MSI-SuperDARN Radars | Spacecraft Shielding | Ionospheric Convection | GICs | Publications
Scientists at four institutions (Virginia Tech, Dartmouth College, the University of Alaska Fairbanks, and the Johns Hopkins University Applied Physics Laboratory) will build eight (8) SuperDARN-style HF radars at middle geomagnetic latitudes across the U.S. and in the Azores between 2009 and 2012. This collaborative effort was made possible by a generous grant from the National Science Foundation (NSF) through the Mid-Sized Infrastructure (MSI) program.
The MSI SuperDARN radars, together with existing mid-latitude SuperDARN radars, will provide unprecedented measurements of the drifting plasma with coverage that spans over 12 hours in local time and extends from ~50 degrees magnetic latitude all the way to the pole. The array of radars, coupled with the existing SuperDARN network, will provide exciting new measurements of ionospheric plasma irregularities in regions of the plasmaspheric boundary layer and during magnetic storms.
Spacecraft Radiation Shielding
Manned missions to planets such as Mars require extended missions that will expose astronauts to harmful radiation in the form of energetic particles from solar and galatic sources. Traditional methods for protecting spacecraft and occupants from these forms of radiation involve some configuration of a massive material shield to absorb the energy of incoming particles. For the high energy galactic cosmic rays (GCRs) that astronauts will be exposed to, these so-called passive shields are too massive to be practical and will likely produce showers of secondary radiation that could be more harmful than the GCRs themselves.
Active shields which rely on magnetic (or electric) fields to deflect energetic particles offer a potential solution to the problem. Designing a magnetic shield that is strong enough to deflect GCR particles but weak enough to not harm astronauts is a challenge. Investigating possible solutions involves a combination of electromagnetic theory, numerical analysis, engineering practicality, and an astronaut's sense of exploration.
Ionospheric Electric FieldsA combination of reconnection and viscous processes occurring at the magnetopause and in the magnetotail are responsible for creating large-scale electric fields. These fields map down geomagnetic field lines into the high-latitude ionosphere where they cause the plasma to 'E x B' drift. By measuring the motion of this ionospheric plasma it is, therefore, possible to infer a great deal about the magnetospheric processes that are responsible for the convection.
Scientists from all over the world are involved in a cooperative program which operate HF radars for the purpose of measuring the ionospheric plasma drift (or equivalently, the ionospheric electric field.)
Geomagnetically Induced Currents (GICs)Large-scale currents flowing overhead in the ionosphere induce electric and magnetic fields on the surface of the Earth. So-called Geomagnetically Induced Currents (GICs) can in turn be induced in technologically networks located underneath these currents, such as railroads, power transmission lines, and pipelines. During electromagnetic storm periods caused by the Sun these GICs can be large, often exceeding several hundred Amperes, and cause catastrophic consequences to the system in which they flow.
Scientists at Dartmouth are attempting to predict the occurence of GICs using physics-based models of the global magnetosphere, ionosphere, and Earth conductivity together with input from a satellite located in the upstream solar wind. The electric (and magentic) field at the surface of the Earth over North America will be determined with 30-90 minutes warning, allowing an advance warning of GICs to be calculated for specific conducting networks.
More details can be found on the Darmtouth College GIC Page
- Shepherd, S. G., and J. P. G. Shepherd, Toroidal magnetic spacecraft shield used to deflect energetic charged particles, JOURNAL OF SPACECRAFT AND ROCKETS, VOL. 46, doi:10.2514/1.37727, 2009.
- Shepherd, S. G., and B. T. Kress, Stormer theory applied to magnetic spacecraft shielding, SPACE WEATHER, VOL. 5, NO. 4, S04001, doi:10.1029/2006SW000273, 2007.
- Shepherd, S. G., and B. T. Kress, Comment on "Applications for Deployed High Temperature Superconducting Coils in Spacecraft Engineering: A Review and Analysis" by J. C. Cocks et al., JOURNAL OF THE BRITISH INTERPLANETARY SOCIETY, VOL. 60, PAGES 129--132, 2007.
- Shepherd, S. G., Polar Cap Potential Saturation: Observations, Theory, and Modeling, JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS, VOL. 69, doi:10.1016/j.jastp.2006.07.022, PAGES 234--248, 2007.
- Bristow, W. A., R. A. Greenwald, Shepherd, S. G., J. M. Hughes, On the observed variability of the cross-polar cap potential, JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 109, NO. A2, A02203, doi:10.1029/2003JA010206, 2004.
