The primary purpose of ACE was to determine and compare the isotopic and elemental composition of several distinct samples of matter, including the solar corona, the interplanetary medium, the local interstellar medium, and Galactic matter.
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 and Spacecraft Characteristics
The spacecraft was 1.6 meters across and 1 meter high, not including the four solar arrays and the magnetometer booms attached to two of the solar panels. At launch, it weighed 785 kg, which included 189 kg of hydrazine fuel for orbit insertion and maintenance. The solar arrays generated about 500 watts of power. The spacecraft spun at 5 rpm, with the spin axis generally pointed along the Earth-sun line and most of the scientific instruments on the top (sunward) deck. In order to get away from the effects of the Earth's magnetic field, the ACE spacecraft travelled almost 1.5 million km from the Earth to the Earth-sun libration point (L1). By orbiting the L1 point, ACE stayed in a relatively constant position with respect to the Earth as the Earth revolved around the sun. Science Goals The primary purpose of ACE was to determine and compare the isotopic and elemental composition of several distinct samples of matter, including the solar corona, the interplanetary medium, the local interstellar medium, and Galactic matter. The nine scientific instruments on ACE performed: