this instrument over Earth at that altitude, we could see individual buildings and their shapes.”
Yet, the time of closest approach will not mark the end of the mission’s reconnaissance of Pluto. Following its flyover of the distant planet’s surface in July, New Horizons will be positioned in such a way that it will be able to observe Pluto occult the distant Sun, allowing scientists to study the planet’s night-time surface and atmospheric temperatures, and search for any additional rings. New Horizon’s departure from the Pluto system is also divided into three phases that span the remainder of the year from July to December, during which the spacecraft will conduct remote sensing of Pluto’s moons until it reaches the limits of its imaging systems’ resolution, as it will gradually recede away. From then on, New horizons will delve deeper into the Kuiper Belt, awaiting NASA’s evaluation for a possible extended mission within the 2018-2019 timeframe, that will see it passing by at least one of the Kuiper Belt objects that the Hubble Space Telescope has discovered along the spacecraft’s trajectory out of the Solar System. Regardless of the prospects for these future ventures into the Kuiper Belt however, New Horizon’s upcoming close flyby of Pluto, makes 2015 the year of the dwarf planets, with NASA’s Dawn mission being well on its way for its rendezvous with Ceres this April, in the asteroid belt between Mars and Jupiter.
Despite their classification, dwarf planets will be the center of everyone’s attention this year, while the discoveries that will come out from their detailed study will be anything but minor.
Video Credit: NASA/JHUAPL
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