Japan and the US  plan to launch 1,000 miniature low-orbit observation satellites to detect incoming missiles, reports the Nikkei.

The satellites cost about $5 million each. 200 of them will have heat-detecting IR sensors for missile defence.

The whole programme will cost $9 billion and will be completed in the 2020s.

The move comes as China develops low-flying hypersonic missiles and North Korea develops missiles which change trajectory – both of which are designed to avoid detection by current missile shield systems.