New Horizons

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This article is about the space probe. For other uses, see New Horizons (disambiguation).
New Horizons
New Horizons Transparent.png
The New Horizons space probe
Mission type Pluto flyby
Operator NASA
COSPAR ID 2006-001A
SATCAT № 28928
Website pluto.jhuapl.edu
www.nasa.gov
Mission duration Primary mission: 9.5 years
Spacecraft properties
Manufacturer APL · Southwest Research Institute
Launch mass 478 kilograms (1,054 lb)
Power 228 watts
Start of mission
Launch date January 19, 2006 (2006-01-19) 19:00 UTC
(9 years, 6 months and 9 days ago)
Rocket Atlas V 551
Launch site Cape Canaveral SLC-41
Contractor International Launch Services
Flyby of Moon
Closest approach January 20, 2006 (2006-01-20) 04:00 UTC
(9 years, 6 months and 8 days ago)
Distance 189,916 km (118,008 mi)
Flyby of (132524) APL (incidental)
Closest approach June 13, 2006 (2006-06-13) 04:05 UTC
(9 years, 1 month and 15 days ago)
Distance 101,867 km (63,297 mi)
Flyby of Jupiter (Gravity assist)
Closest approach February 28, 2007 (2007-02-28) 05:43:40 UTC
(8 years and 5 months ago)
Distance 2,300,000 km (1,400,000 mi)
Flyby of Pluto
Closest approach July 14, 2015 (2015-07-14) 11:49:57 UTC
(14 days ago)
Distance 12,500 km (7,800 mi)
New Horizons - Logo2 big.png

New Horizons is an interplanetary space probe that was launched as part of NASA's New Frontiers program.[1] Engineered by the Johns Hopkins University Applied Physics Laboratory (APL) and the Southwest Research Institute (SwRI), with a team led by S. Alan Stern, the spacecraft was launched to study Pluto, its moons and the Kuiper belt, performing flybys of the Pluto system and one or more other Kuiper belt objects (KBOs).[2][3][4][5]

New Horizons is the result of many years of work on missions to send a spacecraft to Pluto, starting in 1990 with Pluto 350, with Alan Stern and Fran Bagenal of the "Pluto Underground", and in 1992 with the Jet Propulsion Laboratory's Pluto Fast Flyby; the latter inspired by a USPS stamp that branded Pluto as "Not Yet Explored". The ambitious mission aimed to send a lightweight, cost-effective spacecraft to Pluto, later evolving into a Kuiper belt object mission named Pluto Kuiper Express. However, because of underwhelming support from NASA and growing projected cost, the project was eventually cancelled altogether in 2000.

Following backlash from the cancellation, the New Frontiers program was established for missions that fit in between the big budgets of the Flagship Program and the low budgets of the Discovery Program. The Applied Physics Laboratory, with a team consisting of former Pluto Kuiper Express team members, won a competition to fund their New Horizons project, based on work left off from Pluto Kuiper Express, under the New Frontiers program. However, funding for the mission was not secured until after a financial standoff between the team and then-NASA Administrator Sean O'Keefe. After three years of construction, and several delays at the launch site, New Horizons was launched on January 19, 2006, from Cape Canaveral, directly into an Earth-and-solar-escape trajectory with an Earth-relative speed of about 16.26 kilometers per second (58,536 km/h; 36,373 mph); it set the record for the highest launch speed of a human-made object from Earth.

After a brief encounter with asteroid 132524 APL, New Horizons proceeded to Jupiter, making its closest approach on February 28, 2007, at a distance of 2.3 million kilometers (1.4 million miles). The Jupiter flyby provided a gravity assist that increased New Horizons‍ '​ speed by 4 km/s (14,000 km/h; 9,000 mph). The encounter was also used as a general test of New Horizons‍ '​ scientific capabilities, returning data about the planet's atmosphere, moons, and magnetosphere. Most of the post-Jupiter voyage was spent in hibernation mode to preserve on-board systems, except for brief annual checkouts.[6] On December 6, 2014, New Horizons was brought back online for the Pluto encounter, and instrument check-out began.[7] On January 15, 2015, the New Horizons spacecraft began its approach phase to Pluto. On July 14, 2015 11:49 UTC (07:49 EDT), it flew 12,500 km (7,800 mi) above the surface of Pluto,[8][9] making it the first spacecraft to explore the dwarf planet.[5][10] Thirteen hours later at 00:52:37 UTC (20:52:37 EDT)[11] NASA received the first communication from the probe following a flyby at the time expected. Engineering data indicated that the flyby was successful and the probe operated in all respects as expected.[12][13][14]

Contents

History[edit]

Exploring Pluto was contemplated since its discovery by Clyde Tombaugh in 1930. One of many possibilities for the Voyager 1 spacecraft after its flyby of Saturn in 1980 was to use Saturn as a slingshot towards Pluto for a flyby as early as March 1986.[15] However, scientists on the Voyager program decided that a flyby of Titan during the Saturn encounter would be a more important scientific objective. A flyby of Pluto was impossible, as not only did the spacecraft make a close approach of Titan, it was also on a trajectory that slingshot the spacecraft upwards out of the ecliptic.[16] Because no mission to Pluto was planned by any space agency at the time, it would be left unexplored by interplanetary spacecraft for years to come. Shortly after Voyager 2‍ '​s flyby of Neptune and its findings at Triton in August 1989, scientists sought interest in a mission to Pluto and further studies for the existence of a Kuiper belt and Kuiper belt objects, potentially similar to Triton.[17]

The Pluto Underground, Pluto 350 and Mariner Mark II[edit]

One of the many early concepts for a mission to Pluto was to send a Mariner Mark II spacecraft. The idea would later be ruled out in favour of a smaller, less expensive spacecraft similar to the Pluto 350 concept.

In May 1989, a group of scientists and engineers, including Alan Stern and Fran Bagenal, formed an alliance called the "Pluto Underground". It was named in homage of the Mars Underground, another group of scientists that successfully lobbied for the restart of missions to Mars, following the lack of such since the Viking program. The group started a letter writing campaign which aimed to bring to attention Pluto as a viable target for exploration.[18] In 1990, because of pressure from the scientific community, including those of the Pluto Underground, engineers at NASA decided to look into concepts for a mission to Pluto. At the time, it was thought that the atmosphere of Pluto would freeze and fall to the surface during winter, and so a lightweight spacecraft was desirable, as it would be able to reach Pluto before such an event would occur. One of the earliest concepts was for a 40-kilogram spacecraft that would reach Pluto in 5 to 6 years. The idea was shortly scrapped, however, because of the infeasibility of miniaturizing scientific instruments aboard such a spacecraft to that size.[19]

Another mission concept, known as Pluto 350, was developed by Robert Farquhar of the Goddard Space Flight Center, with Alan Stern and Fran Bagenal of the Pluto Underground, who both served as study scientists for the project. Pluto 350 aimed to send a spacecraft, weighing 350 kilograms, to Pluto.[17] The spacecraft's minimalistic design was so to allow it to travel faster and be more cost-effective, in-contrast to most other big-budget projects NASA were developing at the time, such as Galileo and Cassini. Pluto 350, however, would later become controversial among mission planners at NASA, who considered the project to be too small and too high-risk. An alternate plan which was considered at one point was to send to Pluto a configuration of the Mariner Mark II spacecraft, which would weigh 2,000 kilograms and cost US$3.2 billion, in sharp contrast to Pluto 350‍‍ '​‍s $543 million cost.[19] While both projects competed for approval, Pluto 350 was more favored by NASA mission planners, who were starting to adopt smaller missions such as Mars Pathfinder and NEAR Shoemaker.[17]

USPS postage stamp and Pluto Fast Flyby[edit]

Main article: Pluto Fast Flyby
The infamous "Not Yet Explored" USPS stamp that inspired scientists to research into and lobby for a mission to Pluto.

For many years, people had waved that stamp around as sort of a call to arms, as a motivating graphic: "Not yet explored". That stamp had been in so many presentations by that point, I knew it would please people to have it go along.

