AKA: Advanced Composition Explorer. Status: Operational 1997. First Launch: 1997-08-25. Last Launch: 1997-08-25. Number: 1 . Gross mass: 785 kg (1,730 lb). Unfuelled mass: 596 kg (1,313 lb). Height: 1.00 m (3.20 ft).
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 traveled almost 1.5 million km from the Earth to the Earth-sun libation 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:
NASA NSSDC Master Catalog Description
The objective of the Advanced Composition Explorer (ACE) is to collect observations of particles of solar, interplanetary, interstellar, and galactic origins, spanning the energy range from that of KeV solar wind ions to galactic cosmic ray nuclei up to 600 MeV/nucleon. Definitive studies will be made of the abundances of essentially all isotopes from H to Zn (Z = 1-30), with exploratory isotope studies extending to Zr (Z = 40). The ACE payload includes six high resolution spectrometers, each designed to provide the optimum charge, mass, or charge-state resolution in its particular energy range. Each spectrometer has a geometry factor optimized for the expected flux levels, so as to provide a collecting power greater by a factor of 10-1000 times that of previous or planned experiments. The payload also includes three additional instruments of standard design to monitor energetic electrons, H and He ions, and a magnetometer. The ACE spacecraft is based on the design of the Charge Composition Explorer, built at JHU/APL for the Active Magnetospheric Particle Tracer Explorer (AMPTE) program. The spacecraft spin axis is pointed towards the Sun to within +/- 20 degrees, and it occupies a halo orbit about the L1 Earth-Sun libration point. Powered by solar cells, the spacecraft has a design life of at least five years, and it returns data in daily tape recorder dumps, received through NASA JPL's Deep Space Network and initially processed at NASA-GSFC. The average data telemetry rate is 6.7 Kbs.
Credit: Manufacturer Image