By Bill Clayton

Getting a spacecraft into orbit around Mercury has created some astronomical problems for designers. Expense, for one. Complexity, for another. And finally, risk -- the region around the Sun is so hostile that it threatens the craft, its instrumentation and, consequently, the entire exploratory mission. So the challenge for scientists has been, among other things, to develop new designs and relatively new technologies to create instruments that are extremely lightweight yet powerful enough to extract vast amounts of information and can withstand the harshest of environments.

The College of Engineering’s Atmospheric, Oceanic and Space Sciences department (AOSS) solved an important part of that problem when it developed the Fast-Imaging Plasma Spectrometer (FIPS) -- an easier, less expensive and less risky way to collect data in the extremely hostile neighborhood close to the Sun.

Requirements for FIPS

A Coronal Mass Ejection expands into space from the Sun (filtered, shown as a circle) and could hit Mercury, an important solar interaction that FIPS will study.

The roots of Mercury’s exploration -- and the need for FIPS -- go back to the late ‘70s and early ‘80s, when the Helios spacecraft made the first measurements of the solar winds close to the Sun. A long period of relative inactivity followed these initial explorations, and only recently has there been a renewed interest in Mercury, primarily due to two intriguing characteristics -- Mercury’s interior magnetic field and its proximity to the Sun, both of which provide a very interesting test-case for the interaction of solar winds with terrestrial planets. In addition, pick-up ions from Mercury provide a very important, well-defined test case for mass-loading in the solar system. (Mass loading here is the mass of Mercury material entering its space environment per unit of time.)

During a close approach to the Sun, the spacecraft will encounter plasma of a very high temperature and density. Because of their design, current mass spectrometers can’t provide reliable measurements in such extreme conditions. So the challenge was to create a sensor that would withstand an extremely harsh environment, yet be efficient and reliable, provide fast resolution and a three-dimensional field-of-view, have very low weight and be able to suppress potential background signals from energetic particles and high-energy electromagnetic radiation.

The reasons for these requirements are multifold. For one thing, the plasma environment close to the Sun is in constant, unpredictable flux. Furthermore, the instruments would follow highly elliptical Keplerian orbit, traveling at a very high speed during its fly-by of the Sun and, as a result, would require fast time-resolution in order to capture data with sufficient spatial and temporal resolution. In addition, the intensity of energetic particles and electromagnetic radiation is so great that it would render standard detectors useless. Finally, because of the large change in velocity required for the mission, the weight of the instrument will be a crucial factor.

The AOSS Design

George Gloeckler, adjunct professor, Thomas Zurbuchen, assistant research scientist, and their team of Atmospheric, Oceanic and Space Sciences engineers have developed a robust device to measure a variety of cosmological elements -- radiation flux, for example -- in a hostile environment. The size of its energy analyzer (no larger than a Coke can), low mass, low weight and low power will make it an important tool for space exploration. In addition, the configuration of the device suppresses noise coming from an array of sources.

Its method of measurement is particularly noteworthy. An entrance mask allows particles to flow into the device from specific directions and travel along separate channels into an electrostatic potential that deflects the particles into a carbon foil. Detectors record information about time, the instrument’s position and the voltage in the entrance system; these are the data necessary to yield the desired measurements.

The low mass, low weight and low power of the FIPS energy analyzer (prototype shown here with circuit boards) will make it an important tool for the exploration of space.

This new design combines new innovations with previously flown and, therefore, well-understood technology.

NASA, which is funding the project as part of its $200-million Discovery Program, has slated the device for a 2004 launch to Mercury; it should arrive in 2007 and begin to “live and work” in Mercury’s atmosphere. The same device could also go to other planets, e.g., Pluto. In each case, the device will work in extremely hostile conditions -- the heat of Mercury’s atmosphere, and the cold of Pluto’s almost nonexistent atmosphere -- that will test the toughness and reliability of the device. It has potential application in a number of areas, including weather and shipping, and in military undertakings involving security.

AOSS and its Space Physics Research Laboratory (SPRL) -- one of the largest and most successful university-based space science research programs -- receives most of its funding from NASA (approximately $15 million per year) to undertake a broadly-based research program in space science.  Over the years, SPRL has built and launched successfully some 35 flight instruments which have flown on major NASA missions.