Borne by sunlight or pushed by Europe

These could be the choices for future spaceprobes as JAXA reveals that its solar sail mission IKAROS has been detectably accelerated by photon pressure (sunlight) alone. Meanwhile, a mini-energy crisis has hit US and Russian spacecraft as the plutonium isotope whose decay is used to heat and power distance probes through radioisotope thermoelectric generators is getting rather scarce. Regulations in the USA and Russia mean that production of Pu-238, which is radioactive, but not the 239 stuff that goes into bombs, has stopped. In the USA, department of defense funding doesn’t allow for production to restart and so NASA’s dwindling stocks are normally augmented with a delivery from Russia. However, Russia’s dwindling stocks mean that they now want a higher price for these deliveries, which provide the power for probes travelling far from Earth where solar power is limited at best. However, ESA has happilly put up its hand as a potential source of the stuff. They are building up their capacity for production of Pu 238 and might even throw in some Americium-241. This stuff produces energy for longer, but at a lower rate. It is also more hazardous than Pu-238. But horses for courses…