New Horizons is the first mission to explore the “third zone” of our solar system: the dark, cold Kuiper belt. Launched on 19 January 2006, New Horizons tore past Jupiter only a year later. It took another 7 years to begin to approach Pluto. During its July 2015 flyby, New Horizons revealed Pluto to be a surprisingly varied world with craters, crevasses, glaciers, and a frozen “heart” of solid nitrogen ice. Then, in 2019, it flew past 2014 MU69, discovering a weird bi-lobed baby comet. New Horizons is still flying through the Kuiper belt, observing other objects from afar, and searching for one more flyby target.
Were it not for the efforts of The Planetary Society, its members, and its supporters, the New Horizons mission might never have gotten off the drawing board. From 1990 to 2000, NASA considered but ultimately rejected 4 separate Pluto missions before approving New Horizons for further development in 2001. The Planetary Society tirelessly fought for the mission with letter-writing campaigns, Congressional visits, and public outreach.
“The Planetary Society gave continued, strong support for a whole variety of different Pluto missions that never made it off the drawing board,” said New Horizons Principal Investigator Alan Stern in 2015. And while everyone from school children to the National Academy of Science ended up helping get the spacecraft off the ground, “The Planetary Society was always there—no question,” he said.
The New Horizons mission to Pluto cost $780.6 million. But that's not the whole story.
NASA / JHUAPL
Diagram of the New Horizons spacecraft
Mass at launch: 478 kilograms total, including 77 kilograms of fuel and 30 kilograms of science instruments (a highly miniaturized instrument package; for comparison, Cassini’s camera alone weighed twice as much as all of New Horizons’ instruments put together).
Size: 0.7 by 2.1 by 2.7 meters, high-gain antenna 2.1 meters diameter. In other words, about the size and shape of a grand piano.
Power: a single radioisotope thermoelectric generator (RTG) containing 11 kilograms of plutonium dioxide. At the start of the mission, the RTG provided 240 Watts of energy at 30 volts. Power output decreases by 3.5 watts per year.
For information on how New Horizons transmits data back to Earth, see this article.
New Horizons carries 7 science instruments, 4 of which are remote sensing and 3 that collect data in-situ.
Remote Sensing Instruments
Figure 3 from Weaver et al. 2008, "Overview of the New Horizons Science Payload"
New Horizons instrument fields of view (FOVs)
The fields of view (FOVs) of the Ralph MVIC (blue and yellow), Ralph LEISA (red), Alice airglow (green), and LORRI (purple) instruments are projected onto the sky plane; the listed boresights are measured in-flight values. The angular extent of each instrument’s FOV is also listed. The spacecraft +X direction is out of the page, the +Y direction is up, and the +Z direction is to the left. The LORRI field FOV overlaps the narrow portion of the Alice airglow channel, and the MVIC FOV overlaps the wide portion. The LEISA FOV overlaps the MVIC FOV.
Long Range Reconnaissance Imager (LORRI) is New Horizons’ highest-resolution camera. It consists of a telescope with an 20.8-centimeter aperture that focuses visible light onto a 1,024-pixel-square CCD. Its field of view is 0.29 degrees, and pixel scale is 4.95 microradians. It is monochrome, sensitive to wavelengths of light between 350 and 850 nanometers. In addition to high-resolution imaging, it’s used for optical navigation. When taking images for navigation, it often bins images by a factor of 4 in order to increase sensitivity and decrease file size. When New Horizons flew past Pluto, LORRI could perform exposures as long as 10 seconds; for the MU69 flyby, LORRI’s longest exposure time was increased to 30 seconds. Cheng et al. (2008)
Ralph is the color science camera system. It captured high-resolution color maps using a telescope with a 75-millimeter aperture. It splits incoming light into two sub-instruments: the Multispectral Visible Imaging Camera (MVIC), and the Linear Etalon Imaging Spectral Array (LEISA). MVIC has 7 different detectors, 6 of which are 5,024 by 32 pixels in size. All of them operate as pushbroom cameras, using time-delay integration to build up a stronger signal from faint targets, using spacecraft motion to sweep the field of view across the sky. Two of them are panchromatic (400 to 975 nanometers); there are 2 for redundancy. The other 4detectors have filters in front of them, limiting the light that reaches them only to certain wavelengths. One has a blue filter; one has a red filter; one has a near-infrared filter; and one has a methane filter. Because they see less light (it's filtered), they may move the spacecraft more slowly to take color MVIC images, allowing longer integration time on each pixel. Finally, MVIC has one more channel, the framing channel, which is 5,024 by 128 pixels in size and operates like a more traditional framing camera. Its main purpose is to be available for optical navigation in the event that LORRI failed. The field of view across MVIC’s 5,024 pixels is 5.7 degrees, and its pixel scale is 20 microradians. LEISA takes spectral data in near-infrared wavelengths from 1.25 to 2.5 microns. It is designed to be able to separate wavelengths more finely between 2.1 and 2.25 microns in order to map the temperature of surface nitrogen. Reuter et al. (2008) | How Ralph works
Alice is an ultraviolet imaging spectrometer that can be used either to directly image objects in UV light, or to probe an atmosphere by watching a bright star or the Sun pass behind the atmosphere and detect how the chemical species in the atmosphere absorb ultraviolet light. It breaks up ultraviolet light into 1,024 different spectral bands. It is similar to the UVIS instrument aboard Cassini. Stern et al. (2008)
Radio Science Experiment (REX) is coupled to New Horizons' telecommunications system. As with all space missions, the communications antenna can serve a scientific purpose, too. Watching the attenuation of the radio signal as it passes behind an atmosphere can yield a profile of the atmospheric pressure and temperature down to the surface. Extremely precise tracking of a stable signal from the spacecraft provide information on the masses of planets and moons. Tyler et al. (2008)
Solar Wind Analyzer around Pluto (SWAP) measured the interaction between the solar wind and the top of Pluto’s atmosphere in order to determine how fast Pluto’s atmosphere is leaking into space. McComas et al. (2008)
Pluto Energetic Particle Spectrometer Investigation (PEPSSI) searched for neutral atoms that escaped Pluto’s atmosphere and became charged by their interaction with solar wind particles. McNutt et al. (2008)
Finally, the Student Dust Counter (SDC) measures and counts the size of dust particles that the New Horizons mission encounters on its journey, along its entire flight trajectory. At Pluto, it studied the dust in the Pluto system that arises from impacts onto Pluto and its moons. It was built and operated by students at the University of Colorado at Boulder, the first science instrument on a NASA planetary mission to be design, built, and flown by students. Horányi et al. (2008)