FAST Satellite Probes Mysteries of the Aurora

High above the Earth’s polar regions, a phenomenon occurs that has stirred the imaginations of observers throughout time. To viewers on the ground, these events appear as shimmering, shifting curtains of light that seem to float on the air. Sometimes called the northern or southern lights, these amazing exhibitions are properly known as auroras.

Auroras have been a source of fascination and superstition for centuries. In recent decades, however, the phenomenon has become better understood through scientific research, particularly with the aid of spaceflight instrumentation. Data collected by “state-of-the-art” instruments on NASA’s Fast Auroral Snapshot (FAST) Explorer satellite will probe the physical processes that produce these dazzling displays, while adding significantly to our understanding of the Earth’s environment in space.

The FAST mission was proposed by scientists at the University of California at Berkeley, the University of California at Los Angeles, the Lockheed Palo Alto Research Laboratory in California and the University of New Hampshire in Durham. These scientists also designed and built the scientific instruments included on FAST. The spacecraft on which these instruments are carried was designed, built, tested and managed by NASA’s Goddard Space Flight Center, Greenbelt, Md., and is planned to have a lifetime of at least one year.

Earth’s Glowing Crowns

We know from past scientific investigations that auroras are triggered by strong disturbances on the Sun. Ions and electrons continuously flow outward from the Sun, with variable intensity, in its solar wind. Some of the energy from this flow couples into the Earth’s magnetosphere, a large magnetic envelope that surrounds the planet and its atmosphere. It is this energy that then accelerates electrons to high energies to produce auroral displays at high latitudes.
The collision of these accelerated electrons with molecules and atoms in the upper atmosphere causes light to be emitted at altitudes of 60 to 120 miles (95 to 195 kilometers). From the ground, an aurora may appear as a curve or gauzy swirl of light that trails away toward the horizon. At other times, the aurora may be evident as a stable east-west arc, a pulsating emission, or a diffuse light covering the entire sky. Viewed from space, however, auroras acquire their global context – glowing crowns that encircle the polar regions.

Standing on the Earth and looking at the auroral light emitted from the atmosphere is akin to viewing a TV screen. In the television tube, a beam of electrons hits the inside of the screen and causes a chemical reaction that makes it glow, much as accelerated electrons traveling down the Earth’s magnetic field lines collide with molecules and atoms in the upper atmosphere and create the auroral light.

This visual aspect of auroras is fairly well understood. The fundamental unanswered questions concerning the aurora involve understanding the physical mechanisms at much higher altitudes – 1,200 to 6,200 miles (2,000 to 10,000 kilometers) – where the electrons are accelerated. In our analogy, this region is the electron gun at the back of the TV tube and constitutes the “heart” of the aurora. It is to these high altitudes where FAST will journey to explore the unknown physical processes that generate auroras.

FAST will investigate the plasma physics of auroral phenomena in extremely minute detail (high spatial and temporal resolution), since these are the scales on which the acceleration processes are believed to occur. Data from the FAST satellite will be collected by “smart” onboard processors that automatically turn on when auroral acceleration phenomena are encountered. Thus, FAST will be able to collect the data needed to address outstanding critical problems in auroral physics by producing a set of high-resolution measurements unavailable on past, present or planned satellite missions and at altitudes unattainable by sounding rockets.

While FAST collects data from space, other observations of the aurora will be made simultaneously from the ground. In addition, orbiting satellites in the Global Geospace Science program and the International Solar Terrestrial Physics program will contribute related data collected from the outer magnetosphere and solar wind. In this manner, these simultaneous missions will provide an unprecedented exploration of the interaction of energy and particles between the Sun and the Earth.

