I have been fascinated by radioisotope thermal generators (RTGs), aka nuclear batteries, ever since I saw a display at the Maryland Science Center in Baltimore’s Inner Harbor sometime in the early 1990s.
In that energy exhibit, there was a tiny RTG that was designed to power a cardiac pacemaker. What impressed me the most was the fact that the battery could produce continuous power for an incredible period of time – after 10 years it would still be producing 89% of the current that it produced when new. After 87 years of continuous output, the battery would still produce 50% of the current of a new battery.
These long-life nuclear batteries are not only energy dense, but they are also power dense – the current output per unit mass is comparable to that of a lithium ion battery, but they last far longer. I can just imagine what it would be like to have a laptop whose battery never needed to be recharged.
Similar technology is what enabled the Voyager spacecraft to head out into the solar system to take pictures and send them back to Earth. Even in a place where the sun is a distant dot that produces virtually no power and where journeys are measured in decades, engineers had a reliable power source available – the heat produced by radioactive decay of a relatively long lived isotope like plutonium 238.
Until very recently, the last major use of Pu-238 powered RTGs for a space exploration mission was the Cassini voyage. On Saturday, November 26, NASA launched a Mars exploration mission carrying a vehicle named Curiosity that is powered by a Pu-238 enabled battery. That device will provide power for reliable mobility and communications for as long as the vehicle can last.
The US does not currently have any capability left to manufacture the required material, largely thanks to the continuous pressure against anything nuclear by organized opposition. Pu-238 RTGs are anything but cheap sources of power, but I hope you can tell from the below video that a large portion of the cost is due to the extreme measures taken to ensure reliability in space AND to protect people from the largely imaginary risks.
There are other isotopes that are useful for nuclear batteries and other ways to turn the heat or radiation from the batteries into useful electricity. One of my favorites is strontium 90, an isotope that is abundantly produced in all fission power reactors, but which is currently treated as a troublesome waste product whose heat production adds to the complexity of used fuel storage.
For applications where there is a need for reliable, continuous power over long periods of time, radioactive decay should be on the list of options to consider. Unfortunately, opposition to the use of nuclear energy, the recycling of useful nuclear materials and irrational concerns about the effects of low level radiation has virtually eliminated this valuable technology.
It is way past time to reconsider that situation and take action to change it. Since effective action has not yet been taken, there is no time like the present to get started.
You can read more about Curiosity and the Idaho National Laboratory’s involvement in the manufacture and testing of the power source at Dan Yurman’s Idaho Samizdat. His article is titled NASA Mars vehicle will use nuclear power source. The INL web site is also a useful source of information about RTG production and is the place where I found the above video.
INL also has posted additional photos of Curiosity’s RTG power source on its flickr site. You might also want to visit the fact sheet on the Pu-238 battery and the reasons why it was the only available power source that could meet the mission requirements.