Three Days to Pluto: Guiding New Horizons to the Solar System’s Ragged Edge (Part 1)

Artist's concept of the New Horizons spacecraft during its planned encounter with Pluto and its moon, Charon. Image Credit: NASA
Artist’s concept of the New Horizons spacecraft during its planned encounter with Pluto and its moon, Charon. Image Credit: NASA

After 9.5 years, 114 months, more than 490 weeks, and around 3,500 days since launch, NASA’s New Horizons mission is now into double-figure-hours as it initiates the final countdown toward a historic rendezvous on Tuesday, 14 July, with the dwarf world Pluto, its binary companion Charon, and a system of four tiny moons: Nix, Hydra, Kerberos, and Styx. Over the span of just shy of a full decade, New Horizons’ relatively calm and untroubled voyage to the outermost reaches of the Solar System has been juxtaposed by decidedly less calm and more troubled waters back on Earth, as our species has faced a range of challenges, from terrorism and warfare to natural disasters and economic catastrophe. In fact, New Horizons itself—or, at least, its destination—has not been immune to controversy, for Pluto was demoted in August 2006 from its lofty status as the last of the nine “traditional” planets in the Solar System to an object variously described as a dwarf, a trans-Neptunian object, a plutoid, and the largest-known body in the Kuiper Belt. Over the coming days, AmericaSpace’s New Horizons Tracker and a series of articles by Mike Killian, Leonidas Papadopoulos, and myself will cover the exploration of Pluto to date and the unfolding developments as New Horizons seeks to make this unknown world known.

As described in a recent AmericaSpace Pluto history article, the scientific desire to visit what was for three-quarters of a century considered the outermost planet in the Sun’s realm was a strong one. Since the discovery of a thin nitrogen atmosphere and the realization that this might freeze and “snow” onto the surface as Pluto’s highly eccentric orbit carried it farther from the Sun, after 1999, a mission to visit the unknown world remained acute. Early plans had called for Voyager 1 to fly past Pluto in the spring of 1986, following its exploration of Jupiter and Saturn. However, it was instead decided to utilize the spacecraft for close-range observations of Saturn’s rings and its the large moon, Titan, producing a trajectory which carried Voyager 1 northward out of the Solar System, “above” the plane of the ecliptic, and eventually into interstellar space.

This was a pity, for Voyager 1 would undoubtedly have discovered Nix, Hydra, Kerberos, and Styx decades before they were actually found. “Voyager 1 would have brought a magnetometer and a more diverse array of space plasma instruments to bear on Pluto than we will,” explained New Horizons Principal Investigator (PI) Alan Stern in a historical overview paper. “But it’s more important that New Horizons has much more advanced mapping cameras and a far more capable radio science experiment to determine atmospheric pressure and temperature. We also carry a dust impact detector. Voyager did not have such a device to study Pluto’s environment.”

Technicians working on the New Horizons spacecraft in the Payload Hazardous Servicing Facility (PHSF) at NASA's Kennedy Space Center (KSC) in Florida, ahead of its January 2006 launch.  Photo Credit: NASA/KSC
Technicians working on the New Horizons spacecraft in the Payload Hazardous Servicing Facility (PHSF) at NASA’s Kennedy Space Center (KSC) in Florida, ahead of its January 2006 launch. Photo Credit: NASA/KSC

The situation changed in the aftermath of Voyager 2’s spectacular August 1989 encounter with Neptune and, specifically, its large and cryovolcanically active moon, Triton, and by the early part of the following decade the first efforts to despatch a small flyby mission to Pluto began to gather pace. Sadly, both the Pluto Fast Flyby (PFF) and the Pluto Kuiper Express (PKE) were eventually canceled, due to steadily expanding budgets and other issues, but in November 2001—following a campaign by members of the scientific community and the general public—the New Horizons concept was selected for development, targeted initially for a December 2004 launch and expected to reach Pluto in July 2012. However, this was delayed until a four-week “launch window” extending from mid-January through mid-February 2006, producing a rendezvous with Pluto as soon as July 2015.

Aboard the baby-grand-piano-sized New Horizons, which weighed 1,040 pounds (470 kg), were a battery of highly advanced scientific instruments, many of which traced their heritage back to the PFF and PKE mission designs. The original Pluto Express Remote Sensing Investigation (PERSI) was split into two halves—the Alice ultraviolet imaging telescope to determine atmospheric constituents and the Ralph instrument, equipped with a visible-light Multispectral Visible Imaging Camera (MVIC) and the near-infrared Linear Etalon Imaging Spectral Array (LEISA)—which were combined with the Solar Wind at Pluto (SWAP), the Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI), the Radio Science Experiment (REX), and the monochromatic Long-Range Reconnaissance Imager (LORRI). Also aboard was the Student Dust Counter (SDC), later named in honor of Venetia Burney, the English schoolgirl who named Pluto in 1930.