S. Alan Stern on the USPS stamp[19]

In October 1991, the United States Postal Service released a series of stamps commemorating NASA's exploration of the Solar System.[20] The series featured a stamp for all planets, displaying an image of the planet and highlighting an associated spacecraft which was sent to it. The stamp for Pluto, however, depicted a featureless sphere, presented with the phrase "not yet explored" in place of the name of a spacecraft. The stamps were unveiled in a ceremony at the Jet Propulsion Laboratory. Two scientists who attended the event, World Space Foundation president Robert Staehle and JPL scientist Stacy Weinstein, were inspired by Pluto's status on the stamp; such that they started to inquire about the feasibility of sending a spacecraft to Pluto.[21][22] Engineers at the Jet Propulsion Laboratory, inspired by the "Not Yet Explored" status of Pluto, also started to put forward ideas about a mission to Pluto.[23][24]

In 1992, Staehle, with the help of JPL engineers and students from the California Institute of Technology, formed the Pluto Fast Flyby project. The mission heralded the same ideology as the Pluto 350 concept: small in size and cost-effective in scope, so that the spacecraft would be able to get to Pluto faster and be affordable to develop and launch. Described as a "radical" mission concept, the mission would see two spacecraft being sent to Pluto. Both spacecraft were to weigh only around 35-50 kilograms each (including 7 kg worth of scientific instruments), and the project would cost less than US$500 million to develop, excluding launch costs.[21] Described by Staehle as a "faster, better, [and] cheaper" approach than the Pluto 350 and Mariner Mark II projects, it caught the attention of then-NASA Administrator Daniel S. Goldin, who ordered all work on both Pluto 350 and Mariner Mark II to cease and shift all resources to the new Pluto Fast Flyby project instead.[17]

During the development of Pluto Fast Flyby, however, there were multiple concerns from both NASA, Administrator Goldin and the mission's development team. As research and development into the mission progressed, the project's size, scope, and budget all expanded. Additionally, morale among the team and personnel working on interplanetary missions was low following the loss of the Mars Observer spacecraft during its attempted Areocentric orbit insertion in August 1993. Alan Stern would later cite that event as a significant factor towards the low enthusiasm for the Pluto Fast Flyby project.[19] The launch of the spacecraft were intended to be performed using Titan IV rockets, which would have cost US$400 million each, thus raising the budget to over US$1 billion.[17] Because of growing budget constraints, the dual-spacecraft concept was scrapped in favor of sending a singular spacecraft to Pluto. The project was still too expensive, however, in the eyes of Administrator Goldin.[19] Alan Stern, as a compromise, reached an agreement with Russian Space Research Institute scientists in Moscow, in which Pluto Fast Flyby would be launched atop a Proton rocket, saving NASA over US$400 million in launch costs. The proposal was forwarded to Administrator Goldin, but he vetoed the proposal, recommending instead that the JPL look into the feasibility of Pluto Fast Flyby being launched aboard a smaller rocket, such as the Delta II.[17]

Kuiper belt, Pluto Kuiper Express and cancellation[edit]

Main article: Pluto Kuiper Express
Concept art for the Pluto Kuiper Express mission; the last iteration of the original Pluto mission concepts, eventually cancelled in 2000.

During the course of the late 1990s, a number of Trans-Neptunian objects were discovered, confirming the existence of a Kuiper belt. Interest in a mission to the Kuiper belt arose to such that NASA instructed the JPL to re-purpose the mission as not only a Pluto flyby, but also a Kuiper belt object (KBO) flyby. The mission was thus re-branded the Pluto Kuiper Express, after briefly being billed as Pluto Express prior to the revision of the mission. The weight of the spacecraft was raised again, this time to 175 kilograms, and NASA allowed further liberty with the project's budget.[17] However, it was later decided by Goldin that Pluto Kuiper Express was of low importance, and thus cut funding to the project drastically. Eventually, despite official selection of scientific instruments and the appointment of several investigators, then-Science Mission Directorate Edward J. Weiler ordered the cancellation of the entire Pluto and Kuiper belt mission in 2000, citing growing budget constraints, which had plagued the project since its inception in 1992. At the time of cancellation, the projected costs surpassed $1 billion.[19][25]

Alan Stern and New Horizons[edit]

Main article: New Frontiers program
Early concept art of the New Horizons spacecraft. The mission, led by the Applied Physics Laboratory and S. Alan Stern, would become the first mission to Pluto successfully funded and launched, after years of delays and cancellations.

The cancellation of Pluto Kuiper Express angered most of the scientific community, which led to most groups, such as The Planetary Society, lobbying NASA for a reboot of Pluto Kuiper Express or, at the very least, a restart of a mission to Pluto. Internal divisions within NASA, including its Scientific Advisory Council, also voiced support for a Pluto mission.[19] In response to the backlash caused by the cancellation of Pluto Kuiper Express, Weiler decided to inaugurate a new class of missions that would fit between the big-budget Flagship Program and the low-budget Discovery Program, creating a compromise for missions such as the former Pluto Kuiper Express, which proved to be too expensive for the Discovery Program. A competition was held, in which NASA would select a mission concept to fund as part of the first mission of the New Frontiers program.[25]

Stamatios “Tom” Krimigis, head of the Applied Physics Laboratory's space division, one of many entrants in the New Frontiers Program competition, formed the New Horizons team with Alan Stern in December 2000. Appointed as the project's principal investigator, Stern was described by Krimigis as "the personification of the Pluto mission".[25] New Horizons was based largely on Stern's work since Pluto 350 and involved most of the team from Pluto Kuiper Express.[17] The New Horizons proposal was one of five that were officially submitted to NASA. It was later selected as one of two finalists to be subject to a three-month concept study, in June 2001. The other finalist, POSSE (Pluto and Outer Solar System Explorer), was a separate, but similar Pluto mission concept by the University of Colorado Boulder, led by principal investigator Larry W. Esposito, and supported by the JPL, Lockheed Martin and the University of California.[26] However, the APL, in addition to being supported by Pluto Kuiper Express developers at the Goddard Space Flight Center and Stanford University,[26] were at an advantage; they had recently developed NEAR Shoemaker for NASA, which had successfully entered orbit around 433 Eros earlier in the year, and would later land on the asteroid to scientific and engineering fanfare.[27]

In November 2001, New Horizons was officially selected for funding as part of the New Frontiers program.[28] However, the new NASA Administrator appointed by the Bush Administration, Sean O'Keefe, was not supportive of New Horizons, and effectively cancelled it by not including it in NASA's budget for 2003. Weiler prompted Stern to lobby for the funding of New Horizons in hopes of the mission appearing in the Planetary Science Decadal Survey; a prioritized "wish list", compiled by the United States National Research Council, that reflects the opinions of the scientific community. After an intense campaign to gain support for New Horizons, the Planetary Science Decadal Survey of 2003-2013 was published in the summer of 2002. New Horizons topped the list of projects considered the highest priority among the scientific community in the medium-size category; ahead of missions to the Moon, and even Jupiter. Weiler stated that it was a result that "[his] administration was not going to fight".[25] Funding for the mission was finally secured following the publication of the report, and Stern's team were finally able to start building the spacecraft and its instruments, with a planned launch in January 2006 and arrival at Pluto in 2015.[25]

Mission profile[edit]

Artist's impression of New Horizons‍ '​ close encounter with the Pluto–Charon system.

New Horizons is the first mission in NASA's New Frontiers mission category, larger and more expensive than the Discovery missions but smaller than the Flagship Program. The cost of the mission (including spacecraft and instrument development, launch vehicle, mission operations, data analysis, and education/public outreach) is approximately $700 million over 15 years (2001–2016)[29] The spacecraft was built primarily by Southwest Research Institute (SwRI) and the Johns Hopkins Applied Physics Laboratory. The mission's principal investigator is Alan Stern of the Southwest Research Institute (formerly NASA Associate Administrator).

After separation from the launch vehicle, overall control was taken by Mission Operations Center (MOC) at the Applied Physics Laboratory in Howard County, Maryland. The science instruments are operated at Clyde Tombaugh Science Operations Center (T-SOC) in Boulder, Colorado.[30] Navigation is performed at various contractor facilities, whereas the navigational positional data and related celestial reference frames are provided by the Naval Observatory Flagstaff Station through Headquarters NASA and JPL; KinetX is the lead on the New Horizons navigation team and is responsible for planning trajectory adjustments as the spacecraft speeds toward the outer Solar System. Coincidentally the Naval Observatory Flagstaff Station was where the photographic plates were taken for the discovery of Pluto's moon Charon; and the Naval Observatory is itself not far from the Lowell Observatory where Pluto was discovered.

New Horizons was originally planned as a voyage to the only unexplored planet in the Solar System. When the spacecraft was launched, Pluto was still classified as a planet, later to be reclassified as a dwarf planet by the International Astronomical Union (IAU). Some members of the New Horizons team, including Alan Stern, disagree with the IAU definition and still describe Pluto as the ninth planet.[31] Pluto's satellites Nix and Hydra also have a connection with the spacecraft: the first letters of their names (N and H) are the initials of New Horizons. The moons' discoverers chose these names for this reason, plus Nix and Hydra's relationship to the mythological Pluto.[32]

In addition to the science equipment, there are several cultural artifacts traveling with the spacecraft. These include a collection of 434,738 names stored on a compact disc,[33] a piece of Scaled Composites's SpaceShipOne,[34] a "Not Yet Explored" USPS stamp,[22][23] and a Flag of the United States, along with other mementos.[35]

About 1 ounce (30 g) of Clyde Tombaugh's ashes are aboard the spacecraft, to commemorate his discovery of Pluto in 1930.[36][37] A Florida-state quarter coin, whose design commemorates human exploration, is included, officially as a trim weight.[38] One of the science packages (a dust counter) is named after Venetia Burney, who, as a child, suggested the name "Pluto" after its discovery.

Goal[edit]

View of Mission Operations at the Applied Physics Laboratory in Laurel, MD. (July 14, 2015).

