Spacecraft faces delay before Pluto launch

The Atlas V rocket at Cape Canaveral, Florida, with the New Horizons spacecraft aboard, ready for today's launch to Pluto. Picture / Reuters

What's a few days' delay, when a nine-year journey is at stake?

That's one of the questions facing scientists from the US National Aeronautics and Space Administration (Nasa) in Houston today.

The US space agency  has today been forced to delay the liftoff of its first probe to Pluto because of a technical issue, the mission's flight controller said.

The New Horizons probe had been due to take off on a massive unmanned Atlas 5 rocket from Cape Canaveral air force station around 7am today (NZT). Nasa has a window until February 14 to launch the satellite, but postponements could add up to five years to the journey.

Scientists and space afficionadoes everywhere are excited about the planned nine-year journey to the smallest, coldest and least-understood planet in the Solar System - the "ice-dwarf" world of Pluto.

It will be the first ever mission to the most distant planet orbiting the Sun and scientists are hoping that it will shed some much-needed light on the darkest outer-reaches of our planetary neighbourhood.

"What we know about Pluto today could fit on the back of a postage stamp," said Colleen Hartman of the (Nasa).

"The textbooks will be rewritten after this mission is completed."

Light from the Sun takes more than four hours to reach Pluto, which is so faint that it can barely be seen even with some of the best telescopes.

As a result, it was the last planet to be discovered and now it is the last to be explored by spacecraft.

Yesterday an interplanetary probe called New Horizons sat on top of a giant Atlas 5 rocket waiting to blast off from the Cape Canaveral launch pad in Florida to its final destination some 3.1 billion miles from Earth.

If all goes to plan the probe should arrive at Pluto in 2015.

New Horizons is a triangular, piano-sized spacecraft weighing 1,025 pounds.

It will travel so far from the Sun that solar panels would be useless in the dim sunlight.

This is why the probe has a nuclear-powered battery.

The initial propulsion, however, is by conventional rocket engines.

Nine hours after launch, the probe should have passed the orbit of the Moon, the fastest time taken by any spacecraft to reach this point.

In just 13 months it is expected to have arrived at Jupiter where it will use the planet's massive gravitational pull to accelerate its speed still further by making a "sling shot" manoeuvre to catapult it on its way.

Without the extra zip of a Jupiter swing-by, the New Horizons probe would take an extra five years to reach Pluto - such are the vast distances and effort involved in reaching the farthest planet in the Solar System.

Pluto was discovered in 1930, and only then as a result of a fortunate accident that led a young American astronomer called Clyde Tombaugh to make a very careful survey of the night sky.

Calculations based on the motions of Uranus and Neptune, which later turned out to be erroneous, had predicted a "planet X" beyond Neptune.

Clyde, who did not at the time know that the calculations were wrong, started to search the sky for the mystery object and soon identified the ninth planet.

Pluto, which was named after the Roman god of the underworld, perhaps because it is in perpetual darkness, travels round the Sun once every 248 years in a highly eccentric orbit.

The orbit is so eccentric that it sometimes brings Pluto closer to the Sun than Neptune, which occurred between 1979 and 1999.

Pluto is also odd because it rotates in the opposite direction to most of the other planets.

In addition, Pluto is known to be unlike any of the other inner rocky planets, such as Earth, or outer gaseous giant planets like Jupiter - it belongs to a different type of planetary body known as an "ice dwarf".

Smaller versions of these stray objects make up a band of frozen material that orbits the Sun as a swarm of comet-like objects known as the Kuiper Belt, which was only fully recognised about 15 years ago.

In fact, Pluto is now considered to be the first Kuiper Belt object to be identified.

Last year another Kuiper Belt object bigger than Pluto was discovered, raising questions about whether it, too, should be considered a planet - the tenth in the Solar System.

Indeed, following Tombaugh's death in 1997, some astronomers had suggested that Pluto was so small and insignificant that its status as a full-sized planet should be downgraded to that of a minor planet - a suggestion quashed in 1999 by the International Astronomical Union, which has responsibility over such affairs.

If Pluto orbited another planet it would be considered a satellite.

