Hearing, Balance and Hyperloop: Part II

Last week we discussed the development of a concept described as the Vactrain. While the concept began in the 19th century, Robert Goddard, as a freshman at Worchester Polytechnic Institute, substantially refined the idea in a 1906 short story called “The High-Speed Bet” which was summarized and published in a 1909 Scientific American editorial called “The Limit of Rapid Transit“. Goddard’s wife, Esther, was granted a US patent for the vactrain in 1950, five years after his death. In 1972, Robert Salter of the RAND Corp. conceived a well engineered supersonic underground railway that he called the Vactrain but due to the enormous construction costs (estimated as high as US$1 trillion, in 1972) Salter’s excellent proposal was never built. His idea was simply waiting for the right combination of talent, technology, and business case to become a reality.

Today’s growing global economy requires faster, cheaper, safer and more efficient transportation modes. Roads, airports, and ports are congested and there has not been a new form of transportation in 100 years. Why not add a new ultra-fast, on-demand, direct, emission-free, energy efficient, quiet with a smaller footprint than other high-speed transport modes? Proponents say “its about time!” Goddard’s concept of Vactrain has been renamed Hyperloop and is now proposed as a new worldwide mode of transportation moving freight and people quickly, safely, on-demand and direct from origin to destination. The basic concept of the hyperloop is a pair of elevated steel tubes through which capsules carrying 28 passengers glide along at up to 760 mph on extraordinarily thin cushions of air. Capsules would be accelerated via linear motors, the same technology used in maglev trains. But what of the audio-vestibular effects of acceleration and those ups and downs of rapid travel in a tube across the country? What of the noise levels in the tube and the capsule in which passengers ride this train?

Audio-vestibular Effects of Rapid Travel in a Vacuum Tube

The presence of sensory and response systems is a universal attribute of life as we know it. All living organisms on Earth have the ability to sense and respond appropriately to changes in their internal and external environment. Organisms, including humans, must sense accurately before they can react, thus ensuring survival. If our senses are not providing us with reliable information, we may take an action which is inappropriate for the circumstances and this could lead to injury or death. Astronauts experience similar sensations of dizziness and disorientation during their first few days in the microgravity environment of space. Upon returning to Earth after prolonged exposure to microgravity, astronauts frequently have difficulty standing and walking upright, stabilizing their gaze, and walking or turning corners in a coordinated manner. An astronaut’s sense of balance and body orientation takes time to re-adapt to Earth-normal conditions.

It looks like the Hyperloop will have some vestibular issues as well. By enclosing the track, the Hyperloop is able to sidestep worries about air friction and noise that usually limits the speed of trains to under 400mph, but the tube in which the capsules ride presents a unique set of challenges. James Powell PhD, co-inventor of the maglev train, is particularly concerned about the smoothness of the inside of the tube. As Powell points out, the current design allows for just three hundredths of an inch between the tube wall and the skis encircling the pod. “Getting it that smooth won’t be easy,” says Powell, and might require a more expensive production process than the plans currently envision. These subtle differences at 750 MPH cause bumps that are felt by the passengers as well as the lateral G forces that cause nausea effected by the straightness of the path. It seems that at 750 MPH, even a gentle curve will jerk passengers to the side. In physics, this motion is known as lateral G-force, and the human body can only take so much before motion sickness sets in.

As a result, hyperloop planners are always balancing the curviness of their route with their traveling speed and the level of G-force that passengers can withstand. Thus, Hyperloop routes are designed to limit lateral G-forces to a maximum of 0.5 Gs, but it’s significantly higher than any G forces in existing transportation. According to Powell, that’s a problem: “In all our tests, we found people started to feel nauseous when you went above 0.2 lateral Gs.” The closest comparison would be roller coasters, which usually top out around half a G but the Hyperloop wouldn’t just peak at 0.5; it would stay there for the duration of the curve. The result would be well short of blackout, which most studies peg around 4.7 lateral Gs, but it would make the Hyperloop challenging for the faint of stomach. A sick passenger might be less catastrophic than a crash but, given the tight passenger compartments, the results could still be fairly traumatic.