The goal of the mission is to understand the formation of the Pluto system, the Kuiper belt, and the transformation of the early Solar System.[39] The spacecraft will study the atmospheres, surfaces, interiors and environments of Pluto and its moons. It will also study other objects in the Kuiper belt.[40] By way of comparison, New Horizons will gather 5,000 times as much data at Pluto as Mariner did at Mars.[41]

Some of the questions the mission will attempt to answer are: What is Pluto's atmosphere made of and how does it behave? What does its surface look like? Are there large geological structures? How do solar wind particles interact with Pluto's atmosphere?[42]

Specifically, the mission's science objectives are to:[43]

  • map the surface composition of Pluto and Charon
  • characterize the geology and morphology of Pluto and Charon
  • characterize the neutral atmosphere of Pluto and its escape rate
  • search for an atmosphere around Charon
  • map surface temperatures on Pluto and Charon
  • search for rings and additional satellites around Pluto
  • conduct similar investigations of one or more Kuiper belt objects

Design and construction[edit]

Spacecraft subsystems[edit]

New Horizons at the Kennedy Space Center in 2005

The spacecraft is comparable in size and general shape to a grand piano and has been compared to a piano glued to a cocktail bar-sized satellite dish.[44] As a point of departure, the team took inspiration from the Ulysses spacecraft,[45] which also carried a radioisotope thermoelectric generator (RTG) and dish on a box-in-box structure through the outer Solar System. Many subsystems and components have flight heritage from APL's CONTOUR spacecraft, which in turn had heritage from APL's TIMED spacecraft.

New Horizons' body forms a triangle, almost 0.76 m (2.5 ft) thick. (The Pioneers have hexagonal bodies, whereas the Voyagers, Galileo, and Cassini–Huygens have decagonal, hollow bodies.) A 7075 aluminium alloy tube forms the main structural column, between the launch vehicle adapter ring at the "rear," and the 2.1 m (6 ft 11 in) radio dish antenna affixed to the "front" flat side. The titanium fuel tank is in this tube. The RTG attaches with a 4-sided titanium mount resembling a gray pyramid or stepstool. Titanium provides strength and thermal isolation. The rest of the triangle is primarily sandwich panels of thin aluminium facesheet (less than 164 in or 0.40 mm) bonded to aluminium honeycomb core. The structure is larger than strictly necessary, with empty space inside. The structure is designed to act as shielding, reducing electronics errors caused by radiation from the RTG. Also, the mass distribution required for a spinning spacecraft demands a wider triangle.

The interior structure is painted black to equalize temperature by radiative heat transfer. Overall, the spacecraft is thoroughly blanketed to retain heat. Unlike the Pioneers and Voyagers, the radio dish is also enclosed in blankets that extend to the body. The heat from the RTG adds warmth to the spacecraft while it is in the outer Solar System. While in the inner Solar System, the spacecraft must prevent overheating, hence electronic activity is limited, power is diverted to shunts with attached radiators, and louvers are opened to radiate excess heat. While the spacecraft is cruising inactively in the cold outer Solar System, the louvers are closed, and the shunt regulator reroutes power to electric heaters.

Propulsion and attitude control[edit]

New Horizons has both spin-stabilized (cruise) and three-axis stabilized (science) modes controlled entirely with hydrazine monopropellant. Additional post launch delta-v of over 290 m/s (1,000 km/h; 650 mph) is provided by a 77 kg (170 lb) internal tank. Helium is used as a pressurant, with an elastomeric diaphragm assisting expulsion. The spacecraft's on-orbit mass including fuel is over 470 kg (1,040 lb) on the Jupiter flyby trajectory, but would have been only 445 kg (981 lb) for the backup direct flight option to Pluto. Significantly, had the backup option been taken, this would have meant less fuel for later Kuiper belt operations.

There are 16 thrusters on New Horizons: four 4.4 N (1.0 lbf) and twelve 0.9 N (0.2 lbf) plumbed into redundant branches. The larger thrusters are used primarily for trajectory corrections, and the small ones (previously used on Cassini and the Voyager spacecraft) are used primarily for attitude control and spinup/spindown maneuvers. Two star cameras are used to measure the spacecraft attitude. They are mounted on the face of the spacecraft and provide attitude information while in spin-stabilized or 3-axis mode. In between the time of star camera readings, spacecraft orientation is provided by dual redundant miniature inertial measurement units. Each unit contains three solid-state gyroscopes and three accelerometers. Two Adcole Sun sensors provide attitude determination. One detects the angle to the Sun, whereas the other measures spin rate and clocking.

Power[edit]

New Horizons‍ '​ RTG

A cylindrical radioisotope thermoelectric generator (RTG) protrudes in the plane of the triangle from one vertex of the triangle. The RTG will provide about 250 W, 30 V DC at launch, and is predicted to drop approximately 5% every 4 years, decaying to 200 W by the time of its encounter with the Plutonian system in 2015. The RTG, model "GPHS-RTG," was originally a spare from the Cassini mission. The RTG contains 10.9 kg (24 lb) of plutonium-238 oxide pellets. Each pellet is clad in iridium, then encased in a graphite shell. It was developed by the U.S. Department of Energy at the Materials and Fuels Complex, a part of the Idaho National Laboratory.[46] Less power than the original design goal was produced because of delays at the United States Department of Energy, including security activities, that delayed production. The mission parameters and observation sequence had to be modified for the reduced wattage; still, not all instruments can operate simultaneously. The Department of Energy transferred the space battery program from Ohio to Argonne in 2002 because of security concerns. There are no onboard batteries. RTG output is relatively predictable; load transients are handled by a capacitor bank and fast circuit breakers.

The amount of radioactive plutonium in the RTG is 10.9 kg (24 lb), about one-third the amount on board the Cassini–Huygens probe when it launched in 1997. That launch was protested by some. The United States Department of Energy estimated the chances of a launch accident that would release radiation into the atmosphere at 1 in 350, and monitored the launch[47] as it always does when RTGs are involved. It was estimated that a worst-case scenario of total dispersal of on-board plutonium would spread the equivalent radiation of 80% the average annual dosage in North America from background radiation over an area with a radius of 105 km (65 mi).[48]

Flight computer[edit]

The spacecraft carries two computer systems: the Command and Data Handling system and the Guidance and Control processor. Each of the two systems is duplicated for redundancy, for a total of four computers. The processor used for its flight computers is the Mongoose-V, a 12 MHz radiation-hardened version of the MIPS R3000 CPU. Multiple clocks and timing routines are implemented in hardware and software to help prevent faults and downtime. To conserve heat and mass, spacecraft and instrument electronics are housed together in IEMs (integrated electronics modules). There are two redundant IEMs. Including other functions such as instrument and radio electronics, each IEM contains 9 boards.[49]

There have been two "safing" events, that sent the spacecraft into safe mode:

  • On March 19, 2007 the Command and Data Handling computer experienced an uncorrectable memory error and rebooted itself, causing the spacecraft to go into safe mode. The craft fully recovered within two days, with some data loss on Jupiter's magnetotail. No impact on the subsequent mission was expected.[50]
  • On July 4, 2015 there was a CPU safing event caused by over assignment of commanded science operations.[51][52][53]

Telecommunications and data handling[edit]

New Horizons‍ '​ antennas

Communication with the spacecraft is via X band. The craft had a communication rate of 38 kbit/s at Jupiter; at Pluto's distance, a rate of approximately 1 kbit/s per transmitter is expected. Besides the low bandwidth, Pluto's distance also causes a latency of about 4.5 hours (one-way). The 70 m (230 ft) NASA Deep Space Network (DSN) dishes are used to relay commands once it is beyond Jupiter. The spacecraft uses dual redundant transmitters and receivers, and either right- or left-hand circular polarization. The downlink signal is amplified by dual redundant 12-watt traveling-wave tube amplifiers (TWTAs) mounted on the body under the dish. The receivers are new, low-power designs. The system can be controlled to power both TWTAs at the same time, and transmit a dual-polarized downlink signal to the DSN that nearly doubles the downlink rate. DSN tests early in the mission with this dual polarization combining technique were successful, and the capability is now considered operational (when the spacecraft power budget permits both TWTAs to be powered).

In addition to the high-gain antenna, there are two backup low-gain antennas and a medium-gain dish. The high-gain dish has a Cassegrain reflector layout, composite construction, and a 2.1-meter (7 ft) diameter providing over 42 dBi of gain, has a half-power beam width of about a degree. The prime-focus, medium-gain antenna, with a 0.3-meter (1 ft) aperture and 10° half-power beam width, is mounted to the back of the high-gain antenna's secondary reflector. The forward low-gain antenna is stacked atop the feed of the medium-gain antenna. The aft low-gain antenna is mounted within the launch adapter at the rear of the spacecraft. This antenna was used only for early mission phases near Earth, just after launch and for emergencies if the spacecraft had lost attitude control.

New Horizons recorded scientific instrument data to its solid-state memory buffer at each encounter, then transmitted the data to Earth. Data storage is done on two low-power solid-state recorders (one primary, one backup) holding up to 8 gigabytes each. Because of the extreme distance from Pluto and the Kuiper belt, only one buffer load at those encounters can be saved. This is because New Horizons will require approximately 16 months after it has left the vicinity of Pluto (or future target object) to transmit the buffer load back to Earth.[54] At Pluto's distance transmissions from the space probe back to earth took four hours 25 minutes to traverse 4.7 billion km of space.[55]

Part of the reason for the delay between the gathering of and transmission of data is because all of the New Horizons instrumentation is body-mounted. In order for the cameras to record data, the entire probe must turn, and the one-degree-wide beam of the high-gain antenna will almost certainly not be pointing toward Earth. Previous spacecraft, such as the Voyager program probes, had a rotatable instrumentation platform (a "scan platform") that could take measurements from virtually any angle without losing radio contact with Earth. New Horizons‍ '​ elimination of excess mechanisms was implemented to save weight, shorten the schedule, and improve reliability during its 15-year lifetime.

