The emergency calculations made by the captain of the stricken Apollo 13 space module to work out how to bring his crew safely back to earth after an explosion on board are to be auctioned.

After the blast cut power and oxygen supplies in the command module, astronaut Jim Lovell and his two-man crew had to evacuate to the lunar module – designed for the short journey between orbit and the surface of the moon – and then work out how to get that home.

Now the original notepad on which his workings were scrawled is to be sold at auction.

Despite the enormous pressure and with just a few hours available before the oxygen ran out, Captain Lovell solved the complicated orbital calculations required. Having had to manually punch his data into the computer, Lovell then used his calculations, as well as sightings of the sun and the earth, to guide the craft back successfully.

The epic achievement of Jim Lovell, who is now 83, has been celebrated in films and documentaries and must surely make this pad of sums, if not the most glamourous of the many items of Apollo 13 memorabilia available, one of the most significant.

At the time, Lovell told mission control: “if this paperwork isn’t right – who knows where we’ll end up out here.”