Faculty — by Research Area
Astrodynamics & Space Applications
- Measurement and recording of fast enzymatic reactions. Computer methods for the extraction of rate constants.
- Three dimensional reconstruction of biological structures obtained from serial electron microscope sections.
- Computer applications to research and teaching of Microbiology.
- Digital Signal Processing.
- Nonlinear dynamics and chaotic system analysis as applied to biological diversity.
- Satellite Design
- Ground station design for acquisition satellite data.
J. L. Garrison
- Professor Garrison's research interests lie in the development of new instruments, algorithms and missions for Earth remote sensing, utilizing Global Navigation Satellite Systems (GNSS) and other "Signals of Opportunity" (SoOps). He performed some of the earliest theoretical and experimental work (1996-2002) demonstrating that reflections of GNSS signals contain valuable information on surface scattering and that this information could be used for remote sensing, particularly in oceanography. That seminal research sparked subsequent development of, arguably, the first entirely new Earth remote sensing instrument concept to be proposed in decades. Research by multiple institutions around the world culminated in NASA's selection of the CYGNSS mission, scheduled for a 2016 launch. Prof. Garrison is on the science team for CYGNSS, which will observe tropical storm development using GNSS reflections from a constellation of 8 micro-satellites.
Recently, he has been investigating the application of reflectometry methods to the general class of Signals of Opportunity, or SoOps. Ocean remote sensing using commercial satellite S-band and Ku-band transmissions has been demonstrated from aircraft and fixed-tower experiments. Applications of these methods to remote sensing in agriculture and hydrology are of particular interest with the use of low-frequency satellite transmissions to penetrate the soil to decimeter depths and the retrieval of phase measurements from high signal to noise ratio reflections. Professor Garrison was awarded a NASA Instrument Incubator Program (IIP) grant to develop an airborne demonstration instrument for measuring root-zone soil moisture, an important variable not directly observable from any current or planned satellite instrument. He has partnered with the Jet Propulsion Laboratory (JPL) to begin fundamental experimental research in the sensing of snow and ice properties through observing phase, amplitude, and polarization variations in reflected signals. SoOp instruments will also soon fly on the NOAA Hurricane Hunter aircraft.
In addition to reflectometry, Prof. Garrison is actively studying methods for airborne GNSS radio-occultation (RO) and detecting traveling waves in the ionosphere. Working with the Scripps Institution of Oceanography, he has been improving signal processing methods for retrieving humidity profiles from RO measurements made within developing hurricanes to test the hypothesis that changes in these profiles can indicate the onset of storm intensification. He has developed new wavelet-based array-processing methods to extract coherent wave structure in the total electron content (TEC) time-series measured from large arrays of dual-frequency GNSS receivers. These methods have shown multiple ionospheric structures induced from atmospheric waves following Earthquakes and have detected waves produced from the 2006 and 2009 North Korean underground nuclear weapons tests.
Professor Garrison works closely with the Earth science and applications community at Purdue and internationally. He is on the executive committee for the Purdue Climate Change Research Center (PCCRC) and a faculty affiliate of the Ecological Sciences and Engineering (ESE) program.
K. C. Howell
- In the area of astrodynamics, the complex missions envisioned in the next few decades will demand innovative spacecraft trajectory concepts and efficient design tools for analysis and implementation. In support of such plans, current research efforts focus on spacecraft navigation and maneuver requirements, and mission planning, both in the neighborhood of the Earth and in interplanetary space. Some sample projects are mentioned below.
Much recent research activity has involved libration point orbits in the three- and four-body problems. The n-body problem in orbital mechanics generally considers trajectory solutions when (n-1) gravity fields are significant. Spacecraft in the vicinity of libration points thus operate in an environment in which gravity forces due to two or three (or more) celestial bodies may result in trajectories that appear as three-dimensional, quasi-periodic Lissajous paths. Such three-dimensional trajectories are of considerable interest in connection with any future lunar operations. In the near term, missions involving libration point satellites are included in a number of programs that the U. S. is planning with international partners. Technical studies involve trajectory design and optimization including optimal control strategies for out-of-plane motion in consideration of communication and other operational specifications. Analyses of station-keeping requirements for such trajectories are also currently under study.
The subject of optimal transfer trajectories is of considerable importance and rapidly growing in complexity as well. New types of problems now facing mission designers render standard optimization strategies inadequate, particularly for application in the n-body problem. Nominal transfer trajectory determination and optimization is the focus of an expanding investigation. Various projects range from development of new computational techniques to application of geometric nonlinear dynamical systems theory to these problems.
A related problem of interest involves Earth orbiting vehicles that repeatedly pass close to the Moon. Such trajectories use lunar gravity to effect trajectory changes. Not only can such a swingby aid in minimizing mission fuel requirements, it also creates trajectory options that may otherwise be impossible. Analysis is complicated, however, by the strong solar perturbation. Multi-conic analysis has proven promising and work is continuing to develop tools to make optimal trajectory design efficient and accurate. Design strategies can also be extended to other multi-body systems. Such applications are under considerations as well.
J. M. Longuski
- Current research efforts include 1) analytic theory and control of spinning-up and thrusting vehicles, 2) mission design and trajectory design for interplanetary flight, 3) orbit decay and reentry problems, and 4) tethers in space.
In 1) breakthroughs were achieved earlier at the Jet Propulsion Laboratory in the analysis of the Galileo spacecraft maneuvers. The current goal is to extend this work to a general analytic theory (which provides solutions for angular velocity, the attitude, the angular momentum vector and the translational velocity of rigid and elastic bodies subject to arbitrary body-fixed torques and forces) and to develop control laws based on the analytic theory.
In 2) mission design tools developed at the Jet Propulsion Laboratory have been acquired for research use at Purdue. Both theoretical and computational techniques are being employed to analyze the delta V gravity-assist problem in terms of identifying potential trajectories (such as the Voyager Grand Tour and the Galileo VEEGA) and optimizing the launch energy and propellant requirements for these trajectories.
In 3) analytic solutions have been obtained for the probability of immediate reentry and of orbit decay, as well as escape, in the event of misdirected interplanetary injection maneuvers occurring at low earth orbit. The solutions have relevance to safety issues involving nuclear power plants aboard deep space probes.
In 4) the feasibility of using tethers for aerobraking has been demonstrated. The basic idea is to connect an orbiter and a probe together by a long tether, for missions to planets with atmospheres. The probe enters the atmosphere and is used to reduce the hyperbolic speed of the orbiter to capture speed, thus eliminating the large retro maneuver normally required. New issues being addressed include analysis of the flexible tether, tether guidance and control, and spacecraft (endpoint) attitude control.