The Voyager 2 spacecraft experienced platform jamming at Saturn; the demands of long time exposures at Uranus led to modifications of the mission such that the entire probe was rotated to make the time exposure photos at Uranus and Neptune, similar to how New Horizons will rotate.

Science payload[edit]

New Horizons carries seven instruments: three optical instruments, two plasma instruments, a dust sensor and a radio science receiver/radiometer. The instruments are to be used to investigate the global geology, surface composition, surface temperature, atmospheric pressure, atmospheric temperature and escape rate of Pluto and its moons. The rated power is 21 watts, though not all instruments operate simultaneously.[56] In addition, New Horizons has an Ultrastable Oscillator subsystem, which may be used to study and test the Pioneer anomaly towards the end of the spacecraft's life.[57]

Long-Range Reconnaissance Imager (LORRI)[edit]

LORRI—long-range camera

The Long-Range Reconnaissance Imager (LORRI) is a long-focal-length imager designed for high resolution and responsivity at visible wavelengths. The instrument is equipped with a 1024×1024 pixel by 12-bits-per-pixel monochromatic CCD imager with a 208.3 mm (8.20 in) aperture giving a resolution of 5 μrad (~1 arcsec).[58] The CCD is chilled far below freezing by a passive radiator on the antisolar face of the spacecraft. This temperature differential requires insulation, and isolation from the rest of the structure. The Ritchey–Chretien mirrors and metering structure are made of silicon carbide, to boost stiffness, reduce weight, and prevent warping at low temperatures. The optical elements sit in a composite light shield, and mount with titanium and fiberglass for thermal isolation. Overall mass is 8.6 kg (19 lb), with the optical tube assembly (OTA) weighing about 5.6 kg (12 lb),[59] for one of the largest silicon-carbide telescopes flown at the time (now surpassed by Herschel). For viewing on public web sites the 12-bit per pixel LORRI images are converted to 8-bit per pixel JPEG images.[58] These public images do not contain the full dynamic range of brightness information available from the raw LORRI images files.[58]

Principal investigator: Andy Cheng, Applied Physics Laboratory, Data: LORRI image search at jhuapl.edu[60]

Solar Wind At Pluto (SWAP)[edit]

SWAP—Solar Wind At Pluto

Solar Wind At Pluto (SWAP) is a toroidal electrostatic analyzer and retarding potential analyzer (RPA), that makes up one of the two instruments comprising New Horizons‍ '​ Plasma and high-energy particle spectrometer suite (PAM), the other being PEPSSI. SWAP measures particles of up to 6.5 keV and, because of the tenuous solar wind at Pluto's distance, the instrument is designed with the largest aperture of any such instrument ever flown.[citation needed]

Principal investigator: David McComas, Southwest Research Institute

Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI)[edit]

Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) is a time of flight ion and electron sensor that makes up one of the two instruments comprising New Horizons‍ '​ plasma and high-energy particle spectrometer suite (PAM), the other being SWAP. Unlike SWAP, which measures particles of up to 6.5 keV, PEPSSI goes up to 1 MeV.[citation needed]

Principal investigator: Ralph McNutt Jr., Applied Physics Laboratory

Alice[edit]

Alice is an ultraviolet imaging spectrometer that is one of two photographic instruments comprising New Horizons‍ '​ Pluto Exploration Remote Sensing Investigation (PERSI); the other being the Ralph telescope. It resolves 1,024 wavelength bands in the far and extreme ultraviolet (from 50–180 nm), over 32 view fields. Its goal is to determine the atmospheric composition of Pluto. This Alice instrument is derived from another Alice aboard the ESA's Rosetta spacecraft.[citation needed]

Principal investigator: Alan Stern, Southwest Research Institute

Ralph telescope[edit]

Ralph—telescope and color camera

The Ralph telescope, 6 cm (2.4 in) in aperture, is one of two photographic instruments that make up New Horizons‍ '​ Pluto Exploration Remote Sensing Investigation (PERSI), with the other being the Alice instrument. Ralph has two separate channels: a visible-light CCD imager (MVIC- Multispectral Visible Imaging Camera) with broadband and color channels, and a near-infrared imaging spectrometer, LEISA (Linear Etalon Imaging Spectral Array). LEISA is derived from a similar instrument on the EO-1 mission. Ralph was named after Alice's husband on The Honeymooners, and was designed after Alice.[61]

Principal investigator: Alan Stern, Southwest Research Institute

Venetia Burney Student Dust Counter (VBSDC)[edit]

VBSDC—Venetia Burney Student Dust Counter

The Venetia Burney Student Dust Counter (VBSDC), built by students at the University of Colorado Boulder, will operate continuously to make dust measurements.[62] It consists of a detector panel, about 460 mm × 300 mm (18 in × 12 in), mounted on the anti-solar face of the spacecraft (the ram direction), and an electronics box within the spacecraft. The detector contains fourteen polyvinylidene difluoride (PVDF) panels, twelve science and two reference, which generate voltage when impacted. Effective collecting area is 0.125 m2 (1.35 sq ft). No dust counter has operated past the orbit of Uranus; models of dust in the outer Solar System, especially the Kuiper belt, are speculative. The VBSDC is always turned on measuring the masses of the interplanetary and interstellar dust particles (in the range of nano- and picograms) as they collide with the PVDF panels mounted on the New Horizons spacecraft. The measured data is expected to greatly contribute to the understanding of the dust spectra of the Solar System. The dust spectra can then be compared with those from observations of other stars, giving new clues as to where Earth-like planets can be found in the universe. The dust counter is named for Venetia Burney, who first suggested the name "Pluto" at the age of 11. A thirteen-minute short film about the VBSDC garnered an Emmy Award for student achievement in 2006.[63]

Principal investigator: Mihaly Horanyi, University of Colorado Boulder

Radio Science Experiment (REX)[edit]

The Radio Science Experiment (REX) will use an ultrastable crystal oscillator (essentially a calibrated crystal in a miniature oven) and some additional electronics to conduct radio science investigations using the communications channels. These are small enough to fit on a single card. Because there are two redundant communications subsystems, there are two, identical REX circuit boards.

Principal investigators: Len Tyler and Ivan Linscott, Stanford University

Journey to Pluto[edit]

Launch[edit]

Launch of New Horizons. The Atlas V rocket on the launchpad (left) and lift off from Cape Canaveral. New Horizons‍ '​ launch was the fastest ever to date.

On September 24, 2005 the spacecraft arrived at the Kennedy Space Center on board a C-17 Globemaster III for launch preparations.[64] The launch of New Horizons was originally scheduled for January 11, 2006, but was initially delayed until January 17, 2006 to allow for borescope inspections of the Atlas V's kerosene tank. Further delays related to low cloud ceiling conditions downrange, and high winds and technical difficulties—unrelated to the rocket itself—prevented launch for a further two days.[65][66] Although there were backup launch opportunities in February 2006 and February 2007, only the first twenty-three days of the 2006 window permitted the Jupiter flyby. Any launch outside that period would have forced the spacecraft to fly a slower trajectory directly to Pluto, delaying its encounter by 2–4 years. The probe finally lifted off from Pad 41 at Cape Canaveral Air Force Station, Florida, directly south of Space Shuttle Launch Complex 39, at 14:00 EST on January 19, 2006.[67][68]

The Centaur second stage reignited at 14:30 EST (19:30 UTC), followed by the ATK Star 48B third stage, successfully sending the probe on a solar-escape trajectory. New Horizons took only nine hours to reach the Moon's orbit, passing lunar orbit before midnight EST that day.

The probe was launched by a Lockheed Martin Atlas V 551 rocket, with a third stage added to increase the heliocentric (escape) speed. This was the first launch of the Atlas V 551 configuration, which uses five solid rocket boosters, and the first Atlas V with a third stage. Previous flights had used zero, two, or three solid boosters, but never five. The vehicle, AV-010, weighed 570,000 kg (1.26 million lb) at lift-off, and had earlier been slightly damaged when Hurricane Wilma swept across Florida on October 24, 2005. One of the solid rocket boosters was hit by a door. The booster was replaced with an identical unit, rather than inspecting and requalifying the original.[69]

New Horizons is often given the title of Fastest Spacecraft Ever Launched,[citation needed] and left Earth faster than any other spacecraft to date. It is also the first spacecraft launched directly into a solar escape trajectory, which requires an approximate speed of 16.5 km/s (59,000 km/h; 37,000 mph), plus aerodynamic and gravity losses[clarification needed], all to be provided by the launcher. But it is not the fastest spacecraft to leave the Solar System. This record is held by Voyager 1, currently traveling at 17.145 km/s (61,720 km/h; 38,350 mph) relative to the Sun. Voyager 1 attained greater hyperbolic excess velocity from Jupiter and Saturn gravitational slingshots than New Horizons. Other spacecraft, such as the Helios probes, can also be measured as the fastest objects, because of their orbital speed relative to the Sun at perihelion. Because they remain in solar orbit, their specific orbital energy relative to the Sun is lower than New Horizons and other artificial objects escaping the Solar System.

