A Spacecraft Computer for High-Performance Applications

A high-performance processor circuit called the SC-3 has been developed to meet the requirements of advanced experiment and attitude control applications. It is based on the 16 MHz Intel 80386/80387 chip set and implements a dual bus system configuration which allows high-speed, 32-bit wide memory and low-speed. 16-bit wide Input Output(I/O) circuits to be separated. This separation maintains compatibility with a wide range of current I/O circuit designs while exploiting the high-bandwidth memory access capabilities of the 80386. Performance is further enhanced by means of a cache on the 32-bit bus. Gibson, Whetstone, and Dhrystone instruction mixes have been used to evaluate performance under various operating modes. When the SC-3 is constrained to execute from 16-bit memory. the Gibson mix indicates a 32% performance improvement compared to previous 16-bit processors. An average of 1.1 million Whetstones per second are performed over the typical range of memory wait states. The average Dhrystone performance improvement between 32-bit non-cached and 32-bit cached operation over a typical range of memory wait states is 115%. The initial application of this processor circuit is on Stanford University\u27s Gravity Probe-B experiment

The Genesis Solar Wind Concentrator

The primary goal of the Genesis Mission is to collect solar wind ions and, from their analysis, establish key isotopic ratios that will help constrain models of solar nebula formation and evolution. The ratios of primary interest include ^(17)O/^(16)O and ^(18)O/^(16)O to ±0.1%, ^(15)N/^(14)N to ±1%, and the Li, Be, and B elemental and isotopic abundances. The required accuracies in N and O ratios cannot be achieved without concentrating the solar wind and implanting it into low-background target materials that are returned to Earth for analysis. The Genesis Concentrator is designed to concentrate the heavy ion flux from the solar wind by an average factor of at least 20 and implant it into a target of ultra-pure, well-characterized materials. High-transparency grids held at high voltages are used near the aperture to reject >90% of the protons, avoiding damage to the target. Another set of grids and applied voltages are used to accelerate and focus the remaining ions to implant into the target. The design uses an energy-independent parabolic ion mirror to focus ions onto a 6.2 cm diameter target of materials selected to contain levels of O and other elements of interest established and documented to be below 10% of the levels expected from the concentrated solar wind. To optimize the concentration of the ions, voltages are constantly adjusted based on real-time solar wind speed and temperature measurements from the Genesis ion monitor. Construction of the Concentrator required new developments in ion optics; materials; and instrument testing and handling