14 hours and counting ...

2015 has been eventful, and for my brief review of the year I am going to focus on what I think are the moments of most enduring significance. These will tend to be scientific and technological developments whose implications I expect to be more far reaching that political ephemera.

The year included events that made us reflect on what it meant to be human. On 10 September the discovery of an extinct species of homonin was announced. Homo naledi remains had been found at a cave in South Africa. It would seem the individuals had been left in a chamber in a cave system that was difficult to access and was probably only used for ritual purposes. Although they were between 2 and 3 million years old, it seems likely they had been left there during the performance of a funeral ceremony. The species shared with us our modern human awareness of our own mortality.

But although it was not met with perhaps the loudest fanfare, I believe the single most important event in 2015 related, not to our origin as a species, but to our destiny. At the beginning of December, as I have discussed elsewhere, there was a joint meeting of the American and Chinese academies of science to discuss a moratorium on editing human germ line genes. The technology that makes us able to transcend natural selection and vault the generations over which it operates presents opportunities to cure otherwise incurable conditions. However, the attendant risks are existential, as it is possible now to completely rewrite in a single generation what it is that determines who we are at a genetic level.

Other developments have far reaching consequences about our destiny as a species. The New Horizons space probe reached Pluto in July, completing the preliminary phase of our exploration of the Solar System. Back on Earth, the economics of space flight look likely to be revolutionised by advances in reusable launch systems. The Blue Origin New Shepard and SpaceX Falcon 9 systems both successfully landed their primary stages after use, bringing us closer to an era in which an entire launch system is routinely used over and over, simply being refuelled between launches.

This brings me to the title of this article. I have discussed elsewhere the economic and social developments that are required if we are to progress beyond a mere "campfire" economy foraging for energy in an unplanned and unsustainable manner towards one whose sustainable energy consumption merits description in terms of the Kardashev scale. This is becoming increasingly urgent as we consider the impact of anthropogenic climate change, as was discussed at the historic COP21 meeting in Paris in December.

A Kardashev Type I civilisation would use launch vehicles that were recycled and whose fuel was synthesised using highly efficient renewable energy resources. These could be of the sort discussed above or possibly a space elevator to geosynchronous orbit. This suggests to me a number that can be defined to characterise in more detail the sort of Kardashev Type I civilisation the Earth can sustain.

How long would it take for solar irradiation of a square metre of the Earth to generate the energy needed to put one kilogram in geosynchronous orbit?

By my (very rough) reckoning, about 14 hours. The Earth offers a Kardashev Type I civilisation an intrinsic launch countdown of 14 hours per kilogram per square metre.