The spacecraft arrived at the Kennedy Space Center (KSC) in Florida aboard a U.S. Air Force C-17 Globemaster III in September 2005, with launch targeted for the opening of a Jupiter Gravity Assist (JGA) window on 11 January 2006. Shortly before Christmas, New Horizons was transported to Space Launch Complex (SLC)-41 at Cape Canaveral Air Force Station for integration aboard its booster, the largest and most powerful variant of the Atlas V. Flying for the first time in its “551” configuration, the Atlas V was equipped with a 16-foot-diameter (5-meter) Payload Fairing (PLF), together with five strap-on rocket boosters and a single-engine Centaur upper stage. The combined impetus would despatch New Horizons onto an Earth-escape—and solar-escape—trajectory, with a relative velocity of 36,373 mph (58,536 km/h), thereby yielding the fastest departure velocity ever accomplished by a human-fashioned machine. Moreover, by launching before 3 February 2006, the spacecraft would also encounter Jupiter in early 2007 and pick up an enormous JGA “boost” to shave away a significant portion of its journey time, reaching Pluto in July 2015. Launching outside of the first half of the window would have significantly extended the journey time, by between 2-4 years.

The first Atlas V 551 launches on 18 January 2006, carrying NASA's New Horizons spacecraft. Photo Credit: NASA
The first Atlas V 551 launches on 18 January 2006, carrying NASA’s New Horizons spacecraft. Photo Credit: NASA

Borescope inspections of the 206-foot-tall (62.8-meter) Atlas V’s propellant tank forced a delay from the opening day of the window to No Earlier Than (NET) 17 January, followed by a 24-hour scrub, caused by higher-than-allowable ground-level winds at the launch site. At length, on the morning of the 18th, all seemed ready. At T-6 hours and 20 minutes, formal countdown operations got underway, with the activation of flight control systems. Fueled by a mixture of liquid oxygen and a highly refined form of rocket-grade kerosene (known as “RP-1”), the Common Core Booster (CCB) of the Atlas V 551 underwent cryogenic boil-off and required continuous replenishment until close to T-0. With all propellant tanks confirmed at flight levels, the Flight Termination System (FTS)—tasked with destroying the booster in the event of a major accident during ascent—was placed onto internal power and armed. Precisely on time, at 2 p.m. EDT, the ground-shaking rumble of the most powerful Atlas V booster ever to break the shackles of Earth echoed across the marshy Florida landscape.

“ … And liftoff of NASA’s New Horizons spacecraft,” came the call from the launch announcer, “on a decade-long voyage to visit the planet Pluto and then beyond.”

Powered uphill by the 860,000-pound (390,000-kg) impulse of its Russian-built RD-180 first-stage engine and the combined 1.7 million pounds (790,000 kg) of its five solid-fueled boosters, the vehicle executed a fast climb away from SLC-41, after which the avionics of the Centaur upper stage commanded a pitch, roll, and yaw program maneuver to establish it onto the proper flight azimuth to inject New Horizons into space.

Fifty-one seconds into the flight, ascending through partly cloudy skies, the vehicle passed into a period of maximum aerodynamic turbulence—nicknamed “Max Q”—on its airframe and throttled down the RD-180 engine to begin a nominal zero-pitch and zero-yaw angle of attack to minimize these loads. At T+110 seconds, now exhausted, two of the five strap-on boosters were jettisoned, followed by the others about 1.5 seconds later. A little over 3.5 minutes into the mission, with the RD-180 still burning hot and hard, the bulbous PLF was discarded. Booster Engine Cutoff (BECO) took place at T+267 seconds, after which the 41.5-foot-long (12.6-meter) Centaur and attached New Horizons separated. The next step was a pair of successful “burns,” the first of which delivered the spacecraft into an Earth-parking orbit of 101 x 132 miles (162 x 212 km), and the second of which pushed the Pluto-bound craft out of Earth orbit to kick-start its long voyage.

The next stage of its journey, just 13 months hence, was Jupiter.


The second part of this article will appear tomorrow.



Stay with AmericaSpace for regular updates and LIVE COVERAGE of New Horizons’ approach and flyby of the Pluto system.


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