The Advanced Composition Explorer (ACE) launched at 10:39 a.m., August 25, 1997

ACE S/C Status

ACE Science News is available at:

http://www.srl.caltech.edu/ACE/

ACE Browse data may be viewed at:

http://www.srl.caltech.edu/ACE/ASC/view_browse_data.html

Background

ACE was conceived at a meeting on June 19, 1983 at the University of Maryland. The meeting was hosted by George Gloecker and Glen Mason. The participants were Drs. L. F. Burlaga, S. M. Krimigis, R. A. Mewaldt, and E. C. Stone. This meeting had been preceded by preliminary documentation from the Johns Hopkins University Applied Physics Laboratory (APL) and the University of Maryland under the proposal name of Cosmic Composition Explorer. An unsolicited proposal was put together and forwarded to the NASA Explorer Program Office later that year, but was not acted upon.

The proposal was resurrected at the instigation of Dr. Vernon Jones and officially resubmitted to NASA in 1986 as part of the Explorer Concept Study Program. In 1988, the ACE mission was selected for a one-year "Phase A" (concept) Study. This study was a collaborative effort between spacecraft design and science teams.

The ACE Mission officially began on 22 April 1991 when the contract between NASA/GSFC and the California Institute of Technology was signed. APL, designer and builder of the ACE spacecraft, was involved in planning for Phase B (definition). The early ACE Spacecraft effort (April to July 1991) was primarily for ACE mission support, spacecraft system specification and ACE instrument support and interface definition. Phase B of the ACE mission officially began in August 1992.

The Mission Preliminary Design Review was held in November 1993. Phase C/D (implementation) began shortly thereafter.

Mission Summary

The Earth is constantly bombarded with a stream of accelerated particles arriving not only from the Sun, but also from interstellar and galactic sources. Study of these energetic particles will contribute to our understanding of the formation and evolution of the solar system as well as the astrophysical processes involved. The Advanced Composition Explorer (ACE) spacecraft carrying six high-resolution sensors and three monitoring instruments will sample low-energy particles of solar origin and high-energy galactic particles with a collecting power 10 to 1000 times greater than past or planned experiments.

From a vantage point approximately 1/100 of the distance from the Earth to the Sun ACE will perform measurements over a wide range of energy and nuclear mass, under all solar wind flow conditions and during both large and small particle events including solar flares. ACE will provide near-real-time solar wind information over short time periods. When reporting space weather ACE can provide an advance warning (about one hour) of geomagnetic storms that can overload power grids, disrupt communications on Earth, and present a hazard to astronauts.

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ACE Real Time Space Weather

Orbit Geometry

ACE will orbit the L1 libration point which is a point of Earth-Sun gravitational equilibrium about 1.5 million km from Earth and 148.5 million km from the Sun. With a semi-major axis of approximately 200,000 km the elliptical orbit affords ACE a prime view of the Sun and the galactic regions beyond.

Mission Characteristics

• Launched: August 25, 1997
• Launch Vehicle: Delta II
• Primary Mission: Observe energetic particles within the solar system
• Mission Lifetime: Two years with a five-year goal

Spacecraft Characteristics

• Spacecraft Structure: Two octagonal decks, 1.6 m across, 1.0 m high
• Propulsion: Hydrazine for insertion and maintenance in orbit
• Power: 464 W (443 W end-of-life @ 5 years), four fixed solar arrays
• Attitude Subsystem: Spinning spacecraft, Star Sensor and Sun Sensors
• Communication Subsystem: Primary Mission, S-band, DSN;
• Communication Subsystem: NOAA - S-band @ NOAA Receiving Stations, TBD
• Total Onboard Data Storage in Two Solid State Recorders -- 2 Gigabits

Data Rates

• Primary Mission Downlink Rates: 78 & 6.9 kbps and 434 bps
• NOAA Real Time Solar Wind Mission: 434 bps

Instruments

• CRIS Cosmic Ray Isotope Spectrometer
• EPAM Electon, Proton, and Alpha Monitor
• MAG Magnetometer
• SEPICA Solar Energetic Particle Ionic Charge Analyzer
• SIS Solar Isotope Spectrometer
• SWEPAM Solar Wind Electon, Proton, and Alpha Monitor
• SWICS Solar Wind Ionic Charge Spectrometer
• SWIMS Solar Wind Ion Mass Spectrometer
• ULEIS Ultra Low Energy Isotope Spectrometer

Secondary payloads:

• RTSW (Real Time Solar Wind) data format for NOAA
• SLAM (Spacecraft Loads and Acoustic Measurements) from NASA/GSFC

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Exploded View of ACE Instrument Locations

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ACE Instrument Reponsibilities

Mission Responsibilities

NASA Goddard Space Flight Center (GSFC) Explorer Project Office. The GSFC ACE page contains good instrument descriptions.

• Overall mission management
• Ground system (Operations Center)

California Institute of Technology (Caltech )

• Science payload management
• ACE Science Center

Johns Hopkins University Applied Physics Laboratory (JHU/APL)

• Spacecraft development
• Two payload instruments: EPAM and ULEIS
• Observatory integration and test
• Launch operations support

ACE Science Team

Principal Investigator:

• E. C. Stone - Caltech

Co-Investigators:

• W. R. Binns - Washington University
• P. Bochsler - University of Bern
• L. F. Burlaga - GSFC
• A.C. Cummings - Caltech
• W. C. Feldman - Los Alamos Natl. Lab.
• T. L. Garrard - Caltech
• J. Geiss - University of Bern
• G. Gloecker - University of Maryland
• R. E. Gold - JHU/APL
• D. Hovestadt - Max Planck-Institut
• B. Klecker - Max Planck-Institut
• S. M. Krimigis - JHU/APL
• G. M. Mason - University of Maryland
• D. McComas - Los Alamos Natl. Lab.
• R. A. Mewaldt - Caltech
• E. Moebius - University of New Hampshire
• N. F. Ness - University of Delaware
• J. A. Simpson - University of Chicago
• T. T. von Rosenvinge - GSFC
• M. E. Wiedenbeck - Jet Propulsion Laborator

Last Updated 11/106/98

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