They say that practice makes perfect, and the New Horizons mission has had much time in its hands to do just that. After more than eight years of silently cruising through the entirety of the Solar System toward its ultimate destination, the intrepid spacecraft is almost there: Currently located just over 1.5 times the Earth-Sun distance away from mysterious Pluto, New Horizons is set to come out of hibernation for the very last time three weeks from now, prior to the start of its historic encounter operations in January 2015 with this distant world in the outer reaches of the Solar System.
Staying true to the nature of its mythological namesake, Pluto is a mysterious planet which is currently holding the keys to the Solar System’s gates of the unknown, beyond which lies a vast expanse we know very little about. In large part due to its great distance from the Sun, which on average is approximately 5.8 billion km, Pluto is the only planetary body from the Solar System’s total real estate that has never been examined up close by any visiting spacecraft during the 50-year history of planetary exploration, thus essentially remaining remote and exotic, ever since it was discovered by American astronomer Clyde Tombaugh in 1930. The revolutionary discovery since the early 1990s of thousands of minor icy planetary bodies beyond the orbit of Neptune, known as Kuiper Belt Objects, or KBOs, revealed the existence of a previously unknown third region of the Solar System beyond those of the terrestrial and gas giant planets—that of the Kuiper Belt, which comprises a completely uncharted territory of Solar System real estate. This finding also proved to be the important catalyst which prompted the U.S. National Research Council to ultimately propose a dedicated mission concept to the Pluto system in the early 2000s as the highest priority for the then-upcoming 2003-2013 Planetary Science Decadal Survey, resulting to the New Horizons mission finally been selected for implementation by NASA in November 2001, representing the culmination of decades’ worth of efforts by the space agency and the planetary science community alike for the exploration of Pluto and the vast expanses of the Kuiper Belt in the outer regions of the Solar System.
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. 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. Throughout its long interplanetary cruise, New Horizons was nevertheless briefly reawakened each year during short periods of activity, called Active Check Outs, in order for the mission’s science team to check on the spacecraft’s overall health, calibrate its science instruments, upload new commands to its onboard computer, and update its navigation star charts. The latter in particular was of utmost importance, allowing ground controllers to adjust for any trajectory errors that could otherwise lead the spacecraft off course during its journey through the Solar System.
Now, more than eight years after launch and almost 5 billion km away from home, New Horizons is set to come out of hibernation for the very last time. This final wake-up call, which represents the last step prior to the long-awaited start of the Pluto encounter operations, will occur three weeks from now, at 3 p.m. EST (8 p.m. UCT) on Dec. 6, when a preloaded command sequence on New Horizon’s onboard computer will start the spacecraft’s transition out of hibernation mode. This is expected to be completed approximately 1.5 hours later, at 4:37 p.m. (9:37 p.m. UCT), by which time New Horizons will transmit a signal toward Earth in order to inform ground controllers that it has safely emerged from its month-long slumber. Yet, due to the vast distances between Earth and Pluto, everyone back on Earth will have to wait another 4 hours and 25 minutes before the signal, while travelling through interplanetary space at the speed of light, can be received by the mission’s control center at the Johns Hopkins University Applied Physics Laboratory (JHU/APL) in Laurel, Md. Provided that everything goes according to plan, by 9:30 p.m. EST (02:30 a.m UCT on December 7) ground teams will then be ready to begin the mission’s dress rehearsal for the much-anticipated start of the Pluto encounter operations. “New Horizons is healthy and cruising quietly through deep space – nearly three billion miles from home – but its rest is nearly over,” says Alice Bowman, the mission’s operations manager at APL. “It’s time for New Horizons to wake up, get to work, and start making history.”
Following these wake-up activities, the mission’s science and engineering teams will spend the next six weeks conducting a thorough and comprehensive set of checks on the spacecraft’s entire instrument and subsystems arrays, including its primary and backup 10-gigabit memory recorders which will be responsible for storing the vast amounts of science data that New Horizons will collect throughout the entire Pluto encounter timeline, as well as updating the onboard navigation star charts with the latest data that had been collected earlier this summer. The mission’s ground teams will undergo similar preparation routines as well, in order to ensure that they are properly receiving New Horizons’ engineering and navigation data, as well as reviewing and validating the command sequences that will safely guide the spacecraft throughout its approach and encounter with Pluto and beyond. These operational readiness tests have also been conducted multiple times in the past, during the mission’s long hibernation periods, allowing ground teams to better ensure that when the time for the show comes, everything will go by the book. “We’ve worked years to prepare for this moment,” says Mark Holdridge, New Horizons encounter mission manager at APL. “New Horizons might have spent most of its cruise time across nearly three billion miles of space sleeping, but our team has done anything but, conducting a flawless flight past Jupiter just a year after launch, putting the spacecraft through annual workouts, plotting out each step of the Pluto flyby and even practicing the entire Pluto encounter on the spacecraft. We are ready to go.”
