Under any circumstances, there is a very limited market for nuclear rockets. Even if space exploration is raised in the national priority list, the first mission to Mars would probably occur in about 2010. For at least a decade or more after that, trips would probably be infrequent at best.
There would be some utility to such a program; at least it would inspire a whole new generation of science and engineering students to reach for the stars. Realistically, however, it would be very difficult to attract the investments needed to develop an infrastructure to manufacture nuclear rockets if long distance space travel was the only potential market.
Governments would be the only investors and the only potential customers, and their track record of consistent support for long term projects is rather spotty.
However, the nuclear reactor heat source that is needed for a high performance rocket engine is a rather incredible device that is worth developing because of its ability to adapt to other applications. Many human needs and desires can be served if a little creative thinking is employed.
Stepping In Edison’s Shoes
First, we must understand the technical capabilities the nuclear rocket program demonstrates. Then we must think about new ways to apply those capabilities to solve existing problems, meet existing needs or fulfill difficult to achieve dreams.
This is the process that allowed the Wright Brothers to apply the new capabilities represented by lightweight internal combustion engines to the problem of powered flight. It is also the process that allowed Thomas Edison to take advantage of the invention of an efficient vacuum pump and apply it to his desire to design a long-lived electric light bulb.
Even with the materials that were available in the late 1960s, NERVA reactors were able to perform the following feats.
- Increase power from 1 MW to 800 MW in 50 seconds
- Start-up from source level to full power in about 80 seconds
- Produce a thermal power of 1500 MW in a package weighing less than 6800 kg.
- Produce coolant temperatures of 2500 ° C.
These kinds of capabilities shoot all kinds of holes in the general perception of nuclear power. Reactors are not limited to producing steady power in huge generating facilities. They are not limited to providing relatively low quality steam and poor thermodynamic efficiencies.
The numbers show that reactors can:
- Respond at least as rapidly as any combustion heat source
- Be made smaller than a desk
- Be used in high efficiency machines
- Be used as energy sources for weight constrained vehicles
Of course, rockets are normally designed to operate for very brief periods of time in comparison with a normal earth bound application. Their burn times are on the order of hours instead of months or years. It will take some modifications to make the nuclear rocket reactors into useful energy sources for economic engines.
One simple modification that could improve engine longevity considerably is to reduce coolant temperatures to about 2000 ° C. The change would make a huge difference in the rate of corrosion and erosion of the core surfaces. The best combustion engines on the market today operate at about the same temperature, so this change would not require a sacrifice in performance or efficiency compared to existing engines.
Instead of using hydrogen gas for the coolant, an inert gas like helium or maybe nitrogen could be used to reduce corrosion damage. Hydrogen is an explosive hazard and probably not very useful for a power producing engine.
Similar reactors could be used in place of the combustors in a gas turbine engine. If concerns about fission product release persisted, the exhaust gas could be recycled into the intake of the compressor.
Nuclear heated gas turbines could be used to provide power in just about every machine that is currently served by a diesel or combustion gas turbine. Imagine how exciting it could be to own a boat that allowed virtually unlimited travel at speeds only limited by hull design! Imagine having a generator at the local hospital that could run continuously without worrying about how to find fuel in the aftermath of a hurricane.
The number of potential applications are only limited by our imagination. The holy grail of the energy world is a long-lasting, responsive, low cost, emissions free energy source. Perhaps the grail has already been found, but its importance has been overlooked.
Of course, having a program to develop high performance nuclear engines with all these potential uses might just result in a lower cost trip to the Moon or Mars. Would you care to join us in the line for the first tickets?