Galileo Probe Nephelometer experiment

The objective of the Nephelometer Experient aboard the Probe of the Galileo mission is to explore the vertical structure and microphysical properties of the clouds and hazes in the atmosphere of Jupiter along the descent trajectory of the Probe (nominally from 0.1 to > 10 bars). The measurements, to be obtained at least every kilometer of the Probe descent, will provide the bases for inferences of mean particle sizes, particle number densities (and hence, opacities, mass densities, and columnar mass loading) and, for non-highly absorbing particles, for distinguishing between solid and liquid particles. These quantities, especially the location of the cloud bases, together with other quantities derived from this and other experiments aboard the Probe, will not only yield strong evidence for the composition of the particles, but, using thermochemical models, for species abundances as well. The measurements in the upper troposphere will provide ground truth data for correlation with remote sensing instruments aboard the Galileo Orbiter vehicle. The instrument is carefully designed and calibrated to measure the light scattering properties of the particulate clouds and hazes at scattering angles of 5.8°, 16°, 40°, 70°, and 178°. The measurement sensitivity and accuracy is such that useful estimates of mean particle radii in the range from about 0.2 to 20 can be inferred. The instrument will detect the presence of typical cloud particles with radii of about 1.0 , or larger, at concentrations of less than 1 cm³.Deceased.     

Integrated Planning and Execution for Autonomous Spacecraft

An autonomous spacecraft must balance long-term and short-term considerations. It must perform purposeful activities that ensure long-term science and engineering goals are achieved and ensure that it maintains positive resource margins. This requires planning in advance to avoid a series of shortsighted decisions that can lead to failure. However, it must also respond in a timely fashion to a somewhat dynamic and unpredictable environment. Thus, in terms of high-level, goal-oriented activity, spacecraft plans must often be modified due to fortuitous events such as early completion of observations and setbacks such as failure to acquire a guidestar for a science observation. This describes an integrated planning and execution architecture that supports continuous modification and updating of a current working plan in light of a changing operating context.     

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.     

One-kVA, Three-Phase dc-ac Inverter with Digital Control

This paper describes a method of applying digital techniques to the control of a 1-kVA three-phase dc-ac inverter to generate a sinusoidal 400-Hz output, using high-frequency bridge-chopper techniques. The model which was constructed used predominantly off-theshelf digital microcircuits and resulted in a device with an overall efficiency of 85 percent, in a 0.52 cubic-foot package which weighed 19.5 lbs. Sinusoidal output with less than 2 percent harmonic distortion at 115 volts line to neutral was obtained with 28 volts dc input.     

Computerized Medical Devices: Trends, Problems, and Safety

Virtually all of the medical devices utilizing electronics will contain a micro or minicomputer by 1990. These devices accounted for $7 billion in U.S. sales in 1984. Their capabilities can provide the means for new or greatly improved medical procedures, and ensure greater patient safety. However, these benefits can easily be compromised if ``computer safety' is not practiced in the design, manufacturing, testing and clinical use of these devices. Along with a trend to wider usage, the number of recalls of medical devices due to computer-related problems has approximately doubled in the last five years. ``Computer-caused' problems are often not recognized or reported as such, resulting in an underestimation of the prevalence of this type of problem. Our study of technical factors causing problems in computerized devices revealed that software quality assurance (SQA), the quality of the ac power, and electromagnetic interference are primary factors. Selected design and QA techniques that are well-known in military-aerospace industries can be used to prevent the most prevalent problems occurring in computerized medical devices, without significantly affecting overall device manufacturing costs.     

Is information security an oxymoron?

Although weaknesses have been demonstrated in some security techniques (encryption, protocols, mobile code such as Java, etc.), current security technology is quite strong in many areas. Despite this, information security has proved difficult to achieve in large modern software systems. Many problems have been reported in which supposedly secure systems have been penetrated and, in some cases, significant damage done. One problem considered is a buffer-overrun attack. The idea called a 〈wrapper〉 which is a layer of software that logically surrounds a software artifact and enhances the functionality of the artifact in some way, is then discussed. Most proposals for the use of wrappers assume that their presence is transparent to the artifact being wrapped. In other words, the artifact sees its operating environment as unchanged and the artifact does not have to be modified in i order to permit it to be wrapped. Wrappers have been proposed as an approach to dealing with deficiencies in existing systems, deficiencies in security for example. The use of shells as a feasible solution to the problem of security is also considered     

A proposed Comet Nucleus Penetrator for the Comet Rendezvous Asteroid Flyby mission

Among the major objectives of NASA's program of space exploration is a better understanding of the origin and evolution of the solar system. Crucial to this objective is the study of comets, which are thought to be the most primitive, pristine bodies remaining in the solar system. The importance of the study of comets has led NASA to plan a mission to rendezvous with comet Tempel 2 in 1997. Critical to the understanding of comets will be measurements of the nucleus material to determine its elemental and isotopic composition, its mechanical properties, and its thermal state and properties. This paper describes a proposal for a Comet Nucleus Penetrator to accomplish these measurement goals. The Comet Nucleus Penetrator will implant instruments into the comet's nucleus beneath a probable volatile-depleted surface mantle into material more representative of the bulk composition of the nucleus.     

