Space debris from a nuclear fission reactor

SNAPSHOT-10, the first US nuclear powered reactor flow in space. From: Wikipedia. 

In the early days of the space and nuclear era, flying rockets to space was the thing to do, as was building experimental nuclear reactors -- and obviously both of these two futuristic technologies could also be combined. Above is a picture of the SNAPSHOT-10A spacecraft, the only fission powered reactor flown into space by the US. The spacecraft was launched in 1965 into a polar orbit at an altitude of about 1300 km. The spacecraft failed only a little bit over a month into its mission.

In the 70s, the spacecraft began shedding parts. It's not certain why this occurred, presumably due to some type of a system failure or due to a collision by space debris. In any case, there is now a cloud of debris in space associated with this spacecraft. It's not certain what this cloud of debris consists of, but probably there are droplets of sodium-potassium liquid metal coolant and maybe fragments of the spacecraft.

I stumbled upon this interesting factoid is when investigating two clusters of space debris that I identified in a recent beam-park radar observation using the Tromsø and Svalbard radars. There are two clear clusters of space objects, which are not within the NORAD catalog of space objects. These are at an altitude of about 1300 km, and they occur around 10 and 22 UTC. You can see these clusters in the figure shown below. It is perhaps not a coincidence that these cluster occur at the same range and time as the expected crossing of the SNAP-10A spacecraft. The reason for the clustering is somewhat unknown. For an old fragmentation event, one would expect the cloud of debris to have dispersed more -- but it is hard to say without more modeling.

Left: 2018 beam-park radar observation of space debris using the Svalbard high-power large aperture radar. All objects not within the NORAD space object catalog are shown in red. There are two clusters with many objects not in the catalog, occurring at the time of the expected transit of the SNAP-10A spacecraft. Right: Model of space debris detections using the NORAD catalog.

No reason for panic though, it'll be more than 4000 years before this radioactive material re-enters and burns in the Earth's atmosphere.

Here's a short documentary about SNAP-10A on youtube: