The Dawn Spacecraft

The Dawn spacecraft is designed to travel to and operate in orbit around the two largest main belt asteroids, Vesta and Ceres. Developed to meet a ten-year life and fully redundant, the spacecraft accommodates an ion propulsion system, including three ion engines and xenon propellant tank, utilizes large solar arrays to power the engines, carries the science instrument payload, and hosts the hardware and software required to successfully collect and transmit the scientific data back to Earth. The launch of the Dawn spacecraft in September 2007 from Cape Canaveral Air Force Station was the culmination of nearly five years of design, development, integration and testing of this unique system, one of the very few scientific spacecraft to rely on ion propulsion. The Dawn spacecraft arrived at its first destination, Vesta, in July 2011, where it will conduct science operations for twelve months before departing for Ceres.     

Analog clutter cancellation algorithms for dynamic range reduction

A technique that effectively reduces the dynamic range of the input signal in a radar receiver prior to digitization is presented. The dynamic range reduction is accomplished through a process that predicts the next radar return signal from the previous return signals, generates a replica waveform, and subtracts this replica waveform from the radar return signal prior to digitization. This process allows the radar return signal to be digitized without distortion by an analog-to-digital converter (ADC) having a limited dynamic range. The full dynamic range of the radar return signal is then restored by adding the replica waveform to the ADC output. Test and evaluation results using both synthetic and recorded radar data demonstrate in excess of a 30-dB reduction in the dynamic range of the signal at the ADC input when strong clutter is present     

Intelli-FIELDTM: the next generation electrostatic fielddisturbance sensor

Outdoor perimeter volumetric field disturbance sensors must reliably detect perturbations to the field caused by an intruder, while rejecting noise and environmental changes that may be orders of magnitude greater than the target response. Currently, E-Field(R) systems are widely deployed in nuclear, correctional, and industrial sites to provide perimeter security. These systems are effective in rejecting the majority of noise and environmental stimuli through combined fixed attribute threshold comparison techniques. However, some environmental stimuli closely mimic target stimuli, so improved discrimination techniques have been sought. We describe the results of current studies and investigations of electrostatic sensor system response to targets and to various environmental changes. Fundamental principles in the character of sensor response to these varied stimuli are discussed. Techniques and methods that may be used to exploit the difference between intruder and environmental responses, while using cost-effective discrimination methods, are described. We show how the new Intelli-FIELD system was created, using currently available technologies, to provide both excellent detection properties, and an extremely low nuisance alarm rate, while, at the same time, greatly simplifying installation, calibration, and maintenance. The details of the new system hardware components and test results from initial field installations are described. A comparison of field performance with the previous E-Field product is provided to indicate the advantages of this new sensor technology     

Optical orbital debris spotter

The number of man-made debris objects orbiting the Earth, or orbital debris, is alarmingly increasing, resulting in the increased probability of degradation, damage, or destruction of operating spacecraft. In part, small objects (<10 cm) in Low Earth Orbit (LEO) are of concern because they are abundant and difficult to track or even to detect on a routine basis. Due to the increasing debris population it is reasonable to assume that improved capabilities for on-orbit damage attribution, in addition to increased capabilities to detect and track small objects are needed. Here we present a sensor concept to detect small debris with sizes between approximately 1.0 and 0.01 cm in the vicinity of a host spacecraft for near real time damage attribution and characterization of dense debris fields and potentially to provide additional data to existing debris models.     

Quantitative electrocardiography during extended space flight

To assess the effects of prolonged space flight on the electrophysiological properties of the heart, vectorcardiograms (VCG) were obtained on the Skylab crews at regular intervals during flight and the pre- and postflight periods. The VCG signals were telemetered from Skylab and analyzed by digital computer. Conventional 12-lead electrocardiograms were derived from the VCG signals by a lead transformation program. Standardized exercise loads were incorporated into the experiment protocol to increase the sensitivity of the VCG for effects of deconditioning and to detect susceptibility for arrhythmias. In Skylab II, 24 preflight, 21 inflight, and 19 postflight experiments were analyzed. Statistically significant inflight changes observed in two or more crew members included: decreased resting heart rate, increased QRS duration, anterior shift QRS vector, increased QRS vector magnitude, anterior shift T vector, and increased T vector magnitude. One astronaut had occasional premature ventricular contractions (PVC) during the pre- and postflight phases. He had a single episode of multiple PVC's during heavy-load exercise testing in flight. A second astronaut had no arrhythmia during pre- or inflight testing. On postflight day 21 he had multiple PVC's and salvos of ectopic ventricular beats. He has had no recurrence of the arrhythmia. With the exception of the cardiac arrhythmias, no deleterious electrophysiological changes were observed during Skylab II.     

Digital Frequency-Lock Generator

A digital frequency-lock generator has been developed which produces an output pulse train automatically locked to the pulse repetition rate, or frequency, of an input pulse train. This device, which exhibits a wide capture range and has no static output frequency drift, offers several advantages over a phase-lock loop in frequency-locking applications.     

Heavy ions in Jupiter's environment

The extended atmosphere of the Jupiter system consists of heavy-element atoms and ions. This material originates on the satellite Io. Energy is lost from the thermal plasma in collisionally-excited optical and ultra-violet emission. The juxtaposition of Earth and spacecraft measurements provide insight concerning the underlying processes of particle transport and energy supply.