Will NASA Recover Apollo 13's Plutonium 238?

Apollo 13 Astronaut Fred Haise extracts the fuel element for the SNAP-26 RTG during training

Credits: NASA

Somewhere among the jagged trenches of the South Pacific sits a graphite fuel cask containing 3.9 kg of plutonium from Apollo 13.

The fate of the radioactive plutonium-238 has long been overshadowed by the successful return of the three NASA astronauts on board the ill-fated mission.

The plutonium was supposed to fuel the System for Nuclear Auxiliary Power, or SNAP-27 Radioisotope Thermoelectric Generator (RTG), designed to power a set of experiments on the lunar surface but after an explosion crippled the craft and forced the crew to abandon plans of a lunar landing, the plutonium became yet another problem for mission control.

Officials from NASA confidently told The New York Times that the biggest risk was that the 40-pound generator might hit someone when it fell to Earth.

“It will keep a few fish warm,” a NASA official said. The Atomic Energy Commission, on the other hand, conceded the slight possibility that it could become ground into dust and dispersed.

NASA learned its lessons about engineering the fuel casks the hard way: in 1964, the Transit-5-BN mission aborted and the RTG burned up upon reentry above Madagascar, in keeping with its design.

Traces of plutonium were found in the area months later. In 1968, the Nimbus B-1 weather satellite was aborted soon after takeoff from Vandenberg Air Force Base and the plutonium from the SNAP-19B2 RTG plunged into 300 feet of water off the California coast, with no release of radiation.

Apollo 13’s SNAP-27 fuel, as far as we know, slipped beneath the waves and came to rest 6 to 9 kilometers deep in the Tonga Trench, one of the deepest areas in the ocean.

Subsequent testing by the U.S. Department of Energy has shown no spike in background radiation.

Not surprisingly, NASA has no desire to go looking for the small cask, even with advances in submersible technology that would make such a mission at least technically feasible.

“I don’t think that anyone has seriously considered that because of the cost of recovery,” said Leonard Dudzinski, a NASA program executive who deals with radioisotope power systems.

President Nixon (right) presenting the nation’s highest civilian award to the Apollo 13 crew (left to right, J. L. Swigert, F. W. Haise, J. A. Lovell) 

Credits: NASA

Indeed, NASA is trying to source additional plutonium 238 for its future deep space missions, the U.S. no longer produces the isotope and Russia has proved to be an unreliable source, but the useful life of the Apollo 13’s plutonium has expired.

The plutonium poses little danger to the environment: the corrosion resistant cladding should withstand seawater for approximately 870 years, ten times the plutonium’s half life.

According to NASA, the plutonium itself was in oxide form and was both chemically and biologically inert when it plunged into the ocean.

Over the years, the plutonium cask, far out of sight, has fueled two contradictory positions on the safety of RTGs for deep space missions.

For NASA, its safe return to Earth proved the effectiveness of their safety engineering. “We recognize that the Apollo 13 [RTG system] worked,” Dudzinski said. “Follow on RTGs were based on that design and improved on that design.”

Critics have taken different lessons from the untimely plunges of the RTGs. In 1997, a group of safety experts, including physicist Dr. Michio Kaku, warned that 32 kg of plutonium contained in the Saturn-bound Cassini satellite posed a greater danger than NASA would acknowledge, but ultimately, their warnings did not prevented the mission from happening.

NASA Mars Curiosity Rover: MAHLI Captures a mosaic of Mars

A mosaic of MSL MAHLI images acquired on Sol 613. CLICK on the photo to see the full image

Credit: NASA /JPL-Caltech /MSSS

This is Curiosity's latest "selfie," a mosaic made up of about a dozen images acquired with the rover's Mars Hand Lens Imager (MAHLI) instrument on April 27-28, 2014 (Sol 613).

The 5.5-km-high Mount Sharp (Aeolis Mons) rising in the background.

There are plenty of discrepancies in the mosaic tiling but, some say, it imparts some character to Curiosity.

Visible in the mosaic are Curiosity's cylindrical RUHF antenna and a bit of her Radioisotope Thermoelectric Generator (RTG) visible in the lower center.

NASA Galileo spacecraft: Could Jupiter become a star? - Video

Galileo at Jupiter. Credit: NASA

NASA's Galileo spacecraft arrived at Jupiter on December 7, 1995, and proceeded to study the giant planet for almost 8 years.

It sent back a tremendous amount of scientific information that revolutionised our understanding of the Jovian system.

By the end of its mission, Galileo was worn down.

Instruments were failing and scientists were worried they wouldn't be able to communicate with the spacecraft in the future.

If they lost contact, Galileo would continue to orbit the Jupiter and potentially crash into one of its icy moons.

Galileo would certainly have Earth bacteria on board, which might contaminate the pristine environments of the Jovian moons, and so NASA decided it would be best to crash Galileo into Jupiter, removing the risk entirely.

Although everyone in the scientific community were certain this was the safe and wise thing to do, there were a small group of people concerned that crashing Galileo into Jupiter, with its Plutonium thermal reactor (RTG), might cause a cascade reaction that would ignite Jupiter into a second star in the Solar System.

