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Question Your World: How Will We Fuel Long Term Space Exploration?

The Apollo 11 mission in 1969 was one of the most sophisticated scientific experiments of all time. This trip involved over 5 million lbs. of fuel for the round trip to our closest celestial neighbor. That worked well for getting us to the moon and back, but how much fuel could we possibly produce and carry on board for a trip to the distant reaches of our solar system? Listen to the latest Question Your World Radio Report from the Science Museum of Virginia to learn more about renewed production of a different fuel source - Plutonium 238.

In order to traverse the millions, billions, and trillions of miles left to explore, we’re going to need to think outside the box. The jet fuel needed to help us escape Earth’s gravity has proved to be functional, but very expensive. The massive Saturn V rocket used for the Apollo missions worked for the relative close distance to the moon and back, but what about those far off distant places? To go from Earth to Mars takes about nine months, Europa takes about two years, and other stars are so distant that our current methods would not get us anywhere near them for thousands upon thousands of years of traveling. So, the energy needed for operating a spacecraft for long-term travel just can’t come from big heavy bulky tanks of jet fuel.

Enter Plutonium 238! This is a slow decaying radioactive material that has been kicked back into production at the Department of Energy and NASA. This radioactive battery has a very slow decay. This decay is in the form of energy that is harnessed by radioisotope thermal generators to power the ship’s on-board machines. Plutonium 238’s half-life is about 87 years. This used to be the standard for long range travelers such as the New Horizons and the Voyager spacecraft. However, due to some safety concerns the production of this space fuel was shut down in the mid-80s.

Voyager 1 is a great example of how this system works. For 87 years the plutonium battery will decay enough to power all the major functional aspects of this spacecraft. Voyager is pre-programmed to have the plutonium battery powering its systems for the first 87 years based on what is required at the time. After that, half-life decay sets in and the ship’s programming will shut down some systems and continue to power what is left. After 87 more years half-life decay will continue and so on. 

Since August of 1977, Voyager has been using that plutonium 238 battery and it's still working today as Voyager becomes the first human made object to leave our solar system! This on-board battery will be able to power systems on the spacecraft for at least another twelve years or so, when it finally will decay enough to not be as helpful as when it was launched. Regardless, this battery will be the power source that allowed for us to gather information on all the planets and even some readings from the edge of our solar system!

Plutonium 238 will not be the answer to powering our space flights from here to the other side of our galaxy, but it certainly is a lot more efficient than giant tanks of jet fuel. More work and research on these long lasting decay-based power sources will help us understand various aspects of how we can provide energy for these long hauls.

There’s a lot of space out there and these out-of-the-box ideas could help us explore infinity and beyond!

Article by Prabir Mehta, Science Museum of Virginia

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