Genesis' purpose is to bring samples of solar matter to Earth. The solar wind is a convenient sample of the surface layers of the Sun, which have preserved the composition of the original solar nebula from which all planetary objects formed. Genesis will be the first mission in the present millennium to return with a package of extraterrestrial material. Genesis will collect data on almost all of nature's elements and isotopes, and will allow scientists to determine the average composition of the solar system with high precision so that the composition of current solar system bodies can be compared.

Today's solar system holds a dazzling diversity of planets, moons, asteroids and other small bodies, which scientific theories say all formed from a homogeneous solar nebula. The chemicals and isotopes that make up the planets, moons, asteroids and comets contain a record of the processes and events in the early days of our solar system by which homogeneity was converted to diversity. The Genesis mission will provide scientists with new knowledge about the initial composition of the solar nebula, crucial data that are required for theories to explain how this conversion occurred.

Genesis will focus on determining the ratio of isotopes of different elements in solar matter. There are small but important differences in the relative abundances of isotopes of some elements, most notably oxygen and nitrogen, among the various samples of solar system materials available for study in Earth's laboratories. These differences are not explained by the standard model for the origin of the solar system.

Observations from the ground and from past spacecraft have provided a baseline set of data that Genesis' studies will greatly improve. Genesis' goal is to improve current knowledge of the Sun's composition for each element by threefold or better. Many elements are very rare, and data about the relative amounts of the different chemical elements are inaccurate or nonexistent.

Objectives

• Provide data on the isotopic composition of solar matter sufficiently precise for planetary science studies.
  
  
• Significantly improve our knowledge of the elemental composition of solar matter.
  
  
• Provide a reservoir of solar matter sufficient to meet the needs of 21st century planetary science.
  
  
• Provide independent measurements of the different kinds of solar wind.

Science Instruments
The Genesis mission's four instruments will work together to analyze, determine and sample the three types of solar wind.

Genesis' science goals will not be complete until the collector materials are analyzed. This will require developing analytical laboratory instruments on Earth with advanced capabilities beyond those presently available.

Solar Wind Collector Arrays. The solar wind collector arrays are large, metersized (yard-sized) panels, each containing 55 coaster-sized hexagonal tiles about 10 centimeters (4 inches) across. The tiles are made of a variety of materials including silicon, germanium, sapphire, artificially grown diamond and bulk metallic glass. These materials were selected in order to target specific elements during analysis; for example, collecting some of the solar wind material on a thin silicon layer on sapphire makes it easier to extract noble gases later in the laboratory. The tile materials must be extremely pure to guarantee that the atoms analyzed are of pristine solar origin and not due to terrestrial contamination.

There are five collector arrays mounted inside an ultra-clean canister for safe storage when not exposed to the solar wind. One array is mounted in the cover of the canister, and is exposed to the solar wind when the cover is opened. The other four arrays are mounted in a stack. The top array is exposed to the solar wind at all times. One of the other three is deployed depending on the type of solar wind the spacecraft is experiencing, as determined by the monitors. The canister was designed, built and tested by NASA's Jet Propulsion Laboratory, Pasadena, Calif. The canister was cleaned and the collector array materials installed in a new clean room, with only 10 particles of dust per cubic meter (or yard) (called a "class 10" clean room), at NASA's Johnson Space Center in Houston, Texas.

Solar wind ions striking the collector materials embed themselves many atom layers deep in the materials. Typical temperatures of the collector materials as they are heated by sunlight are around 200 degrees Celsius (about 400 degrees Fahrenheit). The collector materials have been selected so that diffusion is negligible after the atoms embed themselves; the collector materials can therefore serve as permanent sample containers for the returned solar matter.

Ion and Electron Monitors. Genesis' solar wind monitors will be able to measure the properties of the solar wind autonomously, allowing the spacecraftıs computer to translate that knowledge into actions for the two Genesis instruments that collect solar wind. The monitors have three functions: to distinguish different types of solar wind in order to deploy the appropriate collector array, to document the properties of the solar wind, and to drive the solar wind concentrator.

Since the three kinds of solar wind can be distinguished by their speed, temperature, helium-hydrogen ratio and direction of travel of electrons, Genesis' ion and electron monitors will work together to identify the types of solar wind.

The ion monitor measures the amount of protons and alpha particles in the solar wind, as well as the energy of these particles. Alpha particles are helium atoms stripped of their electrons, leaving two protons and two neutrons together. About 96 percent of the solar wind is composed of protons, 4 percent alpha particles and less than 1 percent minor ions, of which carbon, nitrogen, oxygen, neon, magnesium, silicon and iron are the most abundant.

The ion monitor will face almost directly into the solar wind. The solar wind will enter a 1-millimeter (0.04-inch) slit in the top of the instrument and travel down between two curved, electrically charged plates. The plates' voltage pulls the ions in the direction of the curvature, allowing the ion monitor to measure the ionsı energy. The amount of incoming ions is then measured over a wide range of energy.