Scientific Instruments and Investigators;
FAST will carry the following five instruments designed to collect the necessary data to carry out this investigation: The Electrostatic Analyzers (ESA) to measure energetic electrons and ions, the Electric Field Experiment (EFE), and the Instrument Data Processor Unit (IDPU), provided by the University of California at Berkeley; the Time-of-Flight Energy Angle Mass Spectrograph (TEAMS), from the Lockheed Martin Advanced Technology Center, the University of New Hampshire in Durham, the University of California at Berkeley and the Max-Planck Institute in Germany; and the Magnetic Field Instrument (MFI), from the University of California at Los Angeles.

The principal investigator for the FAST mission is Dr. Charles Carlson at the University of California at Berkeley. Co-investigators are Drs. Cynthia Cattell, Robert Ergun, James McFadden, Forrest Mozer, and Mike Temerin, University of California at Berkeley; Drs. Dave Klumpar, Bill Peterson, and Ed Shelley, Lockheed Martin Advanced
Technology Center; Dr. Eberhard Moebius, University of New Hampshire; and Dr. Rick Elphic, Los Alamos National Laboratory, N. M.

A NASA “In-House” Product

Although the FAST science instruments were produced by the institutions listed above, the FAST spacecraft that carries them was designed, fabricated, integrated and tested at Goddard Space Flight Center. Engineers, technicians and support contractors performed the engineering, assembly and testing of the spacecraft using Goddard facilities. Building spacecraft in this manner develops the skills and knowledge that young engineers and scientists need to take a complex system from design to launch.

An example of one of the major spacecraft subsystems designed and built for FAST by the Engineering Directorate at Goddard is the Mission Unique Electronics (MUE). The MUE controls several key spacecraft functions, including power distribution and battery charging; thermistors and heaters; the attitude magnetometer, torquing coils and control system; spacecraft commands and data handing; the spacecraft clock and stored commands; and the launch vehicle data and power interface. As NASA continues to produce Small Explorer satellites, these subsystems will, in turn, serve as the building blocks to enable future spacecraft requirements to be met .

The FAST Launch

FAST is scheduled to be launched in August 1996 on a winged Pegasus rocket carried aloft from the Western Test Range, Vandenberg Air Force Base, in Lompoc, Calif. The Pegasus XL launch vehicle, built by Orbital Sciences Corp., is a three-stage, solid-propellant booster system released from an L-1011 jet aircraft. The Pegasus will be released from the aircraft at about 40,000 feet (12,200 meters) at Mach 0.8. The 400-pound (180-kilogram) FAST spacecraft then will be inserted into a polar orbit with an altitude range of 220 to 2,600 miles (350 to 4200 kilometers) above the Earth. A Transportable Orbital Tracking Station (TOTS) has been placed at Poker Flat, Alaska, to collect real-time telemetry while the spacecraft is passing through the northern polar regions. A second TOTS is planned to support the mission from McMurdo Base, Antarctica. The TOTS is a portable ground station designed and maintained by NASA’s Wallops Flight Facility in Virginia. Northern Hemisphere data also will be collected by the European Space Agency using the tracking station at Kiruna, Sweden.

The SMEX Program
FAST is the second mission of NASA’s low-cost, quick-turnaround Small Explorer (SMEX) program. The first was the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX), launched July 3, 1992, which is investigating the composition of local interstellar matter and solar material and the transport of magnetospheric charged particles into the Earth’s atmosphere.

The Submillimeter Wave Astronomy Satellite (SWAS) is scheduled for launch in late 1996 or early 1997. SWAS will provide the first look at the water and molecular oxygen that are thought to dominate the chemistry of interstellar clouds, and at carbon monoxide and atomic carbon, which are believed to be major reservoirs of carbon in these clouds.

Mission Management

FAST is managed by Goddard Space Flight Center for the Office of Space Science at NASA Headquarters in Washington, D.C.

Dr. David Gilman, Program Manager, NASA Headquarters
Dr. Robert Carovillano, Program Scientist, NASA Headquarters
James Watzin, Project Manager, Goddard Space Flight Center
Dr. Rob Pfaff, FAST Project Scientist, Goddard Space Flight Center

October 1994