Near-optimal geostationary transfer maneuvers with cooperative en-route inspection using hybrid optimal control

This research investigates the performance of bi-level hybrid optimal control algorithms in the solution of minimum delta-velocity geostationary transfer maneuvers with cooperative en-route inspection. The maneuvers, introduced here for the first time, are designed to populate a geostationary constellation of space situational awareness satellites while providing additional characterization of objects in lower-altitude orbit regimes. The maneuvering satellite, called the chaser, performs a transfer from low Earth orbit to geostationary orbit, during which it performs an inspection of one of several orbiting targets in conjunction with a ground site for the duration of the target?s line-of-site contact with that site. A three-target scenario is used to test the performance of multiple bi-level hybrid optimal control algorithms. A bi-level hybrid algorithm is then utilized to solve fifteen-, and thirty-target scenarios and shown to have increasing benefit to complete enumeration as the number of targets is increased. Results indicate that the en-route inspection can be accomplished for a small increase in the delta-velocity required for a simple transfer to geostationary orbit given the same initial conditions.     

Plasma Experiment for Planetary Exploration (PEPE)

The Plasma Experiment for Planetary Exploration (PEPE) flown on Deep Space 1 combines an ion mass spectrometer and an electron spectrometer in a single, low-resource instrument. Among its novel features PEPE incorporates an electrostatically swept field-of-view and a linear electric field time-of-flight mass spectrometer. A significant amount of effort went into developing six novel technologies that helped reduce instrument mass to 5.5 kg and average power to 9.6 W. PEPE’s performance was demonstrated successfully by extensive measurements made in the solar wind and during the DS1 encounter with Comet 19P/Borrelly in September 2001. P. Barker is deceased.     

Next generation space avionics: layered system implementation

Advances in electronics over the past decade have produced major improvements in the power and flexibility of computer systems. Unfortunately current avionics systems for space applications typically have not leveraged these COTS advantages. A decade ago, the state-of-the-art for avionics systems made a step change to the Integrated Modular Avionics (IMA) used in the Boeing 777. This next generation avionics architecture is not based upon traditional Byzantine redundancy structures, but on a truth-based scheme where each element knows when an internal failure occurs and removes itself from the system. IMA utilizes a lock-step microprocessor design that communicates to a COTS Backplane for input/output, and to a Virtual Backplane/spl trade/ (a reliable high-speed serial bus) for intra-system communication. The system functions are implemented using a time and space partitioned operating system. The entire system provides the simplicity of a simplex system, implements the highest level of reliability providing complete flexibility to reconfigure both software applications and hardware interfaces, allows for rapid prototyping using low-cost COTS hardware, and is easily expandable beyond the initial point implementation. As the only 5/sup th/ generation avionics architecture, the concepts incorporated into Honeywell's IMA are ideally suited to be the backbone of the next generation Space Exploration Program avionics architectures.     

A molecular probe of dark energy

Many theoretical models of dark energy invoke rolling scaler fields which in turn predict time varying values of the fundamental constants. Establishing the value of the fundamental constants at various times in the universe can probe and test the various dark energy theories. One of the constants that is predicted to vary is the ratio of the electron to proton mass μ. It was established early on that molecular spectra are sensitive to the value of μ and can be used as probes of that value. This article describes the use of the spectrum of molecular hydrogen in high redshift Damped Lyman Alpha systems (DLAs) as a sensitive probe of the time evolution of μ.     

Tropical storm structure revealed by stereoscopic photographs from Skylab

A stereo pair of photographs taken by Skylab astronauts over Hurricane Ellen, September 19, 1973, resulted in the first stereo analysis over tropical storms. This pair is also the first evidence to indicate the existence of “supercell” convection in developing tropical storms. The photos are analyzed to determine the cloud top structure of the intense convection occurring in one quadrant of the storm. This type of supercell convection in tropical storms has recently been correlated with subsequent rapid deepening. The stereo analysis revealed that a circular cloud feature over the storm center was a dome which protruded 3–4 km above the undisturbed cirrus clouds. The center of the dome was capped by smaller scale convective turrets which protruded another 1–2 km above the dome. The existence of shear induced waves in the cloud tops is shown with wave amplitude ranging from 150–300 m and wave lengths ranging from 2–4 km. The existence of gravity waves at the cloud tops is also shown with wave amplitudes of 500–600 m and wavelengths of 10–12 km.