Thirty-one astronauts have made a return-trip to Mars. Well, not quite but they have put in the requisite hours in space. That's just one of the surprising insights to come out of a recent attempt to chart humanity's 52-year history in space.

Gilles Clment and Angelia Bukley of the International Space University in Illkirch-Graffenstaden, France, used publicly available information from the US, Russian and Chinese space programmes. Between 12 April 1961, when Yuri Gagarin took a single orbit around the Earth on board the Soviet Vostok-1 craft and December 2013, they counted the humans who have flown to space, how long they collectively spent there and who they were.

We picked out our favourites six insights, then put them in context with data from elsewhere.

1. Astronauts are as common as Nobel prizewinners

As of 31 December 2013, 539 individuals had been to space, defined as reaching an altitude of 100 kilometres or more. That's a rate of about 10 per year, and roughly equivalent to the 566 people who have ever won a Nobel prize in a science subject (physics, chemistry, or physiology/medicine).

(Note: Clment and Bukley's analysis does not include the two commercial astronauts who piloted the SpaceShipOne test flights in 2004, who were in space for just a few minutes each.)

2. Space trips last days, months but rarely years

Gagarin's single orbit of the Earth lasted just 108 minutes. Clment and Bukley found that of a total of 1211 person-flights, defined as a single crew member flying one mission, most last less than a month. Presumably these short hops were trips to the moon and missions spent inside NASA's now-retired space shuttle, to build and repair the International Space Station. But a significant minority spent five or six months, representing stays on board the ISS.

Originally posted here:

A brief history of space flight - in numbers