Correct. The exact nature of the pile determines the amount of heat that can be generated which in turn determines the maximum specific impulse. Hydrogen ends up being a good reaction mass because of its low molecular weight.
As to the safety of the rocket, chemical rockets today are little more than well controlled bombs. That's the primary reason why launches occur in equatorial coastal regions, i.e. if it goes boom, it goes boom over fishies instead of us. I think you could make safe and reliable piles that would survive the destruction of the rocket. The problem would be continuing to dissipate the heat they would generate. Seawater seems like a pretty good coolant to me. The key would be to have the containment vessel maintain its integrity even in corrosive environments.
Having said all that, my favorite propulsion technology remains plasma based, either Kauffman ion sources or variable Isp plasma rockets.
Just Google NERVA. It's not impossible and research rockets have been test fired. All a rocket is needs is a high energy source with some sort of expansion through a nozzle to work. Nuclear piles provide lots of thermal energy and their rocket nozzles don't have to be designed any differently than a conventional chemical rocket. A link to some of the history can be found at http://www.astronautix.com/project/nerva.htm.
No one aside from SF writers having fun is talking about a launch system using Orion. It has too many obvious problems.
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As to the safety of the rocket, chemical rockets today are little more than well controlled bombs. That's the primary reason why launches occur in equatorial coastal regions, i.e. if it goes boom, it goes boom over fishies instead of us. I think you could make safe and reliable piles that would survive the destruction of the rocket. The problem would be continuing to dissipate the heat they would generate. Seawater seems like a pretty good coolant to me. The key would be to have the containment vessel maintain its integrity even in corrosive environments.
Having said all that, my favorite propulsion technology remains plasma based, either Kauffman ion sources or variable Isp plasma rockets.
No one aside from SF writers having fun is talking about a launch system using Orion. It has too many obvious problems.