Keith Cowing
Thursday, July 17, 2008
I recently learned that NASA has made some limited use of human cadavers in testing during the development of the Orion spacecraft.
Now, on first blush, this might sound somewhat macabre. In fact, it is more common than you might expect. There is also a practical reason for using this approach.
Let me start by providing the statement that the NASA Public Affairs Office provided me with today in response to an inquiry I made regarding the use of human cadavers in the Orion program:
"Human cadavers have been used as part of NASA's testing protocol. NASA is sensitive to the issues involved in using postmortem human subjects (cadavers) to test its systems. Human cadavers are rarely used in testing and only when it is determined that crash test dummies and mathematical models can not provide the information necessary to ensure the safety of the crew.
To evaluate the effects of accelerations incurred during normal and extreme landing scenarios of the Orion crew exploration vehicle, NASA has engaged both military and academic experts to conduct a series of impact tolerance tests to study the effect on humans. To do that, NASA uses instrumented dummies and cadavers.
Most of this testing was performed using Hybrid III automotive mannequins to measure the response of seated occupants and the amount of internal pressure exerted on the body. Mannequin testing allows engineers to analyze the reaction loads transmitted to the seat and the occupant in a controlled laboratory environment. However, it is widely recognized in the field of injury biomechanics that the information gained using mannequins does not always correlate directly into predictions for how humans could be injured.
In limited cases, postmortem human subject tests may be performed when insufficient data are available from simulations that use dummies or from mathematical modeling of the human body responses. This is particularly critical where the dynamic responses of internal organs and soft tissue must be evaluated. Using a combination of test methods, the engineering and scientific teams at NASA are able to enhance astronaut safety by designing landing attenuation systems that will minimize accelerations imparted to the crew and significantly reduce the potential for injuries."
Simulating a human body
Nothing simulates the effects of a dynamic and potentially hazardous environment on a living organism better than an actual living organism. Given that humans are large, upright bipeds, the biomechanics of a human body are unique from most other large animals. How an animal moves affects how the body handles physical stresses in normal and abnormal situations. Animals that walk on all fours handle biomechanical stresses differently than do humans. Indeed, the internal architecture of their bones is different given that there bones are internally constructed to handle the loads that a quadruped experiences - not only as it grows - but as it moves around on a daily basis.
As such, putting a 200 pound pig carcass in a space capsule couch and dropping the capsule onto a desert is not the best way to understand stresses on a human vertebral column, arms, and legs.
Using an instrumented crash dummy or mannequin is often better than animal carcasses since you can design the dummies to mimic one or more aspects of how a human body moves and how its structures handles physical stress - and you can measure these forces and reactions with great precision with the appropriate placement of sensors within the dummy - something you can't really do with people.
However, these dummies are limited in the assortment of biomechanical and physical factors that they can be engineered to simulate collectively at any one time. And they are expensive too.
Using human bodies is the ideal way to test vehicles for their ability to protect human life - and what happens when such systems exceed their design capacity and the chance of injury results. Also, given the inherent nature of testing of such risks, using volunteers is often unethical.
The next best thing to using living humans is to use human cadavers. Often times such human tissue is not available. Other times it is not practical to use due to the nature of the test, scarcity (i.e. how many test runs you need to do), expense, and regulations regarding the use of human remains. In the case of human tissue, there are also ethical and social concerns that must be addressed.
If you have seen shows such as "Myth Busters" on TV then you have heard their explanations why they often go to great lengths to use organic material (large animal bodies) or create synthetic human bodies out of ballistic gel, bone, and other materials. While these alternatives to human cadavers are often adequate (for TV), they are approximations, at best.
You can make something that looks like a liver out of gelatin and get some gross approximations as to what happens when it encounters certain stresses within a simulated body. But a liver is a complex amalgam of various microstructures - some of them incredibly delicate. How that organ handles sudden stresses, and how it is damaged internally - even at the tiniest level of tissue organization - affects whether or not a human with such damage will survive a crash - even if no bones are ever broken.
Human Cadavers and Space Radiation
In addition to physical trauma, there are other things that NASA needs to understand about the human body so as to assure a safe and productive environment for human crews. One of these factors is radiation.
NASA has made use of cadavers in the past. Several Space Shuttle missions flew with an item called the "Phantom Torso" which also spent time aboard the International Space Station. The Phantom Torso was constructed of materials that simulate human soft tissue and organs surrounding a specially configured human skeleton (torso, neck skull, but no extremities). This item was used to document radiation exposure during long term spaceflight.
The Phantom Torso on ISS during Expedition 2 (NASA).
Back in the 1990s, a human cadaver skull packed with radiation sensors was also flown on several DoD-sponsored Space Shuttle missions with a presumedly similar purpose.
The need to closely replicate the various tissues and their geometric arrangement in a human body is important so as to fully model how various forms of ionizing and non-ionizing radiation interact with variou tissues as they impact and traverse across the body. The dosage received on the outside of a body can be different than what is experienced within a body. Often times it is radiation damage to internal organs and sensitive tissues they contain that is of greatest concern to space medicine community.
Similar approaches are used to test non-living spacecraft components that will be exposed to the space radiation environment. Some parts act as shielding for others. Yet other materials shatter when hit by some types of radiation causing damage to other structures nearby. The Phantom Torso was equipped with a series of dosimeters that recorded radiation exposure over long periods of time.
With living humans, it is easy to place dosimeters on the surface of a body but to put them in the places within the body where the greatest concerns lie (bone marrow etc.) is difficult - if not impossible to do - with a living person. The Phantom Torso allowed optimal placement of dosimeters so as to get good readings of internal radiation exposure inside a simulation of a human body.
Specifics and Ethics
NASA did not provide me with much information as to the specific uses of these cadavers in the Orion program other than to state that they were being used in the process of designing and testing landing attenuation systems. Given that bipedal humans in a recumbent position receive very specific forces and vibrations during hard landings, the best way to understand whether the system can truly protect a human crew is to test it on human bodies.
Given the potentially hazardous nature of the tests required, cadavers must be used in the place of living persons. Some people may think that this practice has ethical problems. For starters, these cadavers were provided through strict legal channels, often willed for such postmortem uses by their former users, so to speak. Indeed, not to use cadavers in testing such system would be, in my opinion, not only unwise, but unethical in and of itself.