InSight Mars Lander Robotics Instrument Deployment System

The InSight Mars Lander is equipped with an Instrument Deployment System (IDS) and science payload with accompanying auxiliary peripherals mounted on the Lander. The InSight science payload includes a seismometer (SEIS) and Wind and Thermal Shield (WTS), heat flow probe (Heat Flow and Physical Properties Package, HP³) and a precision tracking system (RISE) to measure the size and state of the core, mantle and crust of Mars. The InSight flight system is a close copy of the Mars Phoenix Lander and comprises a Lander, cruise stage, heatshield and backshell. The IDS comprises an Instrument Deployment Arm (IDA), scoop, five finger “claw” grapple, motor controller, arm-mounted Instrument Deployment Camera (IDC), lander-mounted Instrument Context Camera (ICC), and control software. IDS is responsible for the first precision robotic instrument placement and release of SEIS and HP³ on a planetary surface that will enable scientists to perform the first comprehensive surface-based geophysical investigation of Mars’ interior structure. This paper describes the design and operations of the Instrument Deployment Systems (IDS), a critical subsystem of the InSight Mars Lander necessary to achieve the primary scientific goals of the mission including robotic arm geology and physical properties (soil mechanics) investigations at the Landing site. In addition, we present test results of flight IDS Verification and Validation activities including thermal characterization and InSight 2017 Assembly, Test, and Launch Operations (ATLO), Deployment Scenario Test at Lockheed Martin, Denver, where all the flight payloads were successfully deployed with a balloon gravity offload fixture to compensate for Mars to Earth gravity.     

Ultra wideband technology for aircraft wireless intercommunications systems (AWICS) design

Current intercommunications system (ICS) designs for military, multicrew aircraft utilize lengthy, encumbering cords to physically attach the crewmember's helmet or headset to a distributed audio intercom system. Typical ICS long-cords are approximately 100 feet in length and allow crewmembers to maintain communications as they move about the aircraft while performing their mission duties. These cords also allow crewmembers to maintain communications with the aircraft when disembarked, as when they are controlling aircraft during engine start-up. Unfortunately, the current wired topology significantly reduces mission effectiveness, impedes crewmember movement, and greatly increases the crewmember's risk of injury. These drawbacks are more pronounced onboard military rotary winged aircraft (helicopters) where several crewmembers have been injured or killed during emergencies requiring the aircraft to ditch at sea. During ditching, crewmembers often became entangled in their lengthy ICS cord, preventing or delaying aircraft egress. This paper discusses the development of an aircraft wireless intercommunications system (AWICS) which utilizes ultra wideband (UWB) technology to address mission requirements for these multicrew, military aircraft. UWB offers unique advantages in this application - multipath mitigation, low probability of detection, low probability of interference to onboard legacy systems, and high throughput in a multiuser environment.     

Background in space-borne low-energy γ-ray telescopes

The scope of observational astronomy in the gamma-ray region of the spectrum is vast. The intimate relationship of these energetic photons with their parent particles and fields provides a direct probe of the high-energy physics phenomena which take place throughout the Universe. As an added bonus the gamma-ray domain contains a wealth of diagnostic information within discrete emission lines, which are derived from a variety of processes including nuclear de-excitation, cyclotron emission, and matter-antimatter annihilation. Consequently observational gamma-ray astronomy addresses directly some of the most fundamental problems in both physics and astrophysics. However, low-energy gamma-rays are the most penetrating photons encountered in nature, and, whilst this factor provides a deep probe of cosmic objects, it ensures that gamma-ray telescopes are massive, both in terms of the stopping power required in the detector systems as well as their shields. Furthermore, the intimate relationship of gamma-rays with nuclear de-excitations ensures that the telescope itself becomes a bright source of background noise, a factor which is aggravated by the necessity that gamma-ray telescopes are obliged to operate in regions pervaded by intense particle fluxes. The background noise experienced in gamma-ray telescopes is, therefore, both high and extremely complex in its origin, and due to the high-energy content of individual photons, their numbers which arrive from distant cosmic sources are necessarily low, even for those objects which radiate the bulk of their power at gamma-ray wavelengths. Current gamma-ray telescopes are thus obliged to operate under conditions of intrinsically low signal-to-noise ratio and it is vital that techniques are developed which reduce the background noise level to more acceptable levels, thus improving the sensitivity. To achieve such a goal, a thorough understanding of the sources of background noise is first required before effective measures can be taken for its reduction.In this paper the sources of background noise are reviewed with the aim to obtain a quantitative analysis of individual contributions, as derived from the various classes of irradiative particle fluxes. The estimated contributions from the individual sources are combined in order to evaluate the total background level of a given telescope in a specific radiation environment, which for practical considerations generally relates to the orbit choice and detailed design of the telescope. The published background noise spectra of a number of past missions are compared to the computed values so as to provide an assessment of the validity of the overall calculations. The level of agreement achieved indicates that a good understanding of the sources of background noise exists. Finally some possibilities for the improvement of the sensitivity of future gammaray telescopes, in terms of the reduction of the background noise, are discussed.