The Star 48B third-stage is also on a hyperbolic Solar System escape trajectory, and reached Jupiter before the New Horizons spacecraft. The Star 48B is expected to cross Pluto's orbit on October 15, 2015.[70] Because it is not in controlled flight, it did not receive the correct gravity assist, and will only pass within 200 million km (120 million mi) of Pluto.[70] The Centaur stage did not achieve solar escape velocity, and is in heliocentric orbit.[71] The launch was dedicated to the memory of launch conductor Daniel Sarokon, who was described by space program officials as one of the most influential people in the history of space travel.[72]

Inner Solar System[edit]

Trajectory corrections[edit]

On January 28 and 30, 2006, mission controllers guided the probe through its first trajectory-correction maneuver (TCM), which was divided into two parts (TCM-1A and TCM-1B). The total velocity change of these two corrections was about 18 meters per second (65 km/h; 40 mph). TCM-1 was accurate enough to permit the cancellation of TCM-2, the second of three originally scheduled corrections.[73] On March 9, 2006, controllers performed TCM-3, the last of three scheduled course corrections. The engines burned for 76 seconds, adjusting the spacecraft's velocity by about 1.16 m/s (4.2 km/h; 2.6 mph).[74] Further trajectory maneuvers were not needed until September 25, 2007 (seven months after the Jupiter flyby), when the engines were fired for 15 minutes and 37 seconds, changing the spacecraft's velocity by 2.37 m/s (8.5 km/h; 5.3 mph),[75] followed by another TCM, almost three years later on June 30, 2010, that lasted 35.6 seconds, when New Horizons had already reached the halfway point (in time traveled) to Pluto.[76]

In-flight tests and Mars orbit[edit]

During the week of February 20, 2006, controllers conducted initial in-flight tests of three onboard science instruments, the Alice ultraviolet imaging spectrometer, the PEPSSI plasma-sensor, and the LORRI long-range visible-spectrum camera. No scientific measurements or images were taken, but instrument electronics, and in the case of Alice, some electromechanical systems were shown to be functioning correctly.[77] On April 7, 2006, the spacecraft passed the orbit of Mars, moving at roughly 21 km/s (76,000 km/h; 47,000 mph) away from the Sun at a solar distance of 243 million kilometers.[78][79][80]

Asteroid 132524 APL[edit]

Asteroid 132524 APL viewed by New Horizons in June 2006
First images of Pluto in September 2006

Because of the need to conserve fuel for possible encounters with Kuiper belt objects subsequent to the Pluto flyby, intentional encounters with objects in the asteroid belt were not planned. After launch, the New Horizons team scanned the spacecraft's trajectory to determine if any asteroids would, by chance, be close enough for observation. In May 2006 it was discovered that New Horizons would pass close to the tiny asteroid 132524 APL on June 13, 2006. Closest approach occurred at 4:05 UTC at a distance of 101,867 km (63,297 mi). The asteroid was imaged by Ralph (use of LORRI was not possible because of proximity to Sun), which gave the team a chance to test Ralph's capabilities, and make observations of the asteroid's composition as well as light and phase curves. The asteroid was estimated to be 2.5 km (1.6 mi) in diameter.[81][82][83] The spacecraft successfully tracked the asteroid over June 10–12, 2006. This allowed the mission team to test the spacecraft's ability to track rapidly moving objects. Images were obtained through the Ralph telescope.[83]

First Pluto sighting[edit]

The first images of Pluto from New Horizons were acquired September 21–24, 2006, during a test of the LORRI. They were released on November 28, 2006.[84] The images, taken from a distance of approximately 4,200,000,000 km (2.6×109 mi) or 28.07 AU, confirmed the spacecraft's ability to track distant targets, critical for maneuvering toward Pluto and other Kuiper belt objects.

Jupiter encounter[edit]

Jupiter viewed by LORRI in January 2007
Ralph sees Jupiter in infrared in February 2007.

New Horizons used LORRI to take its first photographs of Jupiter on September 4, 2006 from a distance of 291 million kilometers (181 million miles).[85] More detailed exploration of the system began in January 2007 with an infrared image of the moon Callisto, as well as several black-and-white images of Jupiter itself.[86] New Horizons received a gravity assist from Jupiter, with its closest approach at 05:43:40 UTC on February 28, 2007 when it was 2.3 million kilometers (1.4 million miles) from Jupiter. The flyby increased New Horizons‍ '​ speed by 4 km/s (14,000 km/h; 9,000 mph), accelerating the probe to a velocity of 23 km/s (83,000 km/h; 51,000 mph) relative to the Sun and shortening its voyage to Pluto by three years.[87]

The flyby was the center of a 4-month intensive observation campaign lasting from January to June. Being an ever-changing scientific target, Jupiter has been observed intermittently since the end of the Galileo mission in September 2003. Knowledge about Jupiter benefited from the fact that New Horizons‍ '​ instruments were built using the latest technology, especially in the area of cameras, representing a significant improvement over Galileo's cameras, which were modified versions of Voyager cameras, which, in turn, were modified Mariner cameras. The Jupiter encounter also served as a shakedown and dress rehearsal for the Pluto encounter. Because Jupiter is much closer to Earth than Pluto, the communications link can transmit multiple loadings of the memory buffer; thus the mission returned more data from the Jovian system than it is expected to transmit from Pluto.[88]

One of the main goals during the Jupiter encounter was observing its atmospheric conditions and analyzing the structure and composition of its clouds. Heat-induced lightning strikes in the polar regions and "waves" that indicate violent storm activity were observed and measured. The Little Red Spot, spanning up to 70% of Earth's diameter, was imaged from up close for the first time.[87]

Recording from different angles and illumination conditions, New Horizons took detailed images of Jupiter's faint ring system, discovering debris left over from recent collisions within the rings or from other unexplained phenomena. The search for undiscovered moons within the rings showed no results. Travelling through Jupiter's magnetosphere, New Horizons collected valuable particle readings.[87] "Bubbles" of plasma that are thought to be formed from material ejected by the moon Io, were noticed in the magnetotail.[89]

The Tvashtar volcano erupting on Io during flyby

Jovian moons[edit]

The four largest moons of Jupiter were in poor positions for observation; the necessary path of the gravity-assist maneuver meant that New Horizons passed millions of kilometers from any of the Galilean moons. Still, its instruments were intended for small, dim targets, so they were scientifically useful on large, distant moons. Emphasis was put on Jupiter's innermost Galilean moon, Io, whose active volcanoes shoot out tons of material into Jupiter's magnetosphere, and further. Out of eleven observed eruptions, three were seen for the first time. That of Tvashtar reached an altitude of up to 330 kilometers. The event gave scientists an unprecedented look into the structure and motion of the rising plume and its subsequent fall back to the surface. Infrared signatures of a further 36 volcanoes were noticed.[87] Callisto's surface was analyzed with LEISA, revealing how lighting and viewing conditions affect infrared spectrum readings of its surface water ice.[90] Minor moons such as Amalthea had their orbit solutions refined. The cameras determined their positions, acting as "reverse optical navigation".

Outer Solar System[edit]

After passing Jupiter, New Horizons spent most of its journey towards Pluto in hibernation mode: redundant components as well as guidance and control systems were shut down to extend their life cycle, decrease operation costs and free the Deep Space Network for other missions.[91] During hibernation mode, the onboard computer monitored the probe's systems and transmitted a signal back to Earth: a "green" code if everything was functioning as expected or a "red" code if mission control's assistance was needed.[91] The probe was activated for about two months a year so that the instruments could be calibrated and the systems checked. The first hibernation mode cycle started on June 28, 2007,[91] the second cycle began on December 16, 2008,[92] the third cycle on August 27, 2009,[93] and the fourth cycle on August 29, 2014 after a 10-week test.[94]

New Horizons crossed the orbit of Saturn on June 8, 2008,[95] and Uranus on March 18, 2011.[96] After astronomers announced the discovery of two new moons in the Pluto system, Kerberos and Styx, mission planners started contemplating the possibility of the probe running into unseen debris and dust left over from earlier collisions with the moons. A study based on 18 months of computer simulations, Earth-based telescope observations and occultations of the Pluto system revealed that the possibility of a catastrophic collision with debris or dust was less than 0.3% on the probe's scheduled course.[97][98] If the hazard increased, New Horizons could have used one of two possible contingency plans, the so-called SHBOTs (Safe Haven by Other Trajectories): the probe could have continued on its present trajectory with the antenna facing the incoming particles so the more vital systems would be protected, or, it could have positioned its antenna to make a course correction that would take it just 3000 km from the surface of Pluto where it was expected that the atmospheric drag would clean the surrounding space of possible debris.[98]

While in hibernation mode in July 2012, New Horizons started gathering scientific data with SWAP, PEPSSI and VBSDC. Although it was originally planned to activate just the VBSDC, other instruments were powered on the initiative of principal investigator Alan Stern who decided they could use the opportunity to collect valuable heliospheric data. Before activating the other two instruments, ground tests were conducted to make sure that the expanded data gathering in this phase of the mission would not limit available energy, memory and fuel in the future and that all systems are functioning during the flyby.[99] The first set of data was transmitted in January 2013 during a three-week activation from hibernation. The command and data handling software was updated to address the problem of computer resets.[100]

Possible Neptune trojan targets[edit]

