Goddard Space Flight Center

May 26, 1998


The first results from NASA's Advanced Composition Explorer (ACE) spacecraft are challenging the current understanding of the acceleration of particles by explosions on the Sun.

The researchers, led by Dr. Edward C. Stone of the California Institute of Technology (Caltech), Pasadena, Calif., used explosive solar events, called flares, to sample matter from the Sun with the ACE spacecraft. Solar flares that occurred between Nov. 5 and 7, 1997, shot particles from the Sun in quantities that differed from predictions. Some of the elemental isotope abundances which were observed differed from those which were predicted, implying that either the model for particle acceleration efficiency by solar flares is incorrect, that the solar element abundances are different than expected, or that some other phenomenon is affecting the measured abundances. Since the majority of the material in the solar system is contained in the Sun, studying the solar composition can tell researchers about the history and evolution of the Solar System.

"Trying to unravel the history and evolution of solar system material is comparable to trying to estimate how much gold is in a mountain by standing at the bottom and measuring the gold concentration in a stream flowing down from the top. You pick up other stuff along the way. Similarly, in the Solar System, geologic, chemical and nuclear processes all affect the original material composition," said ACE Project Scientist Dr. Jonathan F. Ormes of NASA's Goddard Space Flight Center, Greenbelt, Md.

The six high-resolution spectrometers on the ACE spacecraft determine the composition of particles of solar, local interstellar, and galactic origin, with collecting powers 10 to 1,000 times greater than previously available. Three other instruments provide real-time data to the NOAA space weather alert system.

The increased resolution of the instruments on ACE allows scientists to distinguish between the various isotopes of elements. The identity of an element is determined by the number of positively-charged protons in its atomic nucleus. The positive charge is generally balanced out by the atom's negatively-charged electrons. But these electrons are stripped off at the extremely high temperatures around the Sun, leaving a positively-charged ion which can be accelerated in the Sun's magnetic field.

In addition to the protons in an atomic nucleus, there are also neutrons. Each neutron has about the same mass as a proton, but no charge. The number of neutrons in an atomic nucleus determines the isotope. For a particular element, heavier isotopes result in ions which are less positively charged in relation to their mass. With this relationship between electric charge and mass, scientists are able to make predictions about the abundances of the various isotopes which are accelerated during a solar flare such as those which occurred Nov. 5 through 7.

ACE was launched on Aug. 25, 1997, and arrived at the L1 libration point in December. L1 is the point where the gravitational pulls of the Earth and Sun balance, keeping ACE at an ideal location for its observations, far outside the Earth's magnetic field and with a clear view of charged particles in the solar system. Its mission is expected to continue for at least five years, to the next maximum in solar activity.

ACE has begun its mission to provide high resolution observations of particles in space, providing new information about the origin of the elements, the formation of the Sun's corona and the acceleration of the solar wind, and allowing the detection of impending interplanetary geomagnetic storms which can affect satellite communications and electric power lines on Earth.

The ACE mission is managed by NASA Goddard, and the lead scientific institution is the California Institute of Technology (Caltech), Pasadena, Calif. The spacecraft was built by the Applied Physics Laboratory of Johns Hopkins University in Laurel, Md.

Information on the ACE spacecraft and science can be found at: http://www.srl.caltech.edu/ACE/.


Tuesday, February 3, 1998

ACE satellite now in place between Earth and sun; will seek to determine what sun is made of

PASADENA -- Tanning aficionados, beach bums, surfers, and other solar enthusiasts may not realize it yet, but there is a new satellite making a huge looping halo around the sun. And it's a satellite that's going to be a benefit to weather forecasters in predicting solar flares as well as to astrophysicists in understanding the nature of the universe.

The satellite is called the Advanced Composition Explorer, or ACE for short. Launched August 25, the satellite has reached its destination about a million miles from Earth toward the sun at a position known as L1. That's the point at which the gravitational pull from Earth and sun, plus centrifugal effects, exactly balance each other.

'So, a spacecraft can orbit this invisible point, maintaining a fixed distance from Earth as Earth orbits the sun,' says Ed Stone, Morrisroe Professor of Physics at Caltech and principal investigator of the ACE science mission.

