Scientific ballooning services

The services available for scientific ballooning are described with special emphasis on the facilities of the NCAR Balloon Flight Station at Palestine, Texas. The preparations for a typical launching, the operations during the launch, the flight and the recovery are described for illustrative purposes. Considerations on the future development of scientific ballooning are given; technological problems for extended flights are considered to be less serious than the political problems.     

The Galileo Probe Atmosphere Structure instrument

The Galileo Probe Atmosphere Structure Instrument will make in-situ measurements of the temperature and pressure profiles of the atmosphere of Jupiter, starting at about 10^-10 bar level, when the Probe enters the upper atmosphere at a velocity of 48 km s^-1, and continuing through its parachute descent to the 16 bar level. The data should make possible a number of inferences relative to atmospheric and cloud physical processes, cloud location and internal state, and dynamics of the atmosphere. For example, atmospheric stability should be defined, from which the convective or stratified nature of the atmosphere at levels surveyed should be determined and characterized, as well as the presence of turbulence and/or gravity waves. Because this is a rare opportunity, sensors have been selected and evaluated with great care, making use of prior experience at Mars and Venus, but with an eye to special problems which could arise in the Jupiter environment. The temperature sensors are similar to those used on Pioneer Venus; pressure sensors are similar to those used in the Atmosphere Structure Experiment during descent of the Viking Landers (and by the Meteorology Experiment after landing on the surface); the accelerometers are a miniaturized version of the Viking accelerometers. The microprocessor controlled experiment electronics serve multiple functions, including the sequencing of experiment operation in three modes and performing some on-board data processing and data compression.     

Chaos and Determinism: A Paradigm

Policy makers depend upon ability to predict the outcome of their policies. Increasingly, in the field of international security ? in matters of war and peace ? prediction is based upon quantitative models. The point made here is that just because a model is mathematical, it does not follow that it can be used to make predictions, that non-linear models allow both predictive and chaotic regimes. After illustrating these matters with physical models, the paper turns to the modeling of an arms race between two antagonistic nations (or groups of nations). After discussing static and dynamic arms race models which are predictive, we turn to a simple non-linear arms race model which allows a transition from predictabililty to chaos. We then postulate that such a transition describes the transition from peace to war in the two party hostile competitive system being modeled by the nonlinear equations, that peace is to war in reality as determinism is to chaos in a mathematical model of that reality. Thus, escalation from peace to war through various levels of hostility may not be controllable, the ``slipping' from peace to war may be as inadvertent as the slipping from laminar flow to turbulence as an aircraft stalls and loses control. The lessons to be learned are to stay away from critical transition points if at all possible and ? more importantly ? to be very wary of claims of controllability in any escalation of a crisis.     

Retrieval of a wind profile from the Galileo Probe telemetry signal

Ultrastable oscillators onboard the Galileo Probe and Orbiter will permit very accurate determinations of the frequency of the Probe's telemetry signal as the Probe descends from a pressure level of several hundred mb to a level of about 20 bars. Analysis of the time-varying frequency can provide, in principle, a unique and important definition of the vertical profile of the zonal wind speed in the Jovian atmosphere. In this paper, we develop a protocol for retrieving the zonal wind profile from the Doppler shift of the measured frequency; assess the impact of a wide range of error sources on the accuracy of the retrieved wind profile; and perform a number of simulations to illustrate our technique and to assess the likely accuracy of the retrieval.Because of unavoidably large uncertainties in the absolute frequencies of the oscillators, we use time-differenced frequencies in our analysis. Nevertheless, it is possible to recover absolute wind speeds as well as wind shears, since the Orbiter/Probe geometry changes significantly during the Probe relay link. We begin with the full relativistic Doppler shift equation. Through the use of power series expansions and a basis function representation of the wind profiles, we reduce the basic equation to a set of linear equations that can be solved with standard linear least-squares techniques.There are a very large number of instrumental and environmental factors that can introduce errors into the measured signal or to the recovery of zonal winds from the data. We provide estimates of the magnitudes of all these error sources and consider the degree to which they may be reduced by a posteriori information as well as the results of calibration tests. The most important error source is the a posteriori uncertainty in the Probe's entry longitude. The accuracy of the retrieved winds is also limited by errors in the Probe's descent velocity, as obtained from atmospheric parameters measured by several Probe experiments, and in the a posteriori knowledge of secular drifts in the oscillators' frequencies during the relay link, due, for example, to aging and radiation damage.Our simulations indicate that zonal winds may be retrieved from the Doppler data to an accuracy of several m s^-1. Therefore, it may be possible to discriminate among alternative models for the basic drive of the zonal winds, since they differ significantly in the implied zonal wind profile.     

Fading from Irregular Surfaces for Line-of-Sight Communications

This paper is concerned with the communications channel between a planetary flyby or orbiting spacecraft and an ejected probe that is traveling toward the planet. Since the mission requires that a significant part of the probe's transmitted energy be reflected from the irregular planet's surface, we will be concerned with the effect of the scattered signal for line-of-sight communications. The statistical distribution of the received field and the fading rate are considered so that the fading margin may be determined for some required probability of satisfactory performance. Typical examples are given for a Martian atmospheric probe.