Not all of the RTGs that have been produced have been designed for use in space. Here on earth, there are some applications where even extremely expensive RTGs have been able to successfully compete with other power supply alternatives.
Here are the criteria that seem to be necessary to make RTGs a potential choice under current economic conditions and regulations:
- High value application
- Remote location
- Non availability of sunlight or wind
- Maximum power demand of a few hundred watts
- Government sponsorship
- Long term need for continuous power
One of the more common uses of RTGs was in a place that many would not suppose fit into the above criteria. Tiny, milliwatt capacity RTGs found a home inside the chests of middle aged people in countries like France, Russia and even the United States. These devices – about the same size as a AA battery – were designed to power cardiac pacemakers.
For the customer, the device could be a lifesaver whose cost was of little import. The location of the pacemaker, though often within several feet of an electrical outlet, is difficult to serve with wires because of the risk of infection. Chemical batteries require occasional replacement; in this case, replacement could mean another risky surgical procedure.
The use of plutonium fueled pacemaker RTGs has virtually ceased. In the US, the culprit was federal regulators who were troubled with the prospect of thousands of tiny plutonium batteries to control; in Russia, adverse public reaction following the Chernobyl accident eliminated the market demand.
Another place where hundreds of RTGs have been used is at the bottom of the ocean. Just as on the moon, there are excellent reasons for locating sensing and communications devices in the deep ocean. RTGs were selected to power these sensors for the same reasons that they found a demand in space. Combustion is not possible, solar energy is unavailable, and chemical batteries cannot store enough energy for a long duration mission.
The Soviet Union also placed a significant number of RTG powered sensors on the Arctic ice cap. There, combustion would be possible, but it is limited by the difficulty of resupply and the need for regular maintenance of combustion engines.
Several decades ago, the US Coast Guard showed interest in using RTGs for certain remote, but vital navigation systems. Currently, most of these devices are powered by solar photovoltaic cells with battery back-ups. Under current constraints, solar power systems are much simpler to deploy (for legal reasons) and much cheaper.
There are numerous potential uses for RTGs, ranging from powering fiber optic cable transmitters to powering consumer devices like camcorders and portable computers. There are two rather high hurdles that must be overcome before these uses become economically feasible, however.
A better system for manufacturing the heat sources needs to be developed. Under current legal and regulatory constraints, the only suppliers of isotopes that can be used in thermal generators are government entities set up to provide small amounts of material to specialized government programs. There is room to improve the manufacturing and marketing processes in such a way as to allow cost reductions of several orders of magnitude.
The second barrier is a regulatory barrier. RTGs need to be treated as the simple, failure resistent devices that they are. There is adequate precedence for a simplified regulatory system for dealing with devices that have installed radiation sources. The sealed source regulations, however, cannot currently be applied to RTGs because of their inherently large curie content.
Regulators and policy makers need to understand that the materials that make good RTGs are easy to shield and of little health risk as long as they are not ingested. Their health hazard is not substantially different than that of materials like lead, cadmium, and nickel that are used to make chemical batteries. Under current regulations, however, no manufacturer is willing to make the RTGs on a large scale, claiming that it is simply too hard or too expensive to obtain appropriate licensing permission.
Sadly enough, this statement seemingly holds true even if the customer expressing interest is a huge, well respected international technology company willing to pay tens of millions of dollars for a few hundred cells with end of life power outputs of perhaps ten watts each.
As of September, 2002, the general climate with regard to use of radioisotopes for specialized power source applications may be changing. Positive comments have been published by influential members of the current administration, including the head of NASA. Prominent companies continue to make discrete inquiries. For more general information on this topic, one reader suggested a visit to
http://silver.neep.wisc.edu/~neep533/FALL2001/lecture21.pdf. It is a lecture by Dr. Kulcinski titled “Nuclear Power In Space”. It is a graphically rich PDF file with lots of useful drawings equations.