Stone and Caltech physicist Dick Mewaldt are leading the satellite's science mission at the ACE Science Center at Caltech. There, they obtain spacecraft telemetry from the flight operations team at the Goddard Space Flight Center, and process the data for the astrophysics community.

The satellite is designed to collect a wide range of information on the matter it encounters. Its mission can broadly be classified in two phases:

The satellite incorporates a real-time solar wind system that will provide around-the-clock coverage of interplanetary conditions that affect Earth. This is especially of benefit to those living at high northern and southern latitudes, because Earth's magnetic field is such that a coronal mass ejection can more easily disrupt power systems close to the poles.

While the ACE can do nothing to prevent this phenomenon from occurring, the satellite can at least provide an hour of warning that a coronal mass ejection may create a magnetic storm. The warning could help minimize and perhaps even eliminate some of the outages.

The National Oceanic and Atmospheric Administration (NOAA) will analyze the data and issue forecasts and warnings of solar storms. According to NOAA, it will be possible to issue geomagnetic storm alerts with virtually 100 percent accuracy.

The ACE science mission is designed to measure and compare the composition of three samples of matter that can be found in interplanetary space. These are the solar material in the form of the solar wind and energetic particles accelerated by violent eruptions of the sun, the gas from the nearby space between the stars, and high-energy cosmic rays that come from more distant regions in the Milky Way.

Understanding the nature of this matter can help researchers provide answers to fundamental questions about the origin of matter. Additional information on the precise mix of elements in the solar wind, for example, will also serve as a benchmark for understanding the composition of other bodies in the solar system.

The ACE satellite is carrying nine scientific instruments that were developed by a team of scientists representing 10 institutions in the United States and Europe. These instruments are an array of mass spectrometers that measure the mass of individual ions. The satellite is already collecting data, and is expected to do so for at least five years.

'Our first look at the data tells us that the performance of the instruments is excellent,' says Stone. 'We should be learning what the sun is made of in the months ahead.'

Boeing news release

August 26, 1997


CAPE CANAVERAL AIR STATION, Fla., -- A Boeing Delta II 7920 successfully delivered NASA's Advanced Composition Explorer (ACE) observatory at 10:39 a.m. EDT (Aug. 25) to an elliptical transfer orbit in preparation for its one million-mile journey. ACE then will use its own propulsion system to establish an orbit between the Earth and the sun. This is the second launch under the Boeing [NYSE:BA] name and the first from Cape Canaveral.

The Advanced Composition Explorer will study space matter including the solar corona and galactic matter. Study of the energetic particles may contribute to our understanding of the formation and evolution of the solar system. ACE also will provide near-real-time monitoring of solar wind that will allow advanced warning of geomagnetic storms. From ACE's position in orbit, the observatory will have a prime view of the Sun and beyond the galaxy. ACE has a two-year minimum mission lifetime and a goal of five years.

"The success of today's Delta II launch marks another historic role launch vehicles have played in the scientific arena," said Darryl Van Dorn, Boeing director for NASA and commercial Delta programs. "The Delta II team is very enthusiastic in its involvement with over 70 of NASA's scientific missions." This is the ninth of 10 firm launches encompassed in NASA's 1990 Medium Expendable Launch Vehicle Services (MELVS) contract with five options remaining.

Under a second contract, the Medium Light Expendable Launch Vehicle Services (Med-Lite) contract for a medium-light class of NASA satellites, a scaled- down Delta II is scheduled to launch six missions. The six missions scheduled are: Far Ultraviolet Spectroscopy (FUSE), Mars Orbiter-2, and Deep Space-1 in 1998; and Mars Lander-1, STARDUST and EO-1/SAC-C in 1999. Eight options remain in the Med-Lite contract. Earlier this week a Boeing Delta II launched five IRIDIUM" system satellites from Vandenberg Air Force Base, Calif., completing one-third of the 66 satellite constellation.

Subcontractors contributing to the Delta II launch vehicle include the Rocketdyne Divison of Boeing, Canoga Park, Calif., for the main engine, Alliant Techsystems, Magna, Utah, graphite epoxy motors for boost assist; Aerojet, Sacramento, Calif., second-stage engine; and Allied Signal, Teterboro, N.J., Redundant Inertial Flight Control Assembly.


