Everything has to come to an end eventually—as the saying goes—and that has certainly been true for New Horizons’ long, interplanetary cruise. Following an epic journey of almost nine years through the entire Solar System—most of which had been spent in quiet hibernation—the intrepid spacecraft was finally awakened for the last time earlier this week, in order to prepare for its historic, much-anticipated flyby of Pluto in July 2015.
As detailed in a previous AmericaSpace article, sleep time has been a familiar state of affairs for the New Horizons mission. Out of the total 3,244 days that have elapsed to date since it was launched back in January 2006, the spacecraft has spent 1,873 of them (about 66 percent of its time) in hibernation mode. Throughout this time, the spacecraft’s routine had been to mostly broadcast a weekly beacon-status tone back to Earth while quietly passing the orbits of the outer gas giant planets. A set of preloaded command sequences onboard New Horizons briefly awakened the spacecraft only twice a year for short periods of activity called Active Check Outs, or OCOs, which ranged from 36 days to 202 days long and were meant for navigation correction and overall maintenance purposes. The New Horizons mission in particular has been the first to implement these extensive hibernation periods, allowing ground teams to greatly reduce wear and tear on the spacecraft’s instruments and subsystems, while also helping to significantly lower the mission’s operations costs.
Now, an automated command sequence onboard New Horizons, which had been beamed from Earth earlier this summer, brought the spacecraft out of hibernation for the last time. The preloaded wake-up sequence, which was executed at 3 p.m. EST (8 p.m. UCT) on Dec. 6, powered up all of New Horizon’s instruments and subsystems in succession, switching them to active operations mode. Approximately 90 minutes later the spacecraft, while at a distance of 162 million km from Pluto, transmitted a signal back to Earth in order to inform everyone at the mission’s control center at the Johns Hopkins University Applied Physics Laboratory (JHU/APL) in Laurel, Md., that it had successfully transited out of hibernation. Nevertheless, more than four hours would have to pass before the signal, while traversing at the speed of light the 5 billion km that separate Earth and Pluto, could be picked up by the ground stations of NASA’s Deep Space Network. Like clockwork, the much-anticipated signal was eventually received by DSN’s 70-m antenna in Canberra, Australia, much to the delight of the mission’s science and engineering teams. “It’s ALIVE! The @NASANewHorizons mission control just received full confirmation at 9:53 p.m ET! Pluto get ready!” posted NASA on its Twitter account, in the early morning hours on Dec. 7.
New Horizons’ final transition out of hibernation marks the latest major milestone on a decade’s worth of efforts by NASA and the planetary science community to explore Pluto and the vast, uncharted territory of the Kuiper Belt which lays beyond. As Pluto approached perihelion in 1989, many proposals calling for a dedicated mission to the-then ninth 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. A coordinated lobbying campaign by the planetary science ultimately led Congress to reverse this decision and re-authorize NASA to continue development of a Pluto-dedicated mission. It was out of this campaigning effort that the $650-million New Horizons mission arose, as the first one in the agency’s “New Frontiers” series of medium-class planetary exploration missions, which is now literally at the doorstep of the Pluto system. “This is a watershed event that signals the end of New Horizons crossing of a vast ocean of space to the very frontier of our Solar System, and the beginning of the mission’s primary objective: the exploration of Pluto and its many moons in 2015,” said in a statement Dr. Alan Stern, principal investigator for the New Horizons mission at the Southwest Research Institute, in Boulder, Colo.
The mission’s science and engineering teams will now 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.
Even though New Horizons’ long-awaited closest approach to Pluto will take place on 14 July 2015, its science mission will begin in earnest a full six months earlier, on Jan. 15, 2015. This six-month-long approach to the mysterious dwarf planet is further divided into several smaller “approach phases,” during which three optical imaging navigation campaigns will take place, in addition to a previous one that was conducted during the spacecraft’s penultimate wake-up period earlier this summer. These optical navigation campaigns are meant to provide mission planners with much-needed critical data that will help them to reduce any uncertainties in Pluto’s current mass and orbit estimates and allow for the calculation of the proper trajectories for the spacecraft in order for it to correctly pass through the Pluto system as envisioned. “The New Horizons spacecraft will encounter Pluto and its satellites in July 2015,” write the mission’s navigation teams in a study at the California Institute of Technology. “As was the case for the Voyager encounters with Jupiter, Saturn, Uranus and Neptune, mission success will depend heavily on accurate spacecraft navigation, and accurate navigation will be impossible without the use of pictures of the Pluto system taken by the onboard cameras.”
The first of the upcoming optical navigation campaigns will be undertaken between Jan. 25 and Mar. 6 with the help of New Horizons’ Long-Range Reconnaissance Imager, or LORRI, which will be taking pairs of five images of both Pluto and three of it moons—Charon, Nyx, and Hydra—every 12 and 48 hours respectively. During that time, the spacecraft will be taking measurements in order to characterize the background interplanetary dust and particle environment in the vicinity of Pluto as well. The second optical navigation campaign, which will take place between April 5 and May 15 with the Multi-spectral Visual Imaging Camera, or MVIC, of the Ralph Visible and infrared imager/spectrometer instrument as a backup to LORRI, will start to provide images of the Pluto system with a resolution that will exceed those taken with the Hubble Space Telescope. Consequently, the third campaign, scheduled for the period between May 28 and July 16, will provide an imaging resolution that will be steadily increasing until the day of closest approach when New Horizons will be able to take images of Pluto with a resolution of 0.1 km per pixel as it approaches the dwarf planet at a distance of approximately 13,000 km from its surface.
Even though the offering of presents during the holiday season is usually concentrated to our loved ones and a specific few of our acquaintances around the days of Christmas and the New Year, the New Horizons mission will nevertheless be offering treats to everyone on Earth from mid-January and throughout most of 2015, in the form of a continuous stream of magnificent, never-before-seen vistas of unexplored worlds in the outer reaches of the Solar System. “New Horizons is on a journey to a new class of planets we’ve never seen, in a place we’ve never been before,” says Hal Weaver, project scientist for New Horizons at APL. “For decades we thought Pluto was this odd little body on the planetary outskirts; now we know it’s really a gateway to an entire region of new worlds in the Kuiper Belt, and New Horizons is going to provide the first close-up look at them.”
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