The ion monitor is fixed on the side of Genesis that continually faces the Sun. The spacecraft spins slowly around a Sun-pointed axis. Using this spin, the instrument sweeps a narrow field of view through an approximately 50-degree-wide area centered on the average solar wind direction. The solar wind's supersonic speed can vary from 300 to 600 kilometers per second (roughly 700,000 to 1.4 million miles per hour), making its fastest Sun-Earth trip in about 45 hours.

In addition to the average speed, which is important for adjusting the ion concentrator and deploying two of the collector arrays, the ion monitor measures the spectrum of speeds, or energies, of the ions, which can determine their temperature. If the energy spectrum measured in the solar wind is broad, then the ions have many different energies reflecting temperatures possibly as high as 100,000 degrees Celsius (180,000 degrees Fahrenheit). If the solar wind's energy spectrum is narrow, the ions are traveling with much less commotion and are therefore relatively cool, about 10,000 degrees Celsius (18,000 degrees Fahrenheit).

The most important function of Genesis' electron monitors is to determine the direction of travel of the solar wind's electrons. This monitor also measures the energy spectrum of the electrons.

The electron monitorıs sensor head is composed of two half-spheres of charged, gold-covered metal, concentrically nested inside a drum with a slit. The solar wind electrons enter the slit and are forced between the charged plates, allowing energy analysis. The amount of incoming electrons is then measured over a wide range of energy. The instrument is located on the edge of Genesis' equipment deck so that it can look across 180 degrees -- nearly 90 degrees fore and 90 degrees aft -- and, as the spacecraft spins, measure the solar wind electrons coming in all directions.

If the electrons seem to be coming from two opposing directions simultaneously, the solar wind is likely part of a coronal mass ejection, a chunk of charged particles, or "plasma," that has lifted off the Sun's outer layer and is surrounded by magnetic fields. If the electrons are traveling only away from the Sun, the solar wind is of a different type, either "fast" or "slow" solar wind.

The shoebox-sized ion monitor weighs 3.3 kilograms (7.3 pounds) and uses 4 watts of power. It measures 29.4 centimeters (11.6 inches) long, 23.2 centimeters (9.1 inches) tall and 10.8 centimeters (4.3 inches) wide. The electron monitor is nearly the same size, and has a similar power requirement. The instruments were developed and built under the direction of Bruce Barraclough at the Los Alamos National Laboratory in New Mexico. The two monitors are nearly identical to Los Alamos instruments currently operating onboard the Advanced Composition Explorer and the Ulysses spacecraft.

Solar Wind Concentrator. Genesis' solar wind concentrator will attack the problem of collecting a high concentration of oxygen in the solar wind, filtering out the much more numerous particles of hydrogen. Oxygen is one of the most important elements in the solar wind because so much of the solar system's makeup includes oxygen, yet the differing amounts of oxygen isotopes in each type of body are puzzling.

All the oxygen that the instrument gathers will be concentrated into a collector tile made of the purest materials in order to exclude Earth oxygen. In the process, the ions are concentrated by a factor of 20 over the normal solar wind collectors.

The concentrator is installed in the sample canister, always facing the Sun. The solar wind passes through a series of charged grids into a bowl-shaped mirror, which reflects the filtered stream of oxygen and nitrogen ions upwards into the tile, poised in the center.

Several layers of grids made of wires one-quarter the diameter of a human hair manipulate the ions before concentrating them. The first grid layer is at ground potential, to keep the electric fields from the highly charged grids inside the collector from escaping and deflecting the surrounding solar wind. The next layer, called the hydrogen rejection grid, has a positive charge of up to 3,500 volts to repel the hydrogen ions that make up most of the solar wind, protecting the collecting tile. The next grid has a negative charge of minus 6,500 volts so that surviving particles are accelerated to embed them deeper in the collector tile. The acceleration also straightens stray paths of the incoming particles. The ions then pass through a bowl-shaped domed grid, which is nested above the bottom of the concentrator. The domed grid is also negatively charged to contain the electric field from the mirror just below.

The last element is the parabolic solid mirror, which has a strong positive charge. The particles passing through the domed grid are forcefully reflected toward the center of the parabola, where the collector tile waits to receive them. The mirror is a single aluminum piece with a surface consisting of steps 100 microns (.004 inch) tall, which reflect the Sun's incoming light back out of the instrument to avoid damaging the collector tile with focused sunlight.

The target tile, 26 square centimeters (4 square inches), is made of four pie wedges of ultra-pure materials: 1 diamond (carbon 13) wedge, 2 silicon carbide wedges and one wedge of silicon topped with thin diamond. The entire interior of the concentrator is coated with gold to keep all the surfaces oxygen-free.

The solar wind concentrator was developed at Los Alamos National Laboratory by Drs. Roger Wiens and Beth Nordholt. During flight, scientists at Los Alamos will monitor the health of the payload instruments and will keep a history of all solar wind conditions, and array and concentrator exposure times. These data will be made available to the scientific community at large for use in providing context for the data obtained from the returned samples.