Aug. 24, 1997


The launch of a Boeing Delta II rocket with NASA's Advanced Composition Explorer (ACE) has been rescheduled for Monday, Aug. 25 at 10:39 a.m. EDT at the opening of a 25 minute window.

Launch was scrubbed today by Air Force range safety personnel due to two commercial fishing vessels located about 23 nautical miles offshore from launch Pad 17A. The boats were within the Delta's launch danger area, a location where the solid rocket motors would drop into the sea after being jettisoned from the Delta's first stage.

Air Force weather forecasters indicate a 20 percent chance of weather violating launch weather criteria tomorrow due to a chance of clouds and showers in the launch area.

NASA's ACE spacecraft will travel about 900,000 miles from Earth to a point in space where the gravitational pulls of the Earth and the Sun balance out. From there, the spacecraft will spend the next 2-5 years measuring solar particles and other solar phenomena and provide early warnings of solar storms.

ACE launch coverage on NASA TV will begin at 9 a.m.


Aug. 19, 1997


The launch of NASA's Advanced Composition Explorer (ACE) aboard a Boeing Delta II rocket is scheduled for Aug. 24. Liftoff is targeted to occur at the opening of a launch window which extends from 10:41 - 11:06 a.m. EDT, a duration of 25 minutes. Launch will occur from Pad A at Complex 17 on Cape Canaveral Air Station.

ACE, built for NASA by the Johns Hopkins University Applied Physics Laboratory, is a spin-stabilized spacecraft having a combination of nine sensors and instruments. Spinning at five revolutions per minute, it will sample the steady stream of accelerated particles originating from the Sun and from other galactic and interstellar sources that constantly bombard the Earth in an effort to learn more about the origin of matter. The spacecraft will orbit the Libration Point, a location 900,000 miles from Earth where the gravitational effects of the Sun and Earth are balanced. ACE will give scientists information about the formation of solar corona, solar flares, the acceleration of the solar wind and the Sun's effect on the near-Earth environment.

There are also two secondary investigations on the satellite itself. The Real Time Solar Wind Monitor for the National Oceanic and Atmospheric Administration (NOAA) will provide continuous "space weather" information that can give limited advance warning of geomagnetic storms. The Spacecraft Loads and Acoustics Monitor for the Goddard Space Flight Center is a research and development payload which will monitor the sound characteristics a spacecraft experiences within the rocket's nose fairing environment during launch.

NASA Television Coverage

NASA Television will carry live the Delta/ACE Prelaunch News Conference on Saturday, Aug. 23 starting at 11 a.m. On launch day, August 24, launch commentary will begin at 9 a.m. EDT and continue until a successful mission can be confirmed which will be approximately 90 minutes after launch. NASA Television is available on the GE-2 satellite, Transponder 9C, located at 85 degrees West.

Los Alamos National Laboratory

August 20, 1997


LOS ALAMOS, N.M., Aug. 20, 1997 -- After more than 10 years of planning, research and development, Los Alamos National Laboratory space scientists will watch their solar wind sensors leave Earth on board NASA's Advanced Composition Explorer satellite scheduled for launch Sunday (Aug. 24).

In addition to the Los Alamos solar wind detectors, NASA's latest space explorer will carry sensors that have been designed by various universities and laboratories to study energetic particles in the solar system.

"The ACE mission will provide insight into the formation and evolution of the sun and various astrophysical processes," Los Alamos space scientist Dave McComas said. "It will help us understand how the solar system formed and will even teach us about sources of the materials needed for the formation of life."

Earth is bombarded constantly with high speed particles coming from the sun and sources outside the solar system. ACE, orbiting at one hundredth the distance from Earth to the sun, will provide scientists with information about these particles and identify which ones are likely to hit the planet. ACE also will be able to warn scientists of potential geomagnetic storms caused by coronal mass ejections that can destroy satellites and disrupt electronic communications and electrical power grids.

Los Alamos' Solar Wind Electron Proton Alpha Monitor provides the solar wind observations for the ACE mission. These observations provide the context for elemental and isotopic composition measurements for the other experiments on ACE. The data also will provide researchers an opportunity to study solar wind phenomena such as coronal mass ejections, interplanetary shocks and solar wind structure.

