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Personal cushion of air

Inspired by seeds, proposed air-bag system would surround astronauts and protect them during bumpy landings
Throughout August, Sydney Do conducted dozens of "drop tests" of a dummy attached to the airbag system. The system was dropped from different heights that ranged from one foot to 10 feet.
Throughout August, Sydney Do conducted dozens of "drop tests" of a dummy attached to the airbag system. The system was dropped from different heights that ranged from one foot to 10 feet.
Photo: William Litant
Do and two colleagues prepare the system and dummy for a drop test. During these drops, the accelerations experienced by the dummy can be measured to determine the level of injury a human might experience.
Do and two colleagues prepare the system and dummy for a drop test. During these drops, the accelerations experienced by the dummy can be measured to determine the level of injury a human might experience.
Photo: William Litant

Plans for Orion — the capsule that resembles the Apollo program’s spacecraft and was supposed to send humans to the moon by 2020 as part of NASA’s Constellation program — were changed in February when President Obama canceled Constellation, and then announced two months later that NASA would continue to develop Orion as an escape vehicle to be docked at the International Space Station for emergencies.

While it appears that Orion will eventually take flight, NASA continues to struggle with one crucial aspect of its design: minimizing the violent impact that astronauts would experience during landing. Although NASA initially designed Orion’s crew seats to be mounted onto a stiff structure supported by shock absorbers — essentially the same technology used to cushion Apollo’s water landings — this 1,100-pound structure would be too heavy to cushion astronauts if the vehicle landed on land. Whereas the Apollo capsule was designed to land in water, and Orion would likely do the same, NASA wants to make sure that Orion can land on land in case of an emergency.

A graduate student in MIT’s Department of Aeronautics and Astronautics has helped design a smaller alternative: a reusable, 700-pound air-bag system that could inflate during launch and landing, deflate for storage purposes, and partially inflate to provide seating while the vehicle is in space. Not only would the system be lighter than the one NASA originally proposed, but it would also be entirely mechanical, meaning not controlled by computers.

This is important because “the vast majority of accidents and failures in engineering systems” can be traced to computers misinterpreting situations, says Sydney Do, who helped design the air-bag system and spent several weeks in August testing a full-sized prototype designed to protect one astronaut. “Our goal was to see if it was possible to design a landing system that was purely mechanical.”

According to a paper presented at the American Institute of Aeronautics and Astronautics Space 2009 conference by Do and his thesis adviser, Olivier de Weck, an associate professor of aeronautics and astronautics and engineering systems, the air-bag system was inspired by the structure of seeds. Just as a fluid surrounds the embryo in seeds to provide protection as the seed is distributed, the Orion air-bag system would surround each astronaut in “a personal cushion of air,” according to current NASA astronaut Charlie Camarda, who seeks to develop more innovative space-engineering concepts that veer from the traditional. In 2008, Camarda helped organize a group of students from Pennsylvania State University and MIT, including Do, to explore how the physics of seeds could be applied to engineering principles. Do’s design for an Orion air-bag system, Camarda says, represents “a very novel” approach to mechanical design that could inspire more biological-based solutions in engineering.

Valve analysis

NASA’s Engineering and Safety Center agreed to fund the study by the Penn State and MIT students to explore the feasibility of an air-bag system that Orion astronauts could inflate before reentering Earth’s atmosphere. The students’ first step was to conduct tests to observe how the inflated bags behave when they are dropped from increasing one-foot increments while supporting an object that weighs about the same as an average male head — such drops simulate the impact velocity that an astronaut would feel upon landing.

These tests revealed how important timing is in terms of releasing gas from an air bag. Unlike car air bags, which inflate when hot gas is injected into them upon impact, the inflated Orion air bags already contain gas upon impact. If the air bags are either not big enough or don’t have enough air in them, the astronaut’s seat will directly impact the ground. Alternatively, if there is enough gas inside the bag, but it’s not released before the seat hits the ground, the impact will cause the seat to bounce upward, which could injure the astronaut. That’s because as an astronaut falls into the bag during the landing, the kinetic energy created from this motion is combined with the energy of the gas molecules moving inside the bags. This increases the pressure of the gas inside the bag, which could cause bouncing.

To prevent this bounce, enough gas needs to be vented between the point at which the floor of Orion impacts the ground and the point at which the seat and the astronaut impact the ground so that the kinetic energy caused by the falling seat and occupant have been removed. But even after some of this gas is vented, there still needs to be enough gas remaining in the bags to prevent direct impact between the seat and the ground. To get this balance right, the students decided to design valves that are triggered to open at a low pressure, which would allow gas to vent as soon as Orion’s floor comes to rest, but before the seat can impact the ground.

This clip shows several views of a “drop test” of an air-bag system being designed for a space capsule. During the test, a dummy attached to the air-bag system is raised and then dropped, simulating the velocity an astronaut would experience during landing.
Video courtesy of Sydney Do

Drop-test survival

When NASA decided to fund the research for another year last spring, Do took over the research for his master’s thesis and began testing a valve for the system. He then developed a computer model to analyze how certain variables, such as air-bag size, would affect the risk of astronaut injury upon impact. This helped him configure a prototype seat that would have four air bags — each about one foot long by two feet wide — containing two rectangular valves about six inches wide. Do then built the air bags from vectran, a high-strength material that was used to make the air bags for several rovers that landed on Mars.

Earlier this month, he tested the prototype through a series of drop tests conducted from as high as 10 feet involving a crash dummy that measured the acceleration of each drop. While Do still needs to analyze those results before presenting his final design to NASA later this fall, he says that the fact that the system survived dozens of drops suggests that certain variables he chose for the prototype, such as the material and manufacturing of the air bags, are adequate for an Orion landing. According to Camarda, future research could explore ways to ensure “a robust and fail-safe” system in the event that a valve malfunctions.

Do cautions that the air-bag system has one drawback: It’s likely only effective for vertical drops, meaning that the air bags could tip over if Orion descended at a sideways angle. But he says this might not be an issue if Orion is designed to land vertically. Although whatever NASA decides to do with Do’s research ultimately depends on the future of human spaceflight, he is hopeful that even if Orion never takes flight, his research could be used to guide designs of similar capsule-type spacecraft that commercial companies might be interested in building.

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