Other possible targets were Neptune trojans. The probe's trajectory to Pluto passed near Neptune's trailing Lagrange point ("L5"), which may host hundreds of bodies in 1:1 resonance. In late 2013, New Horizons passed within 1.2 AU (180,000,000 km; 110,000,000 mi) of the high-inclination L5 Neptune trojan 2011 HM102,[101] which was identified shortly before by the New Horizons KBO Search Survey team while searching for more distant objects for New Horizons to fly by after its 2015 Pluto encounter. At that range, 2011 HM102 would have been bright enough to be detectable by New Horizons‍ '​ LORRI instrument; however, the New Horizons team eventually decided that they would not target 2011 HM102 for observations because the preparations for the Pluto approach took precedence.[102]

Observations of Pluto and Charon 2013–14[edit]

Images from July 1 to 3, 2013 by LORRI were the first by the probe to resolve Pluto and Charon as separate objects.[103] On July 14, 2014, mission controllers performed a sixth trajectory-correction maneuver (TCM) since its launch to enable the craft to reach Pluto.[104] Between July 19–24, 2014, New Horizons‍ '​ LORRI snapped 12 images of Charon revolving around Pluto, covering almost one full rotation at distances ranging from about 429,000,000 km (267,000,000 mi) to 422,000,000 km (262,000,000 mi).[105] In August 2014, astronomers made high-precision measurements of Pluto's location and orbit around the Sun using the Atacama Large Millimeter/submillimeter Array (ALMA) to help NASA's New Horizons spacecraft accurately home in on Pluto.[106] On December 6, 2014, mission controllers sent a signal for the craft to "wake up" from its final Pluto-approach hibernation and begin regular operations. The craft's response that it was "awake" arrived to Earth at 9:30 PM EST.[107][108][109]

Pluto approach[edit]

Timeline: Pluto science operation
January and February 2015: New Horizons takes images of Pluto, Charon, Nix, and Hydra
The Pluto–Charon system imaged by New Horizons on June 29, 2015

Distant-encounter operations at Pluto began on January 4, 2015.[110] At this date images of the targets with the onboard LORRI imager plus Ralph telescope would only be a few pixels in width. Investigators began taking Pluto and background starfield images to assist mission navigators in the design of course-correcting engine maneuvers that would precisely modify the trajectory of New Horizons to aim the approach.

Animation of the Pluto–Charon system in January 2015

On January 15, 2015, NASA gave a brief update of the timeline of the approach and departure phases.[111]

On February 12, 2015, NASA released new images of Pluto (taken from January 25 to 31) from the approaching probe.[112][113] New Horizons was more than 203,000,000 km (126,000,000 mi) away from Pluto when it began taking the photos, which showed Pluto and its largest moon, Charon. The exposure time was too short to see Pluto's smaller, much fainter, moons. Investigators compiled a series of images of the moons Nix and Hydra taken from January 27 through February 8, 2015, beginning at a range of 201,000,000 km (125,000,000 mi).[114] Pluto and Charon appear as a single overexposed object at the center. The right side image has been processed to remove the background starfield. The yet smaller two moons, Kerberos and Styx were seen on photos taken on April 25.[115] Starting May 11 a hazard search was performed, by looking for until then unknown objects that could be a danger to the spacecraft, such as rings or more moons, which were possible to avoid by a course change.[116]

Also in regards to the approach phase during January 2015, on August 21, 2012, the team announced that they would also spend mission time attempting long-range observations of the Kuiper belt object temporarily designated VNH0004, when the object was at a distance from New Horizons of 75 gigameters (0.50 AU).[117] The object would be too distant to resolve surface features or take spectroscopy, but it would be able to make observations that cannot be made from Earth, namely a phase curve and a search for small moons. A second object was planned to be observed in June 2015, and a third in September after the flyby; the team hoped to observe a dozen such objects through 2018.[117] On April 15, 2015, Pluto was imaged showing a possible polar cap.[118]

Software glitch[edit]

On July 4, 2015, New Horizons experienced a software anomaly and went into safe mode, preventing the spacecraft from performing scientific observations until engineers could resolve the problem.[119][120] On July 5, NASA announced that the problem was determined to be a timing flaw in a command sequence used to prepare the spacecraft for its flyby, and the spacecraft would resume scheduled science operations on July 7. The science observations lost because of the anomaly were judged to have no impact on the mission's main objectives and minimal impact on other objectives.[121]

The timing flaw consisted of performing two tasks simultaneously—compressing previously acquired data to release space for more data, and making a second copy of the approach command sequence—that together overloaded the spacecraft's primary computer. After the overload was detected, the spacecraft performed as designed: it switched from the primary computer to the backup computer, entered safe mode, and sent a distress call back to Earth. The distress call was received the afternoon of July 4, which alerted engineers that they needed to contact the spacecraft to get more information and resolve the issue. The resolution was that the problem happened as part of preparations for the approach, and was not expected to happen again because no similar tasks were planned for the remainder of the encounter.[121][122]

Pluto system encounter[edit]

Eyes on the Solar System simulation of New Horizons' Pluto encounter.
Pluto viewed by New Horizons on July 13, 2015
Charon viewed by New Horizons on July 13, 2015
Alan Stern and the New Horizons team celebrate after the spacecraft successfully completed its flyby of Pluto.

The closest approach of the New Horizons spacecraft to Pluto occurred at 11:49 UTC on July 14, 2015 at a range of 7,750 miles (12,472 km) from the surface[123] and 8,487 miles (13,658 km) from the center of Pluto. Telemetry data confirming a successful flyby and a healthy spacecraft were received on Earth from the vicinity of the Pluto system on July 15, 2015, 00:52:37 UTC,[124] after 22 hours of planned radio silence due to the spacecraft being pointed toward the Pluto system. Mission managers estimated a one in 10,000 chance that debris could have destroyed it during the flyby, preventing it from sending science data to Earth.[125] The first details of the encounter were received later in the day, but the download of the complete data will take 16 months, and analysis of the data will take longer.

Objectives[edit]

The mission's science objectives are grouped in three distinct priorities. The "primary objectives" are required by NASA and a loss of any of these objectives will constitute a partial failure of the mission, while it is expected, but not demanded, that most of the "secondary objectives" will be met. The "tertiary objectives" are desired. These objectives may be attempted, though they may be skipped in favor of the above objectives. An objective to measure any magnetic field of Pluto was dropped. A magnetometer instrument could not be implemented within a reasonable mass budget and schedule, and SWAP and PEPSSI could do an indirect job detecting some magnetic field around Pluto.[citation needed]

  • Primary objectives (required)
    • Characterize the global geology and morphology of Pluto and Charon
    • Map chemical compositions of Pluto and Charon surfaces
    • Characterize the neutral (non-ionized) atmosphere of Pluto and its escape rate
  • Secondary objectives (expected)
    • Characterize the time variability of Pluto's surface and atmosphere
    • Image select Pluto and Charon areas in stereo
    • Map the terminators (day/night border) of Pluto and Charon with high resolution
    • Map the chemical compositions of select Pluto and Charon areas with high resolution
    • Characterize Pluto's ionosphere (upper layer of the atmosphere) and its interaction with the solar wind
    • Search for neutral species such as molecular hydrogen, hydrocarbons, hydrogen cyanide and other nitriles in the atmosphere
    • Search for any Charon atmosphere
    • Determine bolometric Bond albedos for Pluto and Charon
    • Map surface temperatures of Pluto and Charon
    • Map any additional surfaces of outermost moons: Nix, Hydra, Kerberos, and Styx
  • Tertiary objectives (desired)
    • Characterize the energetic particle environment at Pluto and Charon
    • Refine bulk parameters (radii, masses) and orbits of Pluto and Charon
    • Search for additional moons and any rings

Flyby details[edit]

Pluto flyby trajectory on July 14, 2015
Icy mountains on Pluto, July 14, 2015

New Horizons passed within 12,500 km (7,800 mi) of Pluto, with this closest approach on July 14, 2015 at 11:50 UTC. New Horizons had a relative velocity of 13.78 km/s (49,600 km/h; 30,800 mph) at its closest approach, and came as close as 28,800 km (17,900 mi) to Charon. Starting 3.2 days before the closest approach, long-range imaging included the mapping of Pluto and Charon to 40 km (25 mi) resolution. This is half the rotation period of the Pluto–Charon system and allowed imaging of all sides of both bodies. Coverage will repeat twice per day, to search for changes due to snows or cryovolcanism. Because of Pluto's tilt, a portion of the northern hemisphere will be in shadow at all times. During the flyby, LORRI should be able to obtain select images with resolution as high as 50 m/px (if closest distance is around 12,500 km), and MVIC should obtain four-color global dayside maps at 1.6 km resolution. LORRI and MVIC will attempt to overlap their respective coverage areas to form stereo pairs. LEISA will obtain hyperspectral near-infrared maps at 7 km/px globally and 0.6 km/px for selected areas.

