An exact, practical implementation of reliability calculation for combinational circuits can be based on a hierarchical decomposition of the circuit into manageable sub-units, and construction of exact summary tables for each sub-unit. For a simple example of voting logic, this exact reliability analysis reafirms that the reliabzlity of the individual voter inputs is as important as the voter reliability.

Radar backscatter functions Sigma-(carat)(sub 0)(phi) for incidence angles between 0 less than or equal to phi less than or equal to 4-10 deg were derived from Magellan altimetry radar echoes. The procedure includes constrained solution of a system of simultaneous equations for which the echo-spectrum and echo time profile are inputs. A practical and workable set of constraints was applied; optimization and improved results are expected as the analysis matures. The scattering functions yield information on small-scale surface structures (tens of centimeters to tens of meters) but averaged over hundreds of sq km. RMS surface slopes derived from fits of analytic functions to the Sigma-(carat)(sub 0)(phi) results were converted to map form and show patterns similar to those reported using other techniques. While all three forms are found on Venus, fit residuals imply that an exponential scattering function matches data better than either the Hagfors or Gaussian form in most areas, although the Hagfors function may be a better descriptor at some sites. Limited study of image data indicates that average backscatter cross section, and possibly its slope, can be derived at oblique angles (17 deg less than or equal to phi less than or equal to 45 deg). Offsets of the echo peak in altimetry spectra are surprisingly common and are loosely correlated with Venus topography, but no cause for this phenomenon was identified.

Radar backscatter functions for incidence angles 0≤ϕ≤4°–10° have been derived from Magellan altimetry radar echoes. The procedure includes constrained solution of a system of simultaneous equations for which the echo spectrum and echo time profile are inputs. An initially practical and workable set of constraints has been applied; optimization and improved results are expected as the analysis matures. The scattering functions yield information on small scale surface structure (tens of centimeters to tens of meters) but averaged over hundreds of square kilometers. RMS surface slopes derived from fits of analytic functions to the results have been converted to map form and show patterns similar to those reported using other techniques. A scattering law of exponential form matches the data better than either the Hagfors or Gaussian form in most areas, but the Hagfors function is generally best at the smoothest sites. Limited study of radar image data indicates that average backscatter cross section, and possibly its derivative with incidence angle, can be derived at oblique angles (17°≤ϕ≤45°). The altimetry results in combination with those derived from the synthetic aperture radar will strongly constrain the form of over the range 0≤ϕ≤45°. Offsets of the echo peak in altimetry spectra from those expected of nadir echoes are surprisingly common and are loosely correlated with Venus topography; to date no specific cause for this phenomenon has been identified.

An architecture has been developed for a high-performance VLSI digital signal processor that is highly reliable, fault-tolerant, and radiation-hard. The signal processor, part of a spacecraft receiver designed to support uplink radio science experiments at the outer planets, organizes the connections between redundant arithmetic resources, register files, and memory through a shuffle exchange communication network. The configuration of the network and the state of the processor resources are all under microprogram control, which both maps the resources according to algorithmic needs and reconfigures the processing should a failure occur. In addition, the microprogram is reloadable through the uplink to accommodate changes in the science objectives throughout the course of the mission. The processor will be implemented with silicon compiler tools, and its design will be verified through silicon compilation simulation at all levels from the resources to full functionality. By blending reconfiguration with redundancy the processor implementation is fault-tolerant and reliable, and possesses the long expected lifetime needed for a spacecraft mission to the outer planets.<>