- Shepherd, S. G., J. M. Rhuohoniemi, and R. A. Greenwald, Direct measurements of the ionospheric convection variability near the cusp/throat, GEOPHYSICAL RESEARCH LETTERS, VOL. 30, NO. 21, 2109, doi:10.1029/2003GL017668, 2003.
- Shepherd, S. G. and F. Shubitidze, Method of auxiliary sources for calculating the magnetic and electric fields induced in a layered Earth, JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS, VOL. 65, NO. 10, PAGES 1151--1160, doi:10.1016/S1364-6826(03)00159-7, 2003.
- Shepherd, S. G., J. M. Rhuohoniemi, and R. A. Greenwald, Testing the Hill model of transpolar potential with Super Dual Auroral Radar Network observations, GEOPHYSICAL RESEARCH LETTERS, VOL. 30, NO. 1, 1002, doi:10.1029/2002GL015426, 2003.
- Greenwald, R. A., Shepherd, S. G., T. S. Sotirelis, J. M. Ruohoniemi, and R. J. Barnes, Dawn and dusk sector comparisons of small-scale irregularities, convection, and particle precipitation in the high-latitude ionosphere,, JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 107, NO. A9, doi:10.1029/2001JA000158, 2002.
- Shepherd, S. G., R. A. Greenwald, and J. M. Rhuohoniemi, Cross polar cap potentials measured with Super Dual Auroral Radar Network during quasi-steady solar wind and interplanetary magnetic field conditions, JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 107, NO. A7, doi:10.1029/2001JA000152, 2002.
- Rhuohoniemi, J. M., S. G. Shepherd, and R. A. Greenwald, The response of the high-latitude ionosphere to IMF variations, JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS, VOL. 64, NO. 2, PAGES 159-171, JANUARY, 2002.
- Rhuohoniemi, J. M., R. J. Barnes, R. A. Greenwald, and S. G. Shepherd, The Response of the high-latitude ionosphere to the coronal mass ejection event of April 6, 2000: A practical demonstration of space weather nowcasting with the Super Dual Auroral Radar Network HF radars, JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 106, NO. A12, PAGES 30085-30097, DECEMBER 1, 2001.
- Shepherd, S. G. and J. M. Rhuohoniemi, Electrostatic potential patterns in the high latitude ionosphere constrained by SuperDARN measurements, JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 105, NO. A10, PAGES 23,005-23,014, OCTOBER 1, 2000.
- Shepherd, S. G., R. A. Greenwald, and J. M. Rhuohoniemi, A Possible Explanation for Rapid, Large-Scale Ionospheric Responses to Southward Turnings of the IMF, GEOPHYSICAL RESEARCH LETTERS, VOL. 26, NO. 20, PAGES 3197-3200, OCTOBER 15, 1999.
- Shepherd, S. G., J. LaBelle, G. Rostoker, and C. W. Carlson, The latitudinal dynamics of auroral roar emissions, JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 104, NO. A8, PAGES 17,217-17,232, AUGUST 1, 1999.
- Shepherd, S. G., J. LaBelle, R. A. Doe, M. McCready, and A. T. Weatherwax, Ionospheric structure and the generation of auroral roar, JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 103, NO. A12, PAGES 29253-29266, DECEMBER 1, 1998.
- Shepherd, S. G., J. LaBelle, and M. L. Trimpi, Further investigation of auroral roar fine structure, JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 103, NO. A2, PAGES 2219-2229, FEBRUARY 1, 1998.
- Yoon, P. H., A. T. Weatherwax, T. J. Rosenberg, J. LaBelle, Shepherd, S. G., Propagation of medium frequency (1--4 MHz) auroral radio waves to the ground via the z-mode radio window, JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 103, NO. A12, PAGES 29267-29275, DECEMBER 1, 1998.
- Shepherd, S. G., J. LaBelle, and M. L. Trimpi, The polarization of auroral radio emissions, GEOPHYSICAL RESEARCH LETTERS, VOL. 24, NO. 24, PAGES 3161-3164, DECEMBER 15, 1997.
- LaBelle, J., S. G. Shepherd, and M. L. Trimpi, Observations of auroral medium frequency bursts, JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 102, NO. A10, PAGES 22221-22231, OCTOBER 1, 1997.
- Letcher Jr., D. M. Shook, and S. G. Shepherd Relational geometric synthesis: Part 1--framework, COMPUTER-AIDED DESIGN 27 (11): 821-832 NOV 1995.
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