Meanwhile, Alice will characterize the atmosphere, both by emissions of atmospheric molecules (airglow), and by dimming of background stars as they pass behind Pluto (occultation). During and after closest approach, SWAP and PEPSSI will sample the high atmosphere and its effects on the solar wind. VBSDC will search for dust, inferring meteoroid collision rates and any invisible rings. REX will perform active and passive radio science. Ground stations on Earth will transmit a powerful radio signal as New Horizons passes behind Pluto's disk, then emerges on the other side. The communications dish will measure the disappearance and reappearance of the radio occultation signal. The results will resolve Pluto's diameter (by their timing) and atmospheric density and composition (by their weakening and strengthening pattern). (Alice can perform similar occultations, using sunlight instead of radio beacons.) Previous missions had the spacecraft transmit through the atmosphere, to Earth ("downlink"). Low power and extreme distance means New Horizons will be the first such "uplink" mission. Pluto's mass and mass distribution will be evaluated by their tug on the spacecraft. As the spacecraft speeds up and slows down, the radio signal will experience a Doppler shift. The Doppler shift will be measured by comparison with the ultrastable oscillator in the communications electronics.

Reflected sunlight from Charon will allow some imaging observations of the nightside. Backlighting by the Sun will highlight any rings or atmospheric hazes. REX will perform radiometry of the nightside.

Distribution of methane ice on Pluto
(July 12, 2015).

Lesser satellite observations[edit]

New Horizons‍ '​ best spatial resolution of the small satellites is 330 m/pixel at Nix, 780 m/pixel at Hydra, and approximately 1.8 km/pixel at Kerberos and Styx. Estimates for the diameters of these bodies are: Nix, 56 × 26 km; Hydra, 58 × 34 km; Kerberos, 31 km; and Styx, 8 to 28 km. This translates to a resolution of 170, 75, 20, and 5 to 15 pixels in width for Nix, Hydra, Kerberos, and Styx, respectively.

Current status[edit]

New Horizons‍ '​ current position[126]
  • The spacecraft flew by the Pluto–Charon system on July 14, 2015, and has now completed the science of its closest approach phase. New Horizons has signaled the event by a "phone home" with telemetry reporting that the spacecraft was healthy, its flight path was within the margins, and science data of the Pluto–Charon system had been recorded.[14][127]
  • The spacecraft currently travels at 14.52 km/s (9.02 mi/s; 3.06 AU/a; 0.00839 AU/d) relative to the Sun and at 13.77 km/s (8.56 mi/s; 2.90 AU/a; 0.00795 AU/d) relative to Pluto.
  • Radio signals take four and a half hours to travel between the spacecraft and Earth.[126]
  • At that distance, the spacecraft can only transmit data at 1 to 2 Kbps, which means that the transmission of all data will require sixteen months.[128]
  • The brightness of the Sun from the spacecraft is magnitude −19.2.[129]
  • New Horizons is heading in the direction of the constellation Sagittarius.[129]
  • The latest news and photos from the probe are posted on NASA's mission website.[2]

Future mission objectives[edit]

Kuiper belt object (KBO) mission[edit]

Target background[edit]

Big picture: from the inner Solar System to the Oort cloud with the Kuiper belt in between.
Artist's concept of a Kuiper belt object (KBO), targeted by New Horizons[130]
The KBO 2014 MU69, a potential target for the Kuiper belt object mission

After passing Pluto, New Horizons will continue on through the Kuiper belt, making a flyby of a Kuiper belt object (KBO) the next reasonable objective of an extended mission. Mission planners searched for one or more additional Kuiper belt objects (KBOs) of the order of 50–100 km (31–62 mi) in diameter as targets for flybys similar to the spacecraft's Plutonian encounter, but, despite the large population of KBOs, many factors limit the number of possible targets. Because the flight path is determined by the Pluto flyby, and the probe only has 33 kilograms of hydrazine remaining, whatever object is visited will need to be within a cone, extending from Pluto, of less than a degree's width. This ruled out any possibility for a flyby of Eris, a trans-Neptunian object comparable in size to Pluto.[131] It will also need to be within 55 AU, because beyond 55 AU, the communications link will become too weak, and the RTG wattage will have decayed significantly enough to hinder observations. Desirable KBOs would be well over 50 km (31 mi) in diameter, neutral in color (to compare with the reddish Pluto), and, if possible, have a moon that imparts a wobble. After a search along New Horizon's flight path using the Hubble Space Telescope, only three KBOs were found in range, and one of those objects was later dropped from consideration.[132]

Search[edit]

In 2011 a dedicated search for suitable KBOs using ground telescopes was started by mission scientists. Large ground telescopes with wide-field cameras, notably the twin 6.5-meter Magellan Telescopes in Chile, the 8.2-meter Subaru Observatory in Hawaii, and the Canada–France–Hawaii Telescope[101][133] were used to search for potential targets. Through the citizen-science project, the public helped to scan telescopic images for possible suitable mission candidates by participating in the Ice Hunters project.[134][135][136][137][138] The ground-based search resulted in the discovery of about 143 KBOs of potential interest,[139] but none of these were close enough to the flight path of New Horizons.[133] Only the Hubble Space Telescope was deemed likely to find a suitable target in time for a successful KBO mission.[140] On June 16, 2014, time on Hubble was granted.[141] Hubble has a much greater ability to find suitable KBOs than ground telescopes. The probability that a target for New Horizons would be found was estimated beforehand at about 95%.[142]

Suitable KBOs[edit]

On October 15, 2014, it was revealed that Hubble's search had uncovered three potential targets,[130][143][144][145][146] provisionally designated PT1 ("potential target 1"), PT2 and PT3 by the New Horizons team. All are objects with estimated diameters in the 30–55 km range, too small to be seen by ground telescopes, at distances from the Sun of 43–44 AU, which would put the encounters in the 2018–2019 period.[143] The initial estimated probabilities that these objects are reachable within New Horizons‍ '​ fuel budget are 100%, 7%, and 97%, respectively.[143] All are members of the "cold" (low-inclination, low-eccentricity) classical Kuiper belt, and thus very different from Pluto. PT1 (designated 1110113Y on the HST web site[147]), the most favorably situated object, is magnitude 26.8, 30–45 km in diameter, and would be encountered around January 2019.[148] A course to reach it would require about 35% of New Horizons‍ '​ available trajectory-adjustment fuel supply. A mission to PT3 may be preferable, because it is brighter and therefore probably larger than PT1.[143] Once sufficient orbital information was provided, the Minor Planet Center gave official designations to the three target KBOs: 2014 MU69 (PT1), 2014 OS393 (PT2), and 2014 PN70 (PT3). (By the fall of 2014, a possible fourth target, 2014 MT69, had been eliminated by follow-up observations.)

New Horizons principal investigator Alan Stern will make a recommendation to NASA in August 2015 on which of the two KBOs the spacecraft should visit. The preferred flyby target is PT1, a 40–70 km object, but PT3, a slightly bigger object, could also be targeted for a flyby, with the decision to be made in August 2015. PT2 is no longer under consideration.[149][150] Once the target is chosen, a series of trajectory correction maneuvers will be performed in October and November 2015. In order to complete the mission, funding will need to be obligated following a senior review of planetary science missions in 2016, with the results of that review to be announced in August or September 2016. If funded, the KBO flyby would occur in 2019.[132]

Post-KBO mission[edit]

Even though it was launched far faster than any outward probe before it, New Horizons will never overtake either Voyager 1 or Voyager 2 as the most distant human-made object from Earth. Close flybys of Saturn and Titan gave Voyager 1 an advantage with their gravity assist. When New Horizons reaches the distance of 100 AU, it will be travelling at about 13 km/s (29,000 mph), around 4 km/s (8,900 mph) slower than Voyager 1 at that distance.[151]

Public-defined TNO mission[edit]

In August 2013, it was proposed[152] to use the radio-tracking data from New Horizons to discover constraints on the position of a hypothesized trans-Neptunian planetary-sized body.[153]

Gallery[edit]

Images of the launch[edit]

The Atlas V 551 rocket, used to launch New Horizons, being processed a month before launch. 
View of Cape Canaveral Launch Complex 41, with the Atlas V carrying New Horizons on the pad. 
Distant view of Cape Canaveral during the launch of New Horizons on January 19, 2006. 
NASA TV footage of New Horizons‍ '​ launch from Cape Canaveral. (4:00) 

Images of Jupiter flyby[edit]

A composite image of Jupiter and Io, taken on February 28 and March 1, 2007 respectively. Jupiter is shown in infrared, whereas Io is shown in true-color. 
LORRI images of Jupiter's rings. The top image was taken on approach to Jupiter, whereas the bottom image was taken on departure, illuminated by the Sun. 
A composite false-color image of Oval BA, otherwise known as the "Little Red Spot", using New Horizons‍ '​ LORRI and the Hubble Space Telescope‍ '​s WFPC2. 
An MVIC image of Jupiter's equatorial atmosphere, showing Buoyancy waves that travel at 100m/s faster than surrounding clouds. 

