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Fears for Nasa's future missions as agency reveals it is running out of vital Plutonium-238 needed to power probes in space

October 11, 2017 2:40 PM
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Fears for Nasa's future missions as agency reveals it is running out of vital Plutonium-238 needed to power probes in space

Nasa could be out of fuel for its long range missions within eight years, a US government report has warned.

The space agency's mission-ready supplies of radioactive isotope Plutonium-238 are running perilously low and plans to restock may fall short of delivery.

Heat generated by the radioactive decay of Plutonium-238 is used to power the radioisotope thermoelectric generators (RTGs) used in deep space.

The RTGs are the power source for missions such as Mars Curiousity rover and the Voyager 1 and 2 spacecraft.

The plutonium used on Nasa spacecraft is transformed in a laboratory into a silvery-black ceramic material called plutonium dioxide.

Plutonium-238 is an isotope, or variant with a different number of neutrons in its nucleus, that emits steady heat due to its natural radioactive decay.

It has been used to power Nasa's radioisotope thermoelectric generators (RTGs) in more than two dozen missions to date.

The report, issued by the Government Accountability Office (GOA), warns that shortages may jeopardise Nasa's ability to use RTGs as a power source for future missions.

The Department of Energy (DOE) is working to create more Plutonium-238 (Pu-238), which until 2009 was supplied by the Russians.

With cold war stocks dwindling, the race is now on to produce more of the valuable isotope.

The report puts the total amount of Pu-238 isotope available for Nasa missions at around 35 kg (77 lb).

Only half of that amount was up to spec for space travel, which would cover the agency's plans for another eight years.

Writing in the GOA report, its authors said: 'Given Nasa’s current plans for solar system exploration, this supply could be exhausted within the next decade.

'Nasa plans to use about 3.5 kg (7.7 lb) of Pu-238 isotope for one RTG to power the Mars 2020 mission.

'Nasa may also use an additional 10.5 kg (23 lb) of Pu-238 isotope for its New Frontiers 4 mission if three RTGs are used.

The plutonium used on Nasa spacecraft is transformed in a laboratory into a silvery-black ceramic material called plutonium dioxide.

Plutonium-238 is an isotope, or variant with a different number of neutrons in its nucleus, that emits steady heat due to its natural radioactive decay.

It has been used to power Nasa's RTGs in more than two dozen missions to date.

RTGs provide electrical power for spacecraft by converting heat generated by the decay of Pu-238 fuel into electricity using devices called thermocouples.

Since they have no moving parts that can fail or wear out, RTGs have historically been viewed as a highly reliable power option.

Thermocouples have been used in RTGs for a total combined time of over 300 years, and a not a single thermocouple has ever ceased producing power.

The current model used is the Multi-Mission Radioisotope Thermoelectric Generator, or MMRTG.

Each MMRTG carries 4.8 kg (10.6 lbs) of Plutonium-238 dioxide as its nuclear fuel, using eight General Purpose Heat Source (GPHS) modules to produce about 110 Watts of electrical power in total.

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Source: dailymail.co.uk

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