The solar wind is part of the sun's corona that cannot be held down by the sun's gravity. Instead, the outer fringes of the coronal plasma flow away in all directions in a constant stream of particles moving at roughly a million miles an hour. The sun's magnetic field controls how fast the wind moves into outer space.

Near the sun's equator, the magnetic field lets relatively slow-moving particles escape, while at the higher latitudes only the fast-moving ones are released. When the fast-moving particles overtake the slower ones, they produce a shock wave similar to a jet's sonic boom on Earth.

Coronal mass ejections can contribute to these interplanetary shocks by expelling a bubble of gas with a strong magnetic field that may contain billions of tons of matter that travel outward at several million miles per hour. The solar material streaks out among the planets and impacts anything in its path, potentially disrupting satellites, radar, and radio signals.

The scientists at Los Alamos, which is operated by the University of California for the Department of Energy, will measure the solar wind using two instruments that measure in three dimensions the density, energies and directions of travel for electrons and ions.

Each device consumes only five watts of power and together the instruments weigh only 15 pounds. The instruments are curved-plate electrostatic analyzers that fluctuate in voltage to trap incoming electrons and ions.

The solar wind ion and electron detectors collect the particles through apertures directing them into a pathway between a pair of parallel electrically charged metal plates. By adjusting the plates' voltages, the Los Alamos scientists can tune their instruments to collect particles of different energies.

As the satellite spins, the detectors sweep across conical segments of the sky centered on the spacecraft's spin direction. The combination of a particle detection and the spin of the spacecraft provides unique directional information.

The detection units were recycled, refurbished and enhanced from versions of the solar wind instruments from the Ulysses project.

Launched by the space shuttle Discovery in October 1990, Ulysses flew by Jupiter in February 1992. The primary goals of Ulysses were to investigate the properties of the solar wind and the heliospheric magnetic field out of the plane of the planets where all previous spacecraft had been located. In contrast, ACE will stay in this plane but will observe the composition of particles in space with 10 to 1,000 times better sensitivity than was previously possible.

ACE is scheduled to launch from Cape Canaveral, Fla., on board a Delta II rocket.

NASA Headquarters, Washington, DC
Goddard Space Flight Center, Greenbelt, MD

July 23, 1997


The Earth is constantly being bombarded by a stream of accelerated particles arriving not only from the Sun, but also from interstellar and galactic sources. The study of these energetic particles by NASA's Advanced Composition Explorer (ACE) observatory will contribute to the understanding of the formation and evolution of the solar system as well as the astrophysical processes involved.

The space science observatory is scheduled for launch on a Delta II rocket at 10:41 a.m. EDT August 24, from Launch Complex 17 at the Cape Canaveral Air Station, FL.

"The Advanced Composition Explorer observatory is designed to sample the matter that comes near the Earth from the Sun, from the apparently, but not actually, empty space between the planets, and from the Milky Way galaxy beyond the solar system," said Don Margolies, ACE Mission Manager at NASA's Goddard Space Flight Center, Greenbelt, MD.

"While previous missions have studied these particles, the instruments on ACE have a collecting power 10 to 1,000 times greater and will be at least 100 times more sensitive than anything we've ever flown," Margolies said. "We will be able to study known phenomena in much greater detail than previously possible, and discover new ones to give us a better understanding of the interaction between the Sun, the Earth, and the galaxy."

The Advanced Composition Explorer has six high-resolution particle detection sensors and three monitoring instruments. It will sample low-energy particles of solar origin and high-energy galactic particles. The observatory will be placed into an orbit at the L1 libration point, which is almost a million miles (or 1.5 million kilometers) away from the Earth, about 1/100 the distance from the Earth to the Sun.

The ACE payload includes four brand-new, state-of-the-art spectrometers. They are the Cosmic Ray Isotope Spectrometer; Solar Isotope Spectrometer; Solar Energetic Particle Ionic Charge Analyzer; Ultra-Low-Energy Isotope Spectrometer. In addition, there are four spare instruments from other NASA missions that, with appropriate modifications, are being flown on ACE. They are the Solar Wind Electron, Proton, and Alpha Monitor; Solar Wind Ionic Charge Spectrometer; Electron, Proton, and Alpha Monitor; and a Magnetometer. An additional instrument, the Solar Wind Ion Mass Spectrometer, is a newly built copy of a previously flown instrument.