Images of Jupiter's moons[edit]

A LORRI image of Io, taken while New Horizons passed through its penumbra. Volcanic plumes, lava and aurora are all visible in this image. 
New Horizons view of Europa. One of the goals of New Horizons at Europa was to examine the "nature of the icy crust and the forces that have deformed it". 
New Horizons‍ '​ view of Ganymede 
Image of Callisto. The moon was used by the New Horizons team to practice detecting water ice, in preparation for similar experiments at Charon. 
Media related to New Horizons Jupiter system encounter at Wikimedia Commons

Images of Pluto flyby[edit]

April 2015: Pluto and Charon – first color image taken by Ralph during AP1 on April 9, 2015[148][154] 
May 2015: Pluto as seen by LORRI during AP2 from a distance of 75 million km away[155] 
May 2015: Rotating Pluto as seen from about 50–55 million km away 
June 2015: Pluto's closest-approach hemisphere seen from 31 million km away 
June 2015: Pluto image (color) from 18 million km away 
June 2015: Pluto system, taken by the New Horizons space probe. 
June 2015: Pluto (left) and its moon Charon, taken by the New Horizons space probe. 
June 2015: Pluto - two faces - away from Charon (left); toward Charon (right). 
June 2015: Pluto - two different sides - in color. 
July 2015: Pluto System viewed by New Horizons (animation). 
July 2015: Pluto and Charon as imaged by New Horizons. 
July 2015: Pluto images (bw) viewed by New Horizons. 
July 2015: Pluto image (color) viewed by New Horizons. 
July 2015: Pluto image (color) viewed by New Horizons. 
Pluto and Charon as viewed by New Horizons
(highest-resolution; color; July 14, 2015).
 
Pluto and Charon as viewed by New Horizons
(color; July 11, 2015).
 
Pluto and Charon as viewed by New Horizons
(false-color; July 13, 2015).
 
First signs of geological features on Pluto
(annotated; July 10, 2015).
 
Pluto viewed by New Horizons
(annotated; July 11, 2015).
 
Pluto viewed by New Horizons
(9 July 2015)
 
Pluto viewed by New Horizons
(11 July 2015).
 
Pluto viewed by New Horizons
(11 July 2015).
 
Pluto viewed by New Horizons
(12 July 2015).
 
Pluto viewed by New Horizons
(13 July 2015).
 
Pluto as viewed by New Horizons
(color; July 11, 2015).
 
Pluto viewed by New Horizons
(color; animated; July 6, 2015).
 
Pluto as viewed by New Horizons
(color; July 13, 2015).
 
Pluto – Hillary Montes southwest of Tombaugh Regio
(July 14, 2015).
 
Pluto – Norgay Montes near equator
(July 14, 2015).[156]
 
Pluto – Hillary Montes and Norgay Montes
(14 July 2015).[157]
 
Pluto – Sputnik Planum – in center left of Tombaugh Regio
(July 14, 2015).[158]
 
Media related to New Horizons Pluto encounter at Wikimedia Commons

Images of Pluto's moons[edit]

Charon, moon of Pluto, viewed by New Horizons
(July 12, 2015).
 
Charon, moon of Pluto, viewed by New Horizons
(July 11, 2015).
 
Charon, moon of Pluto, viewed by New Horizons
(annotated; July 11, 2015).
 
Charon as viewed by New Horizons
(context; July 14, 2015).
 
Charon as viewed by New Horizons
(closeup; July 14, 2015).
 
Pluto's third most distant moon, Nix, as viewed by New Horizons
(July 11, 2015).
 
Pluto's third most distant moon, Nix, as viewed by New Horizons
(July 13, 2015).
 
Pluto's fifth most distant moon, Hydra, as viewed by New Horizons
(July 14, 2015).
 
Processed image of Hydra with red lines. 
Media related to New Horizons Charon encounter at Wikimedia Commons

Timeline[edit]

Timeline of the New Horizons mission
Phase Date Event Description References
Pre-Launch Phase January 8, 2001 Proposal team meets face-to-face for the first time at the Johns Hopkins University Applied Physics Laboratory [159]
February 5, 2001 New Horizons name chosen. [159][160]
April 6, 2001 New Horizons proposal submitted to NASA. It was one of five proposals submitted, which were later narrowed to two for Phase A study: POSSE (Pluto and Outer Solar System Explorer) and New Horizons. [159]
November 29, 2001 New Horizons proposal selected by NASA. Started Phase B study. [161]
March 2002 Budget zeroed by Bush administration, later overridden [162]

[163]

June 13, 2005 Spacecraft departed Applied Physics Laboratory for final testing. Spacecraft undergoes final testing at Goddard Space Flight Center (GSFC). [164]
September 24, 2005 Spacecraft shipped to Cape Canaveral It was moved through Andrews Air Force Base aboard a C-17 Globemaster III cargo aircraft. [64]
December 17, 2005 Spacecraft ready for in rocket positioning Transported from Hazardous Servicing Facility to Vertical Integration Facility at Space Launch Complex 41. [citation needed]
January 11, 2006 Primary launch window opened The launch was delayed for further testing. [citation needed]
January 16, 2006 Rocket moved onto launch pad Atlas V launcher, serial number AV-010, rolled out onto pad. [165]
January 17, 2006 Launch delayed First day launch attempts scrubbed because of unacceptable weather conditions (high winds). [65][66]
January 18, 2006 Launch delayed again Second launch attempt scrubbed because of morning power outage at the Applied Physics Laboratory. [166]
Launch Phase January 19, 2006 Successful launch at 14:00 EST (19:00 UTC) The spacecraft was successfully launched after brief delay due to cloud cover. [67][68]
Flyby Phase April 7, 2006 Passes Mars The probe passed Mars: 1.7 AU from Earth. [78][167]
June 13, 2006 Flyby of asteroid 132524 APL The probe passed closest to the asteroid 132524 APL in the Belt at about 101,867 km at 04:05 UTC. Pictures were taken. [168]
November 28, 2006 First image of Pluto The image of Pluto was taken from a great distance. [84]
January 10, 2007 Navigation exercise near Jupiter Long-distance observations of Jupiter's outer moon Callirrhoe as a navigation exercise. [169]
February 28, 2007 Jupiter flyby Closest approach occurred at 05:43:40 UTC at 2.305 million km, 21.219 km/s. [170]
June 8, 2008 Passing of Saturn's orbit The probe passed Saturn's orbit: 9.5 AU from Earth. [170][171]
December 29, 2009 The probe became closer to Pluto than to Earth Pluto was then 32.7 AU from Earth, and the probe was 16.4 AU from Earth [172][173][174]
February 25, 2010 Half mission distance reached Half the travel distance of 2.38×109 kilometers (1,480,000,000 mi) was completed. [175]
March 18, 2011 The probe passed Uranus's orbit This is the fourth planetary orbit the spacecraft crossed since its start. New Horizons reached Uranus's orbit at 22:00 GMT. [176][177]
December 2, 2011 New Horizons drew closer to Pluto than any other spacecraft has ever been. Previously, Voyager 1 held the record for the closest approach. (~10.58 AU) [178]
February 11, 2012 New Horizons was 10 AU from Pluto. Distance from Pluto at around 4:55 UTC. [179]
July 1, 2013 New Horizons captures its first image of Charon Charon is clearly separated from Pluto using the Long-Range Reconnaissance Imager (LORRI). [180][181]
October 25, 2013 New Horizons was 5 AU from Pluto. Distance from Pluto [179][182]
July 20, 2014 Photos of Pluto and Charon Images obtained showing both bodies orbiting each other, distance 2.8 AU. [183]
August 25, 2014 The probe passed Neptune's orbit This was the fifth planetary orbit crossed. [184]
December 7, 2014 New Horizons awoke from hibernation. NASA's Deep Sky Network station at Tidbinbilla, Australia received a signal confirming that it successfully awoke from hibernation. [107][108]
January 2015 Observation of Kuiper belt object 2011 KW48 Distant observations from a distance of roughly 75 million km (~0.5 AU) [185]
January 15, 2015 New Horizons is now close enough to Pluto and begins observing the system Distance from Pluto [186][187]
March 10–11, 2015 New Horizons was 1 AU from Pluto. Distance from Pluto [188]
March 20, 2015 NASA invitation NASA invited general public to suggest names to surface features that will be discovered on Pluto and Charon [189]
May 15, 2015 Better than Hubble Images exceed best Hubble Space Telescope resolution. [190]
July 14, 2015 Flyby of the Pluto system: Pluto, Charon, Hydra, Nix, Kerberos and Styx  • Flyby of Pluto around 11:49:57 UTC at 12,500 km, 13.78 km/s.
 • Pluto is 32.9 AU from Sun.
 • Flyby of Charon around 12:03:50 UTC at 28,858 km, 13.87 km/s.
[191]
Science Phase 2015–16 Downlink the observations of the Pluto system back to Earth, and ongoing science discovery based on the observations The bit rate of the downlink is very limited, so it will take until the end of 2015 to get the compressed, “browse” data, and until late 2016 to get all the data in full resolution. [54][191]
2016–20 Flyby of one or more Kuiper belt objects (KBOs) The probe will perform flybys of KBOs reachable from the spacecraft's trajectory after the Pluto system flyby. Heliosphere data collection expected to begin. [192]
2019 Flyby of one Kuiper belt object (KBO): 2014 MU69 or 2014 PN70 2014 MU69 (also labeled "PT1" [193]) is currently the most probable known target in the Kuiper belt. Heliosphere data collection expected to continue. [194][195]
2026 Expected end of the mission, based on RTG plutonium decay. Heliosphere data collection expected to be intermittent if instrument power sharing is required. [196]
Post-Mission Phase 2038 New Horizons will be 100 AU from the Sun. If still functioning, the probe will explore the outer heliosphere. [151]

See also[edit]

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