Trip to Pluto to Take at Least 9 Years (New Horizons)

CAPE CANAVERAL, Fla. - It will be the fastest spacecraft ever launched, zooming past the moon in nine hours and reaching Jupiter in just over a year at a speed nearly 100 times that of a jetliner.

Its target is Pluto — the solar system's last unexplored planet, 3 billion miles from Earth. And the New Horizons spacecraft, set for liftoff on Tuesday, could reach it within nine years.

Pluto, a tiny, icy misfit of a planet — some say it's not a planet at all — neither resembles the rocky bodies of Mercury, Venus, Earth and Mars, nor the giant gaseous planets of Jupiter, Saturn, Uranus and Neptune. For years after its discovery 75 years ago, it was considered a planetary oddball.

But in recent years, astronomers have come to realize that Pluto's class of planetary bodies, ice dwarfs, isn't so odd after all. In fact, ice dwarfs are the most populous group in the solar system. Now, scientists have a chance to learn more about them and the origins of the planetary system.

"Just as a Chihuahua is still a dog, these ice dwarfs are still planetary bodies," said Alan Stern of the Southwest Research Institute in Boulder, Colo., the mission's principal investigator. "The misfit becomes the average. The Pluto-like objects are more typical in our solar system than the nearby planets we first knew."

When the 7-foot-tall New Horizons spacecraft reaches Pluto as early as 2015, the spacecraft will study the ninth planet's large moon, Charon, as well as two other moons just discovered last year. The $700 million mission should provide scientists with a better understanding of the Kuiper Belt, a mysterious region that lies beyond Neptune at the outer limits of the planetary system.

Besides being home to Pluto, the Kuiper Belt is believed to hold thousands of comets and icy planetary objects that make up a third zone of the solar system, the rocky and gaseous planets making up the other two. Scientists believe they can learn about the evolution of the solar system by studying the Kuiper Belt since it possesses debris left over from the formation of the outer solar system. Depending on its fitness after arriving at Pluto, New Horizons will attempt to identify one or two objects in the Kuiper Belt.

"It provides for us a window 4 1/2 billion years back in time to observe the formation conditions of giant planets," Stern said. "This is a little bit about rewriting the textbooks about the outer planets."

A successful journey to Pluto will complete a survey of the planets that NASA began in the early 1960s with the Mariner program's exploration of Mars, Mercury and Venus by unmanned spacecraft. The best images of Pluto currently come from the Hubble Space Telescope, but they suffer from low-resolution fuzziness, making it difficult for scientists to interpret what they're seeing.

The 1,054-pound piano-sized spacecraft will be launched on an Atlas V. The rocket's makers, Lockheed Martin, experienced problems on another Atlas propellant tank similar to the one being flown to Pluto, forcing a delay of New Horizons' launch by several days to give the contractor extra time for inspection.

"Because we have such a long way to go, we put this small spacecraft on one of the largest rockets the U.S. has in its inventory," said project manager Glen Fountain of the Johns Hopkins University Applied Physics Laboratory.

When New Horizons reaches Jupiter in 13 months, it will use that giant planet's gravity as a slingshot, shaving five years off the trip to Pluto. During the trip between Jupiter and Pluto, the probe will go into hibernation, closing down most systems to conserve power. It will send weekly "beeps" back to Earth, providing updates on the vehicle's condition.

If the spacecraft is unable to launch during its monthlong window that closes Feb. 14, the next opportunity is in February 2007, but that would push back an arrival at Pluto to 2020 since New Horizons wouldn't be able to get the gravity assist from Jupiter then.

Powered by nuclear fuel that will produce less energy than is used by two 100-watt lightbulbs, New Horizons is loaded with seven instruments that will be able to photograph the surfaces of Pluto and Charon and examine Pluto's atmospheric composition and structure. Two of the cameras, Alice and Ralph, are named for the bickering couple from television's "The Honeymooners."

The spacecraft has a thermos-bottle design that will allow it to stay at room temperature. Tucked inside the probe will be a U.S. flag and a CD containing about a half million names of ordinary citizens who signed up on a NASA Web site.

Scientists discovered in 2001 that binary objects — pairs like Pluto and Charon — litter the Kuiper Belt, and a year later they learned that Pluto's atmosphere undergoes rapid and dramatic global change. Last summer, scientists discovered Pluto's two extra moons.

Said Stern, "You can see why we think it's going to be like kids in a candy shop."

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Mission FAQs
http://pluto.jhuapl.edu/mission/missionFAQs.html

Mission
Why not go into orbit around Pluto?
What are some of the major challenges of this mission?
How large is the spacecraft and what types of instruments will it carry?

Management
What is the projected cost of this mission?

Why not go into orbit around Pluto?
There are two reasons. The first is an engineering reason. To get to Pluto (which is 5 billion kilometers or 3 billion miles from Earth) in just 9.5 years, as New Horizons plans, the spacecraft must travel very, very quickly. As a result, New Horizons will speed by Pluto at a velocity of about 43,000 kilometers per hour (27,000 miles per hour). To get into orbit, we would have to reduce that speed by over 90%, which would require more than 1,000 times the fuel that New Horizons can carry.

The second reason is scientific: If we did stop to go into orbit, we wouldn't be able to go on to explore the Kuiper Belt!

What are some of the major challenges of this mission?
The huge distance of Pluto from the Sun, about 32 times farther than the Earth-Sun distance, creates "extreme" conditions in several respects. First, it takes a long time to get to Pluto (9.5 years with a gravity boost from Jupiter and about 12 years without), which means that the spacecraft and instruments must have long lifetimes (i.e., their "warranties" must be good for over a decade!). The large distance from the Sun also means that solar cells cannot be used to power the spacecraft, and the onboard systems must be designed to operate in a cold environment. Finally, sending a spacecraft all the way to Pluto requires a powerful rocket and places severe constraints on the weights of the instruments. The more mass you want to carry, the larger the rocket needs to be. Even using the Lockheed-Martin Atlas V rocket, one of the most powerful in the U.S. fleet, New Horizons must weigh less than 1,025 pounds (465 kilograms).

All of the above pose major technical challenges, but the New Horizons team has found ways to overcome all of them and will deliver a spacecraft that can meet all of NASA's primary scientific objectives at Pluto.

How large is the spacecraft and what types of instruments will it carry?
The New Horizons spacecraft is roughly 8 feet (2.5 meters) across and will weigh approximately 1,025 pounds (465 kilograms) — about half a ton — when fueled.

Its design includes seven scientific instruments:

Alice is an ultraviolet spectrometer used for measuring gas composition
Ralph combines an infrared spectrometer (LEISA) for mapping surface composition with a color optical imager (MVIC) for mapping surface structure and composition
REX is a radio experiment for measuring atmospheric composition and temperature
LORRI is an optical telescope that provides the highest resolution imaging of the surface
PEPSSI is a plasma-sensing instrument for measuring particles escaping from Pluto's atmosphere
SWAP is a plasma-sensing instrument for measuring the properties of the solar wind at Pluto, Pluto's atmospheric escape rate, and for searching for a magnetosphere around Pluto. The "solar wind" is a stream of charged particles streaming away from the Sun at high speed.
SDC, an instrument used to measure dust impacts at the New Horizons spacecraft during its entire trajectory, was built by students at the University of Colorado!

How much does a mission to Pluto cost?

The cost of the mission, including the launch vehicle and operations through the Pluto-Charon encounter, will be roughly $650 million. Divided among the population of the United States (according to the U.S. Census clock at http://www.census.gov/main/www/popclock.html) over the 10-year duration of the mission, this comes out to about 20 cents per person, per year.

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