A NASA spacecraft built for trekking to at least two comets is ready for liftoff. During its projected four-year mission, the Comet Nucleus Tour - CONTOUR for short - will make the closest flybys ever of celestial visitors from afar, relaying scientific data perhaps useful in piecing together Earth's lively evolutionary past.

CONTOUR is set for launch July 1, riding skyward atop a Delta II rocket from Cape Canaveral Air Force Station in Florida. The $159 million CONTOUR is the sixth mission in NASA's Discovery Program of cheaper, better, faster spacecraft - each having a scientifically focused set of duties.

If all goes as planned, the spacecraft will fly as close as 62 miles (100 kilometers) from the nucleus of a comet, closer than any previous mission, to obtain detailed data on these diverse objects.

"Humankind has looked at comets for centuries. Yet we know amazingly little about themthat's about to change. We're about to enter into a golden era of comet investigation," said Colleen Hartman, Director, Solar System Exploration Division at NASA Headquarters in Washington, D.C. She said that CONTOUR is joining an ensemble of spacecraft -- such as Stardust, Deep Impact, as well as Europe's Rosetta mission -- that are set to explore comets in detail.

Hartman said that comets might be the source of much of the water that exists in Earth's oceans. "In fact, there is some speculation that human beings are made from comet dustbut I'll leave that one to others," she said.

CONTOUR will provide the most up-close images of a comet nucleus every taken to date, said Joseph Veverka, CONTOUR Principal Investigator at Cornell University in Ithaca, New York.

"Comets are mysterious objects. They are the most abundant and least understood bodies in our solar system. They are the best preserved pieces of the solid materials out of which the planets formed 4.6 billion years ago," Veverka said.

There are primary tasks assigned to CONTOUR's suite of 4 major instruments: Obtaining the best-ever images of a comet nucleus and carry out chemical analyses of the dust and gas that a comet releases.

Veverka leads a CONTOUR science team of 18 co-investigators from universities, industry and government agencies in the U.S. and Europe. He underscored CONTOUR'S value in helping discern Earth's history.

"Is it plausible that the air that we breathe in our atmosphere actually once was comet stuff. Is it likely that the original input of the molecules that led to the origin of life on Earth came from comets? Are we indeed the progeny of comets?," Veverka said.

CONTOUR is an 8-sided solar-powered craft, capable of spending some 60 percent of its primary mission in sleep mode, said Mary Chiu, CONTOUR Project Manager for The Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland. APL built the comet-chasing craft and is managing the project for NASA.

By hibernating between its comet sleuthing responsibilities, CONTOUR is a money saver. No need for constant babysitting from ground controllers, Chiu said.

The spacecraft carries its own bulletproof vests.

A five-layer dust shield of heavy Nextel and Kevlar fabric safeguards the compact probe from comet dust and debris, Chiu said. These materials will protect CONTOUR from swarms of small dust particles that surround a comet nucleus.

The spacecraft is enveloped in solar cells that energize its equipment.

"It's very durable. The only life-limiting part of the spacecraft is the amount of fuel that we have managed to put onboard," Chiu said. CONTOUR comes fully stocked with loads of fuel, she said.

CONTOUR's orbit loops around the Sun and back to Earth for annual "gravity swings" toward its targets; these maneuvers refine or revise CONTOUR's trajectory and help it reach several comets without using much fuel.

"I think we're going to set a new record with four swingbys and possibly more," said Robert Farquhar, APL'S CONTOUR Mission Director.

Hibernation sometimes occurs 9 months at a time, Farquhar said. Almost everything is turned off, except for spacecraft heaters and receivers. "That means we don't have to maintain a large operations team during that time and we don't have to make use of Deep Space Network antennas for a period of time," he added.

Farquhar said that there is always a possibility of an extended mission for CONTOUR. "We have the capability to use further Earth swingbys to go to more and more comets," he said.

"We're really hopeful that someone will be able to discover a bright new comet, like when comet Hale Bopp was found. We have a lot of potential to get to a new comet and that's something we'd really like to do," Farquhar said.

Not only is the study of comets a way to peer back into the pastthey may give us a peek at humanity's future too.

That's the sense of Donald Yeomans, CONTOUR Science Team co-investigator at the NASA Jet Propulsion Laboratory (JPL) in Pasadena, California. Comets are important, perhaps, for future generations. They likely represent the resource that permits humankind to colonize the inner Solar System, he emphasized.

"If we do that, we're going to need raw materials in space to build structures. We're going to need water to sustain life. As a rule comets are largely 50 percent water by mass. You can break the water down into hydrogen and oxygenand that's the most efficient form of rocket fuel," Yeomans said.

"So in some sense comets may one day be the fueling stations and watering holes for the interplanetary colonization process," Yeomans said.

Yeomans said comets are part of a life-death cycle. "We're it not for comets, perhaps we wouldnt even be here," he said.

"So in a sense, we mammals may owe our preeminent position atop the world's food chain to a comet or perhaps an asteroid that took out our principal competition some 65 million years ago, the dinosaurs and associated species," Yeomans said.

Ed Reynolds, APL's Deputy Project Manager for CONTOUR, said that all is going well in preparing the craft for a July 1 departure. The spacecraft will orbit Earth until August 15, when it should fire its main engine and enter a comet-chasing orbit around the sun.

The biggest engineering challenge, Reynolds said, was giving CONTOUR multi-mode control capability.

"We're spinning most of the time, then during encounters were precisely controlled in three-axis. So it's got two different guidance and control scenarios. It's really the first spacecraft to do that," Reynolds told SPACE.com in a telephone interview.

"It's like Noah's Arkit's got two of everything," Reynolds said.

CONTOUR's main dust shield is meant to break up and vaporize any comet particles striking the probe during close encounters. Behind that dust shield, he said, sets of Kevlar-impregnated thermal blankets cover key spacecraft hardware, such as fuel tanks.

Reynolds said that comet Encke should be sporting little dust, given its old age. Schwassmann-Wachmann 3, on the other hand, is expected to be spitting out lots of dust, he said.

"We're going to have a healthy respect for Schwassmann-Wachmann 3," Reynolds said.