When the European Space Agency launches
its Rosetta comet orbiter mission on February 26, two instruments built by
researchers at Southwest Research Institute will be along for the ride.

The Ion and Electron Spectrometer (IES) and Alice ultraviolet imaging
spectrometer, will analyze the dust and gases emanating from the surface of
Comet 67P/Churyumov-Gerasimenko. With these and other instruments, the
Rosetta spacecraft will make the most thorough investigations of a comet
ever attempted. Alice and IES were funded by NASA through a contract with
the Jet Propulsion Laboratory as a part of the U.S. contribution to the ESA
mission.

Both instruments were built with miniaturization of their electronic systems
as a priority. IES was fabricated from magnesium to achieve a total mass of
only 1,040 grams. Despite its small size, laboratory tests showed IES
achieves sensitivity comparable to instruments weighing five times more. The
shoebox-sized Alice has one-third to one-half the mass of comparable UV
spectrometers and yet has more than 10,000 times as many imaging pixels as
did the UV spectrometer aboard NASA’s Galileo Jupiter orbiter mission.

“The miniaturization of these instruments adds up to a considerable savings
in cost, mass, volume and power,” says Dr. James L. Burch, vice president of
the SwRI Space Science and Engineering Division and IES principal
investigator. “That makes them suitable for a variety of other
interplanetary and Earth-orbiting satellite missions, as well.”

IES will simultaneously measure the flux of electrons and ions surrounding
the comet over an energy range extending from the lower limits of
detectability, near 1 electron volt, up to 22,000 electron volts. It uses a
novel, electrostatic scanning technique to view particles from directions
encompassing 70 percent of the celestial sphere.

“We expect Alice to reveal new insights into the origin, composition and
workings of comets — insights that cannot be obtained by either
ground-based or earth-orbital observations,” says Dr. Alan Stern, principal
investigator of the instrument and its scientific investigation. Alice will
be the first UV spectrometer to study a comet up close. A sister instrument
is also set to fly aboard the New Horizons mission to Pluto in January 2006.

IES and Alice both feature an advanced “micro-channel plate” detector,
sophisticated optics and a miniaturized 6,000-volt power supply, and operate
on just 3 watts, roughly 1/25 the power of an average light bulb. “The
Rosetta mission has to operate out to 5 AU (astronomical units), where the
Sun is only 4 percent as bright as it is here on Earth. Because the
spacecraft gathers its energy from the Sun using a large solar array, each
instrument must do its part to be highly efficient,” notes Alice Project
Manager John Scherrer, a senior program manager at SwRI.

Following the launch, the spacecraft will make a 10-year journey to the
comet and will make flybys of the Earth-moon system, Mars and at least one
asteroid. In addition to making observations as it orbits the comet, the
Rosetta Lander will carry a package of European instruments to the comet
surface.

EDITORS: Images to support this story are available at
www.swri.org/press/rosetta.htm.