Santa is at the top of many engineering disciplines - his production line for presents, for example. However one that is often overlooked is the space-domain.
The United States’ North American Aerospace Defense Command (NORAD) not only continuously tracks 32,000 objects in space to avoid collisions, but also Santa’s global progress in delivering presents on Christmas Eve.
From NORAD’s tracks, we can see that he travels at 6.25 km/s (14,000 mph) over oceans (close to the speed of satellites in Low Earth Orbit at 7.7 km/s). However, he travels more slowly, at only 1.4 km/s (3,000 mph) while over the densely populated UK. His route is perfectly optimised for reducing atmospheric drag.
Whilst travelling over oceans he doesn’t need to be at low altitudes (no presents to deliver) so he takes advantage of the thinner atmosphere at higher altitudes. Also, delivering at night-time allows him to both avoid sleeping children and at the same time take advantage of the lower thermospheric densities, as the thermosphere cools and contracts while the Sun isn’t heating it. However, over-populated areas, he travels more slowly in the lower, denser atmosphere, allowing more accurate present delivery while experiencing less heating due to the atmospheric drag.
Delivering at nighttime allows Santa to avoid sleeping children and take advantage of lower thermospheric densities.
Another optimization Santa has made is in the design of his sleigh and selection of reindeer as the method of driving the sleigh. In the atmospheric drag equation, there is a term known as the coefficient of drag, effectively how well something slips through the atmosphere. Smaller, pointier objects have lower coefficients of drag, think about arrows compared to parachutes.
Reindeer have pointy snouts and present a relatively low cross-sectional area for their strength, allowing them to convert their power to speed. Meanwhile having nine reindeer in a 1-2-2-2-2 formation helps to efficiently cut into the air, and make it turbulent before the sleigh travels through, making it experience less drag, just like a cyclist in a peloton.
Rudolph – at the front of the team – takes the brunt of this force due to atmospheric drag, with the majority of the kinetic energy turning into heat energy, leading to his red nose.
Whilst we are not sure if Santa has yet upgraded his Sleigh to using the latest SANTA-NAV (GPS) technology, or whether he uses HF communications to keep in touch with the North Pole, we do know that on Christmas Eve, and throughout the Christmas period, the Space Environment research group at the University of Birmingham (SERENE) will be working with space weather centres around the world to help deliver 24/7 forecasting of the conditions in Earth’s upper atmosphere and its impacts on global position systems, HF communications, atmospheric drag and the need for satellite manoeuvres.
This article was written by Dr Matthew Brown and Professor Sean Elvidge, of the University of Birmingham's Space Environment Research Group (SERENE).
Professor of Space Environment
Staff profile for Professor Sean Elvidge, Professor of Space Environment in the Space Environment and Radio Engineering (SERENE) group in the School of Engineering.
