Radar: The Cassini Titan Radar Mapper

The Cassini RADAR instrument is a multimode 13.8 GHz multiple-beam sensor that can operate as a synthetic-aperture radar (SAR) imager, altimeter, scatterometer, and radiometer. The principal objective of the RADAR is to map the surface of Titan. This will be done in the imaging, scatterometer, and radiometer modes. The RADAR altimeter data will provide information on relative elevations in selected areas. Surfaces of the Saturn’s icy satellites will be explored utilizing the RADAR radiometer and scatterometer modes. Saturn’s atmosphere and rings will be probed in the radiometer mode only. The instrument is a joint development by JPL/NASA and ASI. The RADAR design features significant autonomy and data compression capabilities. It is expected that the instrument will detect surfaces with backscatter coefficient as low as −40 dB.RADAR Team LeaderThis revised version was published online in July 2005 with a corrected cover date.     

Precision bone and muscle loss measurements by advanced, multiple projection DEXA (AMPDXA) techniques for spaceflight applications.

An advanced, multiple projection, dual energy x-ray absorptiometry (AMPDXA) scanner system is under development. The AMPDXA is designed to make precision bone and muscle loss measurements necessary to determine the deleterious effects of microgravity on astronauts as well as develop countermeasures to stem their bone and muscle loss. To date, a full size test system has been developed to verify principles and the results of computer simulations. Results indicate that accurate predictions of bone mechanical properties can be determined from as few as three projections, while more projections are needed for a complete, three-dimensional reconstruction.     

Simulation of launch and re-entry acceleration profiles for testing of shuttle and unmanned microgravity research payloads

Microgravity experiments designed for execution in Get-Away Special canisters, Hitchhiker modules, and Reusable Re-entry Satellites will be subjected to launch and re-entry accelerations. Crew-dependent provisions for preventing acceleration damage to equipment or products will not be available for these payloads during flight; therefore, the effects of launch and re-entry accelerations on all aspects of such payloads must be evaluated prior to flight. A procedure was developed for conveniently simulating the launch and re-entry acceleration profiles of the Space Shuttle (3.3 and 1.7 × g maximum, respectively) and of two versions of NASA's proposed materials research Re-usable Re-entry Satellite (8 × g maximum in one case and 4 × g in the other). By using the 7 m centrifuge of the Gravitational Plant Physiology Laboratory in Philadelphia it was found possible to simulate the time dependence of these 5 different acceleration episodes for payload masses up to 59 kg. A commercial low-cost payload device, the “Materials Dispersion Apparatus” of Instrumentation Technology Associates was tested for (1) integrity of mechanical function, (2) retention of fluid in its compartments, and (3) integrity of products under simulated re-entry g-loads. In particular, the sharp rise from 1 g to maximum g-loading that occurs during re-entry in various unmanned vehicles was successfully simulated, conditions were established for reliable functioning of the MDA, and crystals of 5 proteins suspended in compartments filled with mother liquor were subjected to this acceleration load.     

The telemedicine frontier: going the extra mile

Telemedicine has the potential to have a greater impact on the future of medicine than any other modality and will profoundly alter the medical landscape of the twenty-first century. In the most remote areas, it can bring high-quality health care where none is now available. In global health care, it can enhance and standardize the quality of medical care, including developing countries. In the realm of space flight, it can provide a lifeline to medical expertise and monitoring. Through its mobility, it can provide urgently needed health care in instances of natural disaster. However, a number of challenges exist in its coordination and implementation on a global scale, specifically in the international and remote disaster scenarios. In the area of spaceflight, telemedicine capability will remain a consultation/information ‘lifeline’, but additional onboard medical capability and expertise will become crucial complements as missions become more advanced and remote from Earth.     

