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NASA New Horizons Spacecraft on Its Way to Pluto

19 January 2006

NASA New Horizons Spacecraft on Its Way to Pluto

By Cheryl Pellerin
Washington File Staff Writer

Washington – NASA has launched a spacecraft designed to explore for the first time distant Pluto, its moons and possibly the icy Kuiper Belt mini-worlds 1.6 billion kilometers beyond the orbit of the planet Neptune.

The 476-kilogram piano-sized New Horizons probe lifted off January 19 from Cape Canaveral Air Force Station in Florida, aboard an Atlas V expendable launch vehicle. An initial January 17 launch attempt was cancelled because of strong, gusting ground winds at the launch pad.

New Horizons will reach the unexplored Pluto system in July 2015 to conduct a five-month-long study from the close-up vantage point of a spacecraft.

The value of New Horizons, NASA Administrator Michael Griffin said at a January 17 press briefing, is in being “able to examine the primordial constituents from which the solar system and all the planets and we ourselves were formed.”

It is “fantastically interesting,” he added, “to have a chance, maybe within my lifetime, for scientists to see up close what those objects look like and to begin our reconnaissance of that region of space.”

Pluto, discovered by American astronomer Clyde Tombaugh in 1930, is the only planet in the solar system that never has been visited by a spacecraft.

Pluto is unusually hard to study from Earth because it is so small and far away. When viewed from Earth, it is 50,000 times fainter than Mars, and less than 1 percent of Mars’ apparent diameter when viewed from Earth. Even the Hubble Space Telescope shows only blurry patches of light and dark materials on Pluto’s surface.

The spacecraft and its seven science instruments will examine the global geology and composition of Pluto and Charon, one of its moons, map their surface compositions and temperatures and study Pluto's atmosphere and structure. New Horizons also will study two small moons discovered in 2005 in the Pluto system.

Then, as part of a potential extended mission, it will head deeper into the Kuiper Belt – a vast disk-shaped region past the orbit of Neptune and containing many small icy bodies – to study one or more of the objects there.

"Exploring Pluto and the Kuiper Belt is like conducting an archeological dig into the history of the outer solar system, a place where we can peek into the ancient era of planetary formation," said New Horizons principal investigator Alan Stern of the Southwest Research Institute Department of Space Studies in Colorado.

New Horizons is the fastest spacecraft ever launched; it blasted away from Earth at 16 kilometers per second, the highest velocity of any space vehicle.

The probe will reach the orbital path of the Earth’s moon in nine hours – in contrast with three days for the NASA Apollo missions – and pass Jupiter 13 months later, using the planet’s gravity to increase its speed on the way to Pluto.

A compact disc is on board the spacecraft containing more than 435,000 names of people who, through the New Horizons Web site, signed up to send their names to Pluto. The sign up is an effort to publicize the mission and gain broader understanding of the mission.

The mission will cost about $700 million – including spacecraft and instrument development, launch vehicle, mission operations, data analysis and education/public outreach – over the period 2001-2016.

PLUTO AND ITS MOONS

Pluto – the smallest planet in the solar system and farthest from the sun – is different from the inner, rocky planets (like Earth) or the outer gas giants.

It is called an "ice dwarf" and is one of the largest and brightest members of the Kuiper Belt, a vast region of ancient, icy, rocky bodies more than a billion miles beyond Neptune’s orbit. It orbits the sun once every 248 Earth years and is tipped on its side.

Its exact diameter is close to 2,360 kilometers, but uncertain within about 50 kilometers; that is about two-thirds the diameter of Earth’s moon.

Pluto’s surface composition includes nitrogen, carbon monoxide, methane and water ices. It has a thin but complex atmosphere – made mostly of nitrogen, with traces of methane, carbon monoxide and some heavier hydrocarbons – that undergoes extreme seasonal changes as Pluto orbits the sun.

The planet’s surface has ranges of very bright and dark areas – more contrast than any other planet in the outer solar system.

Charon’s diameter is about 1,200 kilometers, the largest satellite relative to the planet it orbits. Because the two bodies are so close in size, and they orbit about a center of mass that is outside Pluto’s surface, Pluto-Charon is considered a double planet. No other planet in the solar system falls into this category.

Astronomers are eager to know how a system like Pluto and its moons could form, and NASA’s New Horizons mission will be the first trip to a binary world.

Charon has no detectable atmosphere and, like Pluto, its density indicates that it is composed of a mix of ice and rocky material.

In May 2005, scientists trained the Hubble Space Telescope on Pluto and Charon in a continuing search for more satellites. After weeks of processing, analysis and checking, they found two small satellites – provisionally called S/2005 P1 and S/2005 P2 – circling two times to three times farther away from Pluto than Charon.

THE TRIP TO PLUTO

The spacecraft will "sleep" in electronic hibernation for much of the cruise to Pluto. Operators will turn off all but the most critical electronic systems and monitor the spacecraft once a year to check on critical systems, calibrate instruments and perform course corrections, if necessary.

The probe will send back a beacon signal once a week to give operators an instant read on spacecraft health. Beginning about a month after launch, the instruments will be turned on to begin testing and ensure they and their power supplies are operating properly. The entire spacecraft, drawing electricity from a single nuclear generator, operates on less power than a pair of 100-watt household light bulbs.

The payload consists of three optical instruments, two plasma instruments, a dust sensor and a radio science receiver/radiometer:

• Alice is an ultraviolet imaging spectrometer that will probe Pluto’s atmosphere and structure.

• Ralph is a visible and infrared camera that will produce high-resolution color maps and surface composition maps of the Pluto and Charon surfaces.

• The Long-Range Reconnaissance Imager (LORRI) will image Pluto's surface at football-field-sized resolution, resolving features as small as 45.7 meters across.

• Solar Wind Around Pluto (SWAP) will measure charged particles from the solar wind near Pluto to determine whether it has a magnetosphere – a magnetized region around the planet – and how fast its atmosphere is escaping.

• The Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) will search for neutral atoms that escape the planet's atmosphere and become charged by their interaction with the solar wind.

• The Student Dust Counter (SDC), designed by students at the University of Colorado, will count and measure the masses of dust particles along the spacecraft's entire journey, covering regions of interplanetary space never before sampled.

• Radio Science Experiment (REX), a circuit board containing sophisticated electronics that has been integrated with the spacecraft's radio telecommunications system, will study Pluto's atmospheric structure, surface thermal properties, and measure the masses of Pluto, Charon and Kuiper Belt objects.

"The New Horizons payload is a remarkably compact, but powerful suite of instruments that will revolutionize our knowledge of Pluto, its large moon Charon and bodies farther out in the Kuiper Belt," Stern said.

"Hold on to your hats,” he added, “this payload is going to provide a ringside seat as New Horizons explores the deep outer solar system."

Instrument calibrations are planned throughout early and mid-2006, in anticipation of the mission's early-2007 Jupiter flyby on the way to Pluto.

More information about the New Horizons mission is available on the NASA Web site.

(The Washington File is a product of the Bureau of International Information Programs, U.S. Department of State. Web site: http://usinfo.state.gov)