Indeed, seven of the moons in the solar system - the Moon, Io, Europa, Gannymede, Callisto, Titan and Triton - are known to be bigger than Pluto, which is just 1,413 miles in diameter.

Pluto would cover about half the size of North America and its own moon, Charon, discovered in 1978, is not much smaller.

This is why some astronomers have sometimes referred to them as a double planet.

Last year, the Hubble Space Telescope observed two additional moons around Pluto, which are some 5,000 times fainter than the planet itself.

Hubble also captured a patchwork of light and dark areas on the planet's surface, which probably represents mixtures of different types of ice possibly coated with tar-like organic substances.

The light reaching Pluto is so weak that temperatures even in a "summer" rarely reach higher than -230C.

It is believed that its atmosphere goes through a seasonal freezing and thawing, from solid ice to gas and back again each orbit.

"Not even Tombaugh and his mentors could have forecast how fascinating their new planet would turn out to be," said Alan Stern, the principal investigator of the New Horizons mission.

"For the ninth planet was revealed to be the first known world with a satellite so large it could be called a double planet, a world with complex seasons and a chaotic orbit, and the only planet with an atmosphere that freezes out and then is reborn every orbit," Dr Stern said.

"Pluto, replete with polar caps and fresh snows of not one, but three exotic surface ices, methane, nitrogen and carbon monoxide, is an exotic wonderland on the ragged edge of the Solar System's vast outer wilderness," said Dr Stern, a space scientist at the Southwest Research Institute in Boulder, Colorado.

The discovery of the Kuiper Belt fuelled a revolution in the understanding, origin, architecture and richness of the outer solar system, he explained.

"If all goes as planned, New Horizons will cross the entire span of the solar system in record time and conduct flyby reconnaissance studies of the Pluto-Charon system in 2015 and then one or more Kuiper Belt objects before 2020," Dr Stern said.

But the technical problems facing the probe are formidable, even if it survives the rigours of launch and the critical few hours that follow its escape from the influence of Earth's atmosphere and gravity.

The spacecraft is fitted with a nuclear power supply which uses the heat of radioactive decay from 11 kilograms of plutonium-238 to generate 200 Watts of electricity - enough to power a coupe of light bulbs.

Problems with the supply of the plutonium pellets almost jeopardised the mission.

A security breach at the Los Alamos National Laboratory in New Mexico, where the pellets were fabricated, temporarily halted production.

Nasa had to use left-over pellets from another space mission to ensure that everything would be ready on time for the launch window, which ends in mid-February.

In fact, New Horizons has not always been Nasa's favourite mission.

The space administration initially thought that any mission to far-away Pluto would be far too expensive to justify a journey to such a small, insignificant world.

After a political struggle, and lobbying by a 17-year-old high school student who was also a persuasive space enthusiast, the US Congress gave Nasa money for a smaller, more streamlined mission, despite the space agency's reservations.

The total cost of New Horizons is now running at just over US$550m.

The probe will carry a suite of instruments, including ultraviolet and infrared spectrometers, to study the composition of the planet's surface and atmosphere.

Once the probe has completed its flyby of Pluto and Charon - it will not be able to orbit the tiny planet - it will continue on its way to study the mysterious objects of the Kuiper Belt, which are thought to be remnants from the time when the planets first formed some 4.5 billion years ago.

"Exploring Pluto and the Kuiper Belt is like conducting an archaeological dig into the history of the outer solar system, a place where we can peek into the ancient era of planetary formation," Dr Stern said.

A detector will also count the grains of interplanetary dust collected on the nine-year journey, which the probe will spend in electronic "hibernation" with all systems shut down.

Each week the probe is programmed to send beacon signals back to Earth, which will take some four hours to travel through the immense void of interplanetary space.

Once a year, engineers will wake up everything on board to check out the critical computer components, calibrate instruments and perform any necessary course alterations.

Speeding through the darkness of interplanetary space will take New Horizons nine years, even with the help of a Jupiter sling-shout.

It will be a long, silent journey to the god of the underworld.

But when the probe arrives in 2015, the final view should be well worth the wait.

- INDEPENDENT