Flying kiwis no match for Santa
Physics mean nothing to a guy like Santa, writes Hayden Walles.
Nothing in the laws of physics prohibits Santa from making his rounds in time on Christmas Eve. In fact, Einstein’s relativity theories give him a helping hand.
But there are certainly technological challenges, since the mission demands that Santa travel close to the speed of light, where time and space behave differently than we are used to. It would take some effort to catch up with Santa – both literally and figuratively.
We know, for example, that Santa’s sleigh doesn’t fly like a plane. Concorde, the supersonic passenger jet, used to cruise at a little more than twice the speed of sound. Five or six times the speed of sound is about the upper limit for aircraft, which is still more than 150,000 times slower than the speed of light.
For higher speeds you have to turn to rockets. Rockets operate on the principle that every action has an equal and opposite reaction – so if you propel some matter out the back of your vehicle, you’ll move forward, just as a gun recoils when it is fired.
Most rockets are chemical. Fuel is burned to produce rapidly expanding gas, which rushes out the nozzle, generating thrust in the opposite direction. But Santa isn’t using these. The New Horizons spacecraft heading towards Pluto was propelled to more than 57,000 kilometres per hour by chemical rockets. That’s the best yet and nothing to be ashamed of, but a chemical rocket that could reach anything like light speed would require more fuel than exists in the universe.
Electric rocket motors have been getting a lot of attention lately. They use an electric field to hurl ions out the back. Unfortunately electric motors accelerate very gradually, and though they can reach high speeds, they take a long, long time to do it.
The cutting edge, as far as high-power rocketry goes, is the nuclear rocket motor. Nuclear rockets were originally investigated in the middle of the 20th century as a way to power a crewed mission to Mars. Rather ironically, given subsequent political developments, the first American prototypes were named Kiwis because, like our national bird, they were never meant to fly. A nuclear rocket uses a nuclear reactor to heat and expel a propellant like hydrogen, generating thrust.
By the early 1970s descendants of the Kiwis were almost ready to fly, but they never did because interest in Mars had waned and distrust of nuclear technology had grown. Nevertheless, nuclear rockets outperform chemical ones, getting higher speeds from the same size rocket.
Even nuclear rockets can’t compete with Santa, though. It seems most likely that he doesn’t use rockets at all, relying instead on something like anti-gravity, warped space or wormholes, things that break the laws of physics as we know them. The rest of us can only dream of such things at present.
Santa seems happy to keep the secret to himself. However he zips around the globe, it’s pretty clear that he feeds his reindeer something very special indeed.
On the web: Search for ‘‘Historical Perspective of the NERVA Nuclear Rocket Engine’’ to find a 16-page PDF document on the programme, written in 1991.
Things editors do: This story would normally be illustrated with a cute picture of Santa’s sleigh, but this is The Box and we have a much cooler image – a nuclear-powered rocket engine. Some versions were called ‘‘Kiwi’’.