Let Nature Be Your Guide  

Man has copied Mother Nature in many ways in the quest to overcome gravity. Leonardo da Vinci’s drawings and Arthur Cayley’s use of math and engineering in determining the four forces of flight were inspired in part by a keen observation of nature. In more recent times, NASA improved on the original idea of the winglet—a  copy of the upturned end feathers on a bird’s wings.

Graham Warwick’s excellent article “Intelligent Design” (Nov. 13-26, pp. 34-37) outlines his “four pillars” of discovery: Model-based Design, Intelligent Reasoning, Machine Learning and Human Learning. After observing the accompanying photograph that highlighted the Airbus A320 cabin partition, it would seem proper to acknowledge a fifth pillar—Lessons Learned from Nature. Structurally, the partition appears akin to a dragonfly wing. 

Roy Steele
Georgetown, Texas

Tackling Hypoxia

A key to the hypoxia problem is in the penultimate paragraph of “Life Support” (Nov. 13-26, pp. 62-63). “Cobham is looking to include a mitigation capability that automatically adjusts the oxygen concentration being fed to the pilot based on data the Aircrew Mounted Physiological Sensing System (AMPSS) is providing.” 

It seems that the model for the onboard Oxygen Generation System (OBOGS) design assumed a homogeneous distribution of atmospheric gases, but the ratio of concentrations can vary. Consider, for example, flying through the smog over a major city. The OBOGS should be designed to store a reserve of oxygen. The AMPSS data becomes part of a feedback loop that releases extra oxygen from the reserve to maintain optimal levels.

Richard Moscatiello
Decatur, Georgia 

Add Hypocapnia to Equation

I hope the military is putting adequate effort into understanding the role that hypocapnia (a state of reduced carbon dioxide in the blood) may play in their physiological episode studies. I am fairly sure hypocapnia caused me to black out while driving down from the nearly 12,000-ft. summit of Wolf Creek, Colorado. 

The descent followed several hours of intense mental and physical stress while driving up in whiteout conditions and digging out of a snowbank at the top. The blackout occurred at the hill bottom, just as air became plentiful.

It may be that the balance between oxygen and carbon dioxide is the important factor.

Dave Espen
Tijeras, New Mexico

View From the Front

Regarding several reader responses implicating pilots as the source of the problems in aviation safety (Oct. 30-Nov. 12, p. 7), I have some thoughts. True, pilots have been at fault in some accidents. Humans can and do err. Training, procedures, crew teamwork and vigilance are the best protection. Much has been learned the hard way, but I think we can now say that airline travel in the U.S. and most countries is exceptionally safe. 

The situation “Sully” Sullenberger and crew faced is rare indeed and was handled remarkably well. But think of how many less dramatic yet potentially dangerous situations have been averted simply by a crew using their collective experience to change the outcome. I don’t think anyone would have an exact number. All I can say is that in 25 years of airline flying, I’ve seen more than I care to remember. It is part of the job. Handle whatever comes your way in a very dynamic, often challenging and sometimes unpredictable environment. If you get there safely, so will everyone else.

As on the battlefield, the one most positioned to change the situation favorably is the soldier on the front line. These gray hairs on my head say don’t be too eager to dispense with the ones at the front.

Matt Marohn
Maple Lake, Minnesota

Arriving At Mars Safely?

SpaceX’s “Big Falcon Rocket” (BFR) will support the transport of many humans to Mars, per “Elon’s Big Gamble” (Oct. 16-29, p. 54). But would humans be fit for a new world after a zero-g trip? MRIs showed that months aboard the International Space Station caused brain compression from increased head fluid pressure and erosion of visual acuity. These changes apparently largely persist after return. It may not just be the 0g: Is Martian gravity (0.38 of Earth’s) enough to keep body fluids from gathering in the head? How about a Moon base with only 0.166 of Earth’s gravity?

Tests should answer these questions soon. Instead of new space labs with various rotation rates, there may be an easier approach to getting answers. The BFR upper stage (“the ship”) will refuel in low Earth orbit by docking a tanker stern to stern with the ship. Mild acceleration transfers propellants. I assume modest design changes could permit two lightly fueled passenger ships so docked to withstand the stresses of spinning. With humans about 40 m (130 ft.) from each stern (the center of revolution), 2.9 rpm would induce 0.38g (Mars’ equivalent).

SpaceX’s plans apparently will put the ship through suborbital flights, use the booster stage for orbital flights, then verify long-duration life-support capability. That is when the rotational tests could take place. Two crewed ships rotating for 200 days or more, in low Earth orbit, could answer whether a 0.38g level would avert zero-g in-transit damage and look for negative effects of Martian gravity. If there is a problem with Mars’ (or the Moon’s) surface gravity, solutions could be investigated. During large-scale human Mars flight, the numerous ships to leave at each opportunity could go docked in rotating pairs, with healthy humans delivered.

Daniel Gregory
Federal Way, Washington