[meteorite-list] Rosetta Set to Harpoon a Comet Tomorrow

[Ron Baalke]

http://www.jpl.nasa.gov/news/news.php?feature=4373

European Spacecraft Set to Harpoon a Comet Tomorrow
Jet Propulsion Laboratory
November 11, 2014

Early tomorrow morning, the European Space Agency's Rosetta spacecraft 
will deploy its comet lander, "Philae." A little over seven hours later 
(8 a.m. PST/11 a.m. EST), the experiment-laden, harpoon-firing Philae 
is scheduled to touch down on the surface of comet 67P/Churyumov-Gerasimenko. 
It will be the first time in history that a spacecraft has attempted a 
soft landing on a comet. Rosetta is an international mission led by the 
European Space Agency (ESA), with instruments provided by its member states, 
and additional support and instruments provided by NASA.

"I know it sounds like something out of Moby Dick, but when you think 
about the gravity field of a comet, it makes a lot of sense to harpoon 
one," said Art Chmielewski, project manager for the U.S. participation 
in Rosetta, from NASA's Jet Propulsion Laboratory in Pasadena, California. 
"Comet 67P has approximately 100,000 times less gravity than Earth does. 
So, if you don't want to float away, you have to go to extraordinary measures 
to attach yourself to its dusty surface. The Philae lander has two harpoons, 
shock-absorbing landing gear, and a drill located on each of the lander's 
three feet. It even has a small, upward-firing rocket engine. All this 
to help keep it on the surface."

The descent of Philae begins at 1:03 a.m. PST (4:03 a.m. EST) when Rosetta 
releases the 220-pound (100-kilogram) Philae from an altitude of about 
14 miles (23 kilometers) from the center of the comet's nucleus. As Philae 
descends, it will fall slowly without propulsion or guidance, gradually 
gathering speed in the comet's weak gravitational field. During the seven-hour 
descent, the lander will take images and conduct science experiments, 
sampling the environment close to the comet. It will take a "farewell" 
image of the Rosetta orbiter shortly after separation, along with a number 
of images as it approaches the comet surface.

The targeted landing site is called Agilkia after an island in the Nile 
River in southern of Egypt where ancient buildings from the Nile's flooded 
Philae island were relocated. Once the lander has touched down and safely 
anchored, it will begin a primary science mission, which extends to about 
two-and-a-half days. Philae will take a panorama of its surroundings and 
perform on-the-spot analysis of the composition of the comet's surface. 
It can drill samples from a depth of nine inches (23 centimeters) and 
feed them to the onboard laboratory for analysis. The lander will also 
measure electrical and mechanical characteristics of the surface of the 
nucleus.

After the Philae landing is completed, Rosetta will begin the next major 
part of its mission, the escort phase. The orbiter will continue to maneuver 
around the comet at walking pace, collecting dust and gas samples and 
making remote sensing observations as the comet warms up and the nucleus 
and its environment evolve. The comet will reach its closest point to 
the sun (perihelion) in August 2015. Rosetta will then track the waning 
of activity as the comet heads back toward the cold, far reaches of the 
outer solar system, through 2015.

Three NASA science instruments are aboard the Rosetta spacecraft; the 
Microwave Instrument for Rosetta Orbiter (MIRO); an ultraviolet spectrometer 
called Alice, and the Ion and Electron Sensor (IES). They are part of 
a suite of 11 science instruments on the orbiter.

MIRO is designed to provide data on how gas and dust leave the surface 
of the nucleus to form the coma and tail that give comets their intrinsic 
beauty. Studying the surface temperature and evolution of the coma and 
tail provides information on how the comet evolves as it approaches and 
leaves the vicinity of the sun. MIRO has the ability to study water, carbon 
monoxide, ammonia and methanol.

Alice will analyze gases in the comet's coma, which is the bright envelope 
of gas around the nucleus of the comet developed as a comet approaches 
the sun. Alice also will measure the rate at which the comet produces 
water, carbon monoxide and carbon dioxide. These measurements will provide 
valuable information about the surface composition of the nucleus.

Alice also will measure the amount of argon present, an important clue 
about the temperature of the solar system at the time the comet's nucleus 
originally formed more than 4.6 billion years ago.

IES is part of a suite of five instruments to analyze the plasma environment 
of the comet, particularly the coma. The instrument will measure the charged 
particles in the sun's outer atmosphere, or solar wind, as they interact 
with the gas flowing out from the comet while Rosetta is drawing nearer 
to the comet's nucleus.

NASA also provided part of the electronics package for the Double Focusing 
Mass Spectrometer, which is part of the Swiss-built Rosetta Orbiter Spectrometer 
for Ion and Neutral Analysis (ROSINA) instrument. ROSINA is the first 
instrument in space with sufficient resolution to be able to distinguish 
between molecular nitrogen and carbon monoxide, two molecules with approximately 
the same mass. Clear identification of nitrogen will help scientists understand 
conditions at the time the solar system was formed.

U.S. scientists are partnering on several non-U.S. instruments and are 
involved in seven of the mission's 26 instrument collaborations. NASA's 
Deep Space Network is supporting ESA's Ground Station Network for spacecraft 
tracking and navigation.

"Landing a spacecraft on a comet is a remarkable challenge and we wish 
them well," said Claudia Alexander, project scientist for the U.S. Rosetta 
project from JPL. "It is the overture, opening for what has already become 
an exciting mission of exploration. Whatever happens tomorrow, the main 
part of the Rosetta mission will continue with the Rosetta orbiter monitoring 
the comet as it sweeps through the inner-solar system."

Comets are time capsules containing primitive material left over from 
the epoch when the sun and its planets formed. Rosetta's lander will obtain 
the first images taken from a comet's surface and will provide comprehensive 
analysis of the comet's possible primordial composition by drilling into 
the surface. Rosetta also will be the first spacecraft to witness at close 
proximity how a comet changes as it is subjected to the increasing intensity 
of the sun's radiation. Observations will help scientists learn more about 
the origin and evolution of our solar system and the role comets may have 
played in seeding Earth with water, and perhaps even life.

Rosetta is a European Space Agency mission with contributions from its 
member states and NASA. Rosetta's Philae lander is provided by a consortium 
led by the German Aerospace Center, Cologne; Max Planck Institute for 
Solar System Research, Gottingen; National Center of Space Studies of 
France (CNES), Paris; and the Italian Space Agency, Rome. NASA's Jet Propulsion 
Laboratory in Pasadena, California, a division of the California Institute 
of Technology, manages the U.S. participation in the Rosetta mission for 
NASA's Science Mission Directorate in Washington.

For more information on the U.S. instruments aboard Rosetta, visit:

http://rosetta.jpl.nasa.gov

More information about Rosetta is available at:

http://www.esa.int/rosetta

Media Contact
DC Agle
818-393-9011
Jet Propulsion Laboratory, Pasadena, Calif.
agle at jpl.nasa.gov

Dwayne Brown
202-358-1726
NASA Headquarters, Washington
dwayne.c.brown at nasa.gov

Markus Bauer
011-31-71-565-6799
European Space Agency, Noordwijk, Netherlands
markus.bauer at esa.int

2014-392