Rosetta soars on ambitious comet intercept mission

Posted: March 2, 2004

Embarking on its epic voyage to gain new insights into comets and the history of our solar system, the Rosetta spacecraft was successfully launched today to rendezvous with a cosmic snowball and deploy a tiny lander onto its icy heart.

The Ariane 5 rocket launches with Rosetta. Credit: ESA/CNES/Arianespace
The Ariane 5 rocket fired up at 0717:44 GMT (2:17:44 a.m. EST), exactly when the booster could place the probe on the first leg of its ten-year course to comet Churyumov-Gerasimenko.

The Ariane solid rockets and first stage put Rosetta on an arcing suborbital ballistic trajectory about ten minutes after launch. The upper stage's Aestus engine fired nearly two hours after liftoff to send the 6,700-pound craft out of Earth's grasp and into solar orbit.

Rosetta aims to give scientists a wealth of knowledge about comets, frozen time capsules from billions of years ago, while helping the public at large wrestle some of the most fundamental questions that humans can ask.

"I think it is very hard to imagine that you don't wonder sometimes what is it all about? Where did it all come from?" says European Space Agency science director David Southwood. "Once we were all star dust. How did we turn out to be the complicated beings that we are now? I think we are looking for some of the clues that will help us put that story together."

Today's launch has been in the works since the Rosetta project began in 1993. Since then, the Rosetta team has been thrown a number of curves -- most recently the decision to delay the launch from January 2003 due to concerns with the reliability of the Ariane 5 rocket.

An artist's concept shows Rosetta and its looping route to the comet. Credit: EADS Astrium
Delaying the launch from 2003 to 2004 caused managers to change targets for the probe, which required extensive studies of Churyumov-Gerasimenko to see if it was suitable to approach with a $1 billion spacecraft and safe to land upon with a tiny robot explorer.

Rosetta will take a circuitous route through the solar system and will arrive back in the vicinity of Earth next March for its first crucial gravity assist fly-by. The probe will reach Mars in March 2007, followed by two additional close approaches of Earth to tweak its course toward Churyumov-Gerasimenko.

Heading further from the Sun and past the asteroid belt, Rosetta will fly near several of these space rocks and study them from a distance of over a thousand miles before entering a hibernation period in mid-2011.

"These brief encounters are a scientific opportunity and also a chance to test Rosetta's instrument payload," explained Rosetta project scientist Gerhard Schwehm from the European Space Agency.

For two-and-a-half years, Rosetta's systems will be completely shutdown with the exception of its primary computer and radio receivers in order to conserve power. Fitted with two solar wings spanning almost 100 feet, the spacecraft will be the first to fly near the orbit of Jupiter and rely entirely on solar power.

"To provide the probe with the power it needs in space, we have given it the biggest solar panels ever carried by a European satellite," said Manfred Warhaut, Rosetta's operations manager.

An artist's concept shows the Rosetta orbiter and its lander. Credit: EADS Astrium
Rosetta will also undergo a number of other extended periods of inactivity between key mission events during the journey to Churyumov-Gerasimenko to relieve manpower and electrical constraints.

Power production is strained for Rosetta because it will be traveling over 500 million miles from the Sun, where light levels are only four percent of those found on Earth.

Controllers will bring Rosetta back to life in early 2014 for a thruster firing to slow the probe's approach to the comet before entering orbit and beginning its mapping and scientific mission to characterize the surface.

"Rosetta carries more instruments than any previous scientific spacecraft -- that makes it challenging and one of the most exciting missions ever," said Claudia Alexander, U.S. project scientist for the mission from NASA's Jet Propulsion Laboratory. "We anticipate major discoveries, just like Galileo and Cassini."

By the end of the summer in 2014, Rosetta will be in orbit around Churyumov-Gerasimenko and science operations should be in full swing. A major priority will be the determination of favorable landing sites for a small 220-pound lander carried aboard Rosetta named Philae.

Technicians work on the lander during pre-flight activities. Credit: EADS Space
The three-legged Philae will touch down on the surface in November 2014, firing a harpoon to keep the tiny craft anchored on the comet so it doesn't float away in the weak gravitational field. It will snap high-resolution pictures and acquire data about the comet's organic crust and molecules for transmission up to the orbiter for later relay to Earth.

Operating at least one week, perhaps significantly longer, Philae's instrument suite even includes a tiny drill that can bore a few inches into the comet for subsurface investigations.

Together the orbiter and lander will observe the traits and changes the comet goes through as it approaches the Sun. Officially, the mission is slated to come to conclude in late 2015.

"This will be our first ever chance to be there, first hand, so to speak, as a comet comes to life," Schwehm said. "As we will be accompanying Churyumov-Gerasimenko for two years, until the comet reaches its closest point to the Sun and travels away from it, we can at long last hope to acquire new knowledge about comets."

Comet Churyumov-Gerasimenko was discovered in 1969 and is considered a dusty comet that is roughly two by three miles in diameter. The Hubble Space Telescope was chartered to observe the comet for 21 hours in March 2003 to gather more specific details about Churyumov-Gerasimenko to allow project officials to decide whether to pursue it as a potential target.

"This comet has only about three-hundred-thousandths the gravity of Earth," said Alexander. "The Rosetta spacecraft will be able to make observations from as close as 2 kilometers (1.2 miles). The data from our state-of-the-art instruments will be amazing."

An artist's concept of the Rosetta orbiter and its tiny lander nearing the comet. Credit: ESA/AOES Medialab
Scientists believe comets are made of the very same primitive materials that were present when the Sun and the solar system were formed an estimated 4.6 billion years ago.

Comets are balls of ice and rock believed to be formed far beyond the orbit of Pluto where conditions are cold and dark, much like they were as the solar system was born. Some of these objects are drawn toward the inner solar system and they become comets -- giving us a unique view of almost the same primordial materials that played such important roles in the formation of the Sun and the planets.

"They are the keys to understanding the way the whole solar system, the Earth, and how even we came into being. And with Rosetta we will be able to observe, study and analyze this primordial material up close for more than a year," said Paul Weissman of NASA's Jet Propulsion Laboratory.

"We are confident we will come a step nearer to understanding the origins and formation of our solar system and the emergence of life on Earth," said Schwehm.

Rosetta gets its name from the stone tablet found by French soldiers in Egypt in 1799 that contained the key to deciphering Egyptian hieroglyphics. Scientists hope this mission may unveil the mysteries surrounding how our planet and life came to be as we know it today.

The Rosetta spacecraft is illustrated in this artist's concept. Credit: EADS Astrium
ESA managers are not lost on the difficulties associated with the mission.

"Rosetta is one of the most challenging missions undertaken so far. No one has ever attempted such a mission, unique for its scientific implications as well as for its complex and spectacular interplanetary space maneuvers," Southwood said.

"This mission will turn science fiction into science fact. Every aspect of comet Churyumov-Gerasimenko will be analyzed, resulting in the most comprehensive set of scientific measurements ever obtained of a comet," said Professor Ian Halliday, chief executive of the Particle Physics and Astronomy Research Council, which funded two of the instruments.