Hydrogen bombs are ignited by detonating plutonium, and Jupiter's got a lot of hydrogen.Since we don't have a second star, you'll be glad to know this didn't happen.

Could it have happened? Could it ever happen? The answer, of course, is a series of nos. No, it couldn't have happened. There's no way it could ever happen… or is there?

Jupiter is mostly made of hydrogen, in order to turn it into a giant fireball you'd need oxygen to burn it. Water tells us what the recipe is.

There are two atoms of hydrogen to one atom of oxygen. If you can get the two elements together in those quantities, you get water.



In other words, if you could surround Jupiter with half again more Jupiter's worth of oxygen, you'd get a Jupiter plus a half sized fireball.

It would turn into water and release energy but that much oxygen isn't handy, and even though it's a giant ball of fire, that's still not a star anyway. In fact, stars aren't "burning" at all, at least, not in the combustion sense.

Our Sun produces its energy through fusion. The vast gravity compresses hydrogen down to the point that high pressure and temperatures cram hydrogen atoms into helium. This is a fusion reaction.

It generates excess energy, and so the Sun is bright. And the only way you can get a reaction like this is when you bring together a massive amount of hydrogen.

In fact… you'd need a star's worth of hydrogen. Jupiter is a thousand times less massive than the Sun. One thousand times less massive.

In other words, if you crashed 1000 Jupiters together, then we'd have a second actual Sun in our Solar System.

Jupiter as captured by Michael Phillips on July 25th, 2009 

But the Sun isn't the smallest possible star you can have.

In fact, if you have about 7.5% the mass of the Sun's worth of hydrogen collected together, you'll get a red dwarf star.

So the smallest red dwarf star is still about 80 times the mass of Jupiter.

You know the drill, find 79 more Jupiters, crash them into Jupiter, and we'd have a second star in the Solar System.

There's another object that's less massive than a red dwarf, but it's still sort of star like: a brown dwarf.

This is an object which isn't massive enough to ignite in true fusion, but it's still massive enough that deuterium, a variant of hydrogen, will fuse.

You can get a brown dwarf with only 13 times the mass of Jupiter. Now that's not so hard, right? Find 13 more Jupiters, crash them into the planet?

As was demonstrated with Galileo, igniting Jupiter or its hydrogen is not a simple matter.

We won't get a second star unless there's a series of catastrophic collisions in the Solar System.

And if that happens… we'll have other problems on our hands.

NASA halts work on MMRTG nuclear generator for deep space exploration

MSL’s Pu-238 fueled MMRTG in the laboratory. Credit: NASA

Another blow was dealt to deep space exploration this past weekend.

The announcement comes from Jim Green, NASA's Planetary Science Division Director.

The statement outlines some key changes in NASA's radioisotope program, and will have implications for the future exploration of the outer solar system.

We've written about the impending plutonium shortage and what it means for the future of spaceflight, as well as the recent restart of plutonium production.

NASA is the only space agency that has conducted missions to the outer planets—even the European Space Agency's Huygens lander had to hitch a ride with Cassini to get to Titan—and plutonium made this exploration possible.

Probably the most troubling aspect of the announcement is the discontinuation of procurement by NASA of flight hardware for what was to be NASA's next generation nuclear power-source for exploration, the Advanced Stirling Radioisotope Generator, (ASRG).

This was to replace the Multi-Mission Radioisotope Generator, (MMRTG) that has been in use on spacecraft for decades.

An Advanced Stirling Converter prototype in the laboratory. 

Credit: NASA

The announcement states:

"With an adequate supply of Pu-238… NASA has decided to discontinue procurement of ASRG flight hardware."

"We have given direction to the Department of Energy… to end work on the flight units."

"The hardware procured under this activity will be transferred to the Glenn Research Center to continue development and testing of the Stirling technology."

The announcement cites the current budget-constrained environment that NASA and planetary space exploration finds itself up against.

What the exact future role is of NASA Glenn beyond basic research and development isn't entirely clear, but two ASRG units that were to be flight-ready for missions in 2016 are shelved for now.

The announcement does mention that NASA will continue to utilize flight-proven MMRTG's in the near term, which provide the same approximate power output as the ASRG, albeit with less efficiency.


Plutonium is vital for outer solar system exploration. As you get farther away from the Sun, solar energy ceases to become a viable alternative power source.

Pioneers 10 & 11, Voyagers 1 & 2, Galileo, and Cassini all utilized nuclear RTGs, as does the Mars Curiosity rover and New Horizons mission headed out explore Pluto in during its July 2015 flyby.

NASA's Juno spacecraft scheduled to reach Jupiter in 2016 will be the first-ever mission without an RTG to explore the outer solar system, and it must employ three enormous solar panels to do so.

A labeled cutaway of an ASRG. Credit: 

Wikimedia Commons And although the production of the Pu-238 isotope used in space exploration was a side-benefit of the Cold War, it isn't the same stuff as its isotopic cousin Pu-239, which is used in nuclear weapons. 

Plutonium production in the United States ceased in 1989, and although the U.S. government announced earlier this year that NASA will restart the plutonium production pipeline for space exploration, production levels are only expected to reach 1 to 1.5 kilograms per year.

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