A little over two years ago, in the summer of 2015, I was anxiously refreshing the APL/NASA website page waiting for new pictures from the New Horizons mission. Up until this point, there had been no pictures of the (dwarf) planet Pluto other than some extremely pixelated blobs from the Hubble Space Telescope. This icy world, containing more land than the continent of Europe, was only recently explored, and even then the surface was only scratched. New Horizons vastly expanded our knowledge of Pluto and its complicated system of moons, and will continue to widen what is known about the distant Kuiper Belt as it continues to operate.

New Horizons might just be my all-time favorite spacecraft, and because of it we have tons of new pictures and data from the Pluto system that would have otherwise been impossible to gather.

Let's see what it did and how it did it!

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Pluto, the world on the edge of the solar system

Pluto is one of the biggest worlds in the Kuiper Belt, a collection of large icy objects orbiting the sun in highly elliptical, distance orbits past Neptune. Despite being discovered almost a century ago, Pluto went from unconfirmed object to planet to dwarf planet with absolutely no real pictures of it. Prior to 2015, here is one of the absolute best pictures of Pluto that existed:

Not very impressive, is it?
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Pluto lies at a similar distance from the sun as Neptune, but is much harder to image. Why? It's simple: Neptune is about 24 times wider than Pluto, and as such it is far easier to get high resolution pictures of Neptune using telescopes than it is for Pluto. To actually get better images than the pixelated mess above and actually collect close-up environmental data, we need something that can physically be at Pluto: Enter New Horizons.

Ice Peaks on Pluto from New Horizon. I want to emphasize that this is a real place. You could stand down there, on that ridge, and look around at the dim landscape just as you would on Earth at sunset.
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Pluto is really an incredible place for a host of reasons, including its non-negligible atmosphere, giant moon Charon, possible geologically active surface, and the shear size/distance of the planet. To properly provide a decent overview of Pluto, Charon and the rest would take up so much space that I would never get to the New Horizons spacecraft - so this will be in another post sometime in the future.

So far, only one mission to Pluto has ever been executed, using the New Horizons spacecraft.

Spacecraft Overview

New Horizons is a relatively small spacecraft (<500 kilograms) that was sent on a solar-escape trajectory onto a flyby of Pluto and its moons. Pluto's massive distance from the sun (and Earth) makes missions difficult: In order to limit the amount of propellant needed to a reasonable amount, you must either plan a flyby that will arrive in a decade or so (but only be able to study the world for one pass) or plan an orbiter mission that will take much, much longer to arrive. New Horizons' mission was the former: The spacecraft was planned to fly past Pluto, once, never to return.

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Above is a picture of the New Horizons spacecraft. The giant dish antenna is used to send data back to Earth. I still find it incredible that we can reliably download pictures and data from a metal box 8 billion kilometers away.

After the flyby, New Horizons was sent on a slightly corrected trajectory to pass by a much smaller Kuiper Belt Object (KBO) known as 2014 MU69(only about 20 kilometers across). This will occur in just under a year on New Years 2019, and will provide high resolution images of a second KBO other than Pluto.

Notice that huge light speed latency of over 8 hours. That means that signals coming from New Horizons take 8 hours to reach us travelling at the speed of light. Or, to put it another way, it takes 8 hours for anything that happens on Pluto to "happen" for us here on Earth.
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It takes a very long time to get to Pluto even on the fast flyby trajectory New Horizons used - The mission launched in 2006 and only arrived at Pluto in 2015. Due to the very high relative velocity between New Horizons and Pluto (made necessary by the "quick" 9 year transfer time), New Horizons will sail out of the solar system never to return, just as Voyager has done.

Launch and Mission Highlights

New Horizons launched on January 19th, 2006 on board an Atlas V rocket from Florida, USA. The Atlas V is a type of rocket built by United Launch Alliance, and is still commonly used to this day (I have actually had the good fortune of being able to see a few of these fly in person down at Vandenberg Air Force Base. If you live in California or Florida, I highly recommend watching a rocket launch when you get the chance as they are absolutely incredible).

The launch of New Horizons. The payload of this rocket has traveled farther from us than almost any other man-made object.
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After being sent off on an Earth escape trajectory by the launch vehicle, New Horizons travelled onward, past the orbit of Mars. Coincidentally the spacecraft passed very close to a 2 kilometer wide asteroid in the asteroid belt known as 132524 APL, the best image of which is shown below:

New Horizons view of asteroid 132524 APL/2002 JF56. This asteroid remains unexplored.
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Next, New Horizons flew by the planet Jupiter, altering its trajectory via a gravity assist. While in the vicinity of Jupiter, the spacecraft's instruments were tested prior to the Pluto encounter. Here's a picture of one of Jupiter's moons taken by New Horizons:

Ganymede, a massive moon of Jupiter, as seen by the New Horizons spacecraft. This world is physically larger than the planet Mercury but not as well known. Its surface remains unexplored.
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After passing Jupiter in the fall of 2006, New Horizons traveled for almost 9 more years before reaching Pluto and its moons.