Also onboard are two secondary instruments, the Spacecraft Loads and Acoustic Measurements, designed to measure spacecraft environments during the first five minutes of launch, and the Real Time Solar Wind experiment, which will provide real- time data to the National Oceanic and Atmospheric Administration (NOAA). NASA and nine universities in the U.S. and Europe built the instruments.

The ACE spacecraft's instruments and experiments will work together to add to our understanding of solar events ranging from "solar storms" to the origin and evolution of solar and galactic matter.

The scientific goal of the ACE mission is to measure accurately the composition of several different types of matter, including particles coming from the Sun, the very thin gas between the planets, the even thinner gas just outside the solar system, and matter from distant parts of the galaxy. The particles that ACE measures are moving very fast, up to 3.5 million miles per hour, and are atomic and subatomic.

ACE also has an Earth applications goal. It will provide NOAA's Space Environment Center, Boulder, CO, with continuous real-time solar wind "space weather" information, which will give an advance warning (about one hour) of geomagnetic storms that can affect electric power grids, Earth-orbiting spacecraft, and radio communications on Earth.

The 1,730-pound observatory was built by the Johns Hopkins Applied Physics Laboratory, Laurel, MD, where its instruments were integrated. ACE was tested at the Applied Physics Laboratory and at Goddard.

The science payload was provided under the direction of the Payload Management Office at the California Institute of Technology, Pasadena, CA. Flight operations will be conducted from Goddard; the Science Center is located at Caltech. The ACE mission is managed by the Explorer Program at Goddard for the Sun-Earth Connections Program in the Office of Space Science, NASA Headquarters, Washington, DC

Kennedy Space Center

June 13, 1997


NASA's Advanced Composition Explorer (ACE), to be launched aboard a McDonnell Douglas Delta II rocket in August, arrived today at the Kennedy Space Center (KSC) to begin prelaunch processing. The spacecraft, built for NASA by the Johns Hopkins University Applied Physics Laboratory, was shipped by truck from the Goddard Space Flight Center in Greenbelt, Md., yesterday.

ACE is a spin-stabilized spacecraft having a combination of nine sensors and instruments. Spinning at five revolutions per minute, it will investigate the origin and evolution of solar phenomenon, the formation of the solar corona, solar flares and the acceleration of the solar wind. The spacecraft will orbit the Libration Point, a location 900,000 miles from Earth where the gravitational effects of the Sun and Earth are balanced. ACE will be able to give scientists information about the effect of the Sun on the near-Earth environment, as well as interplanetary space while also providing clues about the lifestyle of similar stars.

There are also two secondary investigations on the satellite itself. The Real Time Solar Wind Monitor for the National Oceanic and Atmospheric Administration (NOAA) will provide continuous "space weather" information that can give limited advance warning of geomagnetic storms. The Spacecraft Loads and Acoustics Monitor for the Goddard Space Flight Center is a research and development payload which will monitor the sound characteristics a spacecraft experiences within the rocket's nose fairing environment during launch.

The ACE spacecraft will undergo final experiment integration and functional testing at the Spacecraft Assembly and Encapsulation Facility-2 (SAEF-2) located in the KSC Industrial Area. The solar arrays and magnetometer booms will be deployed and tested. The communications systems of the spacecraft will also be checked out which will include a compatibility test with the Deep Space Network. Finally, the propulsion system tanks will be fueled and the spacecraft will be spin tested. About ten days before launch, ACE will be transported to Space Launch Complex 17 and erected atop a Delta II 7920-8, a two-stage rocket manufactured by McDonnell Douglas.

The buildup of the Delta vehicle on Pad 17-A is scheduled to be performed the week of July 21. This will include the erection of the first and second stages and attachment of the nine strap-on solid rocket boosters. Atop the launch vehicle, the nose fairing is to be installed around the spacecraft four days before launch.

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