Permanent Human Settlement of the Earth, Space and Ocean Frontiers

Tuesday, May 01, 2007

Space Time

Ralph Buttigieg

Sydney, NSW


the watch from 2001 Space Odyssey

The measurement of time will be just as essential to a Space colonist as it is to anyone on Earth. In fact it may be more so as regular monitoring and maintenance of a habitat is a matter of life or death.

Colonist will properly need to keep three time measurements, Universal Time the old Greenwich Mean Time, Mission Elapsed Time the time at mission control on Earth and Mean Local Time, the time in the habitat.

Planetary habitats will try to match the natural rotation of the planet for local time. However humans have evolved to cope with a 24 Earth hour cycle, the only planet with a similar cycle is Mars which has a day about 39 minutes longer then ours. The other planets have very different cycles. It would be impossible for humans to match the Moon's month long rotation or Saturn's 10 and half hours rotation. So the habitats will need to keep their own time system.

This is were the fun starts. People have proposed various unique time systems. Author Kim Stanly Robinson gave his Martians a special 39 minute hour at midnight to match their clocks with Earth. Others have proposed some sort of decimal time.

What people forget is that our 24 hour time system is essential for navigation. Longitude is a measurement of time. To give a planet a different time system you would also need to invent a different navigation system. Astronomers have long ago given planets longitude and latitude co-ordinates . Each planet effectively has a different “second” with the unit stretched or shrunk to match the planet's rotation. Space agencies like NASA use the time systems as they have to work with the planet's environment. A good example of this is the current Mars rovers missions. The Mars rovers are solar powered so the controllers have to be very aware the Martian day/night cycle. NASA even had to ask watchmakers to develop special Mars timepieces to keep time with the Martian Sol (day).

Now you can see what confusion this will cause. A colonist on say, the moon, will need to have a watch that keeps two times, the habitat's time system and the real Moon time. Imagine trying to pick the best time to ring Auntie Martha on Mars and cousin Tim on the floating Saturnian cloud cities. Its enough to make my head spin faster then the seconds hand of a Jovian clock.

Theres going to be a need to have some sort of standard time that will be a universal yardstick. A Standard (Space?) Second will need to be agreed upon otherwise interplanetary commerce will just not work. For larger units Earth's Universal Time could be used but I think the hours and minutes will just cause more confusion, besides theres no need to have any direct reference to Earth time for a yardstick. SF author Joan Vinge worked out a perfectly usable Space Time system years ago in The Outcasts of Heaven's Belt . The second is the base unit and other units are just metric multiplications of that. Other SF authors have used it and a explanatory chart is linked here.

More on time and other good stuff can be found on Winchell Chung's website.