You are here

Ensuring Safety on Earth from Nuclear Sources in Space


Nuclear power sources have been used recently on probes, landers and rovers on missions that have left Earth orbit, such as the Cassini mission seen in an artist's rendition here which was launched to explore Saturn and its moons. Global emergency preparedness and response arrangements are in place for satellites carrying nuclear power sources. (Photo: NASA)

In early 1978, the world steeled itself as gravity pulled an uncontrolled satellite powered by a small reactor fueled with 45 kg of highly enriched uranium towards Earth. Since COSMOS 954’s impact point could not be predicted accurately, emergency responders had to assume that an inhabited area could be contaminated, and they feverishly prepared equipment and response procedures. This was the world’s first experience with the uncontrolled re-entry of a space object with radioactive materials.

The radioactive materials launched into Earth orbit, or traveling in spacecraft, can potentially harm people or the environment in case of an accident and for which strict emergency response planning and effective information sharing at the international level are required. This was the topic of an IAEA webinar held last week for emergency response experts.

In the majority of nuclear and radiological emergencies there will be enough information to know the location of a potential release of radioactivity, but with space activities the exact location of impact cannot always be predicted. “The IAEA has developed arrangements to share information about any pending nuclear-powered satellite re-entry. Using the data, countries can quickly respond to protect the public and the environment from the radioactivity that might spread as a result of an accident,” said Frederic Stephani, Incident and Emergency Assessment Officer in the IAEA, during the webinar.

COSMOS 954 eventually crashed in the Northwest Territories in Canada on 24 January 1978, scattering radioactive debris over a 600 km footprint and spreading radioactivity over 100 000 km2. The clean-up operation, called “Operation Morning Light,” jointly coordinated by Canada and the US, recovered 80 radioactive items.

The COSMOS 954 crash became a prototype for global emergency preparedness and response arrangements for satellites carrying nuclear power sources.

Exploring space with nuclear power

As space objects are propelled towards new scientific discoveries in space, often far away from the Sun, they require nuclear power sources. But accidents can occur during the launch, operation and end-of-service mission phases of space nuclear power source applications. These accidents could expose the nuclear power source to extreme physical conditions leading to a radioactive release into the Earth’s atmosphere.

For space agencies such as the United States National Aeronautics and Space Administration (NASA), different safety requirements will apply depending on the unique features of each mission. “The US uses a well-established National Response Framework to respond to a broad range of incidents, and this includes a lot of key assets that are specific to radiological  events, including monitoring and assessment capabilities,”  said Don Helton, Nuclear Flight Safety Assurance Manager at NASA.

International cooperation in emergencies

Globally, clear obligations have been set out. Under the Convention on Early Notification of a Nuclear Accident, in case of an accident with a satellite or other space object with a nuclear power source or with a radioactive source on board, the countries that launched the space object must notify potentially affected States and the IAEA. The IAEA has established operational arrangements to support countries to meet this obligation.

The IAEA’s Unified System for Information Exchange in Incidents and Emergencies (USIE) — a secure 24/7 monitored website — provides a platform for countries to exchange urgent notifications and follow-up information during a nuclear or radiological emergency. The Joint Radiation Emergency Management Plan of the International Organizations (JPLAN) sets out a framework for the coordinated actions of international organizations during an emergency.

The United Nations Office for Outer Space Affairs (UNOOSA), as the lead UN entity for outer space affairs, has clear responsibilities under the JPLAN. “In the event of an accident, we would liaise with the launching state to gather information on the object and, if necessary, with other countries who can track space objects to determine re-entry timeframe and probable impact coordinates. We would then ensure that the most up-to-date trajectory and impact predictions are provided to the IAEA for further dissemination to aid emergency response efforts,” said Natercia Rodrigues, Programme Officer in UNOOSA, during the webinar.

Current threats and future plans

UNOOSA also maintains the UN Register of Objects Launched into Outer Space. To date over 86 per cent of all satellites, probes, landers, crewed spacecraft and space station flight elements launched into Earth orbit or beyond have been registered with UNOOSA.

So, what is the likelihood of another COSMOS 954-type crash happening in the future?

Sam Harbison, Chair of the United Nations Working Group on nuclear power sources in outer space, established in the year after Cosmos 954, explained that countries are no longer using nuclear power sources in Earth orbits because of the rapid improvements in solar panel technology and in order to avoid unnecessary potential releases of radioactive material. “All the nuclear power source satellites presently in Earth orbit were launched during the 1960’s to 1980’s and it is estimated it will be more than a hundred years before the earliest of them will re-enter Earth's atmosphere.”

More recent uses of nuclear power sources have been on probes, landers and rovers on missions that have left Earth orbit. Examples include the Cassini mission to explore Saturn and its moons, and robotic rovers such as the recently launched Mars 2020 Perseverance mission which will reach Mars early next year. There are aspirations to use nuclear power sources to support human colonies on the moon or Mars. “Solar panels are not sufficient for such prolonged missions, at great distances from the Sun,” Harbison said. “They would have to be complemented by rocket propulsion, which is bulky, heavy and expensive. Nuclear power sources will be needed both for the return journey and to sustain human activities on the surface of the Moon or Mars.”  


  1. Employment
  2. Women
  3. Press

Stay in touch