Rosetta shows - we can keep space plutonium-free!

Rosetta approaching its destination after a 6 billion km journey. Image: ESA.
Rosetta approaching its destination after a 6 billion km journey. Image: ESA.
Deep space missions have previously run on nuclear power, writes Karl Grossman - and have twice showered Earth with radioactive debris. But the ESA's Rosetta probe, about to reach its destination, is 100% solar-powered - showing that space can be nuclear-free.
Rosetta is the first space mission to journey beyond the main asteroid belt relying solely on solar cells for power generation.

A demonstration that in space as on Earth, solar power is an alternative to dangerous nuclear power is to come tomorrow when a solar-powered spacecraft called Rosetta will rendezvous with a comet 375 million miles from the Sun.

Ten years after its 2004 launch, the European Space Agency's Rosetta space probe, energized with solar power, is to meet up with Comet 67P/Churyumov-Gerasimenko. It will begin making observations, relaying back to Earth high-resolution images and information from its sensors, of the two-and-a-half mile wide comet.

Rosetta will subsequently send a lander down to the comet that will drill into it and perform a variety of experiments. For a year, Rosetta will fly alongside the comet, named after the two Ukranian astronomers who discovered it in 1969.

And Rosetta, says the ESA "relies entirely on the energy provided by its innovative solar panels for all onboard instruments and subsystems."

Two serious nuclear accidents in space already

For decades, the United States and the Soviet Union, and now Russia, stressed the use of atomic energy as a source of power in space - and there have been accidents as a result.

The first serious incident was the fall-back to Earth of a US satellite with a SNAP-9A plutonium-238 radioisotope thermal generator on board in 1964, disintegrating as it fell, dispersing plutonium worldwide.

Pu-238 is an exotic isotope characterised by its half life of just 88 years. That makes it intensely radioactive compared to other more common isotopes - like the Pu-239 used for nuclear fission in both bombs and nuclear reactors, with its half life of 24,000 years.

In 1978 SNAP-9A was followed by the Soviet Cosmos Satellite 954, with its on-board atomic reactor. It too broke up, spreading nuclear debris for hundreds of miles across the Northwest Territories of Canada.

The late Dr. John Gofman, professor of medical physics at the University of California at Berkeley, long connected the SNAP-9A accident and its dispersal of plutonium with a global increase in lung cancer. Canada demanded compensation for the Cosmos-954 accident which the Soviet Union eventually paid - in part.

ESA demonstrates - we can do it with solar

At the distance at which Rosetta will encounter Comet 67P / Churyumov-Gerasimenko, or at which Juno will be doing experiments involving Jupiter or ESA's Jupiter Icy Moons Explorer will work, energy from the Sun is but a small fraction of what it is on Earth.

Still, it can be effectively utilized for power generation, the ESA declares - because even in the remote outer solar system, there's still enough sunlight to power the smart solar cells it developed for the purpose: 

"The solar cells in Rosetta's solar panels are based on a completely new technology, so-called Low-intensity Low Temperature Cells. Thanks to them, Rosetta is the first space mission to journey beyond the main asteroid belt relying solely on solar cells for power generation.

Rosetta is the first space mission to journey beyond the main asteroid belt relying solely on solar cells for power generation.

"Previous deep-space missions used nuclear RTGs, radioisotope thermal generators. The new solar cells allow Rosetta to operate over 800 million kilometres from the Sun, where levels of sunlight are only 4% those on Earth. The technology will be available for future deep-space, such as ESA's upcoming Jupiter Icy Moons Explorer."

The US - sitting on the nuclear fence

Now all satellites are solar-powered, as is the International Space Station. But there has been a push to continue to use nuclear power on space probes with NASA and formerly Soviet and now Russian space authorities insisting that solar power cannot be harvested far from the Sun.

NASA's last space probe mission to Jupiter, Galileo, launched in 1989, was plutonium-powered - and NASA officials insisted, including in sworn testimony countering a challenge to Galileo in federal court, that this was the only energy choice.

There were numerous protests against Galileo and have been to subsequent nuclear space shots led by the Global Network Against Weapons & Nuclear Power in Space.

But NASA has begun to follow ESA's lead. It went with solar power for its Juno mission to Jupiter that is now underway. Launched in 2011, energized by solar power, the Juno space probe is to arrive at Jupiter in 2016.

Life, the Solar System, and everything

Rosetta is named after the Rosetta Stone, a slab of basalt found in Egypt in 1799 with inscriptions carved on it that enabled the deciphering of hieroglyphics, the ancient language of Egypt.

"As a result of this breakthrough, scholars were able to piece together the history of a lost culture", notes ESA. "Rosetta's prime objective is to help understand the origin and evolution of the Solar System."

"The comet's composition reflects the composition of the pre-solar nebula out of which the Sun and the planets of the Solar System formed, more than 4.6 billion years ago ... an in-depth analysis of Comet 67P / Churyumov-Gerasimenko by Rosetta and its lander will provide essential information to understand how the Solar System formed."

ESA adds that comets have played a huge part in the Earth's development, and may be responsible for the evolution and persistence of life:

"There is convincing evidence that comets played a key role in the evolution of the planets, because cometary impacts are known to have been much more common in the early Solar System than today.

"Comets, for example, probably brought much of the water in today's ocean. They could even have provided the complex organic molecules that may have played a crucial role in the evolution of life on Earth."

The first expedition to land on a comet

Rosetta "will be undertaking several 'firsts' in space exploration", says ESA, as "the first mission to orbit and land on a comet", and "the first spacecraft to witness, at close proximity" the changes in a comet as it approaches the Sun.

Rosetta's lander, Philea - named after Philea Island in the Nile where an obelisk was found that supplemented the use of the Rosetta Stone in the deciphering of hieroglyphics - "will obtain the first images from a comet's surface and make the first in-situ subsurface analysis of its composition."

Philea is to touch down on the comet's surface in November, and attach itself using a 'harpoon' system. A drilling system will obtain samples down to 23 cm below the surface and feed them to spectrometers for analysis, determining the comet's chemical and isotopic composition. 

"Other instruments will measure properties such as near-surface strength, density, texture, porosity, ice phases and thermal properties ... In addition, instruments on the lander will study how the comet changes during the day-night cycle, and while it approaches the Sun."

A noble quest - and one that poses no nuclear threat

The cost of the mission is €1.3 billion ($1.75 billion at current exchange rates). So why spend such a huge amount of public money on studying remote stones in space?

ESA responds: "ESA's task is to explore the unknown. In the case of Rosetta, scientists will be learning about comets, objects that have fascinated mankind for millennia."

Comets "are thought to be the most primitive objects in the Solar System, the building blocks from which the planets were made. So Rosetta will provide exciting new insights into how the planets, including Earth, were born and how life began."

If the Rosetta mission is a success it will be a superb example of a space quest with the highest of purposes - exploring the mysteries of the Solar System and the origins of life.

And - setting an example for all deep space missions to follow - it will represent no nuclear threat to life on Earth.



Karl Grossman is professor of journalism at the State University of New York/College at Old Westbury, is the author of 'The Wrong Stuff: The Space Program's Nuclear Threat to Our Planet' and narrator and writer of the television documentary 'Nukes in Space: The Nuclearization and Weaponization of the Heavens' (

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