Comet Orbiting Space Craft Shipped to Launch Site

Twenty instruments on the European Space Agency’s comet-
chasing Rosetta spacecraft, including three from NASA, are in
final tests for launch early next year.

Launch from the Kourou spaceport in French Guiana, on
the northeastern coast of South America, is scheduled for a
19-day window beginning Jan. 13, 2003. Shipment to Kourou
last month from the European Space Research and Technology
Centre in Noordwijk, the Netherlands, followed more than 10
months of rigorous testing. “With the move from Europe to
Kourou, we have now entered the most exciting phase of the
Rosetta program so far — the launch campaign,” said Claude
Berner, Rosetta’s payload and assembly, integration and
verification manager.

NASA is funding three research instruments and a key
part of a fourth for the collaborative mission. NASA also
provides one of the Rosetta’s interdisciplinary scientists,
Dr. Paul Weissman, of NASA’s Jet Propulsion Laboratory,
Pasadena, Calif., and operational support from JPL’s Deep
Space Network of ground-based antennas. “Rosetta is an
ambitious mission with great international cooperation,” said
JPL’s Dr. Claudia Alexander, project scientist for the U.S.
role in the mission. “We’re eager to get it launched.”

Rosetta will fly for nearly nine years, passing by two
asteroids, by Earth twice and by Mars before reaching its
destination, comet Wirtanen, in November 2011. At that
point, the comet will be about four times as far from the Sun
as Earth is. Then, as Rosetta orbits Wirtanen at distances as
close as one kilometer (0.6 mile), the orbiter’s instruments
will examine how the comet changes while it moves closer to
the Sun during the following 20 months. Rosetta will also
drop a lander onto the surface of Wirtanen’s icy nucleus. The
NASA instruments will examine Wirtanen from the orbiter.
International teams of scientists expect to see dramatic
changes as the comet approaches the Sun. Gases and dust
escaping from the surface of a comet form a cloud-like “coma”
around the nucleus and a tail pointing away from the Sun.

Rosetta carries more instruments than any other
spacecraft in history. The orbiter’s payload includes a
camera to study surface details, a microscope to analyze dust
grains coming off the nucleus, spectrometers to examine
surface and coma materials in various wavelengths, and an
experiment to probe the comet’s interior with radio waves.

With all instruments installed, the spacecraft was put
through its paces during testing at the European Space
Research and Technology Centre. It was placed in a large
vacuum chamber while the instruments were tested in heat and
cold simulating the extremes the spacecraft will experience
when it is closest to the Sun and when it will be almost as
distant as Jupiter. Vibration and acoustic tests demonstrated
that the whole spacecraft can survive a launch environment.
Another set of tests checked whether any instruments cause
electromagnetic interference with any others. Verification of
many essential functions included commanding the spacecraft
from the European Space Operations Centre in Germany, just as
it will be in orbit. At Kourou, each instrument will again be
tested by itself and with the other instruments before
engineers can finally declare everything “green” for launch.

JPL supplied the Microwave Instrument for Rosetta
Orbiter, the first of its type for any interplanetary
mission. This instrument can reveal the abundances of
selected gases, their temperatures, the speed at which
they’re coming off the nucleus, and the temperature of the
nucleus. Scientists will use it to monitor changes in how
vapors are released from the nucleus as the coma and tail
grow. They will be studying water, carbon monoxide, ammonia
and methanol gases, four of the most abundant gases from
comets. JPL’s Dr. Samuel Gulkis is principal investigator.

The Southwest Research Institute, based in San Antonio,
Texas, supplied two NASA instruments for Rosetta. One is
named Alice. It is the first in a new generation of
miniaturized ultraviolet spectrometers and is capable of
analyzing the composition both of gases released by the comet
and of the comet’s surface. One goal of scientists using it
will be to learn about the temperatures at which the comet
formed and evolved by determining its abundances of noble
gases, such as helium, neon and argon. Principal
investigator for the ultraviolet instrument is Dr. Alan Stern
of the institute’s Space Studies Department in Boulder, Colo.

Dr. James Burch, of the institute’s Instrumentation and
Space Research Division, San Antonio, is principal
investigator for Rosetta’s Ion and Electron Spectrometer.
This device will measure the environment of charged particles
surrounding comet Wirtanen. It will also study the
interaction between that environment and the solar wind of
charged particles speeding outward from the Sun.

Key electronics for a fourth instrument, the Rosetta
Orbiter Spectrometer for Ion and Neutral Analysis, have been
supplied by the Lockheed Martin Advanced Technology Center,
Palo Alto, Calif. This instrument will examine gases
surrounding the comet.

Information is available about Rosetta at
http://sci.esa.int/rosetta and about the microwave instrument
at http://mirowww.jpl.nasa.gov . JPL, a division of the
California Institute of Technology in Pasadena, manages the
microwave instrument for NASA’s Office of Space Science,
Washington, D.C.