Scan-based emitter passive localization

This paper investigates the problem of estimating the position of a scanning emitter using a passive scan-based geolocation technique. This is achieved by taking advantage of the geometric constraints introduced by the uniform rotating motion of the antenna main beam as it sweeps across a number of separate receivers. A detailed analysis of the estimation process and accuracy of the emitter position is given and a number of computer simulations showing the benefits of this geolocation technique are also included     

Analysis of a Multiplicative Feed System for Monopulse Tracking Applications

In angle tracking antenna applications, the angle sensing boresight accuracy capabilities are important. The ability of an antenna to precisely determine the bearing angle to a point source is determined by the slope of the control function pattern at boresight. In the presence of extraneous interference, the magnitudes of the sidelobe and backlobe responses are important. Control pattern slope (angular sensitivity) is primarily a function of aperture illumination. It can be described by a current distribution in intensity and phase at every point. Once distribution is defined, lobe structure is defined by the associated transform. When more than one feed is used, the distribution will be a vector sum of the individual feed distributions. The resulting secondary pattern can be defined in terms of the amplitude distribution and the phase center locations of the contributing feeds. With a four-horn monopulse configuration, the feed phase centers are displaced from the boresight axis. Placing the phase centers on the boresight axis by rotating the feeds through 45 degrees results in a different set of intensity and phase values. A quite different secondary pattern results. The control function obtained by the subtraction of the powers from a paired set of on-axis feeds results in a lower sidelobe level than that obtained with a conventional monopulse combiner for a given feed taper.     

The ACE Magnetic Fields Experiment

The magnetic field experiment on ACE provides continuous measurements of the local magnetic field in the interplanetary medium. These measurements are essential in the interpretation of simultaneous ACE observations of energetic and thermal particles distributions. The experiment consists of a pair of twin, boom- mounted, triaxial fluxgate sensors which are located 165 inches (=4.19 m) from the center of the spacecraft on opposing solar panels. The electronics and digital processing unit (DPU) is mounted on the top deck of the spacecraft. The two triaxial sensors provide a balanced, fully redundant vector instrument and permit some enhanced assessment of the spacecraft's magnetic field. The instrument provides data for Browse and high-level products with between 3 and 6 vector s−1 resolution for continuous coverage of the interplanetary magnetic field. Two high-resolution snapshot buffers each hold 297 s of 24 vector s−1 data while on- board Fast Fourier Transforms extend the continuous data to 12 Hz resolution. Real-time observations with 1-s resolution are provided continuously to the Space Environmental Center (SEC) of the National Oceanographic and Atmospheric Association (NOAA) for near- instantaneous, world-wide dissemination in service to space weather studies. As has been our team's tradition, high instrument reliability is obtained by the use of fully redundant systems and extremely conservative designs. We plan studies of the interplanetary medium in support of the fundamental goals of the ACE mission and cooperative studies with other ACE investigators using the combined ACE dataset as well as other ISTP spacecraft involved in the general program of Sun-Earth Connections. This revised version was published online in June 2006 with corrections to the Cover Date.     

The Huygens Doppler Wind Experiment ' Titan Winds Derived from Probe Radio Frequency Measurements

A Doppler Wind Experiment (DWE) will be performed during the Titan atmospheric descent of the ESA Huygens Probe. The direction and strength of Titan's zonal winds will be determined with an accuracy better than 1 m s⁻¹ from the start of mission at an altitude of ∼160 km down to the surface. The Probe's wind-induced horizontal motion will be derived from the residual Doppler shift of its S-band radio link to the Cassini Orbiter, corrected for all known orbit and propagation effects. It is also planned to record the frequency of the Probe signal using large ground-based antennas, thereby providing an additional component of the horizontal drift. In addition to the winds, DWE will obtain valuable information on the rotation, parachute swing and atmospheric buffeting of the Huygens Probe, as well as its position and attitude after Titan touchdown. The DWE measurement strategy relies on experimenter-supplied Ultra-Stable Oscillators to generate the transmitted signal from the Probe and to extract the frequency of the received signal on the Orbiter. Results of the first in-flight checkout, as well as the DWE Doppler calibrations conducted with simulated Huygens signals uplinked from ground (Probe Relay Tests), are described. Ongoing efforts to measure and model Titan's winds using various Earth-based techniques are briefly reviewed. This revised version was published online in August 2006 with corrections to the Cover Date.