The end of this six-week operational readiness review period will officially mark the start of the Pluto encounter operations, which are set to begin in 15 January 2015. From then on, every passing day is bound to be much more exciting than the previous one, as New Horizons will approach ever closer to Pluto for its scheduled close flyby with the distant world in July. “This is much more than a single day,” commented Dr. Hal Weaver, project scientist for New Horizons at APL, during a press conference on November 13 at the 46th annual meeting of the American Astronomical Society’s Division for Planetary Sciences in Tucson, Ariz. “Of course, July 14th, 2015, is the day when we’ll reach the closest approach point to Pluto and most of our best results will come from a few days around that time period, but I really want to emphasize that we’ll have lots of juicy, historic science accumulated well before the day of closest approach … 2015 is the year of the Pluto encounter.”
The approach phase itself has been divided by the mission’s science team into several smaller periods. Following the start of the encounter operations on Jan. 15, New Horizons will be mostly taking optical navigations images of Pluto in order to ensure that the spacecraft is maintaining its correct trajectory, as well as taking measurements of the background interplanetary dust and particle environment. The images of Pluto that New Horizons will be returning by mid-April will have a resolution that will exceed those taken with the Hubble Space Telescope, while the imaging resolution will be steadily increasing with each passing day, until the day of closest approach when New Horizons will be able to take images of Pluto’s surface with a resolution of 0.1 km per pixel.
Throughout this time, New Horizons will provide humanity with its first-ever close-up images and data of the Solar System’s last unexplored frontier, beaming back photographs of vistas never before seen from the surfaces of Pluto and its moons Charon, Nix, Hydra, Kerberos, and Styx, with the help of its science payload which includes the following instruments:
Ralph: Visible and infrared imager/spectrometer; provides color, composition and thermal maps.
Alice: Ultraviolet imaging spectrometer; analyzes composition and structure of Pluto’s atmosphere and looks for atmospheres around Charon and Kuiper Belt Objects (KBOs).
REX: (Radio Science EXperiment) Measures atmospheric composition and temperature; passive radiometer.
LORRI: (Long Range Reconnaissance Imager) telescopic camera; obtains encounter data at long distances, maps Pluto’s far side and provides high-resolution geologic data.
SWAP: (Solar Wind Around Pluto) Solar wind and plasma spectrometer; measures atmospheric “escape rate” and observes Pluto’s interaction with solar wind.
PEPSSI: (Pluto Energetic Particle Spectrometer Science Investigation) Energetic particle spectrometer; measures the composition and density of plasma (ions) escaping from Pluto’s atmosphere.
SDC: (Student Dust Counter) Built and operated by students; measures the space dust peppering New Horizons during its voyage across the solar system.
The journey farther into the Kuiper Belt following the closest approach with Pluto had been characterized by great uncertainty, due to the fact that the mission’s science team had been unable after many years of searching with some of the biggest ground-based telescopes, to locate a suitable KBO that laid close enough to New Horizons’ path for the spacecraft to visit. Nevertheless, an intensive observing campaign that was conducted earlier this year utilizing the superior capabilities of the Hubble Space Telescope, successfully identified, to the scientists’ great relief, three small potential KBO targets between 20 and 55 km across which fall well within the spacecraft’s outward trajectory, without posing any prohibiting fuel requirements for course trajectory corrections. “We started to get worried that we could not find anything suitable, even with Hubble, but in the end the space telescope came to the rescue,” says John Spencer, science team member at the Southwest Research Institute, in Boulder, Colo. “There was a huge sigh of relief when we found suitable KBOs; we are ‘over the moon’ about this detection.” Nevertheless, much work remains until the mission’s science team finally selects the most suitable KBO that will ultimately comprise New Horizons’ next stop beyond Pluto, around the 2018-2019 timeframe.
In the meantime, following its epic trek through most of the Solar System, New Horizons is currently located at the doorsteps of the planetary god of the Underworld, ready to open the gates to unimagined vistas of new knowledge, turning the last unexplored major planetary body in the Solar System from a blurred image into a real world. “From my standpoint, this is a Christmas present sitting under the tree, that’s been waiting while we sped across the Solar System to unwrap it,” said Dr. Alan Stern, principal investigator for New Horizons at the Southwest Research Institute., during the AAS press conference. “And we’re so looking forward to turning this very fuzzy little picture of this very distant and small planet into something real and to do it by taking the world along as a part of that.”
With the coming of the New Year, all of humanity will have the opportunity to finally unwrap a present, courtesy of the New Horizons mission, which will reveal an entire new world in the furthest reaches of the Solar System, for the first time in history for everyone to witness.
What a priceless present that will be!
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