Stephen J Smith Stephen J Smith Stephen J Smith is a Senior Investigator at the Allen Institute for Brain Science. Previously, Dr. Smith was Professor of Molecular and Cellular Physiology at the Stanford University School of Medicine. In 1990, Smith published an article in the journal "Science", which proposed that certain glial cells in the human brain known as astrocytes would be able to communicate through chemical signals, rather than electrical. By utilizing the neurotransmitter glutamate, he was able to show that these cells, which had once been perceived as inert tissue between neurons, in fact were actively communicating with the rest of
Electrically powered spacecraft propulsion for a prescribed duration) or unsteady (pulsed firings accumulating to a desired impulse). However, these classifications are not unique to electric propulsion systems and can be applied to all types of propulsion engines. Electrically-powered rocket engines provide lower thrust compared to chemical rockets by several orders of magnitude because of the limited electrical power possible to provide in a spacecraft. A chemical rocket imparts energy to the combustion products directly, whereas an electrical system requires several steps. However, the high velocity and lower reaction mass expended for the same thrust allows electric rockets to run for a long time. This