Upon arrival in 2015, New Horizons changed everything scientists knew about Pluto with high-resolution images and close-up data collection. Again, I can't possibly go into everything that was discovered upon arrival in this post as it would take away from the main point, but I highly recommend that you go looking yourself if you're interested - you can find a massive repository of New Horizons images here on NASA's mission page.

Charon, Pluto's giant moon, is around half the width of Pluto itself. Prior to the flyby, little was known about this object due to its sheer distance.
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Spacecraft Equipment

This spacecraft had to survive 9 years in the vacuum of space far from the sun in order to reach Pluto intact. Many of its systems are designed with this in mind, and allow the spacecraft to continue operating to this day at mind boggling distances from the sun and our home planet.

Like many spacecraft, New Horizons contains 16 individual thrusters to allow it make trajectory adjustments and rotate itself. Spacecraft positional knowledge (attitude) is provided by star trackers, which use the position of relatively fixed known stars to determine the orientation of the spacecraft.

Past the orbit of Jupiter, it becomes impractical to use solar cells for power due to the rapidly decreasing energy available from the sun at greater distances. Because of this fact, solar cells would be almost useless at the endless twilight of Pluto. New Horizons avoids this issue by utilizing a RTG (Radioisotope Thermoelectric Generator) for power. RTGs are pretty fascinating devices and deserve their own post altogether, but in short they harvest electricity from the radioactive decay of a huge chunk of alpha-emitting material. In the case of New Horizons, this material is Plutonium-238, which is present in such high quantities that the chunk of metal literally glows red-hot from the massive amount of alpha radiation. From the heat produced by this alpha decay, electrical energy can be extracted. This allows New Horizons to have a source of extremely reliable power for decades without relying on ineffective solar cells. Many other spacecraft, such as the Curiosity rover and Voyager also use these generators.

The RTG for New Horizons. The large metal fins serve as radiators. The dish antenna for the spacecraft is visible in the background.
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New Horizons also has a huge antenna as previously mentioned. This 2-meter dish uses high frequency microwaves (in the X-band) to send and receive signals and data. This large metal dish is incredibly necessary for sending electromagnetic signals (that decrease in strength with distance) across the 7.5 billion kilometers of vast nothingness that separates Pluto and Earth. Since data downlink from New Horizons is slow at these massive distances, the spacecraft had to take quite a long time to send back all of the collected data after the Pluto flyby.

Payloads

New Horizons has onboard numerous scientific payloads, used at Jupiter, Pluto, and beyond. One of the most interesting to us looking at pictures of Pluto is LORRI, or LOng-Range Reconnaissance Imager (spacecraft acronyms are often a bit silly...). LORRI is primary the source of the Pluto images you have seen previously in this post.

Technicians integrating LORRI into the spacecraft
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Other instruments include a device that analyzes solar wind plasma (SWAP), an ultraviolet imager (ALICE), and a student-built dust collector (VBSDC). You can read more about the various payloads by clicking here.

#What's Next?

The data collected by New Horizons will continue to fuel discoveries about Pluto for some time to come. Already an incredible amount has been learned about the dwarf planet despite the fact that the actually flyby of Pluto by New Horizons lasted only a short time. As previously mentioned, New Horizons still has more to discover, as it will be flying by a 20 kilometer icy asteroid beyond Pluto in less than a year, sending back high resolution images for us to see. I am personally quite looking forward to this upcoming encounter.

Exaggerated rendering of New Horizon's flyby of 2014 MU69
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As of now, New Horizons lies almost 11 light hours from Earth and only gets further away every second that passes. Eventually, it will leave the solar system and it will never come back. Once its nuclear battery decays to very low power outputs, New Horizons will no longer operate, but will obviously remain physically intact for a very, very long time. As far as I know, there are no current missions planned for returning to Pluto, but I hope that changes soon as there is still a ton to learn - after all, one side of Pluto wasn't even imaged well due to the fast flyby.

I hope you were able to learn something about this amazing spacecraft! Let me know if you have any comments, questions, or corrections.

Thanks for reading!

Thanks to New Horizons, we can enjoy this close-up view of some ice craters on the surface of Pluto.
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Sources for additional reading:
New Horizons Wikipedia Entry
Highly Recommended New Horizons Pluto Encounter Image Gallery
New Horizons NASA Mission Page
New Horizons APL Mission Page
Twitter Updates for New Horizons